U.S. patent application number 10/224759 was filed with the patent office on 2004-02-26 for refrigeration system employing multiple economizer circuits.
Invention is credited to Lifson, Alexander, Tang, Yan.
Application Number | 20040035122 10/224759 |
Document ID | / |
Family ID | 31495301 |
Filed Date | 2004-02-26 |
United States Patent
Application |
20040035122 |
Kind Code |
A1 |
Lifson, Alexander ; et
al. |
February 26, 2004 |
REFRIGERATION SYSTEM EMPLOYING MULTIPLE ECONOMIZER CIRCUITS
Abstract
The refrigeration system of the present invention includes
multiple economizer circuits. After flowing through the condenser,
a first path of refrigerant is split from the main path. The
refrigerant in the first path is expanded to a lower pressure and
cools the refrigerant in the main path in the high pressure
economizer heat exchanger. The refrigerant in the first path then
returns to the compressor in a high pressure economizer port. A
second path of refrigerant is then split from the main path. The
refrigerant in the second flow path is expanded to a lower pressure
and cools the refrigerant in the main path in the low pressure
economizer heat exchanger. The refrigerant in the second path then
return to the compressor in a low pressure economizer port. The
refrigerant in the main path is then evaporated. The dual stage
economizer refrigeration system can be employed with a screw
compressor or a scroll compressor.
Inventors: |
Lifson, Alexander; (Manlius,
NY) ; Tang, Yan; (Daphne, AL) |
Correspondence
Address: |
CARLSON, GASKEY & OLDS, P.C.
400 WEST MAPLE ROAD
SUITE 350
BIRMINGHAM
MI
48009
US
|
Family ID: |
31495301 |
Appl. No.: |
10/224759 |
Filed: |
August 21, 2002 |
Current U.S.
Class: |
62/113 ;
62/513 |
Current CPC
Class: |
F25B 2400/13 20130101;
F25B 1/10 20130101; F04C 18/0261 20130101; F25B 1/047 20130101;
F04C 29/0007 20130101; F04C 18/16 20130101 |
Class at
Publication: |
62/113 ;
62/513 |
International
Class: |
F25B 041/00 |
Claims
What is claimed is:
1. A refrigeration system comprising: a compressor for compressing
a refrigerant to a high pressure; a condenser for cooling said
refrigerant; a high pressure economizer heat exchanger, said
refrigerant being split into a first passage provided with a high
pressure expansion device and a second passage and then exchanging
heat therebetween in said high pressure economizer heat exchanger,
said first passage returning to said compressor and said second
passage flowing to a low pressure economizer heat exchanger; said
low pressure economizer heat exchanger, said refrigerant being
split into a first passage provided with a low pressure expansion
device and a second passage and then exchanging heat therebetween
in said low pressure economizer heat exchanger, said first passage
returning to said compressor and said second passage flowing to an
expansion device; said expansion device for reducing said
refrigerant to a low pressure; and an evaporator for evaporating
said refrigerant.
2. The system as recited in claim 1 wherein said compression device
is a screw compressor including a male rotor, a first female rotor,
and a second female rotor, each of said rotors having a plurality
of threads, said plurality of threads of said male rotor said
plurality of threads of said first female rotor engaging to create
a plurality of high pressure compression chambers, and said
plurality of threads of said male rotor and said plurality of
threads of said second female rotor engaging to create a plurality
of low pressure compression chambers, refrigerant from said high
pressure economizer flowing into said high pressure compressor
chambers and refrigerant from said low pressure economizer flowing
into said low pressure chambers.
3. The system as recited in claim 2 wherein said refrigerant from
said evaporator enters said screw compressor through a high
pressure suction and a low pressure suction port for compression in
said high pressure and said low pressure compression chambers,
respectively, and said refrigerant from said low pressure and said
high pressure economizer heat exchangers enters said low pressure
and said high pressure compression chambers, respectively, through
a low pressure and a high pressure economizer port, respectively,
and said refrigerant in said high pressure and said low pressure
compression chambers exits said compressor through a high pressure
and a low pressure discharge port, respectively.
4. The system as recited in claim 1 wherein said compression device
is a scroll compressor including a non-orbiting scroll member
including a base and a generally spiral wrap extending from said
base and an orbiting scroll member including a base and a generally
spiral wrap extending from said base, said generally spiral wrap of
said non-orbiting and orbiting scroll members interfitting to
define at least one compression chamber, one of said scroll members
having at least one high pressure injection port and at least one
low pressure injection port, said refrigerant from said high
pressure economizer heat exchanger and said low pressure economizer
heat exchanger entering said at least one compression chamber
through said at least one high pressure injection port and said at
last one low pressure injection port, respectively.
5. The system as recited in claim 4 wherein communication of said
refrigerant between said high pressure economizer heat exchanger
and said low pressure economizer heat exchanger is prevented at a
point of injection.
6. The system as recited in claim 4 wherein said refrigerant is
injected through said at least one high pressure injection port and
said at least one low pressure injection port into at least one
high pressure compression chamber and at least one low pressure
compression chamber, respectively.
7. The system as recited in claim 4 wherein said at least one low
pressure injection port and said at least one high pressure
injection port are located such that refrigerant injection through
said injection ports begins after a suction port is closed to said
compression chamber.
8. The system as recited in claim 6 wherein refrigerant injection
through said injection ports ends before opening of said
compression chamber to a discharge port.
9. The system as recited in claim 1 wherein said refrigerant from
said high pressure economizer heat exchanger and said low pressure
economizer heat exchanger enters said compressor through a high
pressure economizer port and a low pressure economizer port,
respectively, said refrigerant from said evaporator enters said
compressor through a suction port, said refrigerant from said
compressor exits said compressor through a discharge port.
10. The system as recited in claim 9 further including a first
valve which controls flow of said refrigerant between said high
pressure economizer port and said low pressure economizer port and
a second valve which controls flow of said refrigerant between said
low pressure economizer port and said suction port.
11. The system as recited in claim 10 wherein said first valve and
said second valve are opened to bypass said refrigerant from said
high pressure economizer port and said low pressure economizer port
to said suction port.
12. The system as recited in claim 10 wherein said first valve is
opened and said second valve is closed to bypass said refrigerant
from said high pressure economizer port to said low pressure
economizer port.
13. The system as recited in claim 10 wherein said first valve is
closed and said second valve is opened to bypass said refrigerant
from said low pressure economizer port to said suction port.
14. The system as recited in claim 1 wherein at least one of said
high pressure expansion device and said low pressure expansion
device is closed.
15. A refrigeration system comprising: a compressor for compressing
a refrigerant to a high pressure, said refrigerant entering said
compressor through a suction port and exits said compressor through
a discharge port; a condenser for cooling said refrigerant; a high
pressure economizer heat exchanger, said refrigerant being split
into a first passage provided with a high pressure expansion device
and a second passage and then exchanging heat therebetween in said
high pressure economizer heat exchanger such that said refrigerant
in said second passage is cooled by said refrigerant in said first
passage, said first passage returning to said compressor and said
second passage flowing to a low pressure economizer heat exchanger;
said low pressure economizer heat exchanger, said refrigerant being
split into a first passage provided with a low pressure expansion
device and a second passage and then exchanging heat therebetween
in said low pressure economizer heat exchanger such that said
refrigerant in said second passage is cooled by said refrigerant in
said first passage, said first passage returning to said compressor
and said second passage flowing to an expansion device; said
expansion device for reducing said refrigerant to a low pressure;
an evaporator for evaporating said refrigerant; a first valve which
controls flow of said refrigerant between said high pressure
economizer port and said low pressure economizer port; and a second
valve which controls flow of said refrigerant between said low
pressure economizer port and said suction port.
16. A method of operating a refrigeration system comprising the
steps of: compressing a refrigerant to a high pressure; cooling
said refrigerant; subcooling said refrigerant by splitting said
refrigerant into a first passage and a second passage, expanding
said refrigerant in said first passage, exchanging heat between
said refrigerant in said first passage and said refrigerant in said
second passage, returning said refrigerant in said first passage to
said step of compressing and flowing said refrigerant in said
second passage to a step of further subcooling; further subcooling
said refrigerant by splitting said refrigerant into a first passage
and a second passage, expanding said refrigerant in said first
passage, exchanging heat between said refrigerant in said first
passage and said refrigerant in said second passage, returning said
refrigerant in said first passage to said step of compressing and
flowing said refrigerant in said second passage to a step of
expanding; expanding said refrigerant to a low pressure; and
evaporating said refrigerant.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates generally to a refrigeration
system employing multiple economizer circuits to increase capacity
and efficiency of the refrigeration system.
[0002] System capacity can be increased by increasing the
subcooling of the refrigerant leaving the condenser. In a standard
(non-economized) refrigeration system, the amount of subcooling
typically ranges from 0 to 15.degree. F. An economizer can be
employed to additionally subcool the liquid refrigerant exiting the
condenser, increasing the capacity and efficiency of the
refrigeration system.
[0003] In an economized system, the refrigerant is split into two
flow paths after leaving the condenser. The first flow path is
expanded to a low pressure by an expansion valve prior to passing
into the economizer heat exchanger. The second flow path flows
directly into the economizer heat exchanger and is cooled by the
refrigerant in the first flow path. The refrigerant from the first
path then flows along an economizer return path and is injected
through economizer ports into the compressor. The vapor refrigerant
in the second path is then expanded by a main expansion valve. By
employing an economizer, both system capacity and efficiency is
increased.
[0004] It would be beneficial to employ multiple economizer
circuits to further increase the capacity of the refrigeration
system. The benefits of employing multiple economizer circuits are
especially pronounced for a refrigeration system operating with a
high discharge to suction pressure ratio. Multiple economizers have
not been employed in prior refrigeration systems as the refrigerant
flow from each of the economizers mixes at the point of injection.
For example, prior screw compressors include a pair of rotors. As
only two rotors are employed, the rotational angle of the
compression process is not large enough to prevent vapor
communication among the suction port, the low pressure economizer
port, the high pressure economizer port, and the discharge
port.
SUMMARY OF THE INVENTION
[0005] The multiple stage economizer refrigeration system of the
present invention includes a compressor, a condenser, a high
pressure economizer circuit, a low pressure economizer circuit,
expansion valves, and an evaporator. After the refrigerant exits
the condenser, the refrigerant splits into two flow paths. The
first path of refrigerant is expanded to a lower pressure in an
expansion valve prior to flowing into the high pressure economizer
heat exchanger. Refrigerant from the main path flows through the
high pressure economizer heat exchanger and is cooled by the
refrigerant in the first path. The refrigerant in the first path is
returned to the compressor through the high pressure economizer
port.
[0006] After being cooled in the high pressure economizer, the
refrigerant from the main path again splits into two flow paths.
Refrigerant in the second path is expanded to a low pressure in an
expansion valve prior to flowing into the low pressure economizer
heat exchanger. Refrigerant from the main path passes through the
low pressure economizer heat exchanger and is cooled by the
refrigerant in the second path. The refrigerant from the second
path is returned to the compressor through the low pressure
economizer port. Thus, additional subcooling of the main flow of
the refrigerant is accomplished by subcooling in two stages. For
even greater subcooling benefits, more than to stages can be
implemented.
[0007] After being cooled in the low pressure economizer heat
exchanger, the refrigerant is expanded in the main expansion valve,
heated in the evaporator, and enters the compressor at the suction
port. After compression, the refrigerant is discharged through the
discharge port.
[0008] The multiple economizer refrigeration system can be employed
in a screw compressor or a scroll compressor. The screw compressor
includes a male rotor including a plurality of helical threads and
a pair of opposing female rotors each including a plurality of
helical threads. The helical threads of the male rotor engage the
helical threads of the female rotors to create two sets of
compression chambers. One set of compression chambers communicates
with refrigerant from the high pressure economizer, and the other
set of compression chambers communicates with refrigerant from the
low pressure economizer.
[0009] Alternately, a scroll compressor is employed in the multiple
economizer refrigeration system. Vapor refrigerant from the low
pressure economizer is injected into the scroll compressor through
a pair of low pressure injections ports. The low pressure ports are
located such that vapor injection initiates shortly after the
suction port is covered and the compression chambers are sealed
from suction. Vapor refrigerant from the high pressure economizer
is injected into the scroll compressor through a high pressure
injection port. The high pressure injection port is located
proximate to the discharge port. Refrigerant injection through the
high pressure injection port and the low pressure injection ports
occurs into separate scroll compressor pockets.
[0010] These and other features of the present invention will be
best understood from the following specification and drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] The various features and advantages of the invention will
become apparent to those skilled in the art from the following
detailed description of the currently preferred embodiment. The
drawings that accompany the detailed description can be briefly
described as follows:
[0012] FIG. 1 illustrates a schematic diagram of a prior art
refrigeration system employing a single economizer circuit;
[0013] FIG. 2 illustrates a graph relating pressure to enthalpy for
the prior art refrigeration system of FIG. 1;
[0014] FIG. 3 illustrates a schematic diagram of the refrigeration
system of the present invention employing dual economizer
circuits;
[0015] FIG. 4 illustrates a graph relating pressure to enthalpy for
the refrigeration system of FIG. 4;
[0016] FIG. 5 illustrates a cross sectional view of a screw
compressor employed in a refrigerant system utilizing dual
economizers taken along line 5-5 of FIG. 6;
[0017] FIG. 6 illustrates a top view of the screw compressor of
FIG. 5;
[0018] FIG. 7 illustrates a scroll compressor employed in a
refrigerant system utilizing dual economizers when injection of
refrigerant begins; and
[0019] FIG. 8 illustrates the scroll compressor of FIG. 7 when
injection of the refrigerant from the low pressure economizer is
still in progress, and injection of refrigerant from the high
pressure economizer is almost complete.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0020] FIG. 1 illustrates a schematic diagram of a prior art single
economizer refrigeration system 20. The system 20 includes a
compressor 22, a condenser 24, a main expansion device 26, an
evaporator 28, and an economizer heat exchanger 30. Refrigerant
circulates though the closed circuit system 20. After the
refrigerant exits the compressor 22 through the discharge port 42
at high pressure and enthalpy, the refrigerant loses heat in the
condenser 24, exiting at lower enthalpy and high pressure. The
refrigerant then splits into two flow paths 32 and 34. Refrigerant
in path 34 is expanded to a low pressure in the expansion valve 36
prior to flowing through the economizer heat exchanger 30. As the
refrigerant in the path 32 flows through the economizer heat
exchanger 30, it is cooled by the refrigerant in path 34.
Refrigerant in path 34 from the economizer heat exchanger 30 is
returned along the economizer return path 56 to the compressor 22
through the economizer port 38 at a pressure between the suction
pressure and the discharge pressure. The refrigerant in line 32 is
expanded by the main expansion device 26 and then heated in the
evaporator 28. The refrigerant enters the compressor 22 at the
suction port 40. Downstream, this refrigerant mixes with the
refrigerant from the return path 56. A graph relating enthalpy to
pressure for the refrigeration system 20 is illustrated in FIG. 2.
The length of the evaporation line 29 illustrates the cooling
capacity of the system 20.
[0021] FIG. 3 illustrates a schematic diagram of the refrigeration
system 120 of the present invention employing dual economizer heat
exchangers 133a and 133b. The system 120 includes a compressor 122,
a condenser 124, a high pressure economizer heat exchanger 133a, a
low pressure economizer heat exchanger 133b, an expansion valve
126, and an evaporator 128. After the refrigerant exits the
compressor 122 at high pressure and enthalpy through the discharge
port 142, the refrigerant loses heat in the condenser 124, exiting
the condenser 124 at low enthalpy and high pressure. The
refrigerant then splits into two flow paths 132a and 134a.
Refrigerant in path 134a is expanded to a low pressure by the low
pressure expansion valve 136a prior to flowing through the
economizer heat exchanger 133a. As the refrigerant in the path 132a
flows through the high pressure economizer heat exchanger 133a, it
is cooled by the refrigerant in path 134a. Refrigerant from the
economizer heat exchanger 133a is returned along the economizer
return path 156a to the compressor 122 through the high pressure
economizer port 138a for compression in compression chambers
148a.
[0022] After being cooled in the high pressure economizer heat
exchanger 133a, the refrigerant in path 132a splits into two flow
paths 132b and 134b. Refrigerant in path 134b is expanded to a low
pressure by the low pressure expansion valve 136b prior to flowing
through the low pressure economizer heat exchanger 133b. As the
refrigerant in the path 132b flows through the low pressure
economizer heat exchanger 133b, it is cooled by the refrigerant in
path 134b. Refrigerant in path 134b from the economizer heat
exchanger 133b is returned along the economizer return path 156b to
the compressor 122 through the low pressure economizer port 138b
for compression in compression chambers 148b.
[0023] Refrigerant from path 132b is then expanded in the main
expansion valve 126. The main expansion valve 126, as well as the
high pressure and low pressure expansion valves 136aand 136b, can
be electronic EXV (electric expansion vales) or TXV valves. After
evaporation in the evaporator 128, the refrigerant enters the
compressor 122 through the suction port 140. Refrigerant from the
paths 134a and 134b enters the compressor 122 through the high
pressure economizer port 138a and the low pressure economizer port
138b, respectively, and mixes with the refrigerant in the
compressor 122 for compression.
[0024] The economizer ports 138a and 138b communicate with the
compression chambers 148a and 148b, respectively, which are each at
a pressure which varies during the compression cycle of the
compressor 122. To prevent high pressure to low pressure leak of
refrigerant from line 156a to 156b, the refrigerant from the
economizer heat exchangers 133a and 133b which flows in the
compression chambers 148a and 148b must remain separate at the
point of injection in the compressor 122.
[0025] Multiple steps of compressor 122 unloading are also possible
with the system 120 of the present invention. In one step, both of
the economizer heat exchangers 133a and 133b are engaged.
Alternatively, in additional steps, either of the economizer heat
exchangers 133a and 133b can be disengaged by shutting off the
expansions valves 136a and 136b, respectively. Both of the
economizer heat exchangers 133a and 133b can be disengaged for
non-economized operation by shutting off both of the expansion
valves 136a and 136b.
[0026] To regulate capacity of the system 120, two additional
solenoid valves 144a and 144b may be employed. A first solenoid
valve 144a regulates the flow of refrigerant between the high
pressure economizer port 138a and the low pressure economizer port
138b. A second solenoid valve 144b regulates the flow of
refrigerant between the low pressure economizer port 138b and the
compressor suction port 140.
[0027] The solenoid valves 144a and 144b can be opened or closed
depending on system 120 requirements to achieve steps of compressor
122 or system 120 unloading. By opening the solenoid valves 144a
and 144, the refrigerant flow from both the high pressure and the
low pressure economizer ports 138a and 138b can be by-passed into
the suction port 140 to reduce cooling. Alternately, by opening the
solenoid valve 144a and closing the solenoid valve 144b, the
refrigerant flow from the high pressure economizer port 138a can be
by-passed into the economizer port 138b. Alternately, by closing
the solenoid valve 144a and opening the solenoid valve 144b, the
refrigerant flow from the low pressure economizer port 138b can be
bypassed into suction line 166.
[0028] By controlling the expansion valves 136a and 136b and
solenoid valves 144a and 144b, the operation of the compressor 122
and system 120 can be adjusted to meet the cooling demands and
achieve optimum capacity and efficiency. A worker of ordinary skill
in the art would know how to control these valves depending on the
system 120 requirements.
[0029] FIG. 4 illustrates a graph relating enthalpy to pressure for
the refrigeration system 120 of FIG. 3 employing dual economizer
heat exchangers 133a and 133b. As shown, the evaporation line 129
of the refrigerant system 120 is longer than the evaporation line
29 of the refrigeration system 20 employing one economizer 30
(illustrated in FIG. 2). This indicates that the refrigeration
system 120 employing dual economizers 133a and 133b has a greater
cooling capacity than the refrigeration system 20 employing a
single economizer 30.
[0030] FIG. 5 illustrates a cross-sectional view of a tri-rotor
screw compressor 222 employed in the dual economizer system 120 of
the present invention. The screw compressor 222 includes a housing
244 having a central portion 246c and a pair of opposing portions
246a and 246b. The central portion 246c houses a male rotor 248c
including a plurality of helical threads 250c. The opposing
portions 246a and 246b each house a female rotor 248b and 248b,
each including a plurality of helical threads 253a and 253b,
respectively. The helical threads 250c of the male rotor 248c
engage the helical threads 253b of the female rotors 248b and 248b,
respectively, to create high pressure compression chambers 252a and
low pressure compression chambers 252b, respectively. Refrigerant
from the high pressure economizer 133a enters the compressor 222
through the high pressure economizer port 238b and is compressed in
the high pressure compression chambers 252a. Refrigerant from the
low pressure economizer 133b enters the compressor 222 through the
low pressure economizer port 238b and is compressed in the low
pressure compression chambers 252b. As the refrigerant from the
economizer heat exchangers 133a and 133b is injected into the
compressor 222 through separate economizer ports 238a and 238b,
respectively, the refrigerant from the economizers 133a and 133b
remains separate at the point of injection into the compressor
222.
[0031] After evaporation, the refrigerant splits into two streams.
As shown in FIG. 6, one stream enters the suction port 254a for
compression in the compression chambers 252a with the refrigerant
from the high pressure economizer 133a, and the other stream enters
suction port 254b for compression in the compression chambers 252b
with refrigerant from the low pressure economizer 133b. After
compression, the refrigerant in the compression chambers 252a and
252b is discharged through the discharge ports 242a and 242b,
respectively, for condensation. As shown, the low pressure
economizer port 238b is positioned closer to the suction ports 254a
and 254b, and the high pressure economizer port 238b is positioned
closer to the discharge ports 254a and 254b.
[0032] As the compression chambers 252a and 252b are separate and
are on opposing sides of the housing 244, there is no communication
between the refrigerant from the high pressure economizer 233a and
the refrigerant from the low pressure economizer 233a. By
optimizing the position and size of economizer ports 238b and 238b,
vapor communication between the compression chambers 252a and 252b,
the suction ports 243a and 243b, and the discharge ports 242a and
242b is prevented, allowing for control of the pressure in each
economizer 133a and 133b.
[0033] FIG. 7 illustrates a scroll compressor 322 employed in the
refrigeration system 120 employing dual economizer heat exchangers
133a and 133b. The scroll compressor 322 includes a non-orbiting
scroll 344, an orbiting scroll 346, and a plurality of compression
chambers 348b and 348b defined therebetween.
[0034] As the refrigerant from the economizer heat exchangers 133a
and 130b is injected into the compressor 322 through separate
economizer ports 338b and 338b, respectively, and as long as
solenoid valve 144a remains closed, the refrigerant in lines 156a
and 156b, respectively, remains separate, and there is no
communication between compression chambers 348b and 348b.
[0035] Vapor refrigerant from the low pressure economizer heat
exchanger 133b is injected into a pair of compression chambers 348b
of the scroll compressor 322 through a pair of low pressure
injections ports 338b. Vapor refrigerant from the high pressure
economizer heat exchanger 133a is injected into the compression
chambers 348b of the scroll compressor 322 through a high pressure
injection port 338a. The high pressure injection port 338b is
located proximate to the discharge port 342. The injection ports
338b and 338b typically extend through the body of the fixed
scrolls 344 and into the compression chambers 348b and 348b,
respectively.
[0036] FIG. 7 illustrates the position of scroll compressor 322
when injection of refrigerant from the dual economizer heat
exchangers 133a and 133b begins. The injection ports 338b and 338b
have just opened to allow the vapor refrigerant from each
economizer heat exchanger 133a and 133b to enter the compression
chambers 348b and 348b, respectively.
[0037] FIG. 8 illustrates the position of the scroll compressor 322
when refrigerant injection from the low pressure economizer 133b
into the compression chambers 348b is still in progress and
refrigerant injection from the high pressure economizer 133a into
the compression chamber 348b is almost complete. At this stage, the
high pressure injection port 338b is separated from the discharge
port 342 as the high pressure injection port 338b is still covered
by the orbiting scroll 346 prior to the initiation of the discharge
process through a discharge valve that may cover the discharge
port.
[0038] The scroll compressor 322 can alternatively include
additional injection ports and compression chambers to allow for
three ore more economizer heat exchangers. If three economizers are
to be employed, the scroll compressor 322 will preferably have more
than 2.5 turns.
[0039] There are several benefits to the refrigerant system 120 of
the present invention.
[0040] For one, a higher operating efficiency is possible employing
multiple economizer heat exchangers 133a and 133b. Additionally, an
increase in refrigeration capacity is possible. Compressor
reliability is also improved due to a decrease in the discharge
temperature. Control of system capacity is also increased by
alternating the engagement of economizer circuits, as well as
initiating bypass operation between the economizer circuits or
between any of the economizer circuits and suction line.
[0041] The foregoing description is only exemplary of the
principles of the invention. Many modifications and variations of
the present invention are possible in light of the above teachings.
The preferred embodiments of this invention have been disclosed,
however, so that one of ordinary skill in the art would recognize
that certain modifications would come within the scope of this
invention. It is, therefore, to be understood that within the scope
of the appended claims, the invention may be practiced otherwise
than as specifically described. For that reason the following
claims should be studied to determine the true scope and content of
this invention.
* * * * *