U.S. patent number RE40,830 [Application Number 11/152,834] was granted by the patent office on 2009-07-07 for compressor capacity modulation.
This patent grant is currently assigned to Emerson Climate Technologies, Inc.. Invention is credited to Jean-Luc Caillat.
United States Patent |
RE40,830 |
Caillat |
July 7, 2009 |
Compressor capacity modulation
Abstract
A pulsed modulated capacity modulation system for refrigeration,
air conditioning or other types of compressors is disclosed in
which suitable valving is provided which operates to cyclically
block flow of suction gas to a compressor. A control system is
provided which is adapted to control both the frequency of cycling
as well as the relative duration of the on and off time periods of
each cycle in accordance with sensed system operating conditions so
as to maximize the efficiency of the system. Preferably the cycle
time will be substantially less than the time constant of the load
and will enable substantially continuously variable capacity
modulation from substantially zero capacity to the full capacity of
the compressor. Additional controls may be incorporated to modify
one or more of the motor operating parameters to improve the
efficiency of the motor during periods of reduced load.
Inventors: |
Caillat; Jean-Luc (Dayton,
OH) |
Assignee: |
Emerson Climate Technologies,
Inc. (Sidney, OH)
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Family
ID: |
22488649 |
Appl.
No.: |
11/152,834 |
Filed: |
June 15, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
Reissue of: |
09139865 |
Aug 25, 1998 |
06206652 |
Mar 27, 2001 |
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Current U.S.
Class: |
417/298;
417/212 |
Current CPC
Class: |
F04C
28/265 (20130101); F04C 28/08 (20130101); F04B
49/22 (20130101); F04C 28/06 (20130101); F25B
5/02 (20130101); F04C 28/02 (20130101); A47F
3/04 (20130101); F04B 49/225 (20130101); F04C
28/28 (20130101); F04C 28/22 (20130101); F04C
28/24 (20130101); F04C 18/0215 (20130101); F25B
1/04 (20130101); F25B 49/022 (20130101); F04C
27/005 (20130101); F04B 49/06 (20130101); G05D
23/1909 (20130101); F25B 49/005 (20130101); F04C
28/00 (20130101); F04B 2205/16 (20130101); F25B
41/22 (20210101); F25B 41/35 (20210101); F25B
2700/21175 (20130101); F04B 2207/043 (20130101); F25B
2600/0261 (20130101); F04C 2270/015 (20130101); F25B
2700/2106 (20130101); Y02B 30/70 (20130101); F04C
23/008 (20130101); F25B 2400/22 (20130101); F25B
41/31 (20210101); F25B 2700/21174 (20130101); F25B
2600/2521 (20130101); F25B 2700/1933 (20130101); F04B
2201/0601 (20130101); F25B 2700/193 (20130101); F25B
2700/2117 (20130101); F04C 2270/58 (20130101); F04C
2270/86 (20130101) |
Current International
Class: |
F04B
49/00 (20060101) |
Field of
Search: |
;417/298,212,279,286,289,222 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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764179 |
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Apr 1953 |
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3422398 |
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2116635 |
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59145392 |
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62-003190 |
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62-003191 |
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S62-29779 |
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JP |
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S62-125263 |
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Jun 1987 |
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JP |
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S61-138490 |
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Sep 1988 |
|
JP |
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H8-284842 |
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Oct 1996 |
|
JP |
|
Other References
Capacity Modulation for Air Conditioning and Refrigeration Systems;
Air Conditioning, Heating & Refrigeration News; Earl B. Muir,
Manager of Research, and Russell W. Griffith, Research Engineer,
Copeland Corp.; Apr.-May 1979; 12 pages. cited by other .
Judgment--Bd.R. 127(b), Jean-Luc Caillat v. Alexander Lifson,
Patent Interference No. 105,288; Jul. 5, 2005; 3 Pages. cited by
other.
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Primary Examiner: Cambell; Thor S
Attorney, Agent or Firm: Harness, Dickey & Pierce,
P.L.C.
Claims
What is claimed is:
1. A capacity modulated compressor comprising: a compression
mechanism .Iadd.disposed between a discharge passage and a suction
chamber, said compression mechanism .Iaddend.having a compression
chamber therein, a suction inlet for supplying suction gas to
.[.the.]. .Iadd.said .Iaddend.compression chamber and a movable
member operative to vary the volume of said compression chamber; a
power source operatively connected to effect movement of said
movable member to thereby compress gas drawn into said compression
chamber through said suction inlet; a valve .Iadd.disposed in said
suction chamber and .Iaddend.provided in the suction gas flow path
to said compression mechanism, said valve being operable between
open and closed positions to cyclically allow and prevent flow of
suction gas into said compression chamber; and control apparatus
for actuating said valve between said open and closed positions,
said control apparatus being operative to cycle said valve
.Iadd.for a time duration .Iaddend.such that its cycle time is
substantially smaller than the time constant of the load on said
compressor.
.[.2. A capacity modulated compressor as set forth in claim 1
wherein said valve is positioned in close proximity to said
compression chamber..].
.[.3. A capacity modulated compressor as set forth in claim 1
wherein said valve is a bidirectional valve..].
4. A capacity modulated compressor as set forth in claim 1 wherein
at least one of said cycle time and .[.the.]. .Iadd.said
.Iaddend.time duration said valve is in said closed position is
varied in response to sensed operating conditions.
5. A capacity modulated compressor as set forth in claim 4 wherein
said power source continues to effect movement of said movable
member as said valve is cycled between said open and closed
positions.
6. A capacity modulated compressor as set forth in claim 4 wherein
said cycle time and said time duration are varied in response to
said sensed operating condition.
7. A capacity modulated compressor as set forth in claim 1 wherein
said valve is actuated by pressurized fluid.
8. A capacity modulated compressor as set forth in claim 7 further
comprising a control valve operative to control the flow of
pressurized fluid to said valve.
9. A capacity modulated compressor as set forth in claim 8 wherein
said control valve is a solenoid actuated valve.
10. A capacity modulated compressor as set forth in claim 7 wherein
said pressurized fluid is supplied from said compression
mechanism.
11. A capacity modulated compressor as set forth in claim 1 wherein
said power source comprises an electric motor.
12. A capacity modulated compressor as set forth in claim 11
wherein said control module operates to vary an operating parameter
of said electric motor when said valve is in said closed position
so as to thereby improve the operating efficiency of said
motor.
13. A capacity modulated compressor as set forth in claim 12
wherein said operating parameter of said motor is varied a
predetermined time period after said valve is moved to said closed
position.
14. A capacity modulated compressor as set forth in claim 1 wherein
said compression mechanism is a reciprocating piston
compressor.
15. A capacity modulated compressor as set forth in claim 14
wherein said reciprocating piston compressor includes a plurality
of pistons and cylinders, said valve being operative to prevent
flow of suction gas to all of said cylinders.
16. A capacity modulated compressor as set forth in claim 15
wherein said valve operates to prevent flow of suction gas to all
of said cylinders simultaneously.
17. A capacity modulated compressor comprising: a hermetic shell
.Iadd.including a suction chamber.Iaddend.; a compression mechanism
disposed within said shell, said compression mechanism including a
compression chamber defined in part by a .[.moveable.].
.Iadd.movable .Iaddend.member, said .[.moveable.]. .Iadd.movable
.Iaddend.member operating to vary the volume thereof; a drive shaft
rotatably supported within said shell and drivingly coupled to said
movable member; .Iadd.a motor disposed in said suction chamber and
operable to rotatably drive said drive shaft; .Iaddend. a suction
inlet passage for supplying suction gas to said compression chamber
from a source remote from said shell; a valve .Iadd.assembly
including a valve member .Iaddend.within said suction inlet
passage, said valve .Iadd.member .Iaddend.being actuable between an
open position to allow flow of suction gas through said inlet
passage and a closed position to substantially prevent flow of
suction gas through said .Iadd.suction .Iaddend.inlet passage; a
controller for cyclically actuating said valve .Iadd.member
.Iaddend.to an open position for first predetermined time periods
and to a closed position for second predetermined time periods, the
ratio of said first predetermined time period to the sum of said
first and second predetermined time periods being less than a given
load time constant and determining the percentage modulation of the
capacity of said compressor.
18. A capacity modulated compressor as set forth in claim 17
wherein said valve .Iadd.assembly .Iaddend.is a bidirectional valve
and is actuable to said closed position by pressurized fluid.
19. A capacity modulated compressor as set forth in claim 18
further comprising a solenoid valve actuable by said controller to
control flow of said pressurized fluid to said valve
.Iadd.assembly.Iaddend..
20. A capacity modulated compressor as set forth in claim 19
wherein said pressurized fluid is discharge gas from said
compressor.
.[.21. A capacity modulated compressor as set forth in claim 17
wherein said valve is positioned in close proximity to said
compression chamber..].
22. A capacity modulated compressor as set forth in claim 17
wherein said compressor is a refrigeration compressor.
23. A capacity modulated compressor as set forth in claim 17
wherein said compressor is an air compressor.
24. A capacity modulated compressor as set forth in claim 17
wherein said compressor is a rotary compressor.
25. A capacity modulated compressor as set forth in claim 17
wherein said compressor is a scroll compressor.
26. A capacity modulated compressor as set forth in claim 17
wherein said sum of said first and second time periods is less than
one half of said load time constant.
27. A capacity modulated compressor as set forth in claim 17
.[.further comprising a motor for rotatably driving said drive
shaft,.]. .Iadd.wherein .Iaddend.said valve .[.being.].
.Iadd.member is .Iaddend.actuable between said open and closed
positions while said motor continues to rotatably drive said drive
shaft.
28. A capacity modulated compressor as set forth in claim 27
wherein said controller operates to vary an operating parameter of
said motor between periods in which said valve .Iadd.member
.Iaddend.is in said closed position and in said open position to
thereby improve the operating efficiency of said motor.
29. A method of modulating the capacity of a compressor forming a
part of a cooling system to accommodate varying cooling load
conditions comprising: sensing an operating parameter of said
cooling system, said parameter being indicative of the system load;
determining a cycle frequency .[.of.]. .Iadd.and .Iaddend.a maximum
.Iadd.time .Iaddend.duration which will minimize variation in the
suction pressure of refrigerant being supplied to said compressor;
determining a first time period during which suction gas will be
supplied to said compressor and determining a second time period
during which suction gas will be prevented from flowing to said
compressor, said first and second time periods being equal to said
cycle frequency; .[.and.]. pulsing a valve between open and closed
positions for said first and second time periods respectively to
thereby modulate the capacity of said compressor in response to
said system operating parameter.Iadd.; and varying a motor
operating parameter when said valve is in said closed
position.Iaddend..
.Iadd.30. A capacity modulated compressor as set forth in claim 1
wherein said valve is a solenoid valve..Iaddend.
.Iadd.31. A capacity modulated compressor as set forth in claim 1
wherein said compression mechanism includes a piston reciprocably
disposed in a cylinder..Iaddend.
.Iadd.32. A capacity modulated compressor as set forth in claim 1
wherein said compression mechanism includes a compression rotor and
vane disposed in a cylinder..Iaddend.
.Iadd.33. A capacity modulated compressor as set forth in claim 1
wherein said compression mechanism includes interleaved scroll
members defining moving fluid pockets..Iaddend.
.Iadd.34. A capacity modulated compressor as set forth in claim 1
wherein said compression mechanism compresses air..Iaddend.
.Iadd.35. A capacity modulated compressor as set forth in claim 17
wherein said valve is a solenoid valve..Iaddend.
.Iadd.36. A capacity modulated compressor as set forth in claim 17
wherein said compression mechanism includes a piston reciprocably
disposed in a cylinder..Iaddend.
.Iadd.37. A capacity modulated compressor as set forth in claim 1
wherein said compression mechanism includes a compression rotor and
vane disposed in a cylinder..Iaddend.
.Iadd.38. A capacity modulated compressor as set forth in claim 1
wherein said compression mechanism includes interleaved scroll
members defining moving fluid pockets..Iaddend.
.Iadd.39. A capacity modulated compressor as set forth in claim 17
wherein said valve is disposed in the suction gas flow path between
said power source and said compression mechanism..Iaddend.
.Iadd.40. A capacity modulated compressor as set forth in claim 1
wherein said power source is disposed in said suction
chamber..Iaddend.
.Iadd.41. A capacity modulated compressor as set forth in claim 40
wherein said cycle time and said time duration are varied in
response to a sensed operating condition..Iaddend.
.Iadd.42. A capacity modulated compressor as set forth in claim 40
wherein at least one of said cycle time and the time duration said
valve is in said closed position is varied in response to a sensed
operating condition..Iaddend.
.Iadd.43. A capacity modulated compressor as set forth in claim 40
wherein said valve is actuated by a pressurized fluid..Iaddend.
.Iadd.44. A capacity modulated compressor as set forth in claim 43
further comprising a control valve operative to control a flow of
said pressurized fluid to said valve..Iaddend.
.Iadd.45. A capacity modulated compressor as set forth in claim 44
wherein said control valve is a solenoid actuated
valve..Iaddend.
.Iadd.46. A capacity modulated compressor as set forth in claim 43
wherein said pressurized fluid is supplied from said compression
mechanism..Iaddend.
.Iadd.47. A capacity modulated compressor as set forth in claim 40
wherein said compression mechanism includes a piston reciprocably
disposed in a cylinder..Iaddend.
.Iadd.48. A capacity modulated compressor as set forth in claim 40
wherein said compression mechanism includes a compression rotor and
vane disposed in a cylinder..Iaddend.
.Iadd.49. A capacity modulated compressor as set forth in claim 40
wherein said compression mechanism includes interleaved scroll
members defining moving fluid pockets..Iaddend.
.Iadd.50. A capacity modulated compressor as set forth in claim 40
wherein said control apparatus operates to vary an operating
parameter of said power source when said valve is in said closed
position..Iaddend.
.Iadd.51. A capacity modulated compressor as set forth in claim 40
wherein said valve is a solenoid valve..Iaddend.
.Iadd.52. A capacity modulated compressor as set forth in claim 1
wherein said valve is disposed in said suction gas flow path
between said power source and said compression
mechanism..Iaddend.
.Iadd.53. A capacity modulated compressor as set forth in claim 52
wherein said cycle time and said time duration are varied in
response to a sensed operating condition..Iaddend.
.Iadd.54. A capacity modulated compressor as set forth in claim 52
wherein at least one of said cycle time and the time duration said
valve is in said closed position is varied in response to a sensed
operating condition..Iaddend.
.Iadd.55. A capacity modulated compressor as set forth in claim 52
wherein said valve is actuated by a pressurized fluid..Iaddend.
.Iadd.56. A capacity modulated compressor as set forth in claim 55
further comprising a control valve operative to control a flow of
said pressurized fluid to said valve..Iaddend.
.Iadd.57. A capacity modulated compressor as set forth in claim 56
wherein said control valve is a solenoid actuated
valve..Iaddend.
.Iadd.58. A capacity modulated compressor as set forth in claim 55
wherein said pressurized fluid is supplied from said compression
mechanism..Iaddend.
.Iadd.59. A capacity modulated compressor as set forth in claim 52
wherein said compression mechanism includes a piston reciprocably
disposed in a cylinder..Iaddend.
.Iadd.60. A capacity modulated compressor as set forth in claim 52
wherein said compression mechanism includes a compression rotor and
vane disposed in a cylinder..Iaddend.
.Iadd.61. A capacity modulated compressor as set forth in claim 52
wherein said compression mechanism includes interleaved scroll
members defining moving fluid pockets..Iaddend.
.Iadd.62. A capacity modulated compressor as set forth in claim 52
wherein said control apparatus operates to vary an operating
parameter of said power source when said valve is in said closed
position..Iaddend.
.Iadd.63. A capacity modulated compressor as set forth in claim 52
wherein said valve is a solenoid valve..Iaddend.
.Iadd.64. A capacity modulated compressor as set forth in claim 1
further comprising a hermetic shell defining said suction
chamber..Iaddend.
.Iadd.65. A capacity modulated compressor as set forth in claim 64
wherein said cycle time and said time duration are varied in
response to a sensed operating condition..Iaddend.
.Iadd.66. A capacity modulated compressor as set forth in claim 64
wherein at least one of said cycle time and the time duration said
valve is in said closed position is varied in response to a sensed
operating condition..Iaddend.
.Iadd.67. A capacity modulated compressor as set forth in claim 64
wherein said valve is actuated by a pressurized fluid..Iaddend.
.Iadd.68. A capacity modulated compressor as set forth in claim 67
further comprising a control valve operative to control a flow of
said pressurized fluid to said valve..Iaddend.
.Iadd.69. A capacity modulated compressor as set forth in claim 68
wherein said control valve is a solenoid actuated
valve..Iaddend.
.Iadd.70. A capacity modulated compressor as set forth in claim 67
wherein said pressurized fluid is supplied from said compression
mechanism..Iaddend.
.Iadd.71. A capacity modulated compressor as set forth in claim 64
wherein said compression mechanism includes a piston reciprocably
disposed in a cylinder..Iaddend.
.Iadd.72. A capacity modulated compressor as set forth in claim 64
wherein said compression mechanism includes a compression rotor and
vane disposed in a cylinder..Iaddend.
.Iadd.73. A capacity modulated compressor as set forth in claim 64
wherein said compression mechanism includes interleaved scroll
members defining moving fluid pockets..Iaddend.
.Iadd.74. A capacity modulated compressor as set forth in claim 64
wherein said control apparatus operates to vary an operating
parameter of said power source when said valve is in said closed
position..Iaddend.
.Iadd.75. A capacity modulated compressor as set forth in claim 64
wherein said valve is a solenoid valve..Iaddend.
.Iadd.76. A capacity modulated compressor comprising: a compression
mechanism disposed between a discharge passage and a suction
chamber, said compression mechanism having a compression chamber
therein, a suction inlet for supplying suction gas to said
compression chamber and a movable member operative to vary the
volume of said compression chamber; a power source disposed in said
suction chamber and operatively connected to effect movement of
said movable member to thereby compress gas drawn into said
compression chamber through said suction inlet; a valve assembly
mounted to said compression mechanism and including a valve member
provided in a suction gas flow path to said compression mechanism,
said valve being operable between open and closed positions to
cyclically allow and prevent flow of suction gas into said
compression chamber; and control apparatus for actuating said valve
between said open and closed positions, said control apparatus
being operative to cycle said valve for a time duration such that
its cycle time is substantially smaller than the time constant of
the compressor load..Iaddend.
.Iadd.77. A capacity modulated compressor as set forth in claim 76
wherein at least one of said cycle time and said time duration said
valve is in said closed position is varied in response to sensed
operating conditions..Iaddend.
.Iadd.78. A capacity modulated compressor as set forth in claim 76
wherein said power source continues to effect movement of said
movable member as said valve is cycled between said open and closed
positions..Iaddend.
.Iadd.79. A capacity modulated compressor as set forth in claim 76
wherein said cycle time and said time duration are varied in
response to a sensed operating condition..Iaddend.
.Iadd.80. A capacity modulated compressor as set forth in claim 76
wherein said valve is actuated by a pressurized fluid..Iaddend.
.Iadd.81. A capacity modulated compressor as set forth in claim 80
further comprising a control valve operative to control a flow of
said pressurized fluid to said valve..Iaddend.
.Iadd.82. A capacity modulated compressor as set forth in claim 81
wherein said control valve is a solenoid actuated
valve..Iaddend.
.Iadd.83. A capacity modulated compressor as set forth in claim 80
wherein said pressurized fluid is supplied from said compression
mechanism..Iaddend.
.Iadd.84. A capacity modulated compressor as set forth in claim 76
wherein said power source includes an electric motor..Iaddend.
.Iadd.85. A capacity modulated compressor as set forth in claim 84
wherein said control module operates to vary an operating parameter
of said electric motor when said valve is in said closed
position..Iaddend.
.Iadd.86. A capacity modulated compressor as set forth in claim 85
wherein said operating parameter of said motor is varied a
predetermined time period after said valve is moved to said closed
position..Iaddend.
.Iadd.87. A capacity modulated compressor as set forth in claim 76
wherein said valve is a solenoid valve..Iaddend.
.Iadd.88. A capacity modulated compressor as set forth in claim 76
wherein said compression mechanism includes a piston reciprocably
disposed in a cylinder..Iaddend.
.Iadd.89. A capacity modulated compressor as set forth in claim 76
wherein said compression mechanism includes a compression rotor and
vane disposed in a cylinder..Iaddend.
.Iadd.90. A capacity modulated compressor as set forth in claim 76
wherein said compression mechanism includes interleaved scroll
members defining moving fluid pockets..Iaddend.
.Iadd.91. A capacity modulated compressor as set forth in claim 76
wherein said valve is disposed in said suction gas flow path
between said power source and said compression
mechanism..Iaddend.
.Iadd.92. A capacity modulated compressor as set forth in claim 76
further comprising a hermetic shell defining said suction
chamber..Iaddend.
.Iadd.93. A capacity modulated compressor as set forth in claim 12
wherein varying an operating parameter of said electric motor
includes adjusting voltage or varying a running capacitance of a
winding of said electric motor..Iaddend.
.Iadd.94. A capacity modulated compressor as set forth in claim 28
wherein varying an operating parameter of said electric motor
includes adjusting voltage or varying a running capacitance of a
winding of said electric motor..Iaddend.
.Iadd.95. A capacity modulated compressor as set forth in claim 29
wherein varying an operating parameter of said electric motor
includes adjusting voltage or varying a running capacitance of a
winding of said electric motor..Iaddend.
.Iadd.96. A capacity modulated compressor as set forth in claim 85
wherein varying an operating parameter of said electric motor
includes adjusting voltage or varying a running capacitance of a
winding of said electric motor..Iaddend.
Description
.Iadd.This application Ser. No. 11/152,834 filed Jun. 15, 2005, is
a Reissue application of Ser. No. 09/139,865 filed Aug. 25, 1998
now U.S. Pat. No. 6,206,652 and is copending with Ser. No.
11/152,836 filed Jun. 15, 2005 which is also a Reissue application
of Ser. No. 09/139,865 filed Aug. 25, 1998..Iaddend.
BACKGROUND AND SUMMARY OF THE INVENTION
The present invention is directed to a system for modulating the
capacity of a positive displacement compressor such as a
refrigeration and/or air conditioning compressor and more
specifically to a system incorporating a valving arrangement for
cyclically blocking suction gas flow to the compressor while the
compressor is continuously driven.
Capacity modulation is often a desirable feature to incorporate in
refrigeration and air conditioning compressors as well as
compressors for other applications in order to enable them to
better accommodate the wide range of loading to which systems
incorporating these compressors may be subjected. Many different
approaches have been utilized for providing this capacity
modulation feature ranging from controlling of the suction inlet
flow such as by throttling to bypassing discharge gas back to the
suction inlet and also through various types of cylinder or
compression volume porting arrangements.
In multicylinder reciprocating piston type compressors utilizing
suction gas control to achieve capacity modulation, it is common to
block the flow to one or more but not all of the cylinders. When
activated, the capacity of the compressor will be reduced by a
percentage nominally equal to the number of cylinders to which
suction gas flow has been blocked divided by the total number of
cylinders. While such arrangements do provide varying degrees of
capacity modulation, the degree of modulation that can be achieved
is available only in relatively large discrete steps. For example,
in a six cylinder compressor, blocking suction to two cylinders
reduces the capacity by 1/3 or 33.3% whereas blocking suction gas
flow to four cylinders reduces capacity by 2/3 or 66.6%. This
discrete step form of modulation does not allow the system capacity
to be matched to the load requirement conditions at all but rather
only to very roughly approach the desired capacity resulting in
either an excess capacity or deficient capacity. As system
conditions will rarely if ever match these gross steps of
modulation, the overall operating system efficiency will not be
able to be maximized.
Compressors in which discharge gas is recirculated back to suction
offer quasi-infinite step modulation of the capacity depending upon
the variation and complexity of the bypassing means. However, when
discharge gas is recirculated back to suction, the work of
compression is lost for that fraction of the gas recirculated than
resulting in reduced system efficiency. Combinations of the
aforementioned methods enables substantially quasi-infinite
capacity modulation at slightly better efficiency but still fails
to provide the ability to closely match the compressor capacity to
the load being served.
Other approaches, which can result in selectively disabling the
compression process of one or more of the cylinders of a
multi-cylinder compressor, such as cylinder porting, stroke
altering or clearance volume varying methods result in similar step
modulation with a resulting mismatch between load and capacity and
additionally suffer from dynamic load unbalance and hence
vibration.
The present invention, however, provides a capacity control
arrangement which utilizes a pulse width modulation of suction gas
flow to the compressor which enables substantially continuous
modulation of the capacity from 0% up to 100% or full capacity.
Thus the capacity output of the compressor can be exactly matched
to system loading at any point in time. Further, in reciprocating
piston type compressors, the suction gas flow to each of the
cylinders may be controlled simultaneously by this pulse width
modulation system so as to eliminate unbalanced operation of the
compressor.
The pulse width modulated compressor is driven by a control system
that supplies a variable duty cycle control signal based on
measured system load. The controller may also regulate the
frequency (or cycle time) of the control signal to minimize
pressure fluctuations in the refrigerant system. The on time is
thus equal to the duty cycle multiplied by the cycle time, where
the cycle time is the inverse of the frequency.
The pulse width modulated compressor of the present invention has a
number of advantages. Because the instantaneous capacity of the
system is easily regulated by variable duty cycle control, an
oversized compressor can be used to achieve faster temperature pull
down at startup and after defrost without causing short cycling as
conventional compressor systems would. Another benefit of the
present invention is that the system can respond quickly to sudden
changes in condenser temperature or case temperature set points.
The controller adjusts capacity in response to disturbances without
producing unstable oscillations and without significant overshoot.
This capability is of particular advantage in applications
involving cooling of display cases in that it allows a much tighter
control of temperature within the case thereby enabling the
temperature setting to be placed at a higher level without concern
that cyclical temperature swings will exceed the temperatures which
are considered safe for the particular goods contained therein.
Operating at higher evaporator temperatures reduces the defrost
energy required because the system develops frost more slowly at
higher temperatures. This also enables the time between defrost
cycles to be lengthened.
The pulse width modulated compressor also yields improved oil
return. The volume of oil returned to the compressor from the
system is dependent in part on the velocity of gas flow to the
compressor. In many capacity modulation systems, the return gas
flow to the compressor is maintained at a relatively low level thus
reducing the return oil flow. However, in the present invention the
refrigerant flow pulsates between high capacity and low capacity
(e.g. 100% and 0%), thus facilitating increased oil return due to
the periods of high velocity gas flow.
Additionally, the pulse width modulated blocked suction system of
the present invention is relatively inexpensive to incorporate into
a compressor in that only a single valve assembly is required.
Further, because of the system's simplicity, it can be easily added
to a wide variety of compressor designs including both rotary and
scroll as well as reciprocating piston type compressors. Also,
because the present invention keeps the driving motor operating
while the suction gas flow is modulated, the stress and strain on
the motor resulting from periodic start-ups is minimized.
Additional improvements in efficiency can be achieved by
incorporating a motor control module which may operate to control
various operating parameters thereof to enhance its operating
efficiency during periods when the motor load is reduced due to
unloading of the compressor.
Additional features and benefits of the present invention will
become apparent to one skilled in the art from the following
detailed description taken in conjunction with the appended
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a section view of a reciprocating piston type compressor
incorporating apparatus by which the suction gas flow to the
compressor may be blocked in a pulse width modulated manner in
accordance with the present invention;
FIG. 2 is a waveform diagram illustrating the variable duty cycle
signal produced by the controller and illustrating the operation at
a constant frequency;
FIG. 3 is a waveform diagram of the variable duty cycle signal,
illustrating variable frequency operation;
FIG. 4 is a graph comparing anticipated temperature dynamics of a
system employing the invention with a system of conventional
design;
FIG. 5 is a view similar to that of FIG. 1 but showing a rotary
type compressor incorporating the pulse width modulation system of
the present invention;
FIG. 6 is a section view of the compressor of FIG. 5, the section
being taken along line 6--6 thereof;
FIG. 7 is a view similar to that of FIGS. 1 and 5 but showing a
scroll type compressor incorporating the pulse width modulation
system of the present invention;
FIG. 8 is a schematic diagram illustrating the inclusion of a motor
control module to modify one or more of the compressor motor
operating parameters during periods of reduced load; and
FIG. 9 is a section view generally illustrating a preferred valving
arrangement for use in the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring now to the drawings and more specifically to FIG. 1 there
is shown a reciprocating piston type refrigeration compressor 10
comprising an outer shell 12 within which is disposed reciprocating
compressor housing 14 on which is mounted an associated driving
motor including stator 16 having a bore 18 provided therein. A
rotor 20 is disposed within bore 18 being secured to crankshaft 22
which is rotatably supported within housing 14 by upper and lower
bearings 24 and 26 respectively. A pair of pistons 28 and 30 are
connected to crankshaft 22 and reciprocably disposed in cylinders
32 and 34 respectively. A motor cover 36 is secured in overlying
relationship to the upper end of stator 16 and includes an inlet
opening 38 aligned with a suction inlet fitting 40 provided through
shell 12. A suction muffler 44 is provided on the opposite side of
motor cover 36 and serves to direct suction gas from the interior
of motor cover 36 to respective cylinders 32, 34 via suction pipe
42 and head assembly 46.
As thus far described, compressor 10 is a typical hermetic
reciprocating piston type motor compressor and is described in
greater detail in U.S. Pat. No. 5,015,155 assigned to the assignee
of the present application, the disclosures of which is hereby
incorporated by reference.
A bidirectional solenoid valve assembly 48 is provided in suction
pipe 42 between suction muffler 44 and head assembly 46. Solenoid
valve assembly operates to control suction gas flow through pipe 42
to thereby modulate the capacity of motor compressor 10. An
exemplary valve assembly suitable for this application is described
in greater detail below.
In order to control solenoid valve assembly 48, a control module 50
is provided to which one or more suitable sensors 52 are connected.
Sensors 52 operate to sense operating system conditions necessary
to determine system loading. Based upon signals received from
sensors 52 and assuming system conditions indicate a less than full
capacity is required, control module 50 will operate to pulse
solenoid valve assembly 48 so as to alternately allow and prevent
the flow of suction gas through conduit 42 to compression cylinders
32 and 34 while the motor continues to drive pistons 28 and 30. The
variable duty cycle control signal generated by the control module
50 can take several forms. FIGS. 2 and 3 give two examples. FIG. 2
shows the variable duty cycle signal in which the duty cycle
varies, but the frequency remains constant. In FIG. 2, note that
the cycle time, indicated by hash marks 53, are equally spaced. By
comparison, FIG. 3 illustrates the variable duty cycle signal
wherein the frequency is also varied. In FIG. 3, note that the hash
marks 53 are not equally spaced. Rather, the waveform exhibits
regions of constant frequency, regions of increasing frequency and
regions of decreasing frequency. The variable frequency illustrated
in FIG. 3 is the result of the adaptive modulation of the cycle
time to further optimize system operation. An adaptive modulation
control system is described in greater detail in assignee's
copending application Ser. No. 08/939,779 the disclosure of which
is hereby incorporated by reference.
Given the speed of rotation of the compressor there would be a
substantial number of compression cycles during which no suction
gas would be supplied to the compression chambers. However
thereafter there would be another number of compression cycles
during which full suction gas flow would be supplied to the
cylinders. Thus on average, the mass flow would be reduced to a
desired percentage of full load capacity. Because the mass flow to
each cylinder is reduced at the same time, the operating balance
between the respective cylinders will be maintained thus avoiding
the possibility of increased vibration. Further, this pulsed form
of capacity modulation will result in alternating periods during
which the driving motor is either operating at full load or
substantially reduced loading. Thus it is possible to incorporate
additional apparatus to vary one or more of the operating
parameters of the motor during the reduce load period of operation
thereby further improving system efficiency as discussed in greater
detail below.
FIG. 4 graphically represents the benefits that the present
invention may offer in maintaining tighter temperatures control in
a refrigerated storage case for example. Note how the temperature
curve 55 of the invention exhibits considerably less fluctuation
than the corresponding temperature curve 57 of a conventional
controller.
It should be noted that valve assembly 48 will be activated between
open and closed positions in a pulsed manner to provide the desired
capacity modulation. Preferably, the cycle time duration will be
substantially less than the time constant of the system load which
typically may be in the range of about one to several minutes. In a
preferred embodiment, the cycle time may be as much as 4 to 8 times
less than the thermal time constant of the load or even greater.
The thermal time constant of system may be defined as the length of
time the compressor is required to run in order to enable the
system to cool the load from an upper limit temperature at which
the system is set to turn on, down to a point at which the
evaporator pressure reaches a lower limit at which the compressor
is shut down. More specifically, in a typical refrigeration system,
flow of compressed fluid to the evaporator is controlled by a
temperature responsive solenoid valve and operation of the
compressor is controlled in response to evaporator pressure. Thus
in a typical cycle, when the temperature in the cooled space
reaches a predetermined upper limit, the solenoid valve opens
allowing compressed fluid to flow to the evaporator to begin
cooling the space. As the compressed fluid continues to flow to the
evaporator and absorb heat, the pressure in the evaporator will
increase to a point at which the compressor is actuated. When the
temperature in the cooled spaces reaches a predetermined lower
limit, the solenoid valve will be closed thereby stopping further
flow of compressed fluid to the evaporator but the compressor will
continue to run to pump down the evaporator. When the pressure in
the evaporator reaches a predetermined lower limit, the compressor
will be shut down. Thus, the actual running time of the compressor
is the thermal time constant of the load.
By use of this pulse width modulated blocked suction system, it is
possible to optimize compressor run times which minimizes the
number of on/off cycles and provides excellent load capacity
matching and superior temperature control for the area being cooled
along with improved overall system efficiency as compared to
conventional capacity modulation systems. As is illustrated in FIG.
4, the pulse width modulated capacity compressor of the present
invention enables extremely tight control of temperature as
compared to conventional capacity modulation systems. When applied
to refrigeration systems, this tight temperature control enables
the average operating temperature to be set at a level more closely
approaching the upper acceptable temperature limit whereas with
conventional systems, the average operating temperature must be set
well below the upper acceptable temperature limit so as to avoid
the larger temperature swings encountered therein from exceeding
this upper acceptable limit. Not only does the use of a higher
average operating temperature result in substantial direct energy
cost savings but the higher average operating temperature maintains
the dew point of the enclosed space at a higher level thus greatly
reducing the formation of frost. Similarly, when applied to air
conditioning systems, the pulse width modulated compressor of the
present invention enables the temperature of the conditional space
to be controlled within a much smaller range than with conventional
systems thus greatly enhancing the comfort level of the occupants
of such space. Even further, this capacity modulation system may
also be advantageously applied to air compressor applications.
Because of the ability of the compressor to very closely track the
load (which in air compressor applications will be the volume of
air being used at a desired pressure), it is possible to greatly
reduce the size of the pressure vessel if not completely eliminate
same. Further, in airconditioning applications additional energy
savings may be realized because the compressor is able to very
closely match the load. This results in lower condensing
temperatures and hence pressures which means that the pressure
against which the compressor is working is lower.
In most air conditioning and refrigeration compressors, the suction
gas flow operates to cool the motor prior to compression. Because
presently existing blocked suction type capacity modulation systems
operate to prevent flow of suction gas to the compression chamber
the compressor cannot be operated in a reduced capacity mode for an
extended period without overheating of the compressor motor. The
present invention, however, offers the additional advantage of
greatly reducing this overheating possibility because the
relatively cool suction gas is supplied to the cylinders on a
rapidly cycling basis. This enables such compressors to operate at
reduced capacity for substantially longer time periods thus also
contributing to its ability to provide tighter temperature control
of the spaces being cooled on a continuous basis as well as reduced
frost build-up in low temperature refrigeration applications.
In determining the desired cycle frequency as well as the duration
of the duty cycle or time period, during which suction gas is to be
supplied to the compressor, it is generally desirable to first
select a cycle time which is as long as possible but yet minimizes
suction pressure fluctuations. Next the duty cycle will be
determined which will be sufficiently high so as to satisfy the
load. Obviously, the duty cycle and cycle time are interrelated and
other factors must also be taken into account in selection thereof.
For example, while it is desirable to make the cycle time as long
as possible, it can not be so long that the time period during
which suction gas flow is interrupted results in excessive heating
of the compressor motor.
While the capacity modulation system of the present invention has
been described above with reference to a multicylinder
reciprocating piston type compressor, it is also equally applicable
to other types of compressors such as, for example, a rotary type
compressor or a scroll compressor. A rotary type compressor
incorporating the capacity modulation system of the present
invention is illustrated in and will be described with reference to
FIGS. 5 and 6 and a scroll compressor incorporating same is
illustrated and will be described with reference to FIG. 7.
As shown in FIG. 5, a hermetic rotary type compressor 54 includes
an outer shell 56 within which is disposed a compressor assembly
and a driving motor 58 incorporating a stator 60 and rotor 62.
Rotor 62 is rotatably supported by and fixed to crankshaft 66 which
.[.is turn in.]. .Iadd.in turn is .Iaddend.rotatably supported by
upper and lower bearings 68 and 70. A compression rotor 72 is
eccentrically mounted on and adapted to be driven by crankshaft 66.
Compression rotor 72 is disposed within cylinder 74 provided in
housing 76 and cooperates with vane 78 .Iadd.(shown in FIG. 6)
.Iaddend.to compress fluid drawn into cylinder 74 through inlet
passage 80. Inlet passage 80 is connected to suction fitting 82
provided in shell 56 to provide a supply of suction gas to
compressor 54. As thus far described, rotary compressor 54 is
typical of rotary type refrigeration and air conditioning
compressors.
In order to incorporate the pulse width capacity modulation system
of the present invention into rotary compressor 54, a valve
assembly 84 is provided being disposed within shell 56 and between
suction fitting 82 and .[.suction gas flow path.]. .Iadd.inlet
passage .Iaddend.80. Operation of valve assembly 84 is controlled
by a control module 86 which receives signals from one or more
sensors 88 indicative of the system operating conditions.
Operation of valve assembly 84, control module 86 and sensor 88
will be substantially identical to that described above with valve
assembly 84 operating under the control of control module 86 to
cyclically open and close to thereby modulate the flow of suction
gas into cylinder 74. As with compressor 10, both the cycle
frequency as well as the relative duration of the open and closed
portions of the cycle may be varied by control module 86 in
response to system operating conditions whereby the system
efficiency may be maximized and the capacity varied to any desired
capacity between zero and full load.
FIG. 7 shows a scroll type compressor 144 which includes a
compressor assembly 146 and a driving motor 148 both disposed
within hermetic shell 150.
Compressor assembly 146 includes a mean bearing housing 152 secured
within and supported by outer shell 150, an orbiting scroll member
154 movably supported on bearing housing 152 and a nonorbiting
scroll member 156 axially movably secured to bearing housing 152.
Scroll members 154 and 156 each include end plates 158 and 160 from
which interleaved spiral wraps 162 and 164 extend outwardly. Spiral
wraps 162 and 164 together with end plates 158 and 160 cooperate to
define moving fluid pockets 166, 168 which decrease in size as they
move from a radially outer position to a radially inner position in
response to relative orbital movement between scroll members 154
and 156. Fluid compressed within the moving fluid pockets 166, 168
is discharged through a centrally located discharge passage 170
provided in nonorbiting scroll member 156 into a discharge chamber
172 defined by the upper portion of hermetic shell 150 and muffler
plate 174 and thereafter is supplied to the system via discharge
fitting 176. An Oldham coupling is also provided acting between
scroll members 154 and 156 to prevent relative rotation
therebetween.
A drive shaft 180 is also provided being rotatably supported in
bearing housing 152 and having one end thereof drivingly coupled to
orbiting scroll member 154. A motor rotor 182 is secured to drive
shaft 180 and cooperates with motor stator 184 to rotatably drive
drive shaft 180. As thus far described, scroll compressor 144 is
typical of scroll type compressors and will operate to draw fluid
to be compressed flowing into hermetic shell 150 via inlet 186 into
the moving fluid pockets via suction inlet 188 provided in
nonorbiting scroll member 156, compress same and discharge the
compressed fluid into discharge chamber 172.
In order to incorporate the pulse width capacity modulation system
into scroll compressor 144, a valve assembly 190 is provided being
positioned in overlying relationship to suction inlet 188 so as to
be able to selectively control flow of fluid to be compressed into
respective moving fluid pockets 166 and 168. Operation of valve
assembly 190 is controlled by control module 192 in response to
signals received from one or more sensors 194 in substantially the
same manner as described above. It should be noted that while the
present invention has been shown and described with reference to a
scroll compressor in which the hermetic shell is substantially at
suction pressure, it may also be easily incorporated in other types
of scroll compressors such as those in which the interior is at
discharge pressure or in which both scrolls rotate about radially
offset axes.
As may now be appreciated, the pulsed capacity modulation system of
the present invention is extremely well suited for a wide variety
of compressors and is extremely effective in providing a full range
of modulation at relatively low costs. It should be noted that if
desired the pulsed capacity modulation system of the present
invention may also be combined with any of the other known types of
capacity modulation systems for a particular application.
In the above embodiments, it is intended that the compressor
continue to be driven while in an unloaded condition. Obviously,
the power required to drive the compressor when unloaded (no
compression taking place) is considerably less than that required
when the compressor is fully loaded. Accordingly, it may be
desirable to provide additional control means operative to improve
motor efficiency during these periods of reduced load
operation.
Such an embodiment is shown schematically in FIG. 8 which comprises
a motor compressor 90 which may be of the type described above with
respect to FIG. 1, FIGS. 5 and 6, or FIG. 7 and includes a solenoid
valve assembly connected to a suction line which is operative to
selectively block the flow of suction gas to the compressing
mechanism. The solenoid valve assembly is intended to be controlled
by a control module 92 in response to system conditions sensed by
sensors 94. As thus far described, the system represents a
schematic illustration of any of the embodiments described above.
In order to improve efficiency of the driving motor during reduced
load operation, a motor control module 96 is also provided which is
connected to the compressor motor circuit via line 98 and to
control module 92 via line 100. It is contemplated that motor
control module 96 will operate in response to a signal from control
module 92 indicating that the compressor is being placed in reduced
load operating condition. In response to this signal, motor control
module 96 will operate to vary one or more of the compressor motor
operating parameters to thereby improve its efficiency during the
period of reduced load. Such operating parameters are intended to
include any variably controllable factors which affect motor
operating efficiency including voltage reduction or varying the
running capacitance used for the auxiliary winding of a single
phase motor. Once control module 92 signals motor control module 96
that the compressor is being returned to fully loaded operation,
motor control module 96 will then operate to restore the affected
operating parameters to maximize motor efficiency under full load
operation. There may be some time lag between the closing of the
solenoid valve assembly and the reduced loading on the compressor
which will be primarily dependent upon the volume of suction gas in
the area between the solenoid valve assembly and the compression
chamber. As a result, it may be desirable to provide for an
appropriate time delay before the motor operating parameter is
adjusted for the reduced loading. Of course, it is desirable that
the solenoid valve assembly be positioned as close as possible to
the compression chamber so as to minimize this delayed reaction
time.
It should also be noted that while each of the embodiments has been
described as incorporating a solenoid valve which operates to
control the flow of pressurized discharge gas to the suction gas
flow control valve for controlling suction gas flow, it is also
possible to substitute other types of valves therefor such as, for
example, solenoid valves by themselves or any other suitable
valving arrangement. It is, however, believed that the use of a
solenoid valve for controlling the flow of a pressurized fluid such
as discharge gas to the suction control valve is preferred because
it allows for application of greater actuating forces to the
suction gas control valve and hence faster operation thereof. An
exemplary embodiment of such a valve assembly is shown and will be
described with reference to FIG. 9 it being noted that this valve
assembly may be used in any of the embodiments described above.
As shown in FIG. 9, valve assembly 102 comprises a solenoid control
valve 106 and a pressure actuated valve 104.
Solenoid .[.valve assembly.]. .Iadd.control valve .Iaddend.106
includes a housing 108 within which is provided a valve chamber 110
having a valve member 112 movably disposed therein. A pressurized
fluid supply line 114 opens into chamber 110 adjacent one end
thereof and a vent passage 116 opens outwardly from chamber 110
adjacent the opposite end thereof. An outlet passage 118 is also
provided opening into chamber 110 approximately midway between the
opposite ends thereof. Valve member 112 is secured to one end of
plunger 120 the other end of which extends axially movably along
hermetically sealed bore 121 about which a solenoid coil 122 is
positioned. As shown, plunger 120 will be biased into the position
shown in which valve member 112 overlies and closes off pressurized
fluid supply line 114 and outlet passage 118 is in open
communication with vent passage 116. When solenoid coil 122 is
energized, .[.shaft.]. .Iadd.plunger .Iaddend.120 will operate to
move valve member 112 into a position in which it overlies and
closes off vent passage 116 and allows open communication between
pressurized fluid supply line 114 and outlet 118. The opposite end
of pressurized fluid supply line .Iadd.114 .Iaddend.will be
connected to a suitable source of pressurized fluid such as for
example discharge gas from the compressor.
Pressure actuated valve assembly 104 includes a housing 124 having
a cylinder 126 provided therein within which piston 128 is movably
disposed. A shaft 130 has one end connected to piston 128 and
extends from cylinder 126 through bore 132 into a chamber 134
provided in housing 124. A valve member 136 is secured to the end
of shaft 130, is positioned within chamber 134 and is movable by
shaft 130 into and out of sealing engagement with valve seat 138
provided on partition 140 so as to selectively control flow of
suction gas from chamber 134 into chamber 142 and then through
.[.outlet 144.]. .Iadd.outlet 145.Iaddend.. An .[.inlet 146.].
.Iadd.inlet 147 .Iaddend.is provided for supplying suction gas to
chamber 134.
Fluid outlet line 118 opens into one end of cylinder 126 and serves
to provide pressurized fluid thereto bias piston 128 in a direction
such that valve 136 moves into sealing engagement with valve seat
138 to thereby interrupt the flow of suction gas from .[.inlet 146
to outlet 144.]. .Iadd.inlet 147 to outlet 145.Iaddend.. A
.[.return spring 148.]. .Iadd.return spring 149 .Iaddend.is also
provided within cylinder 126 which serves to bias piston 128 in a
direction so as to move valve member 136 out of sealing engagement
with valve seat 138 in response to venting of the pressurized fluid
from cylinder 126.
In operation, when control module 50 determines that capacity
modulation is in order, it will operate to energize solenoid
control valve 106 thereby moving valve 112 to the right as shown
and allowing pressurized fluid to flow through chamber 110 to
cylinder 126. This pressurized fluid then operates to move piston
128 in a direction to close valve 136 thereby preventing further
flow of suction gas to the compression mechanism. When solenoid
control valve 106 is deenergized by control module 50, valve 112
will move into a position to interrupt the supply of pressurized
fluid to cylinder 126 and to vent same via passage 116 thereby
enabling .[.return spring 148.]. .Iadd.return spring 149
.Iaddend.to move piston 128 in a direction to open valve member 136
such that the flow of suction gas to the compressor is resumed.
It should be noted that valve assembly 102 is exemplary only and
any other suitable arrangement may be easily substituted therefor.
As noted before, in order to facilitate rapid response to capacity
modulation signals, it is desirable that the suction flow shut off
valve be located as close to the compression chamber as possible.
Similarly, the pressurized fluid supply line and vent passages
should be sized relative to the volume of the actuating cylinder
being supplied thereby to ensure rapid pressurization and venting
of same.
It will be appreciated by those skilled in the art that various
changes and modifications may be made to the embodiments discussed
in this specification without departing from the spirit and scope
of the invention as defined by the appended claims.
* * * * *