U.S. patent application number 13/262530 was filed with the patent office on 2012-07-26 for power unit.
Invention is credited to James Peter McDonald.
Application Number | 20120189472 13/262530 |
Document ID | / |
Family ID | 40750037 |
Filed Date | 2012-07-26 |
United States Patent
Application |
20120189472 |
Kind Code |
A1 |
McDonald; James Peter |
July 26, 2012 |
POWER UNIT
Abstract
A hydraulic power unit for subsea use is disclosed. The power
unit includes a housing containing a fluid, an electric motor
mounted in the housing, a distribution pump, a heat exchange unit
provided externally to the housing and at least one distribution
conduit in fluid communication with the heat exchange unit and the
housing.
Inventors: |
McDonald; James Peter;
(Aberdeen, GB) |
Family ID: |
40750037 |
Appl. No.: |
13/262530 |
Filed: |
April 2, 2010 |
PCT Filed: |
April 2, 2010 |
PCT NO: |
PCT/GB2010/050587 |
371 Date: |
April 5, 2012 |
Current U.S.
Class: |
417/372 |
Current CPC
Class: |
B63H 21/383 20130101;
B63H 21/17 20130101; B63J 2/12 20130101; F04D 13/06 20130101; F04C
11/008 20130101; B63B 2021/007 20130101; B63G 8/001 20130101; F04C
15/0096 20130101; B63C 11/52 20130101; F04C 13/008 20130101; B63H
23/26 20130101; F04D 29/586 20130101 |
Class at
Publication: |
417/372 |
International
Class: |
F04B 35/04 20060101
F04B035/04 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 3, 2009 |
GB |
09057837 |
Claims
1-15. (canceled)
16. A hydraulic power unit for subsea use comprising: a housing
containing a fluid in a cooling circuit independent of a hydraulic
power circuit; an electric motor mounted in the housing; a
distribution pump driven by the electric motor; a heat exchange
unit provided externally to the housing; and at least one
distribution conduit in fluid communication with the heat exchange
unit and the housing, whereby the hydraulic power unit is adapted
for the distribution pump to recirculate the fluid around the
cooling circuit which comprises the housing, the heat exchange unit
and the at least one distribution conduit.
17. A hydraulic power unit according to claim 16, wherein the at
least one distribution conduit comprises a nozzle ring.
18. A hydraulic power unit according to claim 16, wherein the
electric motor comprises a rotor and a stator, the stator including
one or more stator coils and wherein the distribution conduit
extends radially around one or more of the motor rotor, the stator
and the one or more stator coils.
19. A hydraulic power unit according to claim 16, wherein the
distribution conduit is disposed on an inner wall of the
housing.
20. A hydraulic power unit as claimed in claim 16, wherein the
power unit is a hydraulic power unit with an energy density between
0.45 kW/kg and 0.35 kW/kg.
21. A hydraulic power unit according to claim 16 wherein the fluid
is any one or more of a coolant and heat transfer fluid.
22. A hydraulic power unit as claimed in claim 16 comprising at
least two pumps.
23. A hydraulic power unit as claimed in claim 22, each pump is
adapted to pump fluid along an associated circuit between the
housing and the heat exchange unit.
24. A hydraulic power unit as claimed in claim 16, further
comprising a compensator.
25. A Remotely Operated Underwater Vehicle comprising a hydraulic
power unit having a hydraulic power circuit for providing hydraulic
power, and further comprising: a housing containing a fluid in a
cooling circuit independent of a hydraulic power circuit; an
electric motor mounted in the housing; a distribution pump driven
by the electric motor; a heat exchange unit provided externally to
the housing; and at least one distribution conduit in fluid
communication with the heat exchange unit and the housing, whereby
the hydraulic power unit is adapted for the distribution pump to
recirculate the fluid around the cooling circuit which comprises
the housing, the heat exchange unit and the at least one
distribution conduit.
26. A method of cooling a hydraulic power unit for use in a
Remotely Operated Underwater Vehicle, the method comprising
circulating fluid in a cooling circuit independent of a hydraulic
power circuit by the steps of: (a) circulating fluid inside a
housing; (b) transferring heat from one or more of a motor rotor, a
stator and one or more stator coils of a motor mounted in the
housing to the fluid; (c) circulating the fluid through a heat
exchange unit provided externally of the housing to cool the fluid
by losing heat to the surrounding water; and (d) passing the cooled
fluid through a distribution conduit inside the housing.
27. A method according to claim 26, wherein steps (a), (c) and (d)
are achieved with the use of a pump.
28. A method according to claim 26, wherein the cooled fluid is
directed from the distribution conduit onto one or more of the
motor rotor, the stator and the stator coils.
29. A method according to claim 27, wherein the cooled fluid is
directed from the distribution conduit onto one or more of the
motor rotor, the stator and the stator coils.
30. A method accordingly to claim 28, wherein the cooled fluid is
sprayed onto one or more of the motor rotor, the stator and the
stator coils.
31. A method accordingly to claim 29, wherein the cooled fluid is
sprayed onto one or more of the motor rotor, the stator and the
stator coils.
Description
[0001] The present invention relates to a power unit and more
specifically, a power unit for use subsea. The power unit may be a
hydraulic power unit, high pressure water pump or task specific
tooling unit suitable for use in a Remotely Operated Underwater
Vehicle (ROV).
[0002] ROVs are commonly used to perform many offshore, subsea
tasks. In order to perform a variety of tasks such as inspection,
repair or installation of new equipment, the ROV will normally have
work lights and a camera to assist control of the ROV by an
operator on the surface, and a manipulator with which to accomplish
the work.
[0003] On an ROV, a Hydraulic Power Unit (HPU) is commonly used to
drive the thrusters and other hydraulically operated subsystems of
the vehicle such as pan and tilt mechanisms for the cameras, and
hydraulically operated tooling to enable the ROV to carry out
intervention tasks on subsea infrastructure. The thrusters are the
main components of the prime mover system used to manoeuvre the ROV
in and around a subsea site as necessary to accomplish its
designated tasks. The HPU typically consists of an electric motor
coupled to a hydraulic pump unit. The motor casing is most commonly
oil-filled and this is maintained at a pressure approximately one
bar higher than the ambient sea pressure so as to provide a balance
between internal and external pressure when the ROV is submerged.
This avoids the need for a pressure proof casing and sophisticated
shaft seals, as would be the case with a standard casing filled
with air at atmospheric pressure as the pressure across the walls
of the casing is balanced so consequently the casing need only be
designed to cater for the mechanical loads associated with the
operation and mounting of the motor. It also enables the HPU to be
used if necessary for operations at full ocean depth of many
thousands of meters without any additional modification. The
pressure differential ensures that any leakage between the casing
and the sea water moves from the casing to the sea water, ensuring
seawater does not enter the motor casing.
[0004] The mechanism for maintaining the oil in the casing at or
above the ambient pressure of the surrounding seawater is typically
known in the industry as a compensator. Known compensators may
typically comprise a spring loaded rolling diaphragm or bellows to
maintain the oil in the casing at the required pressure.
[0005] Such motors are commonly supplied with a normal use/duty
rating. This rating specifies the limits between which the motor
should be used in order to prevent overloading and subsequent
damage to the motor.
[0006] Three of the critical parameters for a competitive ROV
system are the size and weight of the ROV and the diameter of the
umbilical connecting the ROV to a vessel on the surface, all of
which need to be kept to a minimum so as to reduce their effect on
the launch and recovery system and on the manoeuvrability of the
ROV.
[0007] An ROV with a lower in-air weight can use a launch and
recovery system with lower power rating and minimises the required
deck space on the launching vessel. Also, for every 1 kg of weight
added to an ROV, approximately 2 kg of buoyancy must be added to
the ROV to maintain neutral buoyancy when submerged. A smaller ROV
also has increased manoeuvrability when working in restricted
subsea sites.
[0008] Reducing the diameter of the umbilical reduces the drag
caused by subsea currents resulting in increased ROV
manoeuvrability. Reducing the umbilical diameter also results in a
smaller and lighter umbilical winch requiring less deck space and a
smaller support structure.
[0009] Embodiments of the present invention permit increased
performance and available power output of existing motors, such as
those used on an ROV, without increasing the size of the motor.
Alternatively the size and weight of a replacement motor can be
reduced while maintaining the same level of power output.
[0010] According to a first aspect of the present invention, there
is provided a hydraulic power unit for subsea use comprising a
housing containing a fluid, an electric motor mounted in the
housing, a distribution pump, a heat exchange unit provided
externally to the housing and at least one distribution conduit in
fluid communication with the heat exchange unit and the
housing.
[0011] Embodiments of the present invention permit an electric
motor with a power rating twice that of a standard motor and four
times the rating of an air-cooled motor. The weight and size of the
new motors are significantly less than a standard motor, whilst
allowing significant gains in performance.
[0012] Optionally, the power unit is a Hydraulic Power Unit (HPU),
suitable for use in a Remotely Operated Underwater Vehicle (ROV).
Improving the efficiency of an HPU has the advantage of increasing
the payload of the ROV. Alternatively, since the size of the power
unit required for a given ROV can be reduced, the weight of the ROV
can also be reduced.
[0013] The weight saving according to one embodiment of the
invention may be 300 kg. Reducing the size of the power unit and
increasing the efficiency helps to maximise the Hydraulic Power
Unit (HPU) energy density. The energy density of an HPU, according
to the prior art, is typically in range of 0.30 kW/kg to 0.25
kW/kg. The energy density of an HPU according to the present
invention is typically 0.45 kW/kg to 0.35 kW/kg. These figures
relate to the complete HPU comprising the motor and pump unit.
[0014] Optionally, the electric motor comprises a rotor and stator
including stator coils that pass through the stator core and extend
beyond its end faces.
[0015] Optionally, the electric motor is a standard submerged
motor. Optionally, at least one distribution conduit extends
radially around at least one of the stator coils. Typically, there
are provided two distribution conduits surrounding each end of the
stator.
[0016] Typically, the at least one distribution conduit comprises a
nozzle ring. The nozzle ring may be U-shaped in cross-section with
two upstanding flanges forming an annular chamber with the inner
surface of the motor casing or housing, hereinafter referred to as
the motor housing. The port or ports in the nozzle ring provide
fluid communication between the chamber and the inside of the motor
casing.
[0017] Typically, the distribution conduit is disposed on an inner
wall of the motor casing. Optionally, sealing devices seal off a
mating surface between the upstanding flanges and the inner wall of
the motor casing.
[0018] Advantageously, the ports are circumferentially spaced
around the conduit. Typically, the ports direct fluid radially
inwards towards the stator coils. Typically, the ports are
cylindrical. Optionally, the ports are conical.
[0019] According to one embodiment of the invention, nozzle rings
are advantageous in that the even distribution of fluid achieved by
spraying the fluid from the nozzles of the ring simultaneously
around the target being cooled reduces the occurrence of hotspots
developing on the stator coils whilst the motor is in use.
[0020] Optionally, the heat exchange unit is located outside the
casing. Typically, a pipe of the heat exchange unit is serpentine.
Typically, the pump circulates the fluid between the motor casing,
heat exchange unit and annular chamber of the at least one
distribution conduit.
[0021] Advantageously, the fluid is also a coolant or heat transfer
fluid, the fluid being capable of transferring heat produced by at
least one motor rotor bar and/or iron losses in the rotor core,
shaft, stator and stator coils, to a heat exchange unit.
[0022] Optionally, the fluid may be water, ethylene glycol,
hydrochlorofluorocarbon (HCFC) or other coolant provided that
suitable bearing types are used and the winding insulation system
is compatible.
[0023] Advantageously, the fluid is liquid at room temperature and
may be oil. If the fluid is oil, it may be at least one of
transformer oil, mineral oil, silicone oil, or synthetic oil with
electrical insulating properties. The transformer oil is highly
refined and contains few additives giving it the ability to absorb
a quantity of water whilst maintaining an acceptable dielectric
strength. Hydraulic type oil is not suitable due to the additives
it may contain. At the higher running temperatures some of the
additives, for example zinc, are deposited onto the hotter internal
surfaces such as the windings and this compromises the insulating
properties resulting in the early failure of the insulation.
[0024] In specific embodiments of the present invention the fluid
can have a viscosity in the range 10 cSt to 40 cSt at 20.degree. C.
This ensures adequate lubricity of the shaft bearings and
acceptable motor windage losses. Preferably the viscosity is in the
range 10 cST to 15 cSt at 20.degree. C.
[0025] Advantageously, the circulating pump used to circulate the
fluid is mounted on the motor shaft. Advantageously, the
circulating pump is located inside the casing, avoiding the need
for pump shaft seals and thus reducing the risk of the circulation
fluid becoming contaminated with foreign fluids or solids from
outside the casing.
[0026] Optionally, the distribution pump is a centrifugal pump.
Optionally, fins can be provided on the outer surface of the
casing, increasing the effective surface area of the casing and
thereby providing additional cooling of the fluid inside the
casing.
[0027] The Hydraulic Power Unit (HPU) may drive hydraulic thrusters
used for manoeuvring a Remotely Operated Vehicle (ROV) in and
around a subsea site as necessary to accomplish its designated
tasks. Typically, the ROV has two or more vertical and/or
horizontal thrusters.
[0028] Optionally, the ROV has one or more manipulating or cutting
arms, a water sampler, light and temperature sensors.
[0029] Optionally the power unit may comprise at least two pumps.
In a preferred option the power unit comprises two pumps mounted in
the housing.
[0030] Conveniently, each pump may be adapted to pump fluid along
an associated circuit between the housing and the heat exchange
unit.
[0031] Independent heat exchange units and/or distribution conduits
may be associated with each pump.
[0032] According to a second aspect of the present invention, there
is provided a method of cooling a hydraulic power unit for use in a
Remotely Operated Underwater Vehicle, the method comprising the
steps of: [0033] (a) circulating fluid inside a housing; [0034] (b)
transferring heat from one or more of the motor rotor, stator and
one or more stator coils of a motor mounted in the housing to the
fluid; [0035] (c) circulating the fluid through a heat exchange
unit provided externally of the housing to cool the fluid by losing
heat to the surrounding water; [0036] (d) passing the cooled fluid
through a distribution conduit inside the housing.
[0037] In some embodiments of the present invention, the
distribution conduit has at least one distribution port.
[0038] The motor may be part of a Hydraulic Power Unit (HPU) of a
Remotely Operated Vehicle (ROV). Typically, the cooled fluid is
directed from the at least one distribution port onto the motor
parts within the motor casing.
[0039] Currently, the rating of a motor used in a ROV is based on
submerged use where cooling is provided only by the surrounding
water. Heat produced by the motor is dissipated through the motor
casing to the water in which the ROV is operating. The movement of
oil inside the motor casing relies upon convection currents. The
circulation of oil is therefore limited and hot-spots can
develop.
[0040] In some embodiments of the present invention, method steps
(a), (c) and (d) may be achieved with the use of a pump. Optionally
the pump is a centrifugal pump.
[0041] In one embodiment of the present invention method step (c)
can include circulating the fluid through a heat exchange unit
located outside the motor casing.
[0042] In some embodiments of the present invention the
distribution conduit of method step (d) can be a nozzle ring.
[0043] Embodiments of the present invention will now be described
by way of example only and with reference to and as shown in the
accompanying drawings, in which:-
[0044] FIG. 1 is a sectional view of a hydraulic power unit in
accordance with one aspect of the present invention;
[0045] FIG. 2 is a cross-sectional view of an end of the stator of
the hydraulic power unit of FIG. 1; and
[0046] FIG. 3 is a sectional view of an alternative hydraulic power
unit in accordance with another aspect of the present
invention.
[0047] FIG. 1 shows an exemplary embodiment of a hydraulic power
unit for use subsea use comprising an electric motor 10 and pump 17
used to move oil 15 around inside a motor casing 16. When in use,
the motor 10 generates heat which is transferred to the oil 15 in
contact with the motor 10 inside the casing 16. The oil 15 is
cooled by passing it through a heat exchange unit 20.
[0048] The particular embodiment described herein comprises an
electric motor 10 inside a peripheral motor casing 16, within which
a cylindrically shaped rotor 11 is mounted. Annular stator 12
surrounds the rotor 11 within the motor casing 16. Annular stator
12 has ends 14 that extend beyond the ends of the rotor 11, towards
the casing 16.
[0049] The casing 16 is filled with oil 15, although it should be
noted that other fluids may be used, for example transformer oil,
mineral oil, silicone oil, or synthetic oils with electrical
insulating properties.
[0050] In the embodiment shown, the rotor 11 is centrally mounted
within the casing 16. A shaft 25 extends from the centre of the
rotor 11 into a hydraulic pump 13 which is mounted on the end of or
adjacent to the motor casing 16. The other end of the shaft 25 is
mounted in an annular bearing 33 in a wall of the casing 16.
Abutting the bearing 33 on the inside wall of the motor casing 16
is an impeller 17 of a centrifugal pump 27. The shaft 25 passes
through the centre of the impeller 17. The skilled reader will
realise that the centrifugal pump 27, in accordance with this
embodiment of the present invention, may be another type of
rotodynamic pump, positive displacement pump or any other device
for moving fluids. The shaft 25 is supported at one end of the
casing by a central boss 26 inside an endplate 34 and bearings 33
in the casing wall 16. The endplate 34 forms a pump chamber 28 in
which the impeller 17 is mounted. Positioned radially outside the
central boss 26 are ports 36 allowing oil 15 to move from the motor
chamber 37 to the pump chamber 28.
[0051] Two outlet ports 18 positioned at the top and bottom of the
chamber 28 allow fluid communication between the chamber 28 and two
ducts 29 on the outside of the casing 16. The two ducts 29 that
extend from outlet ports 18, converge into one pipe 19. The pipe 19
is in fluid communication with a heat exchange unit 20.
[0052] The heat exchange unit 20 is a continuous serpentine length
of pipe. The particular embodiment described herein refers to a
tubular heat exchange unit 20. The skilled reader will realise the
heat exchange unit 20 could be a plate, shell, adiabatic, phase
change or other type of device for the efficient transfer of heat
from one medium or fluid to another.
[0053] The other end of the heat exchange unit 20 is in fluid
communication with pipe 27 which is also in fluid communication
with fluid diverter 35, from which extend two ducts 30. Inlet ports
31 are provided in the casing 16, for connection to the ducts
30.
[0054] Inside the motor casing 16, there are located two
distribution conduits 32, each distribution conduit 32 encompassing
the ends 14 of the stator 12. The distribution conduits 32 are
U-shaped in cross-section. Two upstanding flanges 23 extend from
each distribution conduit 32 and adjoin at seals 38 with the inner
surface of the casing 16, forming annular chambers 21. Each chamber
21 is in fluid communication with a duct 30, through an inlet port
31. Each distribution conduit 32 forms one chamber 21 and has three
circumferential rows of radial apertures 22, between the two
flanges 23. The skilled reader will realise that any number of
apertures could be used. The apertures 22 provide fluid
communication between the chamber 21 and the inside of the casing
16, proximal to the ends 14 of the stator 12. The distribution
conduits 32 shown in FIG. 1 are nozzle rings with apertures or
distribution ports 22, cylindrical in shape. In an alternative
embodiment the apertures 22 are conical in shape. Any number of
apertures or ports 22 are suitable.
[0055] The outer surface of the casing 16 is covered with fins 24
which increase the surface area of the casing 16 and thus provide
improved cooling.
[0056] In use, circular motion of shaft 25 is used to power
centrifugal pump 27. Oil 15 is moved around motor casing 16 by the
centrifugal pump 17, during which time it is heated through contact
with rotor 11 and stator 12 of the motor 10.
[0057] The oil 15 contacts pump impeller 17 adjacent to the shaft
25 and is accelerated by the rotating impeller 17 into pump chamber
28. The oil 15 is then forced through outlet ports 18 in the casing
16 and into two ducts 29. The oil 15 is then pumped along pipe 19
and through the coils of a heat exchange unit 20. As the oil 15
passes along the pipework of the heat exchange unit 20 the
temperature of the oil 15 is reduced by the transfer of heat from
the oil 15, through the walls of the heat exchanger 20 and into the
relatively cold surrounding water (not shown). The oil 15 cools as
it passes along the tortuous path of the pipe in the heat exchange
unit 20.
[0058] Once the oil 15 has cleared the end of the coils of the heat
exchange unit 20, it moves along a pipe 27 before being divided
between two ducts 30. The cool oil 15 then passes through inlet
ports 31 into chambers 21 of the nozzle rings 32. The oil 15 in
chambers 21 is then pumped through apertures 22 and sprayed into
the casing.
[0059] The oil 15 leaving the apertures 22 is homogeneously
distributed over both ends of 14 of the stator 12. After contact
with the ends 14, the oil 15 is able to circulate inside the casing
16, and in particular to flow along the length of the stator coils
14, before again being drawn into the pump chamber 28 for
recirculation and cooling.
[0060] In use the oil 15 helps to cool the components of the motor
10, so allowing the motor 10 to continue to run without damage at
much higher loadings than those determined by its normal
rating.
[0061] FIG. 2 shows a cross-sectional view of an end 14 of the
stator 12. Stator slots 41 in the stator 12, receive stator coils
40.
[0062] FIG. 3 shows an exemplary embodiment of a hydraulic power
unit 10 comprising all the features shown in FIG. 1 with the
following differences. Ports 18 provide fluid communication between
the pump chamber 28 and a circulation chamber 43. An outlet port 44
provides fluid communication between the circulation chamber 43 and
duct 19 on the outside of the casing 16. The pipe 19 is in fluid
communication with the heat exchange unit 20.
[0063] In use, the oil 15 enters pump chamber 28 and is then forced
through outlet ports 18 in the casing 16 and into circulation
chamber 43. The oil 15 then leaves the circulation chamber 43
through port 44 into pipe 19 and through the coils of the heat
exchange unit 20.
[0064] Modifications and improvements may be made to the foregoing
without departing from the scope of the invention as defined by the
claims. In the embodiments above, the hydraulic power unit is
described as comprising an electric motor 10 and a pump 17. It is
envisaged that in one embodiment of the present invention a second
pump may be provided within the hydraulic power unit. Each pump may
be independently controlled and may also be adapted to pump fluid
to the heat exchange unit, through the same distribution conduit
and back to the housing. Alternatively each pump may be adapted to
pump fluid around an independent circuit from the housing to the
same or independent heat exchange units through the same or
independent distribution conduits and back to the housing.
[0065] By increasing the fluid flow within the hydraulic power
unit, the power output can be increased without increasing the
operating Pressure. Off the shelf components are cost effective for
operating at pressures of up to about 300 bar. Above this rating,
the components tend to be more specialised and therefore more
expensive. Therefore by incorporating a second pump and increasing
the effective flow rate through the hydraulic power unit, whilst
operating at a pressure rating in line with off the shelf
components such as around 250 bar, this allows more tooling to be
operated simultaneously and also results in a reduced utilisation
factor for individual components which extends their reliability
and operational lifespan.
[0066] Such an additional pump may be mounted adjacent the first,
with a consequential increase in rotor shaft length to accommodate
the pump or alternatively the housing of the hydraulic power unit
may be extended on the opposite side from the first pump to provide
a seat for a second pump within the housing.
* * * * *