U.S. patent application number 16/199868 was filed with the patent office on 2020-05-28 for slotted permanent magnets for electric machines.
This patent application is currently assigned to GM Global Technology Operations LLC. The applicant listed for this patent is GM Global Technology Operations LLC. Invention is credited to David J. Brooks, Alireza Fatemi, Thomas W. Nehl.
Application Number | 20200169129 16/199868 |
Document ID | / |
Family ID | 70545961 |
Filed Date | 2020-05-28 |
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United States Patent
Application |
20200169129 |
Kind Code |
A1 |
Fatemi; Alireza ; et
al. |
May 28, 2020 |
SLOTTED PERMANENT MAGNETS FOR ELECTRIC MACHINES
Abstract
Presented are slotted permanent magnets (PM) for electric
machines, motor generator units using slotted PMs, methods for
making/using slotted PMs, and motor vehicles equipped with an
electric traction motor using slotted PMs. An electric machine
includes an annular stator with a hollow core and one or more
internal stator slots. One or more electrically conductive windings
is/are disposed in the stator slot(s). A cylindrical rotor is
rotatably disposed inside the hollow core of the stator. One or
more permanent magnets is/are mounted to the rotor. Each permanent
magnet includes a rigid, single-piece PM body with opposing first
and second faces. A first set of elongated grooves is recessed into
the first face. An optional second set of elongated grooves is
recessed into the second face. Each of the grooves has a depth that
is substantially parallel to a direction of a magnetic field
generated by the permanent magnet.
Inventors: |
Fatemi; Alireza; (Canton,
MI) ; Nehl; Thomas W.; (Shelby Township, MI) ;
Brooks; David J.; (Troy, MI) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
GM Global Technology Operations LLC |
Detroit |
MI |
US |
|
|
Assignee: |
GM Global Technology Operations
LLC
Detroit
MI
|
Family ID: |
70545961 |
Appl. No.: |
16/199868 |
Filed: |
November 26, 2018 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H02K 7/006 20130101;
H02K 1/276 20130101; H02K 1/278 20130101; H02K 15/03 20130101; H02K
21/14 20130101; H02K 1/2766 20130101 |
International
Class: |
H02K 1/27 20060101
H02K001/27; H02K 15/03 20060101 H02K015/03; H02K 7/00 20060101
H02K007/00 |
Claims
1. An electric machine comprising: a stator defining a stator slot;
an electrically conductive winding disposed in the stator slot; a
rotor movable with respect to the stator; and a permanent magnet
mounted to the rotor, the permanent magnet including a rigid
single-piece permanent magnet (PM) body with a first major face on
a first side of the PM body, a second major face on a second side
of the PM body opposite the first side, first and second minor
faces smaller than and adjoining the first and second major faces,
a first set of elongated grooves recessed into the first major face
and extending across a length and/or width of the PM body, and a
second set of elongated grooves recessed into the second major face
and extending across the length and/or width of the PM body, each
of the grooves having a depth that is substantially parallel to a
direction of a magnetic field generated by the conductive
windings.
2. The electric machine of claim 1, wherein the first set of
elongated grooves includes a first series of rectilinear grooves
extending transversely across the width the PM body and spaced from
each other along the length of the PM body.
3. The electric machine of claim 2, wherein the first set of
elongated grooves further includes a second rectilinear groove
extending longitudinally across the length of the PM body and
perpendicular to the first series of rectilinear grooves.
4. The electric machine of claim 2, wherein the first set of
elongated grooves further includes a second series of rectilinear
grooves extending longitudinally across the length of the PM body
and spaced from each other along the width of the PM body.
5. The electric machine of claim 4, wherein the grooves in the
first series of rectilinear grooves are mutually parallel, the
grooves in the second series of rectilinear grooves are mutually
parallel, and the grooves in the first series of rectilinear
grooves are perpendicular to the grooves in the second series of
rectilinear grooves.
6. The electric machine of claim 1, wherein the first and second
sets of elongated grooves extend across the entire length and/or
width of the PM body.
7. An electric machine, comprising: a stator defining a stator
slot; an electrically conductive winding disposed in the stator
slot; a rotor movable with respect to the stator; and a permanent
magnet mounted to the rotor, the permanent magnet including a rigid
single-piece permanent magnet (PM) body with opposing first and
second faces, a first set of elongated grooves recessed into the
first face of the PM body, and a second set of elongated grooves
recessed into the second face of the PM body, each of the grooves
having a depth that is substantially parallel to a direction of a
magnetic field generated by the conductive windings, wherein the
first set of elongated grooves includes a first number of
rectilinear grooves and the second set of elongated grooves
includes a second number of rectilinear grooves distinct from the
first number of rectilinear grooves.
8. An electric machine, comprising: a stator defining a stator
slot; an electrically conductive winding disposed in the stator
slot; a rotor movable with respect to the stator; and a permanent
magnet mounted to the rotor, the permanent magnet including a rigid
single-piece permanent magnet (PM) body with opposing first and
second faces, a first set of elongated grooves recessed into the
first face of the PM body, and a second set of elongated grooves
recessed into the second face of the PM body, each of the grooves
having a depth that is substantially parallel to a direction of a
magnetic field generated by the conductive windings, wherein the
first set of elongated grooves includes a first series of
rectilinear grooves extending transversely across the PM body and
spaced from each other along a length of the permanent magnet, and
the second set of elongated grooves includes a second series of
rectilinear grooves extending transversely across the PM body and
spaced from each other along a length of the permanent magnet,
wherein the grooves in the first series of rectilinear grooves are
interleaved with the grooves in the second series of rectilinear
grooves.
9. The electric machine of claim 8, wherein the first set of
elongated grooves further includes a second rectilinear groove
extending longitudinally across the PM body and perpendicular to
the first series of rectilinear grooves, and the second set of
elongated grooves further includes a fourth rectilinear groove
extending longitudinally across the PM body and perpendicular to
the second series of rectilinear grooves, wherein the second
rectilinear groove is laterally offset from the fourth rectilinear
groove with respect to the PM body.
10. The electric machine of claim 1, wherein each groove in the
first set of elongated grooves has a rectangular transverse
cross-section.
11. The electric machine of claim 1, wherein each groove in the
first set of elongated grooves is filled with a bonded magnet
and/or an epoxy.
12. The electric machine of claim 1, wherein the PM body has a
rectangular polyhedron shape, a toroidal shape, a curvilinear tile
shape, or a bread-loaf shape.
13. The electric machine of claim 1, wherein the permanent magnet
is mounted on an outer diameter surface of the rotor or is mounted
inside a rotor slot defined in the rotor.
14. The electric machine of claim 1, wherein the permanent magnet
includes a plurality of permanent magnets mounted to the rotor.
15-20. (canceled)
21. The electric machine of claim 7, wherein each groove in the
first set of elongated grooves has a rectangular transverse
cross-section.
22. The electric machine of claim 7, wherein each groove in the
first set of elongated grooves is filled with a bonded magnet
and/or an epoxy.
23. The electric machine of claim 7, wherein the PM body has a
rectangular polyhedron shape, a toroidal shape, a curvilinear tile
shape, or a bread-loaf shape.
24. The electric machine of claim 8, wherein each groove in the
first set of elongated grooves has a rectangular transverse
cross-section.
25. The electric machine of claim 8, wherein each groove in the
first set of elongated grooves is filled with a bonded magnet
and/or an epoxy.
26. The electric machine of claim 8, wherein the PM body has a
rectangular polyhedron shape, a toroidal shape, a curvilinear tile
shape, or a bread-loaf shape.
Description
[0001] The present disclosure relates generally to electric
machines. More specifically, aspects of this disclosure relate to
permanent magnets for electromechanical motor/generator units (MGU)
of hybrid-electric and full-electric vehicle powertrains.
[0002] Current production motor vehicles, such as the modern-day
automobile, are originally equipped with a powertrain that operates
to propel the vehicle and power the vehicle's onboard electronics.
In automotive applications, for example, the vehicle powertrain is
generally typified by a prime mover that delivers driving power
through a manually or automatically shifted multi-speed
transmission to the vehicle's final drive system (e.g.,
differential, axle shafts, road wheels, etc.). Automobiles have
historically been powered by a reciprocating-piston type internal
combustion engine (ICE) assembly due to its ready availability and
relatively inexpensive cost, light weight, and overall efficiency.
Such engines include two and four-stroke compression-ignited (CI)
diesel engines, four-stroke spark-ignited (SI) gasoline engines,
six-stroke architectures, and rotary engines, as some non-limiting
examples. Hybrid and full electric vehicles, on the other hand,
utilize alternative power sources to propel the vehicle and, thus,
minimize or eliminate reliance on a fossil-fuel based engine for
tractive power.
[0003] A full electric vehicle (FEV)--colloquially referred to as
an "electric car"--is a type of electric-drive vehicle
configuration that altogether removes the internal combustion
engine and attendant peripheral components from the powertrain
system, relying solely on electric traction motors for propulsion
and for supporting accessory loads. The engine, fuel system, and
exhaust system of an ICE-based vehicle are replaced with an
electric motor, a traction battery pack, and battery cooling and
charging electronics in an FEV. Hybrid vehicle powertrains, in
contrast, employ multiple sources of tractive power to propel the
vehicle, most commonly operating an internal combustion engine
assembly in conjunction with a battery-powered or fuel-cell-powered
electric motor. A hybrid electric vehicle (HEV), for example, is
generally equipped with an ICE assembly and an electric machine
(E-machine), often in the form of a motor/generator unit (MGU),
that operate individually or cooperatively to generate tractive
power. Since hybrid vehicles are able to derive their power from
sources other than the engine, engines in HEVs may be turned off,
in whole or in part, while the vehicle is propelled by the electric
motor(s).
[0004] While innumerable options are available, there are three
primary types of electric machines used for traction motors in
modern electric-drive vehicle powertrains: brushed direct current
(DC) motors, brushless permanent magnet (PM) motors, and
multi-phase alternating current (AC) motors. Permanent magnet
motors have a number of operating characteristics that make them
more attractive for use in vehicle propulsion applications when
compared to their available counterparts, including high
efficiency, high torque, high power densities, and a long
constant-power operating range. A PM motor is an electric machine
that converts electrical energy into rotational mechanical energy
using a stator with multiphase electromagnetic windings, and a
rotatable rotor that bears an arrangement of permanent magnets.
Permanent magnet motors may be categorized to DC or AC, rotary or
linear, and radial flux or axial flux. In radial flux PM motor
designs, the magnet-bearing rotor may be nested inside the stator
or situated outside the stator. Alternatively, a PM motor may take
on an axial flux arrangement in which the stator and rotor are
facing, coaxial disks. The rotor, which has multiple
surface-mounted or interior-mounted permanent magnets, is separated
from the stator by a small air gap. A magnetic field produced by
the flow of current through the stator windings interacts with a
magnetic field produced by the rotor's PMs, thereby causing the
rotor to rotate.
SUMMARY
[0005] Disclosed herein are slotted permanent magnets (PM) for
electric machines, electromechanical motors and generator units
using such slotted PMs, methods for making and methods for using
such slotted PMs, and motor vehicles equipped with an electric
traction motor using such slotted PMs. By way of example, and not
limitation, there are presented manufacturing systems and methods
for fabricating the solid body of a permanent magnet with a
preselected pattern of surface grooves that is engineered to reduce
eddy current losses during operation of an accompanying electric
machine. These grooves may be generated by precision tooling,
extrusion, stamping, or by adding the features during a sintering
process. The surface grooves may comprise a first set of mutually
parallel, rectilinear grooves that is orthogonal with a second set
of mutually parallel, rectilinear grooves. Each elongated groove
may have a polygonal or ovate cross-section with a depth that is
greater than its width (e.g., at least a 3:1 depth to width ratio).
The groove depth is less than the thickness of the permanent magnet
such that the grooves do not extend through PM body. The tooling to
generate the surface grooves may take on a variety of geometrical
shapes and sizes, with the tooling path (groove depth) performed in
planes parallel to the direction of the impinging magnetic field.
These grooves may be introduced on a single side, opposing sides,
multiple select sides, or all sides of the PM body. For some
implementations, the PM body is a rectangular polyhedron with
recessed grooves formed into the opposing major faces with the
greatest surface areas, with each side having a distinct pattern of
grooves.
[0006] The solid PM body may take on innumerable shapes and sizes,
including rectangular block magnets, annular magnets, bread-loaf
magnets, curved tile magnets, etc. In addition, the direction of PM
magnetization during operation of the electric machine may include
radial, parallel, or any combination of the two. A foreseeable
application for any of the disclosed slotted permanent magnets
includes multiphase synchronous PM traction motor/generator units
(MGU) for electric-drive vehicles. Permanent magnet synchronous
motor applications include radial-flux and axial-flux machines with
interior or surface mounted PMs. It is envisioned, however, that
disclosed slotted PMs may be applied to any electric machine that
utilizes permanent magnets. Optionally, the surface grooves may be
filled with high-resistivity bonded magnets or other filler
materials engineered to increase magnetic field density and improve
mechanical strength. As a further option, the PM surface grooves
may be filled with a high-resistivity epoxy to further improve eddy
current loss abatement. In addition to loss reduction, the
superficial grooves may be designed to mechanically fasten the
magnets to a complementary support body, such as a rotor of a PM
electric machine, for added retention strength. High-strength ties
or clips may be used to fasten the PM body to the rotor;
alternatively, the rotor may be fabricated with complementary
interlocking features that slide into or interference fit with the
PM's surface grooves.
[0007] Aspects of this disclosure are directed to electric
machines, such as motors, generators, transformers, etc., that
employ slotted permanent magnets to generate magnetic fields.
Presented herein, for example, is an electric machine with a stator
having a hollow core and one or more slots. One or more
electrically conductive windings is/are disposed in the stator
slot(s). The electric machine also includes a rotor that is movable
with respect to the stator, and one or more permanent magnets
mounted onto or into the rotor. For some applications, the rotor
may be rotatably disposed inside the stator's hollow core. Each
permanent magnet includes a rigid, single-piece PM body with
opposing first and second faces. A first set of elongated grooves
is recessed into the first face, and an optional second set of
elongated grooves is recessed into the second face. Each groove has
a depth that is substantially parallel to a direction of a
time-varying magnetic field generated by the electrified conductive
winding(s). For at least some applications, the superficial grooves
may all share a common depth and shape; alternatively, one or more
of the grooves may have a distinct shape and/or size.
[0008] Other aspects of the disclosure are directed to
electric-drive motor vehicles equipped with a traction motor that
employs slotted permanent magnets to generate magnetic fields. As
used herein, the term "motor vehicle" may include any relevant
vehicle platform, such as passenger vehicles (REV, BEV, PHEV, FEV,
etc.), commercial vehicles, industrial vehicles, tracked vehicles,
off-road and all-terrain vehicles (ATV), motorcycles, farm
equipment, boats, planes, etc. In an example, an electric-drive
motor vehicle includes a vehicle body with multiple road wheels
operatively attached to the vehicle body. An electric traction
motor is mounted onto the vehicle body and electrically connected
to an on-board battery pack. The traction motor may operate alone
(e.g., in a full-electric vehicle (FEV) application) or in
conjunction with an internal combustion engine (e.g., in a
hybrid-electric vehicle (HEV) application) to drive one or more of
the vehicle wheels to thereby propel the vehicle.
[0009] The electric traction motor in the above example includes an
annular stator that is fabricated with a hollow core and multiple
stator slots. Multiple electrically conductive windings are
disposed in these stator slots. The traction motor also includes a
cylindrical rotor that is rotatably disposed inside the stator's
hollow core, and multiple permanent magnets that are mounted on the
outer surface of the rotor or inside complementary slots in the
rotor. Each permanent magnet is fabricated with a rigid,
single-piece PM body with opposing major faces (largest surface
areas) adjoining opposing minor faces (smaller surface areas). A
first set of elongated grooves arranged in a crisscross pattern is
recessed into the first major face, and a second set of elongated
grooves arranged in a crisscross pattern is recessed into the
second major face. Each groove depth is substantially parallel to
the direction of the time-varying magnetic field generated by the
electrified windings.
[0010] Additional aspects of the disclosure are directed to methods
for making and methods for using any of the disclosed slotted
permanent magnets, electric machines, motor/generator units, and
vehicles. In an example, a method is presented for assembling an
electric machine. This representative method includes, in any order
and in any combination with any of the above and below disclosed
options and features: providing a stator with a hollow core and
defining a stator slot; positioning an electrically conductive
winding in the stator slot; positioning a rotor adjacent the state
(e.g., inside the stator's hollow core); and, mounting a permanent
magnet to the rotor. The permanent magnet has a rigid, single-piece
PM body with opposing first and second faces. A first set of
elongated grooves is recessed into the first face. Each of the
grooves has a depth that is substantially parallel to a direction
of a time-varying magnetic field generated by the electrified
conductive winding.
[0011] The above summary is not intended to represent every
embodiment or every aspect of the present disclosure. Rather, the
foregoing summary merely provides an exemplification of some of the
novel concepts and features set forth herein. The above features
and advantages, and other features and attendant advantages of this
disclosure, will be readily apparent from the following detailed
description of illustrated examples and representative modes for
carrying out the present disclosure when taken in connection with
the accompanying drawings and the appended claims. Moreover, this
disclosure expressly includes any and all combinations and
subcombinations of the elements and features presented above and
below.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] FIG. 1 is a schematic illustration of a representative
electric-drive vehicle with a hybrid electric powertrain having an
electric motor/generator unit (MGU) with slotted permanent magnets
in accordance with aspects of the present disclosure.
[0013] FIG. 2 is a schematic side-view illustration of a
representative electric machine with a rotor assembly bearing
multiple slotted permanent magnets in accordance with aspects of
the present disclosure.
[0014] FIG. 3 is a perspective-view illustration of a
representative slotted permanent magnet (PM) in accordance with
aspects of the present disclosure.
[0015] FIG. 4 is a perspective-view illustration of another
representative slotted PM in accordance with aspects of the present
disclosure.
[0016] FIG. 5 is a perspective-view illustration of a
representative rotor with multiple surface-mounted slotted PMs in
accordance with aspects of the present disclosure.
[0017] FIG. 6 is a perspective-view illustration of a
representative rotor with multiple interior-mounted slotted PMs in
accordance with aspects of the present disclosure.
[0018] The present disclosure is amenable to various modifications
and alternative forms, and some representative embodiments are
shown by way of example in the drawings and will be described in
detail herein. It should be understood, however, that the novel
aspects of this disclosure are not limited to the particular forms
illustrated in the above-enumerated drawings. Rather, the
disclosure is to cover all modifications, equivalents,
combinations, subcombinations, permutations, groupings, and
alternatives falling within the scope of this disclosure as
encompassed by the appended claims.
DETAILED DESCRIPTION
[0019] This disclosure is susceptible of embodiment in many
different forms. Representative embodiments of the disclosure are
shown in the drawings and will herein be described in detail with
the understanding that these embodiments are provided as an
exemplification of the disclosed principles, not limitations of the
broad aspects of the disclosure. To that extent, elements and
limitations that are described, for example, in the Abstract,
Introduction, Summary, and Detailed Description sections, but not
explicitly set forth in the claims, should not be incorporated into
the claims, singly or collectively, by implication, inference or
otherwise.
[0020] For purposes of the present detailed description, unless
specifically disclaimed: the singular includes the plural and vice
versa; the words "and" and "or" shall be both conjunctive and
disjunctive; the words "any" and "all" shall both mean "any and
all"; and the words "including," "containing," "comprising,"
"having," and the like, shall each mean "including without
limitation." Moreover, words of approximation, such as "about,"
"almost," "substantially," "approximately," and the like, may be
used herein in the sense of "at, near, or nearly at," or "within
0-5% of," or "within acceptable manufacturing tolerances," or any
logical combination thereof, for example. Lastly, directional
adjectives and adverbs, such as fore, aft, inboard, outboard,
starboard, port, vertical, horizontal, upward, downward, front,
back, left, right, etc., may be with respect to a motor vehicle,
such as a forward driving direction of a motor vehicle when the
vehicle is operatively oriented on a normal driving surface.
[0021] Referring now to the drawings, wherein like reference
numbers refer to like features throughout the several views, there
is shown in FIG. 1 a schematic illustration of a representative
automobile, which is designated generally at 10 and portrayed
herein for purposes of discussion as a passenger vehicle with a
parallel P2 hybrid-electric powertrain. In particular, the
illustrated powertrain is generally composed of a single engine 12
and a single motor 14 that operate, individually and in concert, to
transmit tractive power to a multi-speed power transmission 16
through a hydrokinetic torque converter (TC) 18 to drive one or
more road wheels 20 of the vehicle's final drive system 11. The
illustrated automobile 10--also referred to herein as "motor
vehicle" or "vehicle" for short--is merely an exemplary application
with which novel aspects and features of this disclosure can be
practiced. In the same vein, implementation of the present concepts
into a multiphase, synchronous permanent magnet (PM) motor
generator unit (MGU) should also be appreciated as an exemplary
application of the novel concepts disclosed herein. As such, it
will be understood that aspects and features of the disclosure can
be applied to other electric machine configurations and utilized
for any logically relevant type of motor vehicle. Lastly, only
select components have been shown and will be described in
additional detail herein. Nevertheless, the vehicles and electric
machines discussed below can include numerous additional and
alternative features, and other well-known peripheral components,
e.g., for carrying out the various methods and functions of this
disclosure.
[0022] The representative vehicle powertrain system is shown in
FIG. 1 with a prime mover, such as a restartable internal
combustion engine (ICE) assembly 12, that is drivingly connected to
a driveshaft 15 of a final drive system 11 by a multi-speed
automatic power transmission 16. The engine 12 transfers power,
preferably by way of torque via an engine crankshaft 13 (or "engine
output member"), to an input side of the transmission 16. According
to the illustrated example, the ICE assembly 12 rotates an
engine-driven (first) torsional damper assembly 26 and, through the
torsional damper assembly 26, an engine disconnect clutch 28. This
engine disconnect clutch 28, when operatively engaged, transmits
torque received from the ICE assembly 12 by way of the damper 26 to
input structure of the TC 18. The transmission 16, in turn, is
adapted to receive, selectively manipulate, and distribute tractive
power from the engine 12 to the vehicle's final drive system
11--represented herein by a driveshaft 15, rear differential 22,
and a pair of rear road wheels 20--and thereby propel the hybrid
vehicle 10. The power transmission 16 and hydrokinetic torque
converter 18 of FIG. 1 share a common transmission oil pan or
"sump" 32 for supply of transmission fluid, as well as a shared
transmission pump 34 for sufficient hydraulic pressure to activate
the elements of the transmission 16, TC 18, and clutch 28.
[0023] The ICE assembly 12 operates to propel the vehicle 10
independently of the motor 14, e.g., in an "engine-only" operating
mode, or in cooperation with the motor 14, e.g., in a "motor-boost"
operating mode. In the example depicted in FIG. 1, the ICE assembly
12 may be any available or hereafter developed engine, such as a
two or four-stroke compression-ignited diesel engine or a
four-stroke spark-ignited gasoline or flex-fuel engine, which is
readily adapted to provide its available power output typically at
a number of revolutions per minute (RPM). Although not explicitly
portrayed in FIG. 1, it should be appreciated that the final drive
system 11 may take on any available configuration, including front
wheel drive (FWD) layouts, rear wheel drive (RWD) layouts,
four-wheel drive (4WD) layouts, all-wheel drive (AWD) layouts,
etc.
[0024] FIG. 1 also depicts an electric motor/generator unit 14 or
other suitable traction motor that operatively connects via a motor
support hub 29 (or "motor output member") and torque converter 18
to an input shaft 17 (or "transmission input member") of the
electro-hydraulic transmission 16. The motor/generator unit 14 can
be directly coupled onto a TC input shaft or rigidly mounted to a
housing portion of the torque converter 18. The electric
motor/generator unit 14 is composed of an annular stator 21
circumscribing and concentric with a cylindrical PM-bearing rotor
23. Electric power is provided to the stator 21 through electrical
conductors or cables 27 that pass through the motor housing in
suitable sealing and insulating feedthroughs (not illustrated).
Conversely, electric power may be provided from the MGU 14 to an
onboard traction battery pack 30, e.g., via regenerative braking.
Operation of any of the illustrated powertrain components may be
governed by an onboard or remote vehicle controller, such as
programmable electronic control unit (ECU) 25. While shown as a P2
hybrid-electric architecture with a single motor in parallel
power-flow communication with a single engine assembly, the vehicle
10 may employ other powertrain configurations, such as PS, P1, P3,
and P4 hybrid powertrains, any of which may be adapted for an REV,
PHEV, range-extended hybrid vehicle, fuel-cell hybrid vehicle,
etc.
[0025] Power transmission 16 can use differential gearing 24 to
achieve selectively variable torque and speed ratios between
transmission input and output shafts 17 and 19, respectively, e.g.,
while sending all or a fraction of its power through the variable
elements. One form of differential gearing is the epicyclic
planetary gear arrangement. Planetary gearing offers the advantage
of compactness and different torque and speed ratios among all
members of the planetary gearing subset. Traditionally,
hydraulically actuated torque establishing devices, such as
clutches and brakes (the term "clutch" used to reference both
clutches and brakes), are selectively engageable to activate the
aforementioned gear elements for establishing desired forward and
reverse speed ratios between the transmission's input and output
shafts. While envisioned as an 8-speed automatic transmission, the
power transmission 16 may optionally take on other suitable
configurations, including Continuously Variable Transmission (CVT)
architectures, automated-manual transmissions, etc.
[0026] As indicated above, ECU 25 is constructed and programmed to
govern, among other things, operation of the engine 12, motor 14,
transmission 16, TC 18, and clutch 28. Control module, module,
controller, control unit, processor, and any permutations thereof
may be defined to mean any one or various combinations of one or
more of logic circuits, Application Specific Integrated Circuit(s)
(ASIC), electronic circuit(s), central processing unit(s) (e.g.,
microprocessor(s)), and associated memory and storage (e.g., read
only, programmable read only, random access, hard drive, tangible,
etc.)), combinational logic circuit(s), input/output circuit(s) and
devices, etc., whether resident, remote, or a combination of both.
The foregoing hardware may be configured to execute one or more
software or firmware programs or routines, e.g., using appropriate
signal conditioning and buffer circuitry, and other components to
provide the described functionality. Software, firmware, programs,
instructions, routines, code, algorithms and similar terms may be
defined to mean any controller-executable instruction sets,
including calibrations and look-up tables. An ECU may be designed
with a set of control routines executed to provide the desired
functions. Control routines are executed, such as by a central
processing unit, and are operable to monitor inputs from sensing
devices and other networked control modules, and execute control
and diagnostic routines to control operation of devices and
actuators. Routines may be executed in real-time, continuously,
systematically, sporadically and/or at regular intervals, for
example, each 100 microseconds, 3.125, 6.25, 12.5, 25 and 100
milliseconds, etc., during ongoing vehicle use. Alternatively,
routines may be executed in response to occurrence of an event
during operation of the vehicle 10.
[0027] FIG. 2 illustrates another example of a PM-type electric
machine 114 that employs slotted permanent magnets to convert
electrical energy into mechanical energy, and vice versa. As
discussed herein, the electric machine 114 has a multi-phase stator
assembly 116 that nests therein and circumscribes an interior
PM-assisted synchronous reluctance rotor assembly 118. While
available for use in automotive and non-automotive applications
alike, the electric machine 114 may be particularly suited for use
in a hybrid electric powertrain as a traction motor (e.g., motor 14
FIG. 1) with an engine (e.g., ICE assembly 12), and to operate in
at least an engine-cranking mode, a regenerative-charging mode, and
a torque-assist mode. Electric machine 114 may be designed to
achieve: a relatively high efficiency, such as about 85% efficiency
over a calibrated output power and speed range; a relatively high
power density (e.g., greater than about 1500 watts per liter) and
torque density (e.g., greater than about 5 Newton-meters per
liter); a relatively wide peak power range (e.g., about 4 to 6
kilowatts or greater); a maximum speed of at least about 18,000
rpm; a reduced cost (e.g., by minimizing the number of permanent
magnets); a reduced mass and inertia (e.g., for fast dynamic
response to user output demands); and to fit into a relatively
small packaging space. Various alternative embodiments, including
alternative rotor assembly architectures and/or alternative stator
assembly architectures, may be employed by the electric machine 114
to meet similar or alternative operating parameters.
[0028] With continuing reference to FIG. 2, the stator assembly 116
is coaxial with and surrounds the rotor assembly 118 while
maintaining a small air gap 115 therebetween. In accord with the
illustrated example, this air gap 115 may be not less than about
0.2 millimeters (mm) and not greater than about 1.0 mm, for
example, in order to maximize power output and minimize the number
of slotted permanent magnets 120 borne by the rotor assembly 118 to
provide the desired power output. The representative stator and
rotor assemblies 116, 118 of FIG. 2, both of which are portrayed as
truncated right-circular cylinders with a generally annular shape,
are concentrically aligned about a longitudinal center axis A of
the electric machine 114. The stator assembly 116 has a hollow
stator core 122 that nests therein the rotor assembly 118; the
rotor assembly 118 has a hollow rotor core 124, e.g., that splines
to a motor shaft (not shown). It should be appreciated that a
protective motor housing (also not shown) can surround an outer
periphery of the stator's body 126 and can support the motor shaft
of the electric machine 114.
[0029] Rotor assembly 118 of FIG. 2 is fabricated with a rotor body
128 that supports multiple permanent magnets 120 circumferentially
spaced around the rotor core 124. Specifically, the rotor body 128
is precision machined with multiple rotor slots 130 arranged in
radially spaced barrier layers (e.g., four distinct barrier
layers). A first barrier layer 130A of slots 130 may be positioned
closest to an inner periphery of the rotor body 128, while a fourth
barrier layer 130D of slots 130 may be positioned furthest from the
rotor body's inner periphery than the barrier layers. A second
barrier layer 130B of slots 130 may be radially interposed between
the first and third barrier layers 130A, 130C, while the third
barrier layer 130C of slots 130 may be radially interposed between
the second and fourth barrier layers 130B, 130D. For at least some
embodiments, only select barrier layers (e.g., the first and third
barrier layers 130A, 130C) may house magnets 120, while other
select barrier layers (e.g., the second and fourth barrier layers
130B, 130D) do not house magnets 120 and, thus, act as air
barriers. In other embodiments, only one or all of the barrier
layers may comprise slots storing therein permanent magnets. For
example, the three radially innermost barrier layers 130A-130C may
be filled with magnets 120 while the radially outermost barrier
layer 130D does not include magnets 120. The rotor body 128 may be
fabricated from a metallic material, including a high-grade steel
material, that is engineered to maintain high speed rotational
stress within predetermined limits.
[0030] Stator assembly 116 of FIG. 2 is fabricated with a stator
body 126 that has multiple radially elongated, circumferentially
spaced stator slots 132 (e.g., 60 total slots). These stator slots
132 extend longitudinally through the stator body 126 along the
axis A. The stator slots 132 are configured to house electrically
conductive, multiphase stator windings 134. The stator windings 134
may be grouped into different sets, each of which may carry an
identical number of phases of electrical current, such as three,
five, six, or seven phases. In addition, the stator windings 134
may extend axially beyond the longitudinal ends of the stator body
126. A ratio of an outer diameter of the stator body 126 to an
axial length of the stator assembly 116 (i.e., the distance along
the axis A between the body's longitudinal ends not including any
extending portion of the windings 134) may be, by way of
non-limiting example, not less than 1.5 and not greater than 3.5,
e.g., in order to satisfy predetermined packing space constraints
for a particular application of the electric machine 114, such as
in the vehicle powertrain of FIG. 1.
[0031] For ease of manufacture, simplified assembly, and increased
costs savings, it may be desirable that all of the permanent
magnets 120 share an identical, rectangular polyhedron shape. It
should be recognized, however, that any one or more or all of the
PM bodies may take on innumerable shapes and sizes, including other
polyhedral block-type magnets, ring-shaped (annular) magnets,
bread-loaf block-type magnets (cross-section with quadrilateral
section adjoining semioval section), curved tile magnets, etc. In
one non-limiting example, each permanent magnet 120 may have a
thickness of about 1.5 mm to 2.5 mm to fit within a slot 130 having
complementary dimensions. In at least embodiments, a total mass of
magnet material (i.e., the mass of all magnets 120) used by the
electric machine 114 may be about 150 grams to about 250 grams. By
using less magnetic material but still meeting predetermined
operating parameters, costs are reduced. The permanent magnets 120
of the electric machine 114 may all be fabricated from the same
material, such as Neodymium Iron Boron (NdFeB); alternatively, any
one or more or all of the magnets 120 may employ different
materials, such as Samarium Cobalt (SmCo), Aluminum Nickel Cobalt
(AlNiCo), or any combination of rare earth magnet materials.
[0032] During operation of the electric machine 114, e.g., in a
regenerative-charging mode, the rotor assembly 118 is rotated via
the motor shaft while the stator assembly 116 is held relatively
stationary. In so doing, the permanent magnets 120 are moved past
the multiphase stator windings 134; the magnetic field emitted by
the permanent magnets 120 generates an electric current in the
windings 134 through electromagnetic induction. This induced
electric current may be used to power a load (e.g., recharge
traction battery pack 30 of FIG. 1). Conversely, during operation
of the electric machine 114, e.g., in an engine-cranking mode or
torque-assist mode, an electric current is supplied to the stator
windings 134 by a suitable power source (e.g., traction battery
pack 30). Passing the supplied current through the multiphase
stator windings 134 will generate a magnetic field at the stator
teeth 136. The magnetic field output from the stator teeth 136
interacts with the permanent magnets 120 in the rotor assembly 118
such that the rotor body 128 and attached motor shaft rotate to
generate a rotary driving force.
[0033] FIGS. 3 and 4 illustrate two examples of slotted permanent
magnets 220 and 320, respectively, that may be mounted to the rotor
23 of FIG. 1, the rotor 118 of FIG. 2, or either of the rotors 418
and 518 of FIGS. 4 and 5, for example. Each permanent magnet 220,
320 includes a rigid, single-piece PM body 222, 322 that may be
fabricated from any suitable permanent magnet material using any
appropriate manufacturing process. The representative PM bodies
222, 322 of FIGS. 3 and 4 are portrayed as right rectangular
cuboids with six (6) rectangular faces: opposing first and second
major faces 221, 321 and 223, 323, respectively (i.e., the faces
with the largest surface areas), opposing first and second minor
faces 225, 325 and 227, 327, respectively (i.e., the faces with the
smallest surface areas), and opposing first and second intermediate
faces 229, 329 and 231, 331, respectively (i.e., the faces with
neither the largest or smallest surface areas). As a right
rectangular cuboid, the major faces 221, 321, 223, 323 are
substantially parallel to each other and substantially orthogonal
to the other PM body faces. As indicated above in the discussion of
FIG. 2, each PM body 222, 322 of FIGS. 3 and 4 may take on an
assortment of different shapes and sizes; the permanent magnet 220
of FIG. 3, for example, is portrayed in FIG. 5 as a
surface-mounted, curved tile magnet in which the major faces 221,
223, have arcuate surfaces. In this regard, it is envisioned that
any of the features and options disclosed with reference to the
slotted PM 220 of FIG. 3 can be incorporated, singly or in any
combination, into the slotted PMs 120 of FIG. 2 and/or the slotted
PM 320 of FIG. 4, and vice versa. For at least some applications,
each slotted PM 220, 320 may be provided with a field-stabilizing
coating, a corrosion-resistant plating, high-resistivity epoxy gap
filler, assorted surface treatments, etc.
[0034] Both PM bodies 222, 322 of FIGS. 3 and 4 are fabricated with
preselected patterns of superficial grooves that are engineered to
reduce eddy current losses in the permanent magnets 220, 320 when
exposed to a time varying electromagnetic field during operation of
the accompanying electric machine. In at least the illustrated
examples, the slotted PMs 220, 320 afford a reduction in Solid Loss
(watts) of at least about 70-95% compared to an unslotted PM based
on three-dimensional (3D) electromagnetic finite element (FE)
analysis. Magnet segmentation, in which each magnet region (e.g.,
rotor slot 130 of FIG. 2) contains discrete, insulated PM segments
rather than a single-piece PM, is a conventional technique for
reducing rotor losses as it imposes minimal restrictions on machine
performance. Segmentation, however, increases the total number of
machine parts, which requires additional manufacturing processing
and reduced mechanical integrity of the system. The use of
engineered surface grooves, as described herein, provides
comparable benefits as segmentation while avoiding the additional
parts, costs and manufacturing steps associated with segmentation.
These grooves are not configured as through-holes and, thus, do not
extend through the PM body.
[0035] One optional slotted PM configuration utilizes a cruciform
groove pattern that is applied to both major faces of the
single-piece PM body. The permanent magnet 220 of FIG. 3, for
example, has a first set of elongated grooves 250 that is recessed
into the surface of the first major face 221, and a second set of
elongated grooves 251 (FIG. 5) that is recessed into the surface of
the second major face 223. In this example, the first set of
elongated grooves 250 is composed of two mutually orthogonal,
interconnected rectilinear grooves 252 and 253, and the second set
of elongated grooves 251 is also composed of two mutually
orthogonal, interconnected rectilinear grooves 254 and 255. Grooves
252 and 254 are mutually parallel and coplanar, elongated
longitudinally with respect to the permanent magnet 220. Both
grooves 252, 254 are shown extending the entire length of the PM
body 222, and interconnected by two end grooves 256 and 257 that
are recessed into the minor faces 225, 227, respectively. By
comparison, grooves 253 and 255 are mutually parallel and coplanar,
elongated laterally with respect to the permanent magnet 220. These
grooves 253, 255 are shown extending the entire width of the PM
body 222, and interconnected by two end grooves 258 and 259 that
are recessed into the intermediate faces 229, 231, respectively. It
may be desirable, for at least some embodiments, that the groove
pattern consist essentially of two (2) to six (6) rectilinear
grooves per major face. While shown extending the entire length and
width of the PM body 222, one or more of the rectilinear grooves
253-255 may extend only partway across the PM body 222. In this
regard, the end grooves 256-259 may optionally be eliminated.
[0036] Another optional slotted PM configuration utilizes a
distinct groove pattern for each major face of the of the
single-piece PM body. The permanent magnet 320 of FIG. 4, for
example, has a first set of elongated grooves 350 that is recessed
into the first major face 321, and a discrete second set of
elongated grooves 351 that is recessed into the second major face
323. In this example, the first set of elongated grooves 350 is
composed of a first series of three mutually parallel, rectilinear
grooves 352, each of which extends transversely across the entire
width the PM body 322 and is spaced from neighboring transverse
grooves 352 along the length of the PM body 322. The first set of
elongated grooves 350 also includes a single rectilinear groove 353
that extends longitudinally across the entire length of the PM body
322. This longitudinal groove 353 is perpendicular to all three
transverse grooves 352.
[0037] In contrast to the first set, the second set of elongated
grooves 351 is composed of a second series of four mutually
parallel, rectilinear grooves 354, each of which extends
transversely across the entire width of the PM body 322 and is
spaced from neighboring transverse grooves 354 along the length of
the PM body 322. The first set of elongated grooves 350 also
includes a second series of two mutually parallel, rectilinear
groove 355, each of which extends longitudinally across the entire
length of the PM body 322 and is spaced from neighboring
longitudinal grooves 355 along the width of the PM body 322. These
longitudinal grooves 355 are orthogonally oriented with respect to
the transverse grooves 354. While the first set of grooves 350 is
portrayed as having a first number of rectilinear grooves (e.g.,
four total) and the second set of grooves 351 is portrayed as
having a distinct, second number of rectilinear grooves (e.g., six
total), it is envisioned that the first and second sets of grooves
350, 351 may have the same number of grooves, which may be greater
than or less than what the numbers shown in the drawings.
[0038] The transverse grooves 352 in the first series of
rectilinear grooves 350 of the first major face 321 are
longitudinally offset from the transverse grooves 354 in the second
series of rectilinear grooves 351 of the second major face 323 such
that the grooves 352 are interleaved with the grooves 351 along the
length of the PM body 322. In the same vein, the longitudinal
groove 353 in the first series of rectilinear grooves 350 of the
first major face 321 is laterally offset from the longitudinal
grooves 355 in the second series of rectilinear grooves 351 of the
second major face 323 such that the grooves 353, 355 are
interleaved with one another along the width of the PM body 322.
Alternatively, one or more of the transverse grooves 352 may be
coplanar with one or more of the transverse grooves 354, and the
longitudinal groove 353 may optionally be coplanar with one of the
longitudinal grooves 355. In either of the foregoing optional
configurations, one or more or all of the grooves recessed into the
first major face 321 may be interconnected with one or more or all
of the grooves recessed into the second major face 321, e.g., to
form one or more toroidal grooves that extend continuously around
the PM body 322.
[0039] It may be desirable, for at least some configurations, that
the tooling process to create a slotted permanent magnet be
performed in planes parallel to the direction of the impinging
field. During operation of an electric machine, an induced
electromagnetic field with is a vector field density quantity B
(e.g., measured in Newtons per meter per ampere) is generated via
the stator windings. When passing through a conductive body, such
as a rare-earth permanent magnet, the magnetic field density B may
induce eddy currents in planes perpendicular to the vector's
direction. To increase resistance in the path of the induced eddy
currents, the depths of the superficial grooves extend in planes
parallel to the direction of the magnetic field density B. Put
another way, each groove has a depth D1 (see inset view of FIG. 4)
that is substantially parallel to a direction of the magnetic field
B that is generated by the electric machine's electrically
conductive windings. For eddy current loss reduction, each groove
may take on assorted geometric shapes, such as a triangular, oval,
or rectangular transverse cross-section. From a magnetic
standpoint, it may be desirable that the groove's depth D1 is
significantly larger greater than the groove's width W1 (e.g., at
least a 3:1 depth to width ratio). It is also envisioned that one
or more of the grooves have a distinct shape, size and/or
orientation from one or more of the other grooves. The surface
grooves in the PM bodies 222, 322 may be filled with
high-resistivity bonded magnets (e.g., bonded magnet inserts 260 of
FIG. 4) to increase the magnetic and mechanical strength of the
slotted PMs 220, 320.
[0040] Turning next to FIGS. 5 and 6, any of the herein-described
slotted permanent magnets may be surface-mounted or
interior-mounted to a complementary support body of an electric
machine. FIG. 5, for example, depicts four slotted PMs 220 mounted
onto an outer diameter (OD) surface of a rotor assembly 418, spaced
circumferentially from one another around the outer perimeter of
the rotor body 428. In contrast, FIG. 6 illustrates eight slotted
PMs 320 mounted within four complementary rotor slots 530, spaced
circumferentially from one another around the inner perimeter of
the rotor body 528. The surface grooves may also be configured to
provide increased mechanical retention between the slotted PMs and
their supporting base structure. FIG. 5, for example, illustrates
each PM body 222 being fastened to the rotor body 428 using
high-strength ties, such as carbon fiber straps 460 that pass
through the rectilinear grooves 254, 257 and 258. As another
option, FIG. 6 illustrates each PM body 222 being slidably engaged
with the rotor assembly 518 and aligned with their respective slots
530 using complementary teeth 560 that project into the slots 530
from the rotor body 528 and into the longitudinal rectilinear
groove 353 and 355. While shown as having a generally rectangular
cross-section, these teeth 560 and their receiving surface groove
353 and 355 may take the shape of a T-slot joint, dovetail joint,
etc. The dimensions of the grooves 353 and 355 and the teeth 560
may be determined based on desired mechanical requirements to
withstand any counteracting mechanical forces.
[0041] Aspects of the present disclosure have been described in
detail with reference to the illustrated embodiments; those skilled
in the art will recognize, however, that many modifications may be
made thereto without departing from the scope of the present
disclosure. The present disclosure is not limited to the precise
construction and compositions disclosed herein; any and all
modifications, changes, and variations apparent from the foregoing
descriptions are within the scope of the disclosure as defined by
the appended claims. Moreover, the present concepts expressly
include any and all combinations and subcombinations of the
preceding elements and features.
* * * * *