Magnet assemblies for motor-assisted turbochargers

An integral turbocharger-electric motor assembly permits the elements of an operating electric motor and turbocharger to be easily assembled into a relatively compact and reliable operating unit. To act as an electric motor rotor, the turbocharger shaft carries a magnet assembly in its central portion between the shaft bearings, in such proximity to the stator windings to provide electromagnetic coupling for the effective conversion of electric energy applied to the stator winding into rotational force applied by the magnet assembly to the turbocharger shaft. The magnet assembly includes a plurality of permanent magnets located around a central core and secured against centrifugal force on a non-magnetic outer sleeve. Such magnet assemblies are preferably formed as a unit that can be assembled onto the turbocharger shaft by retaining an annular arrangement of motor magnets in an assembly between central and outer sleeves.

FIELD OF INVENTION 
This invention relates generally to turbochargers used with internal 
combustion engines, and more particularly to turbochargers with integral 
assisting electric motors, and to structures for, and methods of 
combining, the components of the assisting electric motor and the 
turbocharger. 
BACKGROUND OF THE INVENTION 
Turbochargers are well known and widely used with internal combustion 
engines. Generally, turbochargers supply more charge air for the 
combustion process than can otherwise be induced through natural 
aspiration. This increased air supply allows more fuel to be burned, 
thereby increasing power and torque obtainable from an engine having a 
given displacement. Additional benefits include the possibility of using 
lower displacement, lighter engines with corresponding lower total vehicle 
weight to reduce fuel consumption, and use of available production engines 
to achieve improved performance characteristics. Some turbocharger 
applications include the incorporation of an intercooler for removing heat 
(both an ambient heat component and heat generated during charge air 
compression) from the charge air before it enters the engine, thereby 
providing an even more dense air charge to be delivered to the engine 
cylinders. Intercooled turbocharging applied to diesel engines has been 
known, in some applications, to double the power output of a given engine 
displacement, in comparison with naturally aspirated diesel engines of the 
same engine displacement. 
Additional advantages of turbocharging include improvements in thernal 
efficiency through the use of some energy of the exhaust gas stream that 
would otherwise be lost to the environment, and the maintenance of sea 
level power ratings up to high altitudes. 
At medium to high engine speeds, there is an abundance of energy in the 
engine exhaust gas stream and, over this operating speed range, the 
turbocharger is capable of supplying the engine cylinders with all the air 
needed for efficient combustion and maximum power and torque output for a 
given engine construction. In certain applications, however, an exhaust 
stream waste gate is needed to bleed off excess energy in the engine 
exhaust stream before it enters the turbocharger turbine to prevent the 
engine from being overcharged. Typically, the waste gate is set to open at 
a pressure, above which undesirable predetonation or an unacceptably high 
internal engine cylinder pressure may be generated. 
At low engine speeds, such as idle speed, however, there is 
disproportionately less energy in the exhaust stream as may be found at 
higher engine speeds, and this energy deficiency prevents the turbocharger 
from providing a significant level of boost in the engine intake air 
system. As a result, when the throttle is opened for the purpose of 
accelerating the engine from low speeds, such as idle speed, there is a 
significant time lag, i.e., turbo lag, and corresponding performance 
delay, before the exhaust gas energy level rises sufficiently to 
accelerate the turbocharger rotor and provide the compression of intake 
air needed for improved engine performance. The performance effect of this 
turbo lag may be more pronounced in smaller output engines which have a 
relatively small amount of power and torque available before the 
turbocharger comes up to speed and provides the desired compression. 
Various efforts have been made to address the problem of turbo lag, 
including a reduction in the inertia of the turbocharger rotor. In spite 
of evolutionary design changes for minimizing the inertia of the 
turbocharger rotor, however, the turbo lag period is still present to a 
significant degree, especially in turbochargers for use with highly rated 
engines intended for powering a variety of on-highway and off-highway 
equipment. 
Furthermore, to reduce exhaust smoke and emissions during acceleration 
periods when an optimal fuel burn is more difficult to achieve and 
maintain as compared with steady-speed operation, commercial engines 
employ devices in the fuel system to limit the fuel delivered to the 
engine cylinders until a sufficiendy high boost level can be provided by 
the turbocharger. These devices reduce excessive smoking, but the limited 
fuel delivery rate causes a sluggishness in the response of the engine to 
speed and load changes. 
The turbo lag period can be mitigated and, in many instances, virtually 
eliminated by using an external power source to assist the turbocharger in 
responding to engine speed and load increases. One such method is to use 
an external electric power supply, such as the electrical energy stored in 
batteries, to power an electric motor that has been integrated into the 
mechanical design of a turbocharger. By providing the motor components 
within the turbocharger housing, the turbocharger bearings can also serve 
as motor bearings. 
Providing motor components within a turbocharger assembly presents, 
however, a number of problems. Such motor components include permanent 
magnets to provide an electric motor rotor and wire windings to provide an 
electric motor stator, and the permanent magnets and stator windings must 
be in sufficient proximity to permit a relatively efficient conversion of 
electric energy applied to the stator windings into rotational energy 
imparted to the turbocharger rotor by the permanent magnets. The 
attachment of permanent magnets to the shaft exposes the permanent magnets 
to heat which is conducted down the shaft from the exhaust gas turbine 
wheel, and the exposure of the permanent magnets to such heat and their 
resulting temperatures may deleteriously affect the permeability and 
magnet field strength of the rotor magnets and result in insufficient and 
ineffective operation of the electric motor. In addition, the permanent 
magnets are exposed, in their rotation, to significant centrifugal forces 
since the turbocharger shaft can rotate at speeds up to 100,000 rpm and 
higher. The addition of stator windings within a turbocharger assembly 
also presents problems because the high temperatures that are reached in 
the turbocharger assembly can adversely affect the electrical insulation 
of the stator windings leading to possible failure. 
A turbocharger assembly, including an integral assisting motor is disclosed 
in our prior U.S. patent application Ser. No. 08/680,671, filed Jul. 16, 
1996, and U.S. Ser. No. 08/731,142, filed Oct. 15, 1996, which have 
addressed these problems and others. 
Other patents disclosing turbocharger-electrical machine combinations 
include U.S. Pat. Nos. 5,406,797; 5,038,566; 4,958,708, 4,958,497; 
4,901,530; 4,894,991; 4,882,905; 4,878,317, and 4,850,193. 
BRIEF STATEMENT OF THE INVENTION 
The invention provides a new integral turbocharger-electric motor assembly 
in which the elements of an operating electric motor and turbocharger can 
be easily assembled into a relatively compact and reliable operating unit. 
Such a turbocharger-motor assembly includes a central portion between the 
turbocharger turbine and compressor including a housing carrying, in a 
cooled supporting portion, a stator winding for the electric motor and 
providing bearing support adjacent its ends for the turbocharger shaft. To 
act as the electric motor rotor, the turbocharger shaft carries a magnet 
assembly in its central portion between the shaft bearings, in such 
proximity to the stator windings to provide electromagnetic coupling for 
the effective conversion of electric energy applied to the stator winding 
into rotational force applied by the magnet assembly to the turbocharger 
shaft. In preferred such assemblies, the turbocharger housing includes a 
conduit for coolant for the stator windings. 
In the invention, the magnet assembly includes a plurality of permanent 
magnets located around a central core and secured against centrifugal 
force by a non-magnetic outer sleeve. Preferably, such magnet assemblies 
are formed as a unit that can be assembled onto the turbocharger shaft by 
retaining an annular arrangement of motor magnets in an assembly between 
central and outer sleeves. In a preferred embodiment of the invention, the 
magnets can be secured around the central sleeve and within the retaining 
sleeve by a high-temperature structural adhesive, and the retaining sleeve 
can include inwardly projecting portions at its ends for an engagement 
with the ends of the magnets. Such a magnet assembly can be removably 
mounted on the turbocharger shaft between the turbocharger bearings and 
clamped in place by the axial force exerted on its ends by shaft sleeves 
when a rotor lock nut is tightened. The central core of the magnet 
assembly may be formed with a plurality of planar magnet-locating surfaces 
and ends, having a reduced surface area to reduce heat transfer to the 
magnets. In preferred magnet assemblies the inside surface of the central 
sleeve may be relieved in its central portion to reduce the area of 
contact with the turbocharger shaft, and reduce the heat flow from the 
shaft into the magnet assembly. In addition, in the turbocharger-electric 
motor assembly, or in the magnet assembly itself, insulating material may 
be placed between the central sleeve of the magnet assembly and the 
turbocharger shaft to limit heat transfer into the magnet assembly.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring now to the drawings, and particularly to FIG. 1, a turbocharger 
10 combines the elements of an electric machine and a turbocharger in 
accordance with this invention. The turbocharger assembly 10 comprises an 
exhaust gas turbine 11 at one end, a charge air compressor 12 at the other 
end, and an assisting electric motor 13 in a central housing 14 of the 
turbocharger 10. The central housing 14 supports, through bearings at its 
turbine end and compressor end, a multi-vaned turbine wheel 15, a 
compressor wheel 16 having a plurality of vanes 17, and an interconnecting 
rotatable shaft 18. The turbine 11 includes a turbine housing 20 which 
forms an exhaust gas inlet scroll 21 that is connected to receive exhaust 
gas from an internal combustion engine (not shown). Internal combustion 
engines frequently have exhaust manifolds divided into two sections, each 
section receiving exhaust gas from a separate set of cylinders (not 
shown). The exhaust gas is directed from the inlet scroll 21 to drive the 
turbine wheel 15 and shaft 18 in rotation. After passing through the 
turbine wheel 15, the exhaust stream flows out of the turbocharger through 
an exhaust vent 22. 
Rotation of the shaft 18 rotates the compressor wheel 16 at the opposite 
end of the interconnecting shaft 18, and air is drawn in through an air 
intake opening 23 formed in a compressor casing 24 after passing through 
an appropriate air filter (not shown) to remove contaminants. The 
compressor casing 24 includes a scroll 25 for directing the compressed 
combustion air to an engine air intake manifold (not shown). 
In the invention, the elements of electric motor 13 are incorporated in the 
central portion of the turbocharger assembly 10. The elements of the 
assisting electric motor comprise a stator 30, including a plurality of 
pole-forming laminations of magnetic material and wire windings for the 
poles so formed, that is carried by housing 14, and a rotor including a 
plurality of magnets in a magnet assembly 32 that is carried by and 
attached to the rotatable shaft 18. In the assembly the rotor magnets of 
the magnet assembly 32 are carried in electromagnetic proximity to the 
poles formed by the lamination and windings of the stator 30 so that a 
rotating magnetic field formed by the application of electrical energy to 
the stator windings can effectively coupled with the magnetic field of the 
rotor magnets and drive the rotatable shaft 18 in rotation. In the 
preferred assembly of FIG. 1, the housing 14 provides cooled support for 
the stator windings. For example, as shown in FIG. 1, the housing 14 is 
formed with a coolant conduit 29 in such proximity to the housing surfaces 
in contact with the stator 30 that circulation of a coolant, such as 
engine coolant, can maintain the temperature of the stator windings below 
a temperature that may be damaging to their electrical insulation. The 
invention provides an easily assembled and reliably operable 
motor-assisted turbocharger. As set forth below, the rotor 31 of the 
electric motor can comprise a unitary magnet assembly 32 carrying the 
plurality of rotor magnets in a spaced arrangement about the rotatable 
shaft 18 of the turbocharger for effective interaction with the stator 30 
when energized. The unitary magnet assembly 32 may be slipped onto the 
rotatable shaft 18 and fixed to the shaft to transfer rotational force 
from the magnet assembly 32 to the shaft 18 and assist in the rotation of 
compressor wheel 16 by the turbine wheel 15. 
For example, the rotating elements of turbocharger assembly 10 can be 
attached together as a rotating unit by a lock nut 26 that compresses the 
rotating elements against a shoulder 18a formed on the rotating shaft 18. 
As illustrated by FIG. 1, mounted on the shaft 18 in succession are 
compressor wheel 17, sleeve 40, thrust collar 41, bearing sleeve 42, 
magnet assembly 32, seal sleeve 43, with sleeve seal 43 bearing against a 
shoulder 18a on shaft 18. The lock nut 26 exerts an axial force on all 
these members to maintain them as a rotating unitary assembly. The magnet 
assembly 32 is thus clamped tightly on shaft 18 between the bearing sleeve 
42 and the seal sleeve 43 and can apply rotational forces to the shaft 18. 
The stator windings 30 of the motor can be mounted in the turbocharger 
central housing 14 and secured by a set screw (not shown). Winding wires 
27 can exit the housing 14 through passageway 28 for connection to an 
appropriate electronic control and power supply. As shown in FIG. 1, the 
coolant conduit 29 surrounds stator windings 30 and is separated from the 
stator 30 by a relatively thin housing wall, which can transfer heat from 
the stator windings 30 to a coolant in conduit 25. Cooling conduit 29 has 
inlet and outlet connections (not shown) to receive a cooling fluid from 
the internal combustion engine cooling system. 
Thus, when the stator 30 is energized, rotational forces are applied to the 
shaft 18 on which the compressor wheel 17 is mounted and augment the 
torque being applied to the shaft 18 by the exhaust gas turbine 11, 
thereby causing the assembly to rotate faster than if it were not equipped 
with the assisting motor 13. The faster rotation of the shaft 18 when the 
assisting motor 13 is energized drives the compressor wheel 17 to supply 
the engine with a greater flow of charge air at higher pressure, thereby 
improving engine performance while reducing the amount of smoke and 
pollutants emitted during acceleration of the engine. 
The components of the turbocharger not discussed in detail are well known 
in the art, such as shaft bearings and oil seal elements necessary for 
reliably supporting the rotating assembly and for containment of the 
lubricating oil that is conventionally supplied from the engine's 
pressurized oil system to lubricate and cool the bearings. 
FIG. 2 is a cross-sectional view of the magnet assembly 32 of FIG. 1, taken 
at a plane corresponding to line 2--2 of FIG. 1, and FIG. 3 is a 
cross-sectional view of the magnet assembly 32 taken at a plane 
corresponding to line 3--3 of FIG. 2. As shown in FIGS. 2 and 3, magnet 
assembly 32 includes a sleeve-like inner core 33 of a magnetic material, 
such as carbon steel, on which a plurality of permanent motor magnets 34 
are placed. As shown by FIG. 2, the inner core 33 is formed with a 
plurality of planar magnet-locating surfaces 33a for spacing the magnets 
34 about the turbocharger shaft for interaction with the poles formed by 
the stator 30. As also shown in FIGS. 2 and 3, the inner core 33 has ends 
33b with reduced surface areas (e.g., minimal thicknesses) to reduce the 
heat transfer to the magnets 34 from the adjacent turbocharger parts. The 
magnets 34 are encompassed and retained by an outer, non-magnetic sleeve 
35 designed with sufficient strength to hold the magnets 34 in place at 
the maximum rotational speed of the turbocharger. The inner core 33, 
magnets 34 and outer sleeve 35 comprise a unitary magnetic assembly 32 
which serves as the electric motor rotor in the turbocharger assembly 10. 
In preferred embodiments, the components of the magnet assembly can also 
be secured together as a unit by an appropriate high temperature 
structural adhesive. 
FIG. 4 is a cross section of another magnet assembly 36, in which the inner 
core 37 has been formed with a inner surface portion 37a having an 
increased diameter so that it is removed from contact with the shaft 18, 
and radialy-inwardly extending portions 37b bracketing the inner surface 
portion 37a for supporting the core 37 on the shaft 18. The resulting 
reduced contact area between the inner core 37 and shaft 18 reduces the 
heat transfer from the turbocharger shaft 18 to the permanent magnets 34. 
FIG. 5 is a cross-sectional view of the magnet assembly 32 of FIGS. 2 and 3 
assembled onto the shaft 18 with thermal insulating numeral between the 
inner core 33 and the turbocharger shaft 18 to reduce heat transfer from 
the turbocharger shaft 18 to the permanent magnets 34. As shown in FIG. 5 
the thermal insulating material may be conveniently in the form of a 
thermally insulative sleeve 38 between the inner core 33 and shaft 18. 
FIGS. 6 and 7 illustrate further embodiments of a magnet assembly of the 
invention. In the embodiments of FIGS. 6 and 7, the sleeve-like inner core 
can be in all respects identical to the sleeve-like inner core shown in 
FIGS. 2-4, forming a plurality of planar magnet locating surfaces 33a for 
spacing magnets 34 about the turbocharger shaft. In the magnet assembly of 
FIG. 6 the outer non-magnetic metallic sleeve 39 has its ends 39a and 39b 
rolled inwardly over the ends of the permanent magnets 34 as shown in the 
FIG. 6 cross-section. In the embodiment of FIG. 7, the outer non-magnetic 
metallic sleeve 40 comprises two sections 41 and 42 which are preferably 
identical. Each of the sections 41 and 42 is formed with an inwardly 
extending annular flange 41a, 42a, providing a cup-like form. In the 
embodiment of FIG. 7 each of the sections 41 and 42 may be slid over the 
magnets 34 until their inwardly extending annular flanges 41a and 42a 
engage the ends of the magnets 34. In the embodiment of FIG. 7 the two 
cup-like sleeve sections 41 and 42 may be secured in place by suitable 
adhesive or by shrink fit onto the magnets 34. In the embodiments of FIGS. 
6 and 7, the outer sleeves 39 and 40 help prevent axially displacements of 
the magnets 34 of the magnet assembly. 
While preferred embodiments of the invention have been illustrated and 
described, the invention can be incorporated in other embodiments and 
should be limited only by the scope of the following claims and the prior 
art.