ENGINE SUPERCHARGING SYSTEM
BACKGROUND
Engine downsizing has become an increasingly popular option for automotive
manufacturers looking to reduce average carbon dioxide emissions and improve fuel
consumption. Unfortunately, the torque produced by a smaller engine can be markedly less
than that of a larger one, and while end consumers might accept the reduced emissions and
improved fuel economy of a reduced-displacement engine, they often demand the same
driving performance and comfort of a larger-displacement engine.
One solution is to pair a reduced-displacement engine with a turbocharger.
Turbochargers, which get their power from the flowing exhaust gases produced by internal
combustion, are a thermodynamically efficient boosting system, but under some conditions
may suffer from lag as the exhaust flow builds to the point where effective boost can be
delivered. As engine specific outputs increase, this effect is magnified, limiting the
downsizing and carbon dioxide reduction potential offered by conventional turbocharging.
Vehicle manufacturers commonly adopt shorter transmission ratios to mitigate this effect;
however, this generally has an opposite effect to engine displacement downsizing on carbon
dioxide emissions performance.
Another option that overcomes the limitations of turbocharging is pairing a reduced-
displacement engine with a supercharger mechanically driven by the engine's crankshaft.
Although turbo lag may be overcome with the use of a supercharger, conventional
superchargers typically have lower compressor efficiency than turbochargers, and cause
significant parasitic losses when boost is not required, potentially harming fuel economy and
increasing carbon dioxide emissions.
SUMMARY
A supercharging system for an engine is provided that includes an air pump, an
electrical machine, an engine-connected input member and a variable-ratio power
transmission mechanism. The power transmission mechanism includes a sun member
operatively connected to one of the air pump, the electrical machine and the input member.
At least one planet member is drivingly interfaced with the sun member and rotatably carried
by a carrier operatively connected to another one of the air pump, the electrical machine and
the input member. An annulus is drivingly interfaced with the at least one planet member
and operatively connected to the other one of the air pump, the electrical machine and the

input member. The supercharging system also includes a brake configured to selectively
inhibit rotation of at least one of the sun member, the carrier, and the annulus.
BRIEF DESCRIPTION OF THE DRAWINGS
Embodiments of the invention will now be described, by way of example, with
reference to the accompanying drawings, wherein:
FIG. 1 is a schematic illustration of an engine supercharging system according to an
embodiment of the present invention;
FIG. 2 is a schematic illustration of an engine supercharging system according to
another embodiment of the present invention;
FIG. 3 is a graphical illustration of exemplary operating parameters for the engine
supercharging system of FIG. 1;
FIG. 4 is a graphical illustration of exemplary operating parameters for the engine
supercharging system of FIG. 2;
FIG. 5 is a schematic illustration of a control system for use with an engine
supercharging system according to an embodiment of the present invention; and
FIG. 6 is a schematic illustration of a control system for use with an engine
supercharging system according to another embodiment of the present invention.
DETAILED DESCRIPTION
Referring to FIGS. 1 and 2, an engine supercharging system 10 according to
embodiments of the present invention are shown. In the illustrated embodiments,
supercharging system 10 includes an air pump 12, such as a centrifugal (shown), Roots-type,
or screw-type supercharger; an electrical machine 14, such as an electric motor-generator; an
engine-connected input member 15; and a variable-ratio power transmission mechanism 16.
Power transmission mechanism 16 includes a sun member 18 operatively connected to one of
air pump 12, electrical machine 14 and input member 15. At least one planet member 20 is
drivingly interfaced with sun member 18 and rotatably carried by a carrier 22 operatively
connected to another one of air pump 12, electrical machine 14 and input member 15. An
annulus 24 is drivingly interfaced with the at least one planet member 20 and operatively
connected to the other one of air pump 12, electrical machine 14 and input member 15.
In a particular configuration, power transmission mechanism 16 may be a traction-
drive device that includes an elasto-hydrodynamic lubrication oil that creates a film between
sun member 18, planet member 20 and annulus 24. The oil film exhibits a viscosity that is
increasable under pressure created by the closely rotating components of the planetary system
to transmit torque between sun member 18, planet member 20 and annulus 24. Compared to

a conventional toothed-gear transmission, is capable of producing a relatively higher ratio
while generating significantly less noise. In the embodiment shown in FIG. 1, for example,
power transmission mechanism 16 is configured such that the speed ratio between first and
second shafts 28, 30 is approximately fifteen-to-one (15:1); although, the speed ratio is not
necessarily limited thereto. When a centrifugal supercharger is employed, for example, the
ratio may be between about 10:1 and 20:1. It will also be appreciated that the interface
between sun member 18, planetary member 20, and annulus 24 may be a geared interface,
whereby torque is transmitted between the components by meshed gear teeth. When a Roots-
type or screw-type supercharger is employed, for example, the speed ratio between first and
second shafts 28,30 may be between about 2:1 and 5:1.
Sun member 18 may operatively connected to one of air pump 12, electrical machine
14 and input member 15 by a first shaft 28 and carrier 22 may be operatively connected to
another one of air pump 12, electrical machine 14 and input member 15 by a second shaft 30.
A brake 32, such as a shaft brake, is configured to selectively inhibit rotation of sun member
18 or carrier 22 by virtue of its interaction with first shaft 28 or second shaft 30.
Engine-connected input member 15 may, for example, include a belt, gear or chain
driven pulley that receives power from an engine by virtue of its connection to an engine
crankshaft (none shown). In the embodiment shown in FIG. 1, for example, the speed ratio
between engine-connected input member 15 and the engine crankshaft is approximately
three-to-one (3:1) for a total ratio between the engine and the electrical machine of forty-five-
to-one (45:1). However, the net speed ratio and the speed ratio between input member 15 and
the engine crankshaft are not intended to be limited thereto.
Supercharging system 10 may also include a control sjrstem 36 having a controller 38,
such as a microprocessor-based controller, which may communicate with and directs
operation of electrical machine 14 and brake 32. Controller 38 may be a stand-alone
component or may be integrated with another vehicle controller, such as the vehicle engine
controller (not shown). If desired, an energy source 40, such as a battery, may be operatively
connected to electrical machine 14 through a power converter 42, such as a two-quadrant
inverter, to receive power from and/or supply power to electrical machine 14 for operation.
In the embodiment shown in FIG. 1, sun member 18 is operatively connected to
electrical machine 14 through first shaft 28, annulus 24 is operatively connected to engine-
connected input member 15 and carrier 22 is operatively connected to air pump 12 through
second shaft 30. In a mode of operation, controller 38 is configured to activate brake 32 to
inhibit rotation of carrier 22 and to operate electrical machine 14 as a motor to provide power

to rotate sun member 18 and, by virtue of the corresponding rotation of planet member 20,
annulus 24 and engine-connected input member 15 to provide torque to the vehicle engine.
In this mode of operation, electrical machine 14 may be used to crank and start the vehicle
engine, which may eliminate the need for a separate starter motor in the vehicle. Once the
engine is started, controller 38 may continue to operate electrical machine 14 as a motor to
deliver torque to the engine and adjoining powertrain. In this manner, supercharging system
10 may operate as a mild hybrid.
In another mode of operation, controller 38 is configured to deactivate brake 32 to
permit rotation of carrier 22 and to inhibit rotation of sun member 18 using electrical machine
14 to permit torque flow from the engine-connected input member 15, through the power
transmission mechanism 16, and into air pump 12. In this mode of operation, air pump 12 is
powered solely by the engine crankshaft to deliver charged air to the engine.
In another mode of operation, controller 38 is configured to deactivate brake 32 to
permit rotation of carrier 22 and to permit rotation of sun member 18 by operating electrical
machine 14 as a generator. In this manner, torque flows from the engine-connected input
member 15, through variable-ratio power transmission mechanism 16, and into the air pump
12. This mode of operation may be employed when less than full boost is required and
allows a portion of the power provided by the engine to be returned to energy source 40. The
amount of power returned to energy source 40 is generally equal to the generator operating
speed multiplied by the torque reaction from air pump 12. For example, this power may be
as high as 3kW for 20kW of mechanical boosting.
In certain vehicles into which supercharging system 10 may be installed, the
conventional alternator may be eliminated by operating electrical machine as a generator to
provide power to the vehicle electrical system. When supercharging system 10 is being
operated to provide charged air to "boost" the engine at a level other than full boost, power
provided by the engine through input 15 is returned to energy source 40 by virtue of electrical
machine 14 operating as a generator. When the vehicle is traveling on a highway, for
example, and no "boost" is required, electrical machine 14 may be operated, as necessary, to
more rapidly charge energy source 40 by applying brake 32. In an implementation of the
invention, up to lOkW of power may be available for generation and storage.
As noted above, there are several different compressor designs employable in
supercharging system 10, but it is typically the centrifugal compressor, the same design as
most turbochargers, that operatives more effectively when the engine is at full load.
Unfortunately, in more traditional fixed-ratio supercharger drives, the centrifugal compressor

delivers its boost roughly in proportion to the square of its rotational speed with very poor
low speed torque augmentation. Since there is not necessarily a fixed link between the
engine and air pump 12 in the present invention, air pump 12 may be run at its optimum
speed. For example, in another operating mode, controller 38 may be configured to
deactivate first brake 32 to permit rotation of carrier 22 and to rotate sun member 18 by
operating electrical machine 14 as a motor to augment torque flow from the engine-connected
input member 15, through the a variable-ratio power transmission mechanism 16, and into air
pump 12. In this mode of operation, augmentation of low-end "boost" (i.e., when the engine
speed is relatively low) may be obtained by using power from energy source 40 to power
electrical machine 14 as a motor to increase the speed of air pump 12. This feature permits a
vehicle manufacturer to adopt more efficient vehicle transmission ratios and creates a larger
power/speed handling range to air pump 12 for a given peak power capability control system
36.
In the embodiment illustrated in FIG. 2, by contrast, sun member 18 is operatively
connected to air pump 12 and electrical machine 14 is operatively connected to annulus 24,
such as by integrating or connecting an electrical machine rotor 50 to annulus 24 for rotation
therewith. Carrier 22 is operatively connected to engine-connected input member 15. In a
mode of operation, controller 38 may be configured to activate brake 32 to inhibit rotation of
sun member 18 and to operate electrical machine 14 as a motor to provide power to rotate
annulus 24 and, by virtue of the corresponding rotation of planet member 20, to rotate carrier
22 and the engine-connected input member 15 to provide torque to the vehicle engine. In this
mode of operation, electrical machine 14 may be used to crank and start the vehicle engine,
which again may eliminate the need for a separate starter motor in the vehicle. Once the
engine is started, controller 38 may continue to operate electrical machine 14. as a motor to
provide torque to the engine and adjoining powertrain. In this manner, supercharging system
10' may operate as a mild hybrid. When operation of supercharging system 10' as a starter
and mild hybrid are not desired, i.e., when only generator operation is desired, the two-
quadrant motor inverter may be replaced with a less costly rectifier such as shown in FIGS. 5
and 6 and described below.
In another mode of operation, controller 38 is configured to activate brake 32 to
inhibit rotation of sun member 18 and to permit rotation of annulus 24 by operating electrical
machine 14 as a generator such that torque flows from engine-connected input member 15,
through the a variable-ratio power transmission mechanism 16, and into the generator.
Controller 38 may also be configured to deactivate brake 32 to permit rotation of sun member

18 and to inhibit or control rotation of annulus 24 using electrical machine 14 to permit
torque flow from the engine-connected input member 15, through the power transmission
mechanism 16, and into air pump 12. In this so-called "boosting" mode of operation, air
pump 12 is powered by the engine crankshaft to deliver charged air to the engine.
In an exemplary implementation of the present invention, the required electrical
power for driving air pump 12 with an efficiency of about 70% is approximately 12kW,
assuming a maximum engine speed of about 6000 RPM. As will be appreciated, the power
requirement may depend on the required engine torque-speed curve and the efficiency may
not be a steady 70% across the entire curve. Table I illustrates sample operating parameters
for an exemplary implementation of the embodiment of FIG. 2 during the "boosting" mode of
operation.

In Table I, power at air pump 12 is the power required to drive the air pump for a
constant pressure ratio. Sun member speed is the speed required for sun member 18 to
generate the require amount of power at air pump 12. Power transmitted by annulus 24 is the
power generated by electrical machine 14, whereby negative power denotes power flow from
energy source 40 to annulus 24 (electrical machine 14 functioning as a motor) and positive
power denotes power flow from annulus 24 to energy source 40 (electrical machine 14
functioning as a generator).
Referring to FIG. 3, several exemplary operating parameters presented in Table I are
illustrated graphically. For nearly constant engine boost over the permissible speed range of
an engine, power flows from energy source 40 through electrical machine 14 and into
annulus 24 at engine speeds below about 2400 RPM. To accommodate this operation,

electrical machine 14 may be configured, for example, as a brushless direct current motor
utilizing power converter 42 to convert the direct current into three-phase alternating current.
In a mode of operation described above with respect to the embodiment of FIG. 2, rotation of
annulus 24 may be inhibited to provide reactionary torque to maximize the speed of sun
member 18 and, correspondingly, the level of boost generated by air pump 12. Rotation of
annulus 24 may be inhibited by virtue of brake 52 that selectively engages annulus 24, by
shorting electrical machine 14, or by recovering power applied to annulus 24 in energy
source 40. Table II illustrates sample operating parameters for another exemplary
implementation of the embodiment of FIG. 2 during the "boosting" mode of operation.

Referring to FIG. 4, several exemplary operating parameters presented in Table II are
illustrated graphically. For engine speeds up to about 3000 RPM, annulus is generally not
rotating. A comparison of compressor power for the embodiments illustrated in FIGS. 1 and
2 is provided by way of example in the following table.

As shown in FIGS. 3 and 4, performance beyond about 3000 RPM is substantially
similar for each exemplary implementation. The degree of performance degradation

associated with generator-only operation below an engine speed of about 3000 RPM may be
mitigated by increasing the effective ratio of power transmission mechanism 16.
To support generator-only operation, power converter 42 may include a rectifier
(FIGS. 5 and 6), such as a six-diode bridge rectifier, which receives three-phase power from
electrical machine 14 and converts this power into direct current. In the embodiment shown
in FIG. 5, the rectifier may be electrically connected to energy source 40, with a line
conductor 62 and field effect transistor (FET) 64 provided therebetween. Control system 36
may also include a capacitor 66.
At an engine speed of approximately 4000 RPM, for example, a sufficient
electromotive force (EMF), e.g., around 15V, is required to push about 1210W (see, e.g.,
Table II above) to energy source 40. Furthermore, as illustrated in Table II, an increasing
amount of power must be pushed to energy source 40 as the engine speed increases, since it is
generally undesirable to proportionately increase the speed of sun member 18. At about 6000
RPM, for example, the EMF increases to about 22.5V. Additionally, the current supplied to
energy source 40 is controlled by running FET 64 in pulse width modulation (PWM) mode,
with line conductor 62 and capacitor 66 facilitating this operation. In the described
implementation, FET 64 may exhibit a maximum voltage rating of about 75 V and a
continuous mean current rating of about 271 A. If only half the power is required by air pump
12 at an engine speed of about 6000 RPM, for example, then FET 64 may exhibit a
continuous mean current rating of about 135 A. A 3-5kW electrical machine operating as a
generator has an electrical output greater than many conventional vehicle alternators and,
therefore, electrical machine 14 may be operated in a manner that allows the vehicle
alternator to be eliminated.
Alternatively, control system 36 may include a second FET (not shown) that applies a
dead short across the rectifier output (i.e., an eddy current brake). With a back EMF of about
15 V, the second FET may be rated at about 60A (75V). When no boost is required, the first
and/or second FETs may be turn off, allowing annulus 24 to rotate freely and sun member 18
to find a conveniently slower rotational speed dependent on the amount of air being drawn
into the engine.
Referring to FIG. 6, a control system 36' according to another embodiment of the
present invention is shown. Control system 36' is similar to control system 36 described
above with the addition of a switched-mode power supply 68 that performs current and
voltage regulation on the high voltage side of the circuit. Power supply 68 may also be used
to replace a conventional vehicle alternator. In an embodiment, power supply 68 includes a

pair of switching FETs 70, 72 and a four-diode rectifier 74 communicating with the 12V
vehicle electrical system. Assuming a mean voltage of about 300V for control system 36',
FETs 70, 72 may be rated at around 400V, 20A and rectifier 74 may be rated at around 75V,
150A (which can conveniently replace a 150A alternator). Additionally, capacitor 66 may be
configured as an ultra capacitor, allowing a reduction in the peak rating of the FETs under
heavy boost and an averaging of the current being fed back to the 12V vehicle electrical
system.
The present invention has been particularly shown and described with reference to the
foregoing embodiments, which are merely illustrative of the best modes for carrying out the
invention. It should be understood by those skilled in the art that various alternatives to the
embodiments of the invention described herein may be employed in practicing the invention
without departing from the spirit and scope of the invention as defined in the following
claims. It is intended that the following claims define the scope of the invention and that the
method and apparatus within the scope of these claims and their equivalents be covered
thereby. This description of the invention should be understood to include all novel and non-
obvious combinations of elements described herein, and claims may be presented in this or a
later application to any novel and non-obvious combination of these elements. Moreover, the
foregoing embodiments are illustrative, and no single feature or element is essential to all
possible combinations that may be claimed in this or a later application.

CLAIMS
What is claimed is:
1. A supercharging system (10) for an engine, comprising:
an air pump (12);
an electrical machine (14);
an engine-connected input member (15);
a variable-ratio power transmission mechanism (16) including:
a sun member (18) operatively connected to one of the air pump (12), the
electrical machine (14) and the input member (15);
at least one planet member (20) drivingly interfaced with the sun member (18)
and rotatably carried by a carrier (22) operatively connected to another one of the air pump
(12), the electrical machine (14) and the input member (15); and
an annulus (24) drivingly interfaced with the at least one planet member (20)
and operatively connected to the other one of the air pump (12), the electrical machine (14)
and the input member (15); and
a brake (32) configured to selectively inhibit rotation of at least one of the sun
member (18), the carrier (22), and the annulus (24).
2. The supercharging system (10) of claim 1, wherein the air pump (12) is one of a
centrifugal, Roots-type and screw-type supercharger.
3. The supercharging system (10) of claim 1, wherein the power transmission
mechanism (16) is a traction-drive device that includes an elasto-hydrodynamic lubrication
oil that creates a film between the sun member (18), the planet member (20) and the annulus
(24), the oil film exhibiting a viscosity that is increasable under pressure to transmit torque
between the sun member (18), the planet member (20) and the annulus (24).
4. The supercharging system (10) of claim 1, wherein the a sun member (18) is
operatively connected to one of the air pump (12), the electrical machine (14) and the input
member (15) by a first shaft (28) and the carrier (22) is operatively connected to another one
of the air pump (12), the electrical machine (14) and the input member (15) by a second shaft
(30).
5. The supercharging system (10) of claim 4, wherein the brake (32) is configured to
selectively inhibit rotation of the first or second shaft (28, 30).

6. The supercharging system (10) of claim 4, wherein the speed ratio between the first
and second shafts (28, 30) is between approximately two-to-one and five-to-one, when the
air-pump (12) is one of a Roots-type and a screw-type supercharger, and between
approximately ten-to-one and twenty-to-one when the air pump (12) is a centrifugal
supercharger.
7. The supercharging system (10) of claim 1, wherein the speed ratio between the
engine-connected input member (15) and an engine crankshaft is approximately three to one.
8. The supercharging system (10) of claim 1, further including a control system (36)
having a controller (38) configured to operate the electrical machine (14) and the brake (32).
9. The supercharging system (10) of claim 8, wherein the sun member (18) is
operatively connected to the electrical machine (14), the annulus (24) is operatively
connected to the engine-connected input member (15) and the carrier (22) is operatively
connected to the air pump (12), and wherein the controller (38) is configured to activate the
brake (32) to inhibit rotation of the carrier (22) and to operate the electrical machine (14) as a
motor to provide power to rotate the sun member (18) and, by virtue of the corresponding
rotation of the at least one planet member (20), to rotate the annulus (24) and the engine-
connected input member (15) to provide torque to the engine.
10. The supercharging system (10) of claim 8, wherein the sun member (18) is
operatively connected to the electrical machine (14), the annulus (24) is operatively
connected to the engine-connected input member (15) and the carrier (22) is operatively
connected to the air pump (12), and wherein the controller (38) is configured to deactivate the
brake (32) to permit rotation of the carrier (22) and to control or inhibit rotation of the sun
member (18) by operating the electrical machine (14) as a generator to permit torque flow
from the engine-connected input member (15), through the variable-ratio power transmission
mechanism (16) , and into the air pump (12).
11. The supercharging system (10) of claim 8, wherein the sun member (18) is
operatively connected to the electrical machine (14), the annulus (24) is operatively
connected to the engine-connected input member (15) and the carrier (22) is operatively
connected to the air pump (12), and wherein the controller (38) is configured to deactivate the
brake (32) to permit rotation of the carrier (22) and to rotate the sun member (18) by
operating electrical machine (14) as a motor to augment torque flow from the engine-

connected input member (15), through the variable-ratio power transmission mechanism (16),
and into the air pump (12).
12. The supercharging system (10)of claim 8, wherein the sun member (18) is operatively
connected to the air pump (12), the annulus (24) is operatively connected to the electrical
machine (14) and the carrier (22) is operatively connected to the engine-connected input
member (15), and wherein the controller (38) is configured to activate the brake (32) to
inhibit rotation of the sun member (18) and to operate the electrical machine (14) as a motor
to provide power to rotate the annulus (24) and, by virtue of the corresponding rotation of the
planet member (20), to rotate the carrier (22) and the engine-connected input member (15) to
provide torque to the engine.
13. The supercharging system (10) of claim 8, wherein the sun member (18) is
operatively connected to the air pump (12), the annulus (24) is operatively connected to the
electrical machine (14) and the carrier (22) is operatively connected to the engine-connected
input member (15), and wherein the controller (38) is configured to activate brake (32) to
inhibit rotation of the sun member (18) and to permit rotation of the annulus (24) by
operating the electrical machine (14) as a generator such that torque flows from the engine-
connected input member (15), through the variable-ratio power transmission mechanism (16),
and into the generator.
14. The supercharging system (10) of claim 8, wherein the sun member (18) is
operatively connected to the air pump (12), the annulus (24) is operatively connected to the
electrical machine (14) and the carrier (22) is operatively connected to the engine-connected
input member (15), and wherein the controller (38) is configured to deactivate the brake (32)
to permit rotation of the sun member (18) and to control or inhibit rotation of the annulus (24)
using the electrical machine (14) to permit torque flow from the engine-connected input
member (15), through the power transmission mechanism (16), and into the air pump (12).
15. The supercharging system (10) of claim 8, wherein the control system (36) further
includes an energy source (40) operatively connected to the electrical machine (14) through a
power converter (42).
16. The supercharging system (10) of claim 15, wherein the power converter (42)
includes a rectifier electrically connected to the energy source (40) and the control system

(36) further includes a line conductor (62), a field effect transistor (FET) (64) and a capacitor
(66).
17. The supercharging system (10) of claim 16, wherein the control system (3 6) includes
a second field effect transistor (FET) that applies a dead short across an output of the
rectifier.
18. The supercharging system (10) of claim 15, wherein the control system (36') includes
a power supply (68) having a pair of switching field effect transistors (FETs) (70, 72)) and a
rectifier (74) connected to a 12V vehicle electrical system.
19. A supercharging system (10) for an engine, comprising:
anairpump(12);
an electrical machine (14);
an engine-connected input member (15);
a variable-ratio power transmission mechanism (16) including:
a sun member (18) operatively connected to the electrical machine (14);
at least one planet member (20) drivingly interfaced with the sun member (18)
and rotatably carried by a carrier (22) operatively connected to the air pump (12); and
an annulus (24) drivingly interfaced with the at least one planet member (20)
and operatively connected to the input member (15); and
a brake (32) configured to selectively inhibit rotation of the carrier (22).
20. A supercharging system (10) for an engine, comprising:
an air pump (12);
an electrical machine (14);
an engine-connected input member (15);
a variable-ratio power transmission mechanism (16) including:
a sun member (18) operatively connected to the air pump (12);
at least one planet member (20) drivingly interfaced with the sun member (18)
and rotatably carried by a carrier (22) operatively connected to the input member (15); and
an annulus (24) drivingly interfaced with the at least one planet member (20)
and operatively connected to the electrical machine (14); and
a brake (32) configured to selectively inhibit rotation of at least one of the sun
member (18) and the annulus (24).

A supercharging system (10) for an engine includes an air pump (12), an electrical
machine (14), an engine-connected input member (15) and a variable-ratio power
transmission mechanism (16). The power transmission mechanism (16) includes a sun
member (18) operatively connected to one of the air pump (12), the electrical machine (14)
and the input member (15). At least one planet member (20) is drivingly interfaced with the
sun member (18) and rotatably carried by a carrier (22) operatively connected to another one
of the air pump (12), the electrical machine (14) and the input member (15). An annulus (24)
is drivingly interfaced with the at least one planet member (20) and operatively connected to
the other one of the air pump (12), the electrical machine (14) and the input member (15).
The supercharging system (10) also includes a brake (32) configured to selectively inhibit
rotation of at least one of the sun member (18), the carrier (22), and the annulus (24).