U.S. patent application number 15/884536 was filed with the patent office on 2018-08-02 for energy recovery device.
The applicant listed for this patent is Exergyn Limited. Invention is credited to Nicholas Breen, Barry Cullen, Daniel Healy Grace, Robert Kelly, Kevin O'Toole, Keith Warren.
Application Number | 20180216604 15/884536 |
Document ID | / |
Family ID | 45560345 |
Filed Date | 2018-08-02 |
United States Patent
Application |
20180216604 |
Kind Code |
A1 |
Warren; Keith ; et
al. |
August 2, 2018 |
ENERGY RECOVERY DEVICE
Abstract
The present application relates to the field of energy recovery
and in particular to the use of shape memory alloys (SMA) for same.
An energy recovery device is provided which comprises a one way
drive mechanism for incrementally winding a spring. An SMA engine
comprising a length of SMA material is fixed at a first end and
connected at a second end to the one way drive mechanism. The SMA
engine is housed in an immersion chamber and adapted to be
sequentially filled with fluid to allow heating and/or cooling of
the SMA engine to enable high frequency contractions and expansion.
An output transmission is provided which is coupled to and driven
by the spring. In this manner, repeated contractions of the SMA
material incrementally wind the spring to store energy. The spring
is restrained by a release mechanism which may be activated to
allow the spring to drive an output transmission.
Inventors: |
Warren; Keith; (Co. Carlow
Borris, IE) ; Cullen; Barry; (Dublin, IE) ;
O'Toole; Kevin; (Dublin, IE) ; Breen; Nicholas;
(Co. Wexford Gorey, IE) ; Healy Grace; Daniel;
(Co. Wicklow Blessington, IE) ; Kelly; Robert;
(Dublin, IE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Exergyn Limited |
Dublin |
|
IE |
|
|
Family ID: |
45560345 |
Appl. No.: |
15/884536 |
Filed: |
January 31, 2018 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
14365214 |
Jun 13, 2014 |
9885344 |
|
|
PCT/EP2012/074566 |
Dec 5, 2012 |
|
|
|
15884536 |
|
|
|
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
F02G 5/00 20130101; F02B
73/00 20130101; F03G 1/00 20130101; F03G 7/065 20130101 |
International
Class: |
F03G 7/06 20060101
F03G007/06; F03G 1/00 20060101 F03G001/00; F02B 73/00 20060101
F02B073/00; F02G 5/00 20060101 F02G005/00 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 13, 2011 |
GB |
1121361.8 |
Claims
1. An energy recovery device comprising: a one way drive mechanism
for incrementally winding a spring; an SMA engine comprising a
length of SMA material fixed at a first end and connected at a
second end to the one way drive mechanism; an immersion chamber
adapted for housing the SMA engine and adapted to be sequentially
filled with fluid to allow heating and/or cooling of the SMA
engine; and an output transmission for coupling to and being driven
by the spring; and a release mechanism activateable to allow the
spring to drive the output transmission.
2. An energy recovery device according to claim 1, wherein the
immersion chamber comprises an inlet and outlet for receiving and
discharging the fluid.
3. An energy recovery device according to claim 1, wherein the SMA
engine is substantially immersed in fluid during one heating
cycle.
4. An energy recovery device according to claim 1 wherein heat
transfer from the fluid to the SMA engine is primarily by forced
convection as the fluid is pumped through the chamber.
5. An energy recovery device according to claim 1, wherein there
are a plurality of SMA engines each SMA engine being coupled to a
one way drive mechanism for winding a common spring.
6. An energy recovery device according to claim 1 comprising a
multiple clutch system adapted to provide incremental winding of
the spring.
7. The energy recovery device of claim 1 wherein a multiple clutch
system comprises a first clutch mechanism connected to one end of
the spring and adapted such that rotation of the of the clutch
rotates the spring.
8. The energy recovery device of claim 1 wherein a multiple clutch
system comprises a first clutch mechanism connected to one end of
the spring and adapted such that rotation of the clutch rotates the
spring and a second clutch mechanism is positioned in such a way to
prevent reverse movement of the first clutch mechanism and adapted
to allow incremental charging of the spring until a desired energy
storage level is achieved.
9. The energy recovery device of claim 8 comprising a third clutch
mechanism connected to the other end of the spring and adapted to
be held in place by a brake when the spring is being charged.
10. The energy recovery device of claim 8 comprising a third clutch
mechanism connected to the other end of the spring and adapted to
be held in place by a brake when the spring is being charged,
wherein the brake is adapted to be released forcing an inner race
of the third clutch mechanism to rotate thereby passing energy
stored in the spring to provide a continuous flywheel arrangement
to the output transmission.
11. The energy recovery device of claim 8 comprising a third clutch
mechanism connected to the other end of the spring and adapted to
be held in place by a brake when the spring is being charged,
wherein the brake is adapted to be released forcing an inner race
of the third clutch mechanism to rotate thereby passing energy
stored in the spring to provide a continuous flywheel arrangement
to the ouput transmission and the third clutch comprises an outer
race such that when the inner race rotates forces the outer race to
rotate thereby passing energy stored in the spring to the output
transmission.
12. The energy recovery device of claim 8 comprising a third clutch
mechanism connected to the other end of the spring and adapted to
be held in place by a brake when the spring is being charged,
wherein the brake is adapted to be released forcing an inner race
of the third clutch mechanism to rotate thereby passing energy
stored in the spring to provide a continuous flywheel arrangement
to the output transmission and the third clutch comprises an outer
race such that when the inner race rotates forces the outer race to
rotate thereby passing energy stored in the spring to the output
transmission the outer race is adapted to keep rotating when a
brake condition is applied to the inner race.
13. An energy recovery device according to claim 1, wherein the SMA
engine comprises a linear SMA actuator core.
14. An energy recovery device according to claim 1, wherein the SMA
engine comprises a circumferentially arranged SMA actuator
core.
15. An energy recovery device according to claim 1 further
comprising a generator driveable by the output transmission.
16. A starter motor comprising an energy recovery device as claimed
in claim 1.
17. A vehicle comprising a starter motor comprising an energy
recovery device of claim 1 and further comprising an arrangement
for diverting fluid from the engine cooling jacket to the energy
recovery device.
18. A UPS comprising a flywheel and an energy recovery device
according to claim 1, wherein the flywheel is driven by the output
transmission of the energy recovery device.
19. A method of recovering energy using an SMA material, the method
comprising the steps of: a) restraining a first end of a length of
SMA material; b) connecting a second (opposing) end of the length
of SMA material to a one way drive mechanism for incrementally
winding a spring; c) providing a source of heat to the SMA material
to cause it to contract by immersing the SMA material in a heated
fluid, wherein the contraction causes the spring to be wound; d)
removing the source of heat and allowing the SMA material to cool;
and repeating steps c) and d) to incrementally store energy in the
spring e) releasing the incrementally stored energy through an
output transmission.
20. An energy recovery device comprising: a SMA engine comprising a
length of SMA material fixed at a first end and connected at a
second end to the one way drive mechanism; a multiple clutch system
adapted to provide incremental winding of a spring, said multiple
clutch system comprising a first clutch mechanism connected to the
spring and adapted such that rotation of the of the first clutch
rotates the spring and a second clutch mechanism is positioned in
such a way to prevent reverse movement of the first clutch
mechanism; an output transmission for coupling to and being driven
by the spring; and a release mechanism activateable to allow the
spring to drive the output transmission.
21. The energy recovery device as claimed in claim 20 wherein the
wherein the second clutch mechanism is positioned in such a way to
prevent reverse movement of the first clutch mechanism and adapted
to allow incremental charging of the spring until a desired energy
storage level is achieved.
22. The energy recovery device as claimed in claim 20 comprising a
third clutch mechanism connected to the other end of the spring and
adapted to be held in place by a brake when the spring is being
charged.
23. The energy recovery device of claim 20 comprising a third
clutch mechanism connected to the other end of the spring and
adapted to be held in place by a brake when the spring is being
charged wherein the brake is adapted to be released forcing an
inner race of the third clutch mechanism to rotate thereby passing
energy stored in the spring to provide a continuous flywheel
arrangement to the output transmission.
24. The energy recovery device as claimed in claim 20 comprising a
third clutch mechanism connected to the other end of the spring and
adapted to be held in place by a brake when the spring is being
charged wherein the brake is adapted to be released forcing an
inner race of the third clutch mechanism to rotate thereby passing
energy stored in the spring to provide a continuous flywheel
arrangement to the output transmission and the third clutch
comprises an outer race such that when the inner race rotates
forces the outer race to rotate thereby passing energy stored in
the spring to the output transmission.
25. The energy recovery device as claimed in claim 24 comprising a
third clutch mechanism connected to the other end of the spring and
adapted to be held in place by a brake when the spring is being
charged wherein the brake is adapted to be released forcing an
inner race of the third clutch mechanism to rotate thereby passing
energy stored in the spring to provide a continuous flywheel
arrangement to the output transmission and the third clutch
comprises an outer race such that when the inner race rotates
forces the outer race to rotate thereby passing energy stored in
the spring to the output transmission the outer race is adapted to
keep rotating when a brake condition is applied to the inner
race.
26. An energy recovery device according to claim 20, wherein the
SMA engine comprises a linear SMA actuator core.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of U.S. application Ser.
No. 14/365,214, filed Jun. 13, 2014, which is the US National Stage
under 35 USC 371 of International Application No.
PCT/EP2012/074566, filed on Dec. 5, 2012, which claims the benefit
of the priority date of Great Britain Application No. 1121361.8,
filed on Dec. 13, 2011. The contents of each of the
above-referenced applications is incorporated herein by reference
in its entirety.
FIELD
[0002] The present application relates to the field of energy
recovery and in particular to the use of shape memory alloys (SMA)
for same.
BACKGROUND OF THE INVENTION
[0003] Low grade heat, which is typically considered less than 100
degrees, represents a significant waste energy stream in industrial
processes, power generation and transport applications. Recovery
and re-use of such waste streams is desirable. An example of a
technology which has been proposed for this purpose is a
Thermoelectric Generator (TEG). Unfortunately, TEG's are relatively
expensive. Another largely experimental approach that has been
proposed to recover such energy is the use of Shape Memory
Alloys.
[0004] A shape-memory alloy (SMA) is an alloy that "remembers" its
original, cold-forged shape which once deformed returns to its
pre-deformed shape upon heating. This material is a lightweight,
solid-state alternative to conventional actuators such as
hydraulic, pneumatic, and motor-based systems.
[0005] The three main types of shape-memory alloys are the
copper-zinc-aluminium-nickel, copper-aluminium-nickel, and
nickel-titanium (NiTi) alloys but SMAs can also be created, for
example, by alloying zinc, copper, gold and iron.
[0006] The memory of such materials has been employed or proposed
since the early 1970's for use in heat recovery processes and in
particular by constructing SMA engines which recover energy from
heat as motion.
[0007] In a first type, referred to as a crank engine, of which
U.S. Pat. No. 468,372 is an example, convert the reciprocating
linear motion of an SMA actuator into continuous rotary motion, by
eccentrically connecting the actuator to the output shaft. The
actuators are often trained to form extension springs. Some
configurations require a flywheel to drive the crank through the
mechanism's limit positions. A related type are Swash Plate
Engines, which are similar to cranks except that their axis of
rotation is roughly parallel to the direction of the applied force,
instead of perpendicular as for cranks.
[0008] A second type are referred to as a pulley engines, an
example of which is U.S. Pat. No. 4,010,612. In pulley engines,
continuous belts of SMA wire is used as the driving mechanism. A
pulley engine may be unsynchronized or synchronized. In
unsynchronized engines, the pulleys are free to rotate
independently of one another. The only link between different
elements is rolling contact with the wire loops. In contrast, in
synchronized engines, the pulleys are constrained such that they
rotate in a fixed relationship. Synchronization is commonly used to
ensure that two shafts turn at the same speed or keep the same
relative orientation.
[0009] A third type of SMA engine may be referred to as field
engines, an example of which is U.S. Pat. No. 4,027,479. In this
category, the engines work against a force, such as a gravitational
or magnetic field.
[0010] A fourth type of SMA engine is that of Reciprocating Engines
of which U.S. Pat. No. 4,434,618 in an example. These reciprocating
engines operate linearly, in a back-and-forth fashion, as opposed
to cyclically.
[0011] A fifth type of SMA engine is that of Sequential Engines of
which U.S. Pat. No. 4,938,026 is an example. Sequential engines
move with small, powerful steps, which sum to substantial
displacements. They work like an inchworm, extending the front part
by a small step and then pulling the back part along. With the back
part nearby, the front part can extend again.
[0012] A sixth type of SMA engine is shown in U.S. Pat. No.
5,150,770A, assigned to Contraves Italiana S.p.A., and discloses a
spring operated recharge device. There are two problems with the
Contraves device, namely it is difficult to recharge quickly in a
reciprocating manner and secondly it is difficult to discharge the
energy to a transmission system without losses occuring.
[0013] A seventh type of SMA engine is shown in US patent
publication number US2007/261307A1, assigned to Breezway Australia
Pty Limited, and discloses an energy recovery charge system for
automated window system. Breezway discloses a SMA wire that is
coupled to a piston which is used to pump fluid to a pressurised
accumulator. The piston therefore moves in tandem with the SMA wire
as it contracts and expands. By coupling the SMA wire to the piston
in this manner, the SMA wire is in indirect communication with the
energy accumulator via the pumped fluid which is ineffiecient and
the Breezway system suffers from the same problems as
Contraves.
[0014] In addition one of the difficulties with each of these types
of SMA engines has been that of the cycle period of the SMA
material. SMA material is generally relatively slow to expand and
contract (10's of RPM). It has been and remains difficult to
achieve a worthwhile reciprocating frequency that might be usefully
employed in an industrial application (100's to 1000's of RPM).
This is not a trivial task and generally is complicated and
involves significant parasitic power losses.
[0015] The present application is directed to solving at least one
of the above mentioned problems.
SUMMARY OF THE INVENTION
[0016] According to the invention there is provided, as set out in
the appended claims, energy recovery device comprising:
[0017] a one way drive mechanism for incrementally winding a
spring;
[0018] a--SMA engine comprising a length of SMA material fixed at a
first end and connected at a second end to the one way drive
mechanism;
[0019] an immersion chamber adapted for housing the SMA engine and
adapted to be sequentially filled with fluid to allow heating
and/or cooling of the SMA engine; and
[0020] an output transmission for coupling to and being driven by
the spring; and a release mechanism activateable to allow the
spring to drive the output transmission.
[0021] The present application overcomes the problem of low
reciprocating frequency of the SMA material. The SMA material is
heated by being immersed in a fluid in an immersion chamber using a
hot fluid (e.g. water). Once the SMA material has contracted fully,
the heating fluid is diverted and the SMA material is allowed cool.
During the heating part of the cycle, the contracting SMA material
drives a one way mechanism which in turn winds a spring. The SMA
material is immersed sequentially in hot and cold fluids in order
to bring about the contraction and expansion of the material. Heat
transfer is primarily by forced convection from the fluid to the
material as the fluid is pumped through the chamber. It will be
appreciated that the fluid can be a gas in some embodiments. It
will be further appreciated that the term immersion chamber should
be interpreted to mean any housing adapted to accomadate the SMA
engine or material.
[0022] In one embodiment the immersion chamber comprises an inlet
and outlet for receiving and discharging the fluid.
[0023] In one embodiment the SMA engine is substantially immersed
in fluid during one heating cycle.
[0024] In one embodiment heat transfer from the fluid to the SMA
engine is primarily by forced convection as the fluid is pumped
through the chamber.
[0025] In one embodiment there are a plurality of SMA engines each
SMA engine being coupled to a one way drive mechanism for winding a
common spring.
[0026] Once the SMA material has contracted, the energy from the
SMA material has been stored in the spring. The SMA material is
then allowed to cool. By using the one way mechanism, successive
contractions of the SMA material are allowed to contribute energy
to the spring until it is eventually fully wound.
[0027] When the spring is fully wound, the transmission system
allows the energy to be discharged at will without interfering with
the energy recovering portion of the system, the SMA material using
a novel multiple clutch arrangement to enable incremental charging.
The spring does not hamper the SMA material and does not force it
into an unnatural reciprocating frequency. Advantageously, the
present application allows the separation of the recovery portion
of the energy system, and the deployment of the energy. This offers
a means by which to overcome the problem of trying to match the
relatively slow reciprocation of SMA engines to useful application.
The energy stored in the spring for instance may be released
suddenly for example to either an engine flywheel in a starter
motor situation or to an electrical generator.
[0028] This approach is desirable as otherwise use in such
applications would be precluded for SMA engines as they require
relatively high frequencies that SMA engines generally are unable
to provide. By using the proposed system, engine manufacturers (or
those of other similar systems) could recover low grade heat energy
and store it and deploy it at a desired time in a way that is more
suitable to the existing hardware (engine flywheels,
generators).
[0029] In a further embodiment of the invention there is provided
an energy recovery device comprising:
[0030] a SMA engine comprising a length of SMA material fixed at a
first end and connected at a second end to the one way drive
mechanism;
[0031] a multiple clutch system adapted to provide incremental
winding of a spring, said multiple clutch system comprising a first
clutch mechanism connected to the spring and adapted such that
rotation of the of the first clutch rotates the spring and a second
clutch mechanism is positioned in such a way to prevent reverse
movement of the first clutch mechanism; and
[0032] an output transmission for coupling to and being driven by
the spring; and a release mechanism activateable to allow the
spring to drive the output transmission.
[0033] The multiple clutch system enables the SMA core to be
sequentially charged and discharged whilst accumulating energy in
the spring, effectively de-coupling the energy recovery portion of
the operation (i.e. heat absorbed by the SMA material) from the
energy delivery portion (release of the spring to drive the load).
This decoupling can be enabled by the use of a ratchet or sprag or
cam clutch, operated in reverse to prevent the energy stored in the
spring from discharging back through the SMA or otherwise resisting
the expansion/contraction of the SMA material.
[0034] Included in the multiple clutch system is a one-way clutch
to enable the output to continue rotation when the spring has been
fully discharged. In this manner, the energy is transferred from
storage in the spring to mechanical work done by the output shaft.
This allows the output to continue to operate under its own inertia
while the spring/accumulator is recharged.
[0035] In one embodiment the second clutch mechanism is positioned
in such a way to prevent reverse movement of the first clutch
mechanism and adapted to allow incremental charging of the spring
until a desired energy storage level is achieved.
[0036] In one embodiment a third clutch mechanism connected to the
other end of the spring and adapted to be held in place by a brake
when the spring is being charged.
[0037] In one embodiment the brake is adapted to be released
forcing an inner race of the third clutch mechanism to rotate
thereby passing energy stored in the spring to provide a continuous
flywheel arrangement to the output transmission.
[0038] In one embodiment the third clutch comprises an outer race
such that when the inner race rotates forces the outer race to
rotate thereby passing energy stored in the spring to the output
transmission.
[0039] In one embodiment the SMA engine comprises a linear SMA
actuator core.
[0040] Accordingly, an embodiment of the application provides an
energy recovery device as detailed in claims 1 and 18. The
application also provides a method as detailed in claim 11.
Advantageous embodiments are provided in the dependent claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0041] The present application will now be described with reference
to the accompanying drawings in which:
[0042] FIG. 1 is a first view of a first embodiment of the
invention;
[0043] FIG. 2 is a further view of the embodiment of FIG. 1;
[0044] FIG. 3 is a circumferential arrangement of an SMA engine for
use in the second embodiment;
[0045] FIG. 4 is a view of the transmission system presented in
FIG. 3;
[0046] FIG. 5 is a schematic representation of a conventional
internal combustion engine of a motor vehicle;
[0047] FIG. 6 is a representation of a second embodiment configured
as a starter motor for use with the combustion engine of a motor
vehicle;
[0048] FIG. 7 is a further embodiment comprising a plurality of SMA
actuators arranged in a cascade fashion;
[0049] FIG. 8 illustrates exemplary power and efficiency figures
for the cascade arrangement of FIG. 7, and
[0050] FIG. 9 is a further embodiment in which a plurality of SMA
actuators are arranged in a parallel fashion.
DETAILED DESCRIPTION OF THE DRAWINGS
[0051] The proposed device represents a method by which to recover,
convert, store and redeploy energy from low grade heat sources. The
proposed method involves harnessing the Shape Memory Effect of
certain alloys to generate a mechanical force.
[0052] An exemplary embodiment of the application will now be
described with reference to FIG. 1 which provides energy recovery
device employing a SMA engine indicated by reference numeral 1. The
SMA engine 1 comprises an SMA actuation core. The SMA actuation
core is comprised of SMA material clamped or otherwise secured at a
first point which is fixed. At the opposing end, the SMA material
is clamped or otherwise secured to a drive mechanism 2. Thus whilst
the first point is anchored the second point is free to move albeit
pulling the drive mechanism 3. An immersion chamber 4 adapted for
housing the SMA engine and is adapted to be sequentially filled
with fluid to allow heating and/or cooling of the SMA engine.
Accordingly, as heat is applied to the SMA core it is free to
contract. Suitably, the SMA core comprises a plurality of parallel
wires, ribbons or sheets of SMA material. Typically, a deflection
in and around 4% is common for such a core. Accordingly, when a 1 m
length of SMA material is employed, one might expect a linear
movement of approximately 4 cm to be available. It will be
appreciated that the force that is provided depends on the mass of
wire used. Accordingly, depending on the requirements of a
particular configuration and the mass of SMA material needed 10's
or 100's of wires\ribbons\sheets may be employed together in a
single core.
[0053] A shaft is attached to the free end of the actuator core.
This shaft supplies linear mechanical movement and force to a one
way drive (transmission) mechanism. In the exemplary arrangement
shown, the one way drive comprises a ratcheted rack gear 4 driving
a pinion gear 5. The pinion gear in turn is attached to and
configured for winding an associated spring, suitably a coiled
spring 6. It will be appreciated that while a spring is shown in
FIG. 1 other energy storage devices could be used to perform the
same function as the spring. When the SMA core 1 is heated and
contracts, the rack gear meshes with the pinion gear causing it to
rotate. The pinion gear is turn winds the spring 5. It will be
appreciated that the spring will be sized to meet the requirements
of a particular application. Industrial torsion springs are a good
choice for the spring. Similarly, the rack and pinion arrangement
may be sized according to application and the expected degree of
movement from the SMA core.
[0054] A source of heat, in the form of the immersion chamber 4, is
employed to cause contraction of the SMA core. Once the SMA has
contracted, the source of heat may be removed and the SMA core
allowed to cool. The SMA core may then expand. To ensure, the SMA
core returns to its uncontracted state, a spring may be provided to
longitudinally bias the SMA core to this uncontracted state. The
size of this spring is small relative to the energy storage spring.
In one embodiment the SMA engine or material in the actuator core
is enclosed in the immersion chamber. The chamber 4 is adapted to
be sequentially filled with hot and cold fluid (e.g. water), fully
immersing the SMA material. The SMA material absorbs heat from the
heated fluid when it passes through the chamber, causing
contraction of the SMA. It subsequently releases heat to the cooler
fluid when it passes through the chamber, thereby bringing about an
expansion of the SMA material. The heated or cooled fluid can be
supplied through inlet 9 and exit through outlet 10. By
continuously cycling heated and cooled fluid through the chamber in
this way, it is possible to cyclically heat and cool the SMA
material, thereby producing usable mechanical work from the
periodic contraction and return of the material.
[0055] Immersive heating offers advantages over prior art heating
of the SMA through contact with a hot surface, such as is done when
touching the material against the exterior of a heated pipe or
other heated surface. One advantage of the immersion chamber over
the prior art is the ability to place a significantly larger mass
of working material (SMA) in direct contact with the heating fluid,
enabling greater power density for the unit overall.
[0056] Once the SMA core is in its uncontracted state, the heat
source may be re-applied causing the SMA core to contract and the
spring via the rack and pinion arrangement to be wound further. The
cycle may then as before continue with removal of the source of
heat and cooling of the SMA core. In this way with each heating and
cooling cycle, the SMA core contracts and expands and the spring is
incrementally wound.
[0057] Whilst one end of the spring is connected to and wound by
the pinion. The second end is connected to an output transmission
shaft. The shaft is restrained from rotating by a release mechanism
(brake) 10. The brake may be released in which case the energy in
the spring is released through rotation of the output transmission
shaft 11.
[0058] Thus in each cycle the system has successfully recovered the
heat from the heat source and converted it to mechanical energy and
in turn stored this energy in the spring.
[0059] The energy held within the spring may be released by
disengaging the brake. The drive shaft 11 is then free to be
rotated by the spring 6. In this manner, useful work may be
recovered from the spring in one go, i.e. the relatively low energy
incrementally stored from each cycle of the SMA engine may be
released in one go.
[0060] In each cycle, after the contraction is complete, the heat
source, i.e. hot fluid in immersion chamber 4, is removed through
outlet 10 and the core allowed cool by either cool fluid entering
inlet 9 or natural means. When the core has returned to its
starting position, the heat source may again be applied, permitting
the charging cycle to be repeated. In this manner, the spring can
be coiled much further than if only one cycle was completed.
[0061] The advantage of this approach is that in contrast to
previous SMA actuator concepts and designs which have attempted to
recover useful work by using a relatively fast reciprocating motion
involving the application of heating and cooling in a rapid
sequence in order to create an oscillating shaft output for useful
work, the storage of the energy in the spring for later use permits
a longer period heating and cooling cycle which is much more suited
to the specific characteristics of the SMA.
[0062] The heat recovery device has application in any situation
where there is a low grade heat source available. Examples of
applications are for use in automotive power plant, in power
generation systems or to recover heat from industrial processes.
The heat recovery device may also be used for charging flywheel
based Uninterruptible Power Supply (UPS) systems, which are finding
favour over battery based systems because of their durability and
long life spans. For example, in server farms where significant
amounts of heat are generated, energy might be recovered and used
to provide an input drive to a flywheel based UPS.
[0063] Referring again to FIG. 1 a multiple clutch system permits
the incremental charging of the spring 6 and its subsequent release
according to another aspect of the invention. A one-way clutch 3, 5
is driven by the SMA core 1 via a suitable pinion gear, connecting
rod or otherwise. This clutch 3, 5 is connected to the spring 6 via
shaft 11 so that the rotation of the clutch 3, 5 rotates the spring
6. A second one way clutch 12, 13 (such as a ratchet mechanism, a
sprag clutch or similar) is positioned and connected in such a way
as to prevent the reverse movement of the first clutch 3, 5. When
Clutch 3, 5 is therefore connected to the spring 6, this action
would allow the incremental rotation of the spring 6.
[0064] A third one way clutch 14, 15 is connected to the first
clutch 3, 5 via the spring 6. This third clutch 14, 15 is arranged
in such a manner that an inner clutch race is connected to the
spring 6 and an outer race to an output shaft or flywheel 16. This
inner race is also arranged so that it may be held stationary using
a brake.
[0065] The multiple clutch system hereinbefore described with
respect to FIG. 1 is now described in more detail with respect to
FIGS. 3 and 4. In operation Clutch 1 is caused to rotate by the
contraction of the SMA core. Clutch 2 rotates also by the same
amount. When the contraction is completed, both clutches cease
movement. At this point, the SMA core connecting arm causes the
outer race of clutch 1 to rotate back to its starting position.
During this movement, clutch 2 prevents the inner race of clutch 1
from rotating back, thereby maintaining it in its position.
[0066] The inner race of Clutch 1 is connected to one end of a
spring. The other end of the spring is connected to the inner race
of Clutch 3. This inner race of Clutch 3 is held in place by the
brake. Whilst the spring is being charged by Clutch 1, it is
restrained at Clutch 3. This allows the spring to store energy
contributed by the contraction of the SMA core. In addition, the
ratcheting action of Clutch 2 means that Clutch 1 may be rotated by
the SMA core a number of times in succession. In this manner, the
spring may be incrementally charged until a desired energy storage
level is achieved. When the energy is to be released, the brake at
Clutch 3 is released. When this is done, the inner race of Clutch 3
is forced to rotate suddenly by the spring. The inner race in turn
forces the outer race to rotate and thereby passes the energy
stored in the spring to the output shaft/flywheel. Because Clutch 3
is also a one-way clutch, the outer race is free to maintain
rotation, under the inertia of a flywheel or similar, after the
inner race comes to rest after the spring is completely discharged.
Advantageously, whilst the output shaft/flywheel continues to
rotate, the inner race of Clutch 3 may be braked and the charging
process started once again.
[0067] A second embodiment specifically directed at an
automotive\internal combustion engine application will now be
described.
[0068] As would be familiar to people generally, as illustrated in
FIG. 5, a conventional engine for a motor vehicle includes a
flywheel that is driven by the motor typically an internal
combustion engine. Heat generated in the engine is transferred to
and dissipated by the radiator. A starter motor is connected to the
flywheel and is used to turn over the engine when starting. Starter
motors are conventionally electric.
[0069] In an engine system such as that which would be used in
automotive applications or for power generation applications, a
considerable quantity of the energy released through the combustion
of the fuel is lost as low grade heat to the engine cooling water
system. This heat is then rejected to atmosphere through a heat
exchanger (radiator). Often, as much as 30% of the original fuel
energy can be lost this way.
[0070] The second embodiment provides a device\arrangement which
may be used to recover, convert, store and redeploy energy from
this low grade heat source. The proposed method involves harnessing
the Shape Memory Effect in a broadly manner similar to that of the
first embodiment, as shown in FIG. 6.
[0071] The arrangement provides the energy recovery device which
recovers energy from waste heat and in turn stores this energy for
subsequently starting the engine, i.e. the energy stored in the
spring of the energy recovery device is used as the "starter motor"
for turning over the engine when starting.
[0072] The SMA actuator is heated by heat contained within cooling
fluid which is diverted from the normal path between the engine and
the radiator. Valves or other switching means are provided to
divert the cooling fluid as required to the SMA actuator. The
valves may be operated on a timing cycle or in response to the
operation of the SMA actuator. Whilst the arrangement of the energy
recovery is broadly similar to the first embodiment, for ease of
fitting with the space normally provided in the engine compartment
for the starter motor the actuation core may be arranged
circumferentially rather than linearly. Again a one way mechanism
such as a ratcheted rack gear driving a pinion may be employed to
incrementally wind the spring.
[0073] The energy held within the spring, as before, may be
released by disengaging a brake whereupon the energy held in the
spring is released via the drive shaft. The drive shaft is
mechanically geared to the flywheel of the engine, via a clutch
system, in order that mechanical energy stored within the spring
may be released directly to the engine flywheel. In such a manner,
the SMA actuator may act to partially or completely replace the
starter motor of an engine.
[0074] Several SMA engines may be cascaded together to extract
energy from a heat source, as shown for example in FIG. 7. In this
arrangement, a plurality of SMA engines are connected to a shaft
for winding the spring. Each SMA engine is positioned along the
shaft and has a separate one way mechanism. This maximises the
energy that may be recovered from waste heat stream, thus energy is
extracted from a heat source (fluid) by a first engine before
passing to a second engine and then to a third. This "cascade" or
compound arrangement is possible due to the comparable inefficiency
of the individual SMA cores (.about.4%), which means that there is
still sufficient quantity of energy available in the waste heat
stream, at a sufficient temperature to permit the inclusion of
additional SMA cores on the outlet stream of the previous SMA core.
The SMA cores may be arranged in such a way as to allow
simultaneous charging of the power spring or alternatively may be
staggered to allow sequential charging of the spring. Equally it
will be appreciated that each SMA core may employ a separate
spring. In the arrangement of FIG. 7, the drive shaft is connected
to an electrical generator. The drive shaft may be released
periodically to cause the electrical generator to produce power
which may be used to charge a battery.
[0075] The present application allows for energy to be stored in a
coiled spring through repeated ratcheting by SMA engine cycles over
a given time period. This stored energy may be released on demand
through an appropriate mechanical release mechanism. The released
energy is transmitted by rotation of a shaft and may be used to
provide mechanical work or to drive an electrical generator.
[0076] Unexpectedly the savings that may be available from using
such a system are quite considerable as will now be explained with
respect to an example using the configuration of FIG. 7.
[0077] For a 2-Litre petrol fuelled automotive engine, the
following is an approximate energy balance:
TABLE-US-00001 Thermal Sink % Shaft Power 30% Exhaust 25% Jacket
Heat 30% Radiative & Other 15%
[0078] Taking an operating speed of 3000 Rpm and a brake power
output of 30 kW, the engine jacket water output can therefore be
taken as approximately 30 kW also.
[0079] Assuming the compound heat recovery system depicted in FIG.
8 and corresponding to the heat recovery system of FIG. 7, it may
be observed that a 30 kW thermal supply (@ 90 degC approx) is
supplied to the first SMA core. A conversion efficiency of
approximately 4% is considered reasonable for an SMA core under
such conditions, resulting in a power output of 1.5 kW.
[0080] Due to the low efficiency of the conversion, it can be
assumed that the temperature drop across the converter is very low.
Thus when the waste output stream is supplied to a second actuation
core a power supply of approx 28 kW is presented with a 0.5 kw
accounted for by unrecoverable heat loss to radiation, conduction
etc.
[0081] As the temperature is lower in the second engine, there is a
slight efficiency drop to 3%. A power output of 0.84 kW is provided
by second core.
[0082] With the third core, the efficiency may be around 2%.
Considering the waste stream from the second core, the power output
from this actuation core is 0.54 kW. Total power output of the
compound arrangement is therefore 2.88 kW, or 9.6% of the original
30 kW input.
[0083] It will be appreciated that is not fully correct to consider
the instantaneous power output as there is a charging cycle
involved and so it is more correct to consider the total energy
recovered, in Joules.
[0084] Tests on a prototype system have indicated a total charging
cycle time per actuation core of 1 min (20 seconds heating, 40
seconds cooling). Assuming the heating to occur for 20 seconds, the
total energy recovery is:
E=.eta.({dot over (Q)}.sub.int)
Where .eta.E=.eta.({dot over (Q)}.sub.int) is the SMA core
efficiency, E=.eta.({dot over (Q)}.sub.int) {dot over (Q)}.sub.in
is the waste heat supply and t is the charging time. This
gives:
E.sub.1=0.04(30000*0.0056)=0.0067 kWh
[0085] Where t=0.0056 i.e. t=20 s/3600 s. This is to say that on
each 1-minute charging cycle, 0.0067 kWh are recovered from the
waste heat stream.
[0086] Completing similar calculations for core 2 and 3 gives:
E.sub.2=0.03(28000*0.0056)=0.0047 kWh
E.sub.3=0.02(27000*0.0056)=0.003 kWh
[0087] The total energy recovered in a given 1-minute charging
cycle is therefore:
E.sub.total=0.0067+0.0047+0.003=0.0144 kWh
[0088] Whilst this may not appear significant, a significant point
to consider is that in this case, the SMA engine is designed to
supply an onboard electrical charging circuit. In current vehicles
this is typically performed using an alternator that is directly
driven by the driveshaft. The alternator, therefore, represents a
direct parasitic load on the engine. Because it is supplied
directly by the engine driveshaft, when considering the actual
energy saving in terms of fuel, it is necessary to consider the
engine brake fuel consumption i.e. the quantity of fuel that must
be consumed in order to produce 1 kW of mechanical power at the
drive shaft. With a reasonable efficiency value of 30%, it may be
argued that every 1 kW that is supplied to the alternator by the
drive shaft requires 3.3 kW of fuel energy to be combusted. For
every 1 kW of electrical power displaced by the SMA engine,
therefore, the actual real fuel saving is 3.3 kW. The value of
0.0144 kWh in energy recovered mentioned above therefore
corresponds to a total saving of 0.048 kWh per 1-minute charging
cycle.
[0089] To quantify the fuel saving over a typical automotive usage
scenario, we therefore make the following assumption: a 2 litre
petrol engine operating at charging load (3000 Rpm) for 90 minutes
per day for 5 days per week over 50 weeks per year which is in
accordance with average daily commuting times as compiled by the
Central Statistics Office (CSO) in Ireland.
[0090] The total energy saving over the full year for this
situation is therefore:
E.sub.saving,total=0.048*90*5*50=1080 kWh
[0091] An average Higher Calorific Value (HCV) for standard petrol
is approximately 9.7 kWh. The total yearly saving in fuel for this
scenario is therefore
Fuel Volume = ( 1440 9.7 ) kWh = 111 Litres ##EQU00001##
[0092] At current petrol prices (Rep. of Ireland 10/8/2011) of
approximately 1.50/Litre, this corresponds to a total yearly fuel
cost saving of 167.
[0093] With average family car costing approximately 2,000 per
annum in fuel costs (AA Cost of Motoring 2011), this figure equates
to approximately an 8% increase in fuel economy over the whole
year.
[0094] However where the device is employed in a high-usage
regimes, for example a taxi or other commercial vehicle which might
be expected to operate for 8-12 hours per day. Assuming 8 hours of
on-load (3000 Rpm) operation, the total fuel energy savings
become:
E.sub.saving,total=0.048*60*8*5*50=5760 kWh
[0095] And the fuel volume savings therefore become:
Fuel Volume = ( 5760 9.7 ) kWh = 593 Litres ##EQU00002##
[0096] Again, assuming current fuel costs at the pump of
1.50/litre, the total annual saving becomes 890.
[0097] In addition to the cascade arrangement of FIG. 7, it is also
possible to provide combine several SMA engines in a parallel
configuration in which the energy from a heat source is provided in
parallel to each engine. Each SMA SMA engine may be connected to a
common shaft for winding a common spring. Each SMA engine is
positioned along the shaft and has a separate one way mechanism for
winding the spring. The SMA cores may be arranged in such a way as
to allow simultaneous charging of the power spring or alternatively
may be staggered to allow sequential charging of the spring.
Equally it will be appreciated that each SMA core may employ a
separate spring. In the arrangement of FIG. 9, the drive shaft is
connected to an electrical generator. The drive shaft is released
periodically which causes the electrical generator to produce power
which may be used to charge a battery. It will be appreciated that
the configurations of FIGS. 7 and 9 may be employed together with
several groups of SMA engines arranged in parallel as shown in FIG.
9, but with individual SMA engines within a group arranged in
accordance in with FIG. 7.
[0098] When due care is taken to correctly size the springs and to
match the load, it is possible to have the SMA engine system
operate in a near-continuous fashion as opposed to operating with a
charge cycle and a delayed release cycle as described
previously.
[0099] This is achieved by specifying the spring and matching it to
the driven load such that when it is discharged, it accelerates the
load to a given operating speed such that this operating speed is
greater than the charging cycle speed of the SMA core. For example,
a flywheel may be employed as the load or as a buffer load. In this
manner, the spring acts as a step-up transmission system.
[0100] By arranging a plurality of the SMA cores in either a series
or parallel fashion as described above, it is possible to have
periodic charging cycles operating in sequence, out of phase with
each other. This is similar to the operating of pistons in a
combustion engine. For example, three SMA cores could be arranged
120.degree. out of phase. In this matter, a spring or springs might
be charged by three charging pulses according to this phase
difference. It will be appreciated that theoretically, it is
possible to have any number of SMA cores operating in such a
manner, either evenly out of phase i.e. equal gaps between each
cycle, or unevenly out of phase, i.e. varying phase differences
between SMA cores.
[0101] The spring or springs can similarly be discharged in such an
out of phase manner by arranging the release mechanism to be timed
in such a way as allows such out of phase discharge of the spring
to the load. The pulses in the operation may be evened out by
incorporating a flywheel at the spring output.
[0102] This in effect would allow for the system to act as a
continuously operating motor which could be used to drive an
electrical motor or similar in a continuous fashion.
[0103] The words comprises/comprising when used in this
specification are to specify the presence of stated features,
integers, steps or components but does not preclude the presence or
addition of one or more other features, integers, steps, components
or groups thereof.
[0104] The invention is not limited to the embodiments hereinbefore
described but may be varied in both construction and detail.
* * * * *