CA 02335899 2001-O1-26
MALI, Mohammed
Linear Motor with Lubricant Sump
Page 1 of 6
To: Canadian Intellectual Property Office, The Commissioner of Patents
From: Mohammed Mali
Inventor: MALI, Mohammed
Title: INTEGRATED LINEAR MOTOR-DRIVEN COMPRESSOR WITH
LUBRICANT SUMP
Declaration, Formalities:
I, Mohammed MALI, am the inventor and the applicant herein, and I hereby seek
the grant
of a Canadian Patent to protect my invention. I am a resident of Canada, and
fall within the
definition of "small entity" set forth in the Patent Rules, v;rith the mailing
address set forth
below. This document and its attachments set forth a description of my
invention in
accordance with Rule 93 of the Patent Rules to the Patent Act, which together
with the
payment of the requisite fees, is sufficient to permit the: filing of this
material, and the
obtaining of a filing date (and receipt indicating the same) for my
application under section
28( I ) of the Patent Act of Canada.
Field of the Invention:
My invention relates to the conversion of electricity to reciprocal mechanical
motion
through electromagnetic fields controllably induced in a cylindrical stator
within which is
deployed a piston-shaped permanently magnetized rotor, to which rotor is
attached a power
load (such as a compressor, pump, crank-shaft or other similar load).
The invention has particular application (but is not thereby limited) in the
field of provision
of small-volume, quiet, compressors for refrigeration and similar equipment.
Larger scaled
versions could be utilized as motive power for vehicle, or heavier equipment,
where
efficiency, long-life, quietness and reliability are important.
Background of the Invention:
It is well-known to provide for linear electric motors relying; upon a
permanently magnetized
rotor depended within an variably energized electromagnetic stator (for
example, see US
Patents 4687054 Russell and Underwood "Linear Electric Motor for Downhole
Use").
These machines typically utilize a return spring to reposition the rotor
during a lull in the
"energized/dead/energized" cycle of magnetization of the stator. Thus, the
solenoid effect of
the field upon the rotor is used to push the rotor against a spring system
(typically a metal
diaphragm, which may also form some useful purpose such as being the "bellows"
in a
pump - see Eureka November 1997 Article "Shuttling Magnet Ensures Efficient
Gas
Compression" with drawings describing a two-diaphragm-spring linear motor
operative on
solenoid principles, each diaphragm spring being as well a pump bellows
chamber for
CA 02335899 2001-O1-26
MALI, Mohammed
Linear Motor with Lubricant Sump
Page 2 of 6
compression, attached as Appendix 1 hereto, also US Patent 3910729 Jepsen
"Compressor")
and at the same time performing work (i.e. the energy not used in loading the
spring is
captured to drive another machine such as a compressor, p:urnp, or crankshaft,
see US Patent
6092999 Lilie and Berwanger, Reciprocating Compressor with Linear Motor, 1999
for a
good example, another example being US Patent 612'7750 Dadd "Linear Compressor
Motor" 2000, which shows a two-stator motor system also mechanically sprung).
When the
field is dropped, the spring relocates the rotor at the beginning of the
cycle, ready to again be
forced by the field to work against the spring and the load.
The load in typical solenoid-style linear motors is typically external to the
solenoid itself, the
produced energy being transmitted from the solenoid to the; load by a shaft of
some sort. (see
US Patent 5083905 Mohn "Linear Motor Powered Pump Unit", for example, where
the
pump pistons were appended to the rotor's main body and not thus integral).
There have been inventions relating to purposefully modulating the electrical
power to form
the field in order that the power supplied to the rotor by elf;ctromagnetic
means is tailored or
optimized by peaking, for example, at the beginning of a cycle to overcome the
rotor's
inertia, mast of such control circuitry inventions relating to linear motors
being dedicated to
vehicle motive means (e.g. see US Patent 45090001 Wal';abayashi et al
"Brushless Linear
Servomotor" 1985).
It is an object of this invention to overcome limitations in the prior art
having to do with the
transmission of produced power by intermediate means (mechanical losses,
failure of
components) such as by shafts and cranks, and to provide; a novel means of
supporting the
rotor within the field provided by the stator to permit long service and
minimized wear, with
minimal moving parts and easy manufacturability and assembly of subcomponents.
Summary of the InventEOn:
The inclusion of a liquid lubricant-filled sump, with gasket/ring around a
linear motor's
rotor slideably but in an essentially sealed fit into the motor's stator
(preferably in a circular
cross-sectioned rotor forming a piston deployed within a fitting cylinder
which is the
internal cavity of the motor's stator(s)), configured such tlhat the rotor is
piston-like and the
stator is sleeve or cylinder-like to apply and control lubricant. The sump, if
pressurized, may
be relied upon as an improved replacement for the wf;arable springs used in
prior art
reciprocating linear motors to return the piston to its starting position
within a work cycle.
However, the piston's return to start may as well, in one embodiment, be
accomplished by
the deployment of two stators (one at each end of the cylinder within which
the rotor is
deployed) each energized in a timed cycle to drive the piston/rotor from one
end to the other,
in which case a return spring or pressured closed cylinder means would not be
required.
Thus, the stator component, once suitably lubricated by the lubricant in the
sump, provides a
novel support and bearing means to orient the linearly moved rotor in the
linear motor
optimally within the changing magnetic fields produced at the stator.
CA 02335899 2001-O1-26
MALI, Mohammed
Linear Motor with Lubricant Sump
Paae 3 of 6
The stator is, in an exemplary embodiment, formed in three: parts of
substantially equal inner
diameter thus forming one continuous cylinder within which the rotor can fit
and move, to
form a two-electromagnet stator in cylindrical form into which a single
magnetic field rotor
in the shape of a tightly fitted piston is located, oriented and borne.
The outer parts of the stator are each formed of suitable material which when
wound with
electrically-conductive wire or similar coils and when said coil has a direct
electrical current
passing there through, will form a solenoid style of electromagnet. The
magnetic field
produced by said electromagnet acts upon the permanent magnet which is (or is
a significant
part of) the rotor, to move the rotor through the field alon~; its axis as
supported by the said
stator's cylindrical inner cavity. The two electromagnetic parts of the stator
are electrically
and magnetically isolated from each other by a third middle part which is not
conductive of
either power or magnetic flux, and which is mounted between the two
magnetically active
parts.
The rotor and stator thus form a piston and cylinder, respectively. At one end
of the cylinder
is a sump within which lubricant is placed, and the rotor is at that end
fitted with a gasket or
O-ring configured such that the rotor is thus sealed with the cylinder,
keeping the lubricant
within its sump. The sump may be sealed if required to corm a return mechanism
for the
rotor, but in the exemplary two-field stator system, would be open to
atmospheric pressure
but built to contain the lubricant within its cavity.
The rotor's other end may be configured in a number of v~rays to bear a work
load, such as
(by example) to form a piston and cylinder with suitable inlet and outlet
valves to compress
fluid or to pump fluid from inlet to outlet, or to evacuate a:n inlet to form
partial vacuum, or
similar loads; similarly, to that end of the rotor may be attached a drive
shaft which can be
operatively linked to an eccentric to convert the rotor's linear motion to a
rotating drive
motion, for example to a drive shaft.
It is to be noted that a number of these rotor/stator driven-piston/cylinder
systems can be
inter-linked, for example ganged to a crank-shaft, suitablw timed, to form a
mufti-cylinder
motor.
It should also be noted that there are a number of methods of controlling the
electrically
current flow, duration, direction, and power characteristics, responsive to
the motor's
operating characteristics, its design characteristics, the load or desired
power production,
power available, or other means, and may be done electro-mechanically, by
computational
means, responsive to sensors, or self regulating through feedback mechanisms.
CA 02335899 2001-O1-26
MALI, Mohammed
Linear Motor with Lubricant Sump
Paee 4 of 6
Description of Drawings:
Figures 1-6
Show the range of movement of the Piston, from being fully extended to the
outermost
position in figure 1 through a complete cycle through full retraction to an
innermost position
at figures 3 and 4, and back to fully extended; also showing the polarity of
piston
magnetism, circuit diagram of power application and direction of DC current
flow through
solenoid coils) (wrapped on outside of cylinder), and wheaher current flows
through one or
both coils.
The attached drawings (1-6) are cut-away representations of an embodiment,
showing in
"time-lapse" conceptual manner the operation of an example of the invention
through the
main parts of one complete cycle of operation:
Figure 7
Shows a Longitudinal cross-section of the piston/rotor in three variant
embodiments.
Fi u~ re 8
Shows a possible construction, by example, of the cyl:inder's liner comprised
of three
segments (magnetic, nan-magnetic, magnetic).
Figure 9
Shows an embodiment with two coils, two end-caps, an oil reservoir and a stand
mounting
or housing.
Figure 10
Shows a schematic drawing of the components including control circuitry as
"black boxes".
Figure 11
Shows a schematic of the invention driving a compressor/decompressor (fan,
valves, closed
cylinder on end of liner opposite lubricant sump).
Figure 12
Shows a schematic of a variant driven load (by drive shaft to crank or similar
mechanical
device).
CA 02335899 2001-O1-26
MALI, Mohammed
Linear Motor with Lubricant Sump
Page 5 of 6
Detailed Description of the Invention:
A more detailed description of an embodiment of the invention, showing its use
with an
integrated compressor or pump, follows, with reference to the drawings where
useful:
A solenoid pump or compressor apparatus which integrates a power source and a
piston-type
of pump or compressor, consisting of:
a. a single cylinder and piston pump or compressor, configured with inlet and
outlet
valves and control mechanisms to actuate said valves so that the cylinder and
its
contained piston, when the piston is moved within the cylinder, perform the
function
of a pump or a compressor (it should be made clear that the use of a
compressor or
pump as the "load" does not take away the possibility of mounting a rod or
drive
shaft on the rotor to permit the transmission of the rotor's linear motion
into useful
energy in the form of a driven flywheel, for instance;, or drive gear or
pulley);
b. a solenoid-like system of electromagnets fixed adjacent to a cylinder
within which is
deployed a cylindrical shaft comprised of a suitablf; substance which is a
permanent
magnet; said electromagnets being energized by (AC or DC) current controlled
by a
master "on/ofp' switch, through a control circuit (wlhose purpose and
configuration is
to control the induction of magnetic fields) at the electromagnets of suitable
polarity, intensity, and duration);
c. an oil reservoir and suitable sealing and refilling means to provide
lubrication to the
shaft within the electromagnet-containing barrel/cylinder of the body of the
mechanism (note that the oil reservoir may, but does not necessarily, provide
a
damper or an energy store or bumper for the cylinf~~er as well as providing
lubricant,
if desirable, by pressure-sealing the sump); this method of lubrication
provides for
friction-reduction and some cooling to the cylinder and shaft; a smaller
diameter
shaft could be deployed within a different system of bearings suspended
centered
within the cylinder containing the electromagnets, 'where the lubricant was
provided
by a sump at one end of the cylinder, and suitably sealed from splashing or
other
loss.
d. there may be other features in such an exemplary motor, such as the
provision of
bumpers or motion-limiting means to avoid having the pump piston or the shaft
invade the pump cylinder or the oil reservoir in an unwanted way, which are
not
specifically described here, but would be apparent to one skilled in the art.
The descriptions here are meant to be exemplary and not limiting. It is to be
understood that
a reader skilled in the art will derive from this descriptive material the
concepts of this
invention, and that there are a variety of other possible implementations;
substitution of
different specific components for those mentioned here wiill not be sufficient
to differ from
the invention described where the substituted components are functionally
equivalent.
CA 02335899 2001-O1-26
No~emo~, ,99> ~o~e, ~~a,~,e ~~oa MALI ~ APPENDIX 1 oaa~ ,
I.L I:n:!: t ~;c>t l vlf;l l; nlti- c i )W .It t f.a I l:lti
Shuttling magnet ensures efficient gas compression
Tom Shelley reports on a low cost combined linear motor and gas compressor
r1n electric linear motor, whose single moving component that doubles as both
armature and piston, promises radically unproved gas compression efficiency
Its simple construction incurs no side loads or friction penalties and
requires no lubrication.
The prototype designs hope to replace present day conventional compressors
with new types that can cope with 'greener' working Fluids. But the basic
principles can be
applied to any kind of compression operation, including that on air.
In conventional refrigerator compressors, a rotating electric motor drives a
reciprocating pump through a crank. The whole arrangement of motor and pump
resides
within a sealed enclosure and requires oil splash lubrication. the oil is
recovered by condensation processes downstream within the refrigerator and
runs back into the
pump. While CFC and HCFC refrigerants require only low pressures, alternatives
such as ammonia, propane and carbon dioxide require working pressures beyond
the
reach of conventional small compressors. Some recently developed non-CFC
refrigerants work within the range of the conventional small compressors but
are not
compatible with conventional lubricants. So to make greener refrigerators, it
is necessary to deliver a higher pressure or be able to work without
lubrication.
Wei-Min Zhang, a patent agent living in North London, and Dr lvor Day, at
Cambridge University's Whittle Laboratory, have spent some time developing the
concept
of a very simple linear motor and compressor. The basic idea, as patented by
Mr Zhang is simple enough: a permanently magnetised piston shuttles back and
forth
between two electromagnets powered by the SOHz mains. But optimising it for
maximum efficiency at a sensible production cost is another story. Several
linear motor
compressor designs are known for cooling systems in highly specialised
applications, such as cooling infrared sensors in satellites. Such compressors
are usually very
small in capacity and not suitable for mass production.
- --.,~ -
CA 02335899 2001-O1-26
November x997 cover feature snory
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1('t: _tilil '11~'viLlll
The Zhang/Day concept has so far been through a series of designs, prototypes
and modifications, aided by a 1996 DTI Smart Award. The latest design Froduces
a
maximum pressure of 9.5 bar at no flow, from an internal two stage
compression, and delivers a maximum gas flow in excess of 3 litres/minute at 1
bar.
In its simplest embodiment, a piston magnetised as a bar magnet, with a North
pole at one end and a South pole at the other, wilt happily move to and fro
between two
electromagnets energised by an alternating supply.
The inertia of the piston at the end of each stroke is absorbed by compressing
either gas or a spring. This means that the applied frequency must coincide
with the natural
Frequency of the piston, its return springs and gas cushions, damped by gas
being drawn in and pumped out through non-return valves. If the applied
frequency is the
50Hz mains, as in the version shown to Eureka , then the rest of the system
must have a similar natural frequency.
In larger pumps, a lower excitation frequency might be used to match a lower
frequency, or the arrangement can be made self controlling. In su,_h a case,
the motor could
be driven by DC, switched on and off and reversed in response to the posi4on
of the piston detected by Hall Effect or other sensors, in the same way as in
a brushless DC
motor. High frequency DC powered units might find particular favour in motor
vehicle air conditioning and refrigeration systems. The other aspect of the
design, into
which much effort has been put, is to make it electrically efficient by
minimising magnetic flux leakage.
The armature is magnetised so that at its ends, one pole is in the centre and
the opposing pole is around the outside, matching a similar arrangement on the
faces of the
electromagnets.
In the original design, the outer parts of the armature/piston, were to have
been tapered, fitting over cone shaped outer pole piece sections of the
electromagnets. This
was designed to tackle the problem caused by the contradictory requirements of
a long stroke for good gas compression and a small air gap for good
electromagnetic
performance. Such an approach would certainly be efficient, if special kit
could be built foe mass production of the magnet parts. Another idea seriously
considered w
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Mr Zhang has already considered how the design could be scaled up. For larger
units, he thinks there would ham to be at least two sep,,ra to units coupled
side by stde, or
end to end, working in counter phase in order to reduce vibration. For pumps
running on a three phase supply, it might be possible t.~ ILave than units,
each running on
a separate phase pair, mounted along the aides of a triangle.
The development has reached the stage where the refrigerator-sized prototype
demonstrates what can be done, but shows some limil,olous concerning seal life
and other
matters. The team is ,till imp roving the design, while tH~o major UK
manufacturing companies have expre.~sed support taut the nexl a, 1;e, of
finul~' optirtmsinri the
nnouw..waoe eys aamoe co "knea.eoemm
CA 02335899 2001-O1-26
tvovemper n99>.<aven IeaW re stay w'ag" 1
ilesign for m. aimum efficiency and manufac ~ ._J\~SCCm,,9,.008~°' T~ :
';, _~ m ~ ,..~~,. nies inW rested in licensing the technology,
especially 'those that can help to commercial ~ ~-~ i~ ~ .a ~
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Zhang and Day
Design Pointers
* Combined pump and motor design has onlv one main moving part which acts as
both linear motor armature and compressor piston
* There are no side Loads and no need for oil lubrication
* The basic simplicity of the design suggests that eventual manufacturing
costs should be low
Return to list of ,tories oite
CA 02335899 2001-O1-26
~s~~""o~.,~,o" ~.,ve ,
A new type of linear efecfic motor has been developed Dy workers in Oxford's
Oepartmenr of Engueering Science. It could lead to fhe
design and manufacture of improved long-tile refrigeration equipment.
generators and compressors. It might also find appficafions in
banspod and positioning systems. .,
Background
The lifetime of conventional rotary machines is largely determined by whether
or not they are lubricated. Lubricated designs can nave long lifetimes. Oil-
tree
designs generally have short lifetimes because of wear. For certain uses, it
is vital coat oil-free. long-life machines are used, for example in cooling
systems in
space applications. It was this need which fed to the development in Oxford in
the t980's of linear machines with suspension springs and non-contacting
seals.
The seals have a clearance gap small enough to ensure that there is no
significant escape of gas. yet large enough to ensure that no wear can occur.
A typical
gap size is ten microns.
Problem of Existing Motors
These long-life. oil-free systems can only be used in contunction with linear
motors rathe«han the more conventional type of motor that is rotational in
design. A
linear motor can either have a moving coil or a moving magnet. Linear motors
based on moving coils have mainly been used to date in long-life coolers and
compressors, Largely because they are easy to design and make in small
quantities but also because of a lack of satisfactory moving magnet designs.
The
commercial development or tong-life, oil-tree linear machines has been
hampered by the high market costs associated with moving coil designs.
The Oxford Invention
Research workers in Oxford nave now been able to propose a new helical design
that could read to the mass production of cheap. efficient moving magnet
motors. Theirs is one of few designs that seem capable or offering industry a
significantly lower..cost linear motor, suitable for use ~n onl-free long-tile
compressors,
refrigerators and generators.
Commercialisation
Isis Innovation ns interested in discussing suitable a«angements with
companies wishing to develop and utilise this technology.
For further information contact Or Mark A Taylor (Project Manager)
mark.tavlorfW sis.oxac.uk
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