U.S. patent application number 15/054806 was filed with the patent office on 2016-09-01 for vacuum management system.
The applicant listed for this patent is Flybrid Automotive Limited. Invention is credited to Andrew EARLY, Daniel R. JONES.
Application Number | 20160252158 15/054806 |
Document ID | / |
Family ID | 52876282 |
Filed Date | 2016-09-01 |
United States Patent
Application |
20160252158 |
Kind Code |
A1 |
JONES; Daniel R. ; et
al. |
September 1, 2016 |
VACUUM MANAGEMENT SYSTEM
Abstract
The invention provides a flywheel system comprising a flywheel
mounted for rotation within a chamber, a vacuum pump system and a
valve for selectively closing a passage, wherein the chamber is
coupled to an inlet of the vacuum pump system via the passage. The
invention also provides a method of controlling the starting and
stopping of the flywheel system.
Inventors: |
JONES; Daniel R.;
(Buckinghamshire, GB) ; EARLY; Andrew;
(Oxfordshire, GB) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Flybrid Automotive Limited |
Lancashire |
|
GB |
|
|
Family ID: |
52876282 |
Appl. No.: |
15/054806 |
Filed: |
February 26, 2016 |
Current U.S.
Class: |
74/572.1 |
Current CPC
Class: |
F16F 15/30 20130101;
G05D 16/202 20130101; H02K 7/025 20130101 |
International
Class: |
F16F 15/30 20060101
F16F015/30 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 27, 2015 |
GB |
1503396.2 |
Claims
1. A flywheel system comprising: a flywheel; a chamber within which
said flywheel is provided; a passage for connecting the chamber to
an inlet of a vacuum pump; and a valve arranged to selectively open
or close said passage, wherein the flywheel and the vacuum pump are
mechanically coupled.
2. A flywheel system according to claim 1, wherein the valve is
adapted to open or close said passage based at least partially upon
a chamber pressure value corresponding to the pressure in the
chamber.
3. A flywheel system according to claim 2, wherein the valve is
arranged to open the passage when said chamber pressure value
exceeds a first pressure value.
4. A flywheel system according to claim 3 wherein the first
pressure value is between 4 and 8 mbar.
5. A flywheel system according to claim 2 further comprising a
pressure sensor for determining said chamber pressure value.
6. A flywheel system according to claim 1 wherein the valve
includes a sealing means for sealing the flow path through the
passage and wherein the sealing means includes a face seal.
7. A flywheel system according to claim 1 further comprising a
controller adapted to maintain the valve in a closed state until
the flywheel is rotating, and open the valve after the flywheel
begins rotating.
8. A flywheel system according to claim 1 further comprising a
controller adapted to start the flywheel system, wherein the
controller is further adapted to open the valve following start-up
of the flywheel system, when the vacuum pump is rotating at a speed
in excess of a speed threshold value.
9. A flywheel system according to claim 1 further comprising a
controller adapted to determine when the rotating flywheel is to be
shut down, and close the valve before controlling said flywheel to
come to rest.
10. A flywheel system according to claim 1 further comprising a
controller adapted to monitor the pump speed of said flywheel
system, wherein the controller opens the valve when the pump speed
is above a threshold value.
11. A flywheel system according to claim 1 further comprising a
controller adapted to open the valve when a chamber pressure value
corresponding to the pressure in the chamber is above a threshold
value which is between 4 and 8 mbar.
12. A flywheel system comprising: a flywheel; a chamber within
which said flywheel is provided; a passage for connecting the
chamber to an inlet of a vacuum pump a valve arranged to
selectively open or close said passage; and a controller adapted to
determine a chamber pressure value corresponding to the pressure in
the chamber; determine a maximum allowable flywheel speed based on
the determined chamber pressure value; and limit the speed of the
flywheel based on the determined maximum allowable flywheel
speed.
13. A flywheel system according to claim 12, wherein the controller
is further adapted to decrease the value of the determined maximum
allowable flywheel speed with increasing pressure in the
chamber.
14. A method of controlling a flywheel system according to claim
12, wherein the determined maximum allowable flywheel speed value
is less than 10,000 rpm when the chamber pressure value is above 10
mbar.
15. A flywheel system comprising: a flywheel; a chamber within
which said flywheel is provided; a passage for connecting the
chamber to an inlet of a vacuum pump; and a valve arranged to
selectively open or close said passage, at least partially based
upon a chamber pressure value corresponding to the pressure in the
chamber, and wherein the valve is arranged to open the passage when
said chamber pressure value exceeds a value that is between 4 and 8
mbar.
16. A flywheel system according to claim 15 further comprising a
pressure sensor for determining said chamber pressure value.
17. A flywheel system according to claim 15 wherein the valve
includes a seal for sealing the flow path through the passage and
wherein the seal includes a face seal.
18. A flywheel system according to claim 15 further comprising a
controller arranged to start the flywheel system, the controller
adapted to maintain the valve in a closed state until the pump is
rotating; and open the valve after the pump begins rotating.
19. A flywheel system according to claim 18 wherein the controller
is further arranged to open the valve when the vacuum pump is
rotating at a speed in excess of a speed threshold value.
20. A flywheel system according to claim 15 further comprising a
controller arranged to shut down the flywheel system, the
controller adapted to determine when the flywheel system is to be
shut down, and close the valve before controlling the vacuum pump
to come to rest.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application claims priority to GB 1503396.2 filed Feb.
27, 2015 which is hereby incorporated by reference in its
entirety.
FIELD OF INVENTION
[0002] The invention relates to flywheel systems and in particular
to a vacuum management system for such flywheel systems.
BACKGROUND OF THE INVENTION
[0003] Flywheels typically comprise a relatively heavy mass,
mounted on a shaft and arranged to rotate with the shaft. The use
of flywheels in vehicles is known, for example in kinetic energy
recovery systems for recovering kinetic energy from the movement of
part or all of a vehicle and for subsequently returning that energy
to the vehicle. Such systems are used in other applications, for
example where energy is recovered from the boom of a working
vehicle such as a loader. The kinetic or potential energy recovery
is converted to kinetic energy of a flywheel.
[0004] The kinetic energy of a flywheel is directly proportional to
the rotational inertia and the square of the angular velocity. A
flywheel used for energy storage in a vehicle should achieve an
optimum balance of mass, inertia and rotational speed. Consequently
the faster the flywheel can be made to rotate, the smaller and
lighter it will be for a given energy storage capacity.
[0005] High speed flywheels typically operate with maximum
rotational speeds which are at least 15000 rpm. Such flywheels are
usually contained within an enclosure which is at least partially
evacuated, in order to reduce windage losses, i.e. energy losses
caused by drag due to the movement of the flywheel through any
fluid, e.g. air, in the enclosure. This helps to reduce the power
consumption of the flywheel system, increasing the energy
recoverable from the flywheel and also preventing the temperature
of the flywheel from rising too high. This is particularly
important where the flywheel is constructed from composite
materials that include a resin, which are typically sensitive to
high temperatures.
[0006] When a flywheel is contained within an evacuated enclosure,
it is necessary to provide a seal between the housing and the shaft
on which the flywheel is mounted, in order to allow the vacuum
within the enclosure to be maintained. However, even with an
effective seal, it is often necessary to "top-up" the vacuum by
pumping any air or vaporised fluid (such as oil) that has leaked
into the enclosure back out again, to maintain the very low
pressure within the enclosure.
[0007] Creating the required vacuum level inside the enclosure can
be challenging, particularly when creating it in the environment of
a vehicle. Efficient vacuum pumps often require precision parts to
achieve the desired vacuum pressures for flywheel operation. For
example, a vacuum management system for a flywheel arrangement may
include a precision pump in order to achieve the desired vacuum
levels typically less than 4 mbar.
[0008] However the costs of such precision pumps tends to restrict
their application to non-vehicle applications and makes
vehicle-type applications undesirably expensive. Furthermore, in
high mileage commercial vehicles and other challenging conditions,
such as construction vehicles, trucks, distribution vehicles, buses
and so on, durability and reliability are important factors. This
further complicates the specifications of vacuum pumps for these
applications.
[0009] Achieving the desirable vacuum levels within a short
timeframe following start-up of the flywheel is also challenging
because the ability to reduce pressure in the chamber becomes
increasingly difficult as the chamber pressure approaches a true
vacuum. Thus the pressure tends to fall asymptotically, approaching
the final achievable near-vacuum pressure over a period of time. In
other words, reducing the chamber pressure towards zero absolute
pressure takes a considerable period of time.
[0010] This delay in achieving the desirable vacuum level means
there is a period of time where the flywheel is not spun up or
during which the rotation of the flywheel is allowed but results in
undesirable windage losses. Alternatively, to mitigate this, the
designer may install a high specification vacuum pump system. This
will carry a penalty of reduced performance, or increased cost,
respectively.
[0011] Storage and re-use of energy using flywheel storage systems
may be used to reduce energy consumption or exhaust emissions of
machines or vehicles. Enabling the flywheel system to operate
optimally with low windage losses for the maximum time possible
would enable the energy efficiency benefits of using the flywheel
system to be maximised, because the flywheel chamber would be at a
lower pressure for more of the time and so able to operate at its
most efficient.
[0012] There is therefore a need for a flywheel system which is
able to achieve and maintain optimally low flywheel chamber
pressures for increased portions of the flywheel apparatus'
operating time, without the undesirable need to use higher
efficiency pumps which would add to the cost which would be
prohibitive for vehicle-type applications. The present invention
aims to provide a solution which achieves at least some of these
aims.
SUMMARY OF THE INVENTION
[0013] Therefore in accordance with the present invention there is
provided a flywheel system comprising: a flywheel; a chamber within
which said flywheel is provided; a passage for connecting the
chamber to an inlet of a vacuum pump; and a valve arranged to
selectively open or close said passage.
[0014] The invention provides an arrangement which can retain a
high level of vacuum when the vacuum pump system is not in
operation, so that the flywheel achieves a low loss running
condition in a short space of time after restarting. Furthermore,
the invention can be implemented in an arrangement which comprises
easily manufactured valve components and may incorporate a
conventional vacuum pump, and so may be a cost effective
solution.
[0015] The vacuum pump may be used as part of the flywheel system.
Such a flywheel system would allow the chamber to be coupled to the
inlet to the pump for evacuating the chamber.
[0016] Preferably, the operation of the valve is determined at
least partially based upon a chamber pressure value corresponding
to the pressure in the chamber. The chamber pressure value may not
be an exact reflection of the chamber pressure but may be estimate
based on some measurement of the pressure or indirectly by
reference to some other parameter of the system, e.g. resistance
imposed on the flywheel due to rotating in the chamber. An estimate
of the pressure provides a sufficiently accurate indication to
provide adequate control of the system. This avoids the need for
accurate and potentially intrusive pressure measuring devices.
[0017] The valve may be arranged to open the passage when the
chamber pressure value exceeds a first value. The inlet pressure
value may not be an exact reflection of the inlet pressure but may
be estimate based on some measurement of the pressure or indirectly
by reference to some other parameter of the system, e.g. speed of
the vacuum pump. In this way, the valve only opens when the
pressure in the chamber is above a certain value and thus needs
reducing.
[0018] The valve may further be arranged to open the passage when
said chamber pressure value exceeds the inlet pressure value
corresponding to the pressure at the inlet of the vacuum pump. By
ensuring that the pressure at the pump is lower than the chamber
pressure, it can be ensured that the tendency will be for air to
move out of the chamber.
[0019] The first value is preferably between 4 and 8 mbar. In this
way the chamber is preferably maintained at a pressure less than
the first value. The pump may then draw the chamber pressure down
such that it lies in the most preferable range of 4 mbar or less.
Similarly, the valve may be closed when the chamber pressure value
falls below a second value. The second value may be 4 mbar or less.
The valve may be opened at a higher chamber pressure than the
chamber pressure at which the valve is closed, i.e. the second
value may be less than the first value, thus creating a control
cycle which suitably incorporates a control deadband. Where the
valve is of the normally closed type, closing the valve once the
chamber has reached its optimum pressure saves energy because the
valve need not be powered.
[0020] A pressure sensor may be used for determining the chamber
pressure value. In order to obtain a pressure value, a pressure
sensor may be used to directly measure the pressure in the chamber.
Similarly, a pressure sensor may be used for directly determining
the pump inlet pressure value. This can provide an accurate measure
of pressure but, as noted above, would typically require a physical
connection to the chamber, e.g. by a channel or other means.
[0021] The valve preferably includes a sealing means for sealing
the flow path through the passage. In this way, when the valve is
closed, a good seal is provided to prevent ingress of air into the
chamber causing the vacuum to be lost. This is particularly
important for maintaining the low pressure when the system is not
operational or in stand-by where no operational pump may be
available to maintain the pressure.
[0022] The sealing means may include a face seal. The face seal may
comprise a resiliently deformable means that bears against a
sealing face. The resiliently deformable means may be formed from
an elastomer.
[0023] The valve is preferably arranged such that the pressure at
the inlet of the vacuum pump acts on the valve to urge the valve to
close, and the pressure in the chamber acts on the valve to urge
the valve to open. This differential pressure can be used to
provide a net pressure on the valve to prevent the valve opening.
For example, if the pressure at the inlet is higher than the
chamber and the valve were to be opened, the pressure in the
chamber would tend to rise. Whilst this is not desirable operation,
it is possible that, for example, a fault or error in measuring the
pressures may inadvertently cause this. However, by allowing the
valve to be held closed by a pressure differential between the
chamber and the pump inlet, the valve could be prevented from
opening if a significant pressure differential existed. For
example, the valve may be arranged so that a pressure difference of
50 mbar would prevent the valve from opening. In this way, if the
pump inlet pressure was more than 50 mbar higher than the chamber,
the valve would be prevented from opening, thus preventing rapid
heat build-up in and potential damage to the flywheel. The pressure
difference may be selected according to the specific implementation
and other values may be appropriate.
[0024] The valve may include a biasing means acting to urge the
valve to close. The biasing means is preferably a spring. The
preload and stiffness of the biasing means may be used to control
the force needed to open the valve. The force needed to open the
valve may also be dependent upon the pressure difference between
the pump inlet and the chamber, as described above. The force would
typically be supplied by a solenoid.
[0025] The flywheel system of the invention may further comprise a
valve energising means wherein the passage is opened when the valve
is in an energised state. This arrangement means that the valve
would normally be closed providing a failsafe closed position to
preserve any vacuum in the chamber, for example should the valve
control fail. Further, the valve may be de-energised when the
chamber is operating at its preferred pressure, thus lowering power
consumption by the valve.
[0026] Preferably, the valve is a solenoid valve. This allows a
control system to easily control opening of the valve.
[0027] The flywheel and the vacuum pump may be mechanically
coupled. This coupling allows the pump to be driven by the
flywheel, ensuring that when the flywheel is operating and so when
a vacuum is important, the pump is also running. This provides a
degree of certainty that a vacuum can be produced and maintained if
the flywheel is operating, in contrast to a separate drive
arrangement for the pump.
[0028] The vacuum pump may be driven by a pump drive means. The
pump drive means may be selected from one of: a motor; a connection
to a vehicle driveline; and a transmission coupleable to said
flywheel. The use of a separate drive means that the vacuum can be
generated independently of the flywheel operating. This allows a
vacuum to be generated and maintained whilst the flywheel is
stationary ensuring that the chamber pressure is as close to
optimal before the flywheel begins to rotate.
[0029] The present invention further provides a method of
controlling the starting of a flywheel system comprising a
flywheel; a chamber within which said flywheel is provided; a
passage for connecting the chamber to an inlet of a vacuum pump
mechanically coupled to said flywheel; and a valve arranged to
selectively open or close said passage, said method comprising:
maintaining the valve in a closed state until the flywheel is
rotating; and opening the valve after the flywheel begins
rotating.
[0030] This arrangement allows the flywheel to start to rotate and
by virtue of their coupling, the vacuum pump before the valve is
opened. Ideally, the pressure in the chamber will be low enough
from previous operation to allow the flywheel to be safely
operated. Once the flywheel starts to rotate, the vacuum pump will
reduce the pressure at its inlet until it is sufficiently low to
aid in reducing the pressure. Then the valve can be opened without
compromising the chamber pressure.
[0031] The method may further comprise opening the valve when the
pump is rotating at a speed in excess of a third value. The third
value can be selected to reflect a pressure at the inlet to the
vacuum pump which would ensure an adequate pressure for the
flywheel chamber. The third value is preferably 1000 rpm.
[0032] The method preferably further comprises determining an inlet
pressure value corresponding to the pressure at the inlet of the
vacuum pump. The inlet pressure value may be determined from the
speed of the pump, from the time at which the pump has been running
at a certain speed, or from a combination of the two. Typically if
the pump has been operating at a speed of at least 1000 rpm for a
period of at least 2 to 3 seconds, then the pressure at the pump
inlet is deemed to be less than 4 mbar, and therefore the valve may
be opened. Using this value, an appropriate point in time can be
determined for opening the valve.
[0033] The method optionally further includes opening the valve
when said inlet pressure value is below a fourth value. The fourth
value may be 4 mbar or less and more preferably 4 mbar.
[0034] The valve may be opened when the inlet pressure value is
below a chamber pressure value corresponding to the pressure in the
chamber.
[0035] Optionally, the method may further comprise opening the
valve when the inlet pressure value is below a chamber pressure
value corresponding to the pressure in the chamber
[0036] The present invention also provides a method of controlling
the shutting down of a flywheel system comprising: a flywheel; a
chamber within which said flywheel is provided; a passage for
connecting the chamber to an inlet of a vacuum pump mechanically
coupled to the flywheel; and a valve arranged to selectively open
or close said passage, the method comprising: determining when the
rotating flywheel is to be shut down; and closing the valve before
controlling said flywheel to come to rest.
[0037] Controlling the flywheel to come to rest may include
applying a level of torque, either positive, negative or zero, to
the flywheel, such that is slows down. The torque level may be
applied by a flywheel transmission that is coupleable to the
flywheel. Zero torque may be applied, for example, by clutching the
flywheel from the flywheel transmission.
[0038] The present invention also provides a method of controlling
the starting of a flywheel system comprising: a flywheel; a chamber
within which said flywheel is provided; a passage for connecting
the chamber to an inlet of a vacuum pump driven by a pump drive
means, and a valve arranged to selectively open or close said
passage, wherein said pump drive means is selected from one of: a
motor, a connection to a vehicle driveline, and a transmission
coupleable to said flywheel, said method comprising: limiting
rotation of the flywheel to a maximum allowable speed; driving the
vacuum pump system with said pump drive means; opening said valve;
and increasing said maximum allowable speed of rotation of the
flywheel.
[0039] Limiting the maximum allowable speed of the flywheel may
include limiting the speed such that it is substantially not
rotating.
[0040] The method may further comprise opening the valve when the
pump is rotating at a speed in excess of a fifth value. The sixth
value can be selected to reflect a pressure at the inlet to the
vacuum pump which would ensure an adequate pressure for the
flywheel chamber. The fifth value is preferably 1000 rpm.
[0041] The method of controlling the starting of the flywheel
system may further comprise determining an inlet pressure value
corresponding to the pressure at the inlet of the vacuum pump. The
inlet pressure value may be determined from the speed of the pump,
from the time at which the pump has been running at a certain
speed, or from a combination of the two. Typically if the pump has
been operating at a speed of at least 1000 rpm for a period of at
least 2 to 3 seconds, then the pressure at the pump inlet can be
deemed to be less than 4 mbar, and therefore the valve may be
opened. Using this value, an appropriate point in time can be
determined for opening the valve.
[0042] The method may include controlling the valve to open when
said inlet pressure value is below a sixth value. The sixth value
may be 4 mbar or less and more preferably 4 mbar.
[0043] The method may further include controlling the valve to open
when the inlet pressure value is below a chamber pressure value
corresponding to the pressure in the chamber.
[0044] The present invention also provides a method of controlling
the shutting down of a flywheel system comprising a flywheel; a
chamber within which said flywheel is provided; a passage for
connecting the chamber to an inlet of a vacuum pump driven by a
pump drive means, and a valve arranged to selectively open or close
said passage, wherein said pump drive means is selected from one
of: a motor, a connection to a vehicle axle, and a transmission
coupleable to said flywheel, said method comprising: determining
when the rotating flywheel is to be shut down; closing the valve;
and controlling said vacuum pump to come to rest.
[0045] Once it is determined to shut down the flywheel, the valve
can be closed, ideally leaving the chamber at the lowest possible
pressure ready for when the flywheel is restarted. Once the valve
is closed, the vacuum pump can be shut down, which can help to
reduce power consumption.
[0046] The above method may further comprise controlling the
flywheel to come to rest. Optionally, this may be made to happen
before closing the valve. In this way, only once the flywheel has
stopped, is the pump separated from the chamber, which will help to
maintain the pressure in the chamber whilst the flywheel is
turning.
[0047] The present invention also provides a method of controlling
a flywheel system comprising: a flywheel; a chamber within which
said flywheel is provided; a passage for connecting the chamber to
an inlet of a vacuum pump mechanically coupled to said flywheel;
and a valve arranged to selectively open or close said passage, the
method comprising monitoring a value of one of more parameters of
said flywheel system, each parameter having an associated range
above or below a respective threshold, wherein said method
comprises selectively opening or closing said valve when the value
of at least one of said parameters is within said associated
range.
[0048] One of the parameters may be the pump speed, wherein the
valve is opened when the pump speed exceeds a seventh value. The
seventh value is preferably 1000 rpm. In this way, it is known that
the pump will have been operating for the duration of the start-up
(preferably at least 2 to 3 seconds) and will be pumping at an
adequate rate to provide a pressure low enough at its inlet to
connect to the chamber without compromising the pressure in the
chamber and the reliable and efficient operation of the
flywheel.
[0049] One of the parameters may be the pressure at the inlet of
the vacuum pump, and wherein the valve is opened when an inlet
pressure value corresponding to the pressure at the inlet of the
vacuum pump is below a eighth value. By monitoring the pressure at
the inlet directly, the method can ensure that the pressure is low
enough to ensure reliable flywheel operation.
[0050] The eighth value may be a fixed value of 4 mbar. The eighth
value may be set to be a chamber pressure value corresponding to
the pressure in the chamber.
[0051] Alternatively, the eighth value may be set to be a chamber
pressure value corresponding to the pressure in the chamber, less a
ninth value. The ninth value is preferably less than 4 mbar.
[0052] One of the parameters may be the pressure in the chamber,
wherein method comprises opening the valve when a chamber pressure
value corresponding to the pressure in the chamber is above a tenth
value. The tenth value is preferably between 4 and 8 mbar. Once the
chamber has achieved the most preferable pressure level, e.g. less
than 4 mbar, the valve may once again be closed. The valve may
therefore be closed when the chamber pressure value corresponding
to the pressure in the chamber falls below an eleventh value. The
eleventh value is preferably 4 mbar or less.
[0053] The present invention also provides a method of controlling
a flywheel system comprising a flywheel; a chamber within which
said flywheel is provided; a passage for connecting the chamber to
an inlet of a vacuum pump, and a valve arranged to selectively open
or close said passage, said method comprising: determining a
chamber pressure value corresponding to the pressure in the
chamber; determining a maximum flywheel speed value based on the
determined chamber pressure value; and limiting the speed of the
flywheel based on the determined maximum allowable flywheel speed
value.
[0054] The vacuum pump may be driven by a pump drive means which
may be selected from one of: a motor, a connection to a vehicle
axle, the flywheel, and a transmission coupleable to said
flywheel.
[0055] The determined maximum flywheel speed value of the flywheel
may decrease with increasing pressure in the chamber. This can
allow a progressive increase in allowable speed as the chamber
pressure drops towards its optimum.
[0056] The determined maximum flywheel speed value is preferably
set to 10,000 rpm or less when the chamber pressure value is above
10 mbar. Other combinations of pressures and speeds may be
additionally determined based on the parameters of the system such
as the heat generated by the flywheel at a given speed and the heat
capacity and heat conductivity of the flywheel and chamber and so
on. In this way, the temperature of the flywheel can be prevented
from exceeding undesirable levels for the flywheel material. This
is particularly important for flywheels that are made of materials
that are more sensitive to heat, for example composite materials.
Flywheels may be made from a number of materials and different
parts may be made from different materials. The rim of the flywheel
is moving at the fastest rate and so is likely to get hotter than
other parts and so controlling the temperature for the material of
this part is particularly important.
[0057] The above method may be used during any phase of operation,
including normal operation as well as during start-up.
[0058] The above methods may be used in conjunction with each other
and are not intended to be mutually exclusive.
[0059] The present invention also provides a controller for
controlling the operation of a flywheel system to carry out the
steps of the methods described above.
[0060] The flywheel system is preferably mounted on a shaft with
seals provided around the shaft between the chamber housing and the
shaft, to resist airflow into the chamber. Flywheels operate more
efficiently in a vacuum and so sealing the chamber and evacuating
it is important. It is therefore also important to maintain the
lowered pressure in the chamber by providing good sealing where
there is the greatest likelihood of gaps through which air can
enter the chamber, particularly in the vicinity of the seals. The
seals help to isolate the evacuated portion of the chamber from the
bearings and minimise any air ingress.
[0061] The seals preferably include a pair of lip seals that
contact and encircle the shaft, the space between the seals
defining a cavity into which fluid can be provided, for example, by
a lubrication pump. By providing a pair of lip seals separated
along the shaft, a space can be defined which can be filled with
oil. The oil helps to create a hermetic seal between the seal and
the shaft, thus preventing any air transiting through the cavity
and into the chamber. Any oil that leaks into the chamber may also
be extracted by the vacuum pump.
[0062] The cavity preferably includes an inlet and an outlet, and a
lubrication pump can be used to provide fluid to the inlet to
maintain a supply of oil, to replace oil which leaves the cavity
either via the lips or from the outlet. This ensures the cavity is
permanently full of oil. A pair of lips seals is preferably
provided at each side of the flywheel.
[0063] The shaft may be mounted on one or more bearings and the or
a lubrication pump can provide fluid to the bearings to keep them
lubricated.
[0064] The valve may be provided between the inlet to the vacuum
pump and the chamber. The valve can be used to control flow of air
or other fluid between the chamber and the pump. This is
particularly useful during start up and shut down when the pump may
not have achieved an operating pressure. As such by closing the
valve, the pressure in the chamber can be preserved until the pump
achieves a working vacuum pressure or after it has shut down and is
unable to maintain a vacuum pressure. In other words, the valve can
be used to prevent air flowing back into the chamber from the pump
assembly.
[0065] The valve may also be used during normal operation of the
flywheel system (that is, when the flywheel system is not being
started up or shut down).
[0066] As noted above, the valve is preferably controlled by a
solenoid. This allows the valve to be controlled to open and close
at the appropriate time. However, the valve may be mechanically
operated such as based on the pressure in the pump or the
chamber.
BRIEF DESCRIPTION OF THE DRAWINGS
[0067] A specific embodiment of the present invention will now be
described in more detail with reference to the drawings in
which:
[0068] FIG. 1 shows a schematic layout of a flywheel system;
and
[0069] FIG. 2 shows a schematic layout of a flywheel system with a
valve.
DETAILED DESCRIPTION
[0070] FIG. 1 shows a schematic view of a flywheel system 20.
Flywheel 21 is provided within a housing 22. The housing defines a
chamber 23 within which the flywheel can rotate in use. The
flywheel is mounted on a shaft 24 which is supported on bearings
25. The flywheel may rotate at speeds in excess of 15,000 rpm which
results in very high speeds on the surface of the flywheel relative
to the air in which the flywheel is rotating. In use, the chamber
is maintained at a low pressure to reduce windage loss through
rotation of the flywheel.
[0071] In order to enclose the chamber 23, lip seals 26 are
provided around the shaft 24. It is undesirable for the lip seals
to maintain a contact with the shaft and so the space between the
seal lips and the shaft is filled with an oil. The oil is provided
to the space between the pairs of lip seals 26 through a channel 27
from a lubricating oil pump 35. Oil is provided through the
channels 27 to the space between the lip seals so that it can fill
the gap between the lip seals and the shaft and prevent air passing
into the chamber 23. The oil provides a hermetic seal, reduces
losses due to friction and reduces wear of the seals.
[0072] The oil is preferably chosen so that it does not vaporise at
the reduced pressures in the chamber. This is to ensure that the
oil does not vaporise causing the vacuum to become compromised,
particularly when the (vacuum) pump is not operating such as during
periods when the flywheel is not in use, but where it is still
desirable to maintain the vacuum, for example, to minimise start up
time.
[0073] Closing the valve in order to maintain a low pressure in the
chamber is especially effective once the system has been initially
run, for example after commissioning of the system or immediately
following maintenance work, since any gases will have already been
drawn out of grease or the casings and pumped out of the chamber.
Thus the chamber vacuum can be maintained for long periods without
the pump operating and with the valve closed.
[0074] The lubrication pump 35 continuously pumps oil into the
space between the lip seals 26. The oil then passes out again
through passages 28, 28a. The passages 28 return the oil to an oil
reservoir 29. It should be noted that the section of one of the
passages 28, labelled 28a, shown in dotted line simply represents
the hidden path of the channel 28 and does not pass through the
chamber 23.
[0075] In order to provide and maintain the low pressure partial
vacuum in the chamber 23, a pump 30 is provided. The pump 30 draws
any air within the chamber 23 out through channel 31.
[0076] It will be appreciated that oil present in the space between
the lip seals 26 and the shaft 24 will potentially permeate along
the shaft and be deposited within the chamber 23. Having entered
the chamber, the oil will tend to sink to the bottom of the chamber
23. The entrance to the channel 31 is therefore provided at the
bottom of the chamber 23 so that any oil which enters the chamber
collects at the bottom and can be withdrawn by the pump 30 from the
chamber 23. Any oil extracted in this way will be passed through
pump 30 and deposited into the oil reservoir 29 to be
recovered.
[0077] The pump 30 is typically positioned beneath the chamber 23
(although this is not shown in the drawings) so that oil is
encouraged to flow to the inlet of the pump 30. The reservoir 29 is
typically positioned (again not shown in the drawings) above the
inlet to lubrication pump 35, to assist with priming of the pump,
and to potentially allow a lower cost lubrication pump (such as a
gerotor or impellor) to be used.
[0078] In this way, the vacuum pump 30 provides the dual function
of maintaining low pressure within the chamber 23 but also removing
any excess oil which collects in the chamber 23. It will be
appreciated that pump 30 is provided to achieve low pressure within
the chamber 23. The pressure to be achieved and maintained in the
chamber 23 is preferably below 10 mbar, and more preferably below 4
mbar.
[0079] The vacuum pump serves to scavenge fluid (lubrication oil)
from the bottom of the flywheel chamber and return it to a fluid
reservoir 29. As a result the air pumped through the pump 30 may
include both air and oil. Air entrained in the fluid is allowed to
escape prior to the lubrication oil being pumped by the separate
lubrication pump 35 to the sealing cavity between the lip seals
and/or the flywheel bearings. In this embodiment, the separation
occurs in the reservoir 29 although other means may be used to
separate the air from the fluid. As shown in the arrangement of
FIG. 1, the air/oil mixture is fed into the top of the reservoir.
This can help with the separation so that oil passes into the body
of oil in the reservoir but the oil is not aerated by any air in
the mixture. The air can then be collected in an air space above
the oil and the reservoir 29 provided with a breather to release
it.
[0080] As shown in FIG. 1, the vacuum pump 30 is driven directly
from the flywheel using suitable gearing 33, 34 connected to the
shaft 24. Alternatively, the driveshaft 36 may be driven directly
by an electric motor or other means such as off some other
component on the vehicle on which the flywheel is mounted. In
particular, the driveshaft may be driven from a vehicle driveline
such as a final drive arrangement, a transmission output or a
transmission input, e.g. from the main engine, a vehicle axle or
propshaft. The pump may also be driven from a flywheel drive
transmission that controls the power flow between the flywheel and,
for example, the vehicle. This can be advantageous as the pump can
be operated irrespective of the rotation speed of the flywheel. For
example, the vacuum pump may be operated before the flywheel system
is started up. The flywheel transmission may also be decoupleable
from the vehicle driveline.
[0081] FIG. 2 shows a modified flywheel arrangement, similar to the
arrangement of FIG. 1 but with an additional valve and pressure
sensor. The embodiment of FIG. 2 includes the valve 90 on the
outlet from the flywheel chamber 23. The valve is engaged by a
solenoid 91 to close off the exit from the vacuum chamber or
disengaged to leave the channel 31 open. In this way, if the pump
30 is not operating and the pressure at the pump inlet starts to
rise, the vacuum state within the flywheel chamber can be better
maintained by engaging the valve 90 and isolating the chamber 23
from the pump 30.
[0082] The vacuum valve 90 is shown schematically in FIG. 2 but may
take a number of forms. For example, the valve may include a face
seal. This may include a rigid face that compresses a flexible seal
such as an elastomeric seal like an o-ring in order to provide a
reliable seal to maintain the desirable vacuum, i.e. preferably
below 4 mbar. A `normally closed` vacuum valve--that is one that
closes when it receives no energisation (for example, electrical
energisation of a solenoid)--is preferred as the valve will retain
the flywheel chamber vacuum in the event of loss of power to the
valve. The pump preferably includes a spring that biases it to
close when it is not energised or actuated.
[0083] In the embodiment of FIG. 2, the valve is controlled by a
solenoid 91. However, it will be appreciated that the valve may be
operated using different means. For example, the valve may be
mechanically operated, for example by a coupling to a speed related
element or a pressure sensitive element. In the latter case, the
valve may simply be biased into the closed position and the
pressure difference between the chamber and the pump inlet, acting
on the valve, opens the valve if the pressure in the pump inlet is
lower than the chamber.
[0084] In another variation, the valve includes both an actuator
(for example, a solenoid), and also a spool or plunger upon which
two pressures act. Each pressure may bear on a different sized area
of the spool. This may be achieved with a cylindrical spool that
seals against a conical face. The non-sealing end of the spool is
arranged to be exposed to a larger area than the sealing end of the
spool. The vacuum pump inlet pressure may bear against the larger
area of the spool, whilst the flywheel chamber pressure may bear
against the smaller area of the spool. Alternatively the chamber
pressure may not bear against the spool at all. With this
arrangement, when the pump inlet pressure is at a pre-determined
value or at a pre-determined level higher than the chamber
pressure, the actuator and optional bias spring are arranged such
that the available actuation force is insufficient to open the
valve. This prevents the vacuum valve from being opened by the
actuator when the pump inlet pressure is inappropriately high, such
as when the pump system is not operating or when it has developed a
fault. Preventing the solenoid from opening the valve when the pump
inlet pressure is relatively high can prevent damage to the
flywheel due to excessive windage losses and heating.
[0085] Whilst the flywheel is in normal operation (that is, not
during its start-up or shut-down phase), the valve may be closed if
it is determined that the pressure in the chamber is below a level
suitable for optimum operation. The optimum pressure range for the
flywheel is below 4 mbar, and preferably the flywheel operates with
a chamber pressure at this level. By de-energising the valve under
normal operation, the mean power required by the valve is reduced,
thus improving efficiency of the flywheel system.
[0086] As shown in FIG. 2, a pressure sensor 19 is provided for
measuring and determining the pressure in the chamber. However, it
will be appreciated that the pressure may be determined in other
ways, for example by reference to other parameters of the system or
using other pressure sensors. The pressure may not be determined
precisely and instead an estimate of the pressure may be all that
is determined and used to determine the control of the system. For
example, such an estimate may be made by monitoring the drive
effort imparted to the flywheel by a flywheel drive system,
determining the flywheel's speed and/or acceleration, and inferring
the pressure in the chamber.
[0087] The sequence of operation of a vacuum pump in a flywheel
application is important. When the flywheel is initially operated,
it can take a considerable time to generate the desired vacuum
level within the flywheel chamber. Whilst the pressure in the
chamber is higher than the optimum, the air causes increased
flywheel losses. Consequently, between the time when the flywheel
begins to rotate and the time at which the desired vacuum level is
achieved by operation of the pump, increased losses waste energy
causing heating of the flywheel and reduce the efficiency of the
flywheel. It is therefore desirable to maintain the vacuum level in
the flywheel chamber during periods of `off-time` rather than
allowing the chamber to rise to atmospheric pressure and then have
to be reduced again when operation recommences.
[0088] In the arrangement of FIG. 2, the vacuum pump 30 is driven
by the driveshaft 36 coupled to the flywheel and so any pumping
action is dependent on the flywheel operating. In the initial
start-up period, the flywheel will start to spin but the pump 30
will not have operated for a sufficient period of time to reduce
the pressure in the flywheel chamber to the desired operating
pressure. There will therefore be a period when the flywheel is
already rotating before the pressure in the chamber is reduced
below a pressure where increased losses occur, especially if the
flywheel is run up to close to its maximum operating speed.
[0089] This arrangement of coupling the pump 30 to the flywheel
does have the advantage of good reliability because there is no
motor to potentially fail. There is also no need for motor drive
electronics. The flywheel may also be used to drive the lubrication
pump 35. This means that there is the assurance that lubrication
will be available whenever the flywheel is rotating, which
coincides with the time when the need for lubrication is most
important.
[0090] To accommodate `start-up` of the flywheel system, the valve
90 is initially closed, preventing airflow through it (and
preserving any reduced pressure level within the chamber). The
flywheel is then caused to rotate. As the flywheel starts rotating,
the drive shaft 24 will begin to turn. This will cause the shaft 36
to turn and the pump 30 will start to operate, lowering the
pressure in the channel 31 between the pump 30 and the valve
90.
[0091] Once the pressure is low enough, the valve can be opened
allowing the pump to withdraw air from the flywheel chamber 23 and
reduce the pressure within it to the desired operating
pressure.
[0092] Once the flywheel has be running for a period of time, the
pump will have removed the air from the flywheel chamber and the
valve can remain open to allow the pump to maintain the reduced
pressure. As described earlier, it may be desirable to close the
valve even when the flywheel is not to be shut down if it has been
determined that the chamber pressure has reached the optimum level,
as this may reduce the power consumption by the valve solenoid, in
particular, where the valve is of the normally-closed type, i.e.
closed when the solenoid is not energised. The pump 30 may also be
turned off to reduce power consumption. This might be achieved by
using clutch or similar means to selectively connect the pump 30 to
the drive shaft 24 or other drive means. Where the pump is
electrically driven, turning the pump off will clearly save
electrical energy.
[0093] The pressure in the chamber 23 is determined using the
pressure sensor 19 in the embodiment of FIG. 2, although other
methods may be used to determine the pressure. Once the machine or
vehicle to which the flywheel is connected is no longer operating,
it is desirable to shut down the flywheel system. Under normal
operating conditions, the flywheel is allowed or caused to rotate
in the near vacuum conditions. To close the system down, the valve
90 is closed to isolate the flywheel chamber from the pump 30. The
flywheel can then be allowed to come to rest and the vacuum in the
chamber can be largely preserved even after the flywheel (and the
pump) has stopped.
[0094] In this way, when the flywheel is brought back into
operation, the previous low pressure within the chamber is largely
preserved and so the flywheel can operate in close to optimum
vacuum conditions as soon as it starts to rotate rather than having
to wait for the pump to develop the vacuum.
[0095] The arrangement of FIG. 2 may be modified to have a separate
pump drive for the vacuum pump so that it is not dependent on
rotation of the flywheel to operate, e.g. by providing an electric
motor, flywheel transmission (which may be decoupleable from the
flywheel allowing it to be rotating when the flywheel is not) or
vehicle drive to drive it. With such an arrangement, the system can
be operated in a slightly different way.
[0096] Initially, when the flywheel is to be brought into
operation, the separate drive means is used to turn the pump 30.
This begins the process of evacuating the pipes 31 connecting the
flywheel chamber to the pump and the pump chamber itself. During
this process the valve is initially closed. After a period of
operation, the pressure at the inlet to the pump 30 will drop,
ideally to below the pressure in the flywheel chamber. At this
point, opening the valve 90 will allow the pump to start removing
air from the chamber and reduce the pressure within to the
operating pressure. This can all be done before the flywheel is
caused or allowed to rotate, or with the flywheel maximum speed
being restricted.
[0097] In this way, the pressure within the chamber 23 can be at or
close to the operating pressure before the flywheel begins to
rotate at a substantial speed, i.e. a speed at which the windage
effect becomes significant. This minimises losses which may be
caused by rotating the flywheel at a substantial speed in a
pressure above the optimum level. This also prevents heat build-up
in the flywheel due to resistance from the air, which can be
especially important if the flywheel comprises composite materials
such as carbon fibre reinforced plastic (CFRP).
[0098] Once the flywheel is spinning, the valve is kept open to
allow the pump to maintain the pressure in the chamber. However, as
indicated above, the valve may still be closed for periods of time
to reduce energy consumption in the valve and pump.
[0099] When it is desired to shut down the flywheel system, again a
slightly modified procedure can be used. Initially, the flywheel is
rotating or being driven and the valve is open with the vacuum pump
running. When it is determined to shut down the flywheel system,
the first step is to close the valve to isolate the chamber from
the pump. The vacuum pump can then be allowed to come to rest. At
any point after the valve 90 has been closed, the flywheel may also
be brought or allowed to come to rest.
[0100] In this way, the pressure is maintained in the chamber
during normal operation and, by isolating the chamber, even after
the valve is closed. It is preferable to keep the lubrication pump
35 operating whilst the flywheel is run down, since the lubrication
pump continues to operate to maintain good oil supply to the lip
seals which helps to maintain a good seal and preserve the vacuum
in the chamber and also to ensure good lubrication of the various
rotating elements. Only after the flywheel has come to rest is the
lubrication pump shut down, as it is no longer needed.
[0101] Alternatively, when it is determined to shut down the
flywheel system, the vacuum pump may be kept running, where it is
powered separately from the flywheel, e.g. from an electric motor
or drive train take off. The flywheel can then be brought or
allowed to come to rest whilst the pressure is maintained by the
pump. Once the flywheel has come to rest, the valve can be closed
to preserve the vacuum in the chamber and the vacuum pump then
turned off.
[0102] As noted above, the valve is preferably an electrically
operated solenoid valve but may be mechanically operated. In the
direct drive example above, the valve may be arranged to open only
when the vacuum pump is operating at a certain speed or after a
certain pressure is achieved by the vacuum pump system.
[0103] If a sufficient vacuum level has not been established within
the flywheel chamber, the movement of the flywheel through the air
that is present can lead to significant heat being generated. This
can happen at start up when the pump has not sufficiently reduced
the pressure or if the vacuum level is degraded for other reasons
such as a leak. Running the flywheel in a reduced vacuum, i.e. with
more that the desired amount of air in the chamber, can cause the
flywheel itself to heat up which can be disadvantageous, particular
where the flywheel is made using composite materials which can be
heat sensitive.
[0104] To prevent or mitigate this, the pressure in the chamber can
be monitored, for example by using pressure sensor 19, and if the
pressure is not sufficiently low, the flywheel speed can be limited
to prevent excessive build-up of heat. This limit may be staged
such that the flywheel is prevented from exceeding a certain speed
(or from spinning at all) above a certain pressure and then is
allowed to spin up to other maximum speeds depending on the vacuum
pressure level. In this way, as the pressure is progressively
lowered, the maximum allowable flywheel speed is progressively
increased. This may be a continuous relationship and/or set out in
a series of bands with thresholds which must be exceeded to allow
the maximum speed to be raised to the next level.
[0105] By limiting the flywheel speed as a function of the vacuum
level, the heat build-up can be controlled to prevent the
temperature of the flywheel and other components exceeding desired
levels. Limiting the flywheel speed may include maintaining it
stationary, which may be desirable under some conditions.
[0106] The pressure in the chamber may be determined accurately
using a dedicated pressure sensor such as the sensor 19 in FIG. 2.
However, as noted above, the chamber pressure may be determined in
other ways. Alternatively an estimate of the pressure may be used
in place of an accurate pressure measurement. The option of relying
on the estimated pressure applies to determining the pressure in
the chamber as well as the pressures in other parts of the system,
e.g. the inlet to the vacuum pump. For example, the pump inlet
pressure may be estimated from the speed of the pump (or from the
speed of the flywheel in the case where the pump is coupled to the
flywheel).
[0107] In the above embodiments, the valve is preferably a vacuum
valve which forms a hermetic seal to prevent leakage of fluid
around the valve. The valve is operated by a solenoid in the
example although as noted above other valves such as a check valve
or a passive or pilot operated (e.g. pressure-actuated) valve may
be used, in accordance with the invention.
[0108] However, solenoid operated valves have a number of
advantages. A solenoid operated valve may be actuated at will, for
example according to complex logic, perhaps dependant on a number
of parameters. For example, the valve may be operated prior to the
vacuum pump system being brought to rest.
[0109] A check valve or similar, typically has a bias associated
with it in order to achieve effective sealing. Such a bias may
cause a necessary pressure differential between the chamber and the
pump inlet. An externally actuated, e.g. solenoid valve, does not
in itself cause such a pressure differential, so when the valve is
open, the chamber may be brought down to the pressure at the inlet
of the pump rather than slightly above it, due to the pressure
differential.
[0110] In the embodiment above, the flywheel has a direct
mechanical drive to the pump and to provide a coupling, for
receiving and providing power, to a vehicle drive train, typically.
However, the flywheel may be provided in a chamber that is
hermetically, or near-hermetically sealed. In such cases, the
flywheel may be driven by an electric motor/generator at least one
part of which is mounted in the vacuum chamber, or by a magnetic
coupling that communicates through a wall of the chamber
housing.
[0111] As noted above, the flywheel chamber may be evacuated
regularly in service, but alternatively, especially where the
chamber is hermetically sealed, it may be evacuated periodically,
such as only when the chamber pressure has risen above a desirable
level. Thus the vacuum may be `topped up` at longer intervals.
[0112] The vacuum pump may take a number of different forms but for
this application, a vane pump is preferred. Such pumps may not
bring down the chamber pressure as rapidly as, for example, some
reciprocating pumps, but they may be quieter and more durable,
which is desirable for vehicle applications. They are also suitable
for the pumping of both oil and air, thus allowing a single device
to be used rather than needing separate oil and vacuum pumps.
However, a separate vacuum pump (and, if required, oil scavenging
device) may be used. In the case where there is a single pump which
performs both of these functions, the pump inlet is preferably
below the flywheel chamber, so that oil can collect under gravity
at the bottom of the chamber, so that it can then be drawn out with
the air by the vacuum pump.
[0113] If, at any time, a fault is suspected in the vacuum pump
system then the flywheel system may be made to shut down. For
example, if the pressure at the inlet to the vacuum pump system is
estimated as being substantially higher than expected, then the
flywheel system may be made to shut down because it is assumed that
there has been a failure of the pump system. This may include
monitoring the flywheel chamber pressure to make sure that it
falls, as expected, when the valve is opened. If the vacuum pump is
not running or is failing to provide an adequate vacuum then when
the valve is opened, the pressure would tend to rise in the chamber
as opposed to falling, as expected. This unexpected behaviour would
suggest that the pump is not operating correctly and the flywheel
may be shut down or its speed restricted.
* * * * *