U.S. patent number 6,050,780 [Application Number 08/732,037] was granted by the patent office on 2000-04-18 for method for driving a high speed compressor.
This patent grant is currently assigned to Ishikawajima-Harima Heavy Industries Co., Ltd.. Invention is credited to Shunichi Funabashi, Kazumitsu Hasegawa, Kanji Majima, Shinichi Ozaki, Kiwamu Yamada.
United States Patent |
6,050,780 |
Hasegawa , et al. |
April 18, 2000 |
Method for driving a high speed compressor
Abstract
A high speed compressor (10) includes a gear box (11), two
compressing units (12, 13) supported on opposite side walls of the
gear box (11) and a bull gear (32) rotatably placed in the gear box
(11). Each compressing unit includes a scroll (15, 16) and an
impeller (18, 19) rotatably housed in the scroll (15, 16). The
impellers (18, 19) share an impeller shaft (22) extending into the
gear box (11). A pinion gear (23) is mounted on the impeller shaft
(22) such that it engages with the bull gear (32). A drive shaft
(30) extends from the bull gear (32) out of the gear box (11) along
a center axis of the gear box (11). An induction motor (35) is
connected with the drive shaft (30) for causing the impellers (18,
19) to rotate by way of the bull gear (32) and the pinion gear
(23). An inverter (40) is connected with the induction motor (35)
at its one end and with a commercial power source (43) at the other
end for converting an A.C. power from the commercial power source
(43) into an A.C. power having a desired frequency and feeding it
to the induction motor (35) for driving of the induction motor
(35).
Inventors: |
Hasegawa; Kazumitsu (Narashino,
JP), Funabashi; Shunichi (Yokohama, JP),
Majima; Kanji (Yokohama, JP), Yamada; Kiwamu
(Yokohama, JP), Ozaki; Shinichi (Kunitachi,
JP) |
Assignee: |
Ishikawajima-Harima Heavy
Industries Co., Ltd. (Tokyo, JP)
|
Family
ID: |
17588273 |
Appl.
No.: |
08/732,037 |
Filed: |
October 16, 1996 |
Foreign Application Priority Data
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|
|
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Oct 25, 1995 [JP] |
|
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7-277785 |
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Current U.S.
Class: |
417/44.11;
417/423.5; 417/53; 417/423.6; 417/45 |
Current CPC
Class: |
F04D
27/0261 (20130101); F04D 25/163 (20130101); Y02B
30/70 (20130101) |
Current International
Class: |
F04D
25/16 (20060101); F04D 27/02 (20060101); F04D
25/00 (20060101); F04B 049/06 (); F04B
035/04 () |
Field of
Search: |
;417/423.5,426,44.1,44.11,45,321,40.1,53 ;415/60,65 ;60/608
;318/801,111 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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0 440 902 A1 |
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Aug 1991 |
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EP |
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974 418 |
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Dec 1960 |
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DE |
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WO 91/09230 |
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Jun 1991 |
|
WO |
|
Other References
Patent Abstracts of Japan, vol. 8, No. 154 (M-310) [1591], Jul. 18,
1984 (JP 59 049394)..
|
Primary Examiner: Freay; Charles G.
Attorney, Agent or Firm: McCormick, Paulding & Huber
LLP
Claims
What is claimed is:
1. A method for driving a high speed compressor from a commercial
AC power source having a frequency of 60 Hz or less, the high speed
compressor including a gear box having an outer surface and a
center axis, a plurality of compressing units supported on the
outer surface of the gear box, each compressing unit including a
scroll and an impeller rotatably housed in the scroll, each
impeller having an impeller shaft extending into the gear box, a
bull gear placed in the gear box, a drive shaft extending from the
bull gear out of the gear box along the center axis of the gear
box, and a pinion gear drive between each impeller shaft including
a pinion gear mounted on the impeller shaft and engaged with the
bull gear, with a gear ratio between the pinion gear and the bull
gear being about 1/10 to 1/30, said method comprising:
providing an induction motor drivingly connected with the drive
shaft for causing the impellers to rotate by means of the bull gear
and the pinion gear drive so that each impeller is rotatable at a
predetermined maximum speed if the induction motor is directly
powered from the commercial AC power source;
interposing an inverter between the induction motor and the
commercial AC power source for converting the AC power from the
commercial power source into an AC power having a desired frequency
greater than 60 Hz and less than 200 Hz and feeding it to the
induction motor for actuation of the induction motor, whereby each
impeller is rotated at a speed greater than said predetermined
maximum speed;
determining an excessive load on the induction motor by detecting a
current flowing in the inverter; and
providing a frequency controller for controlling an output
frequency of the inverter, whereby the frequency converter causes
the inverter to drop its output frequency when the current detected
exceeds a predetermined current value.
2. The method of claim 1, wherein the plurality of compressing
units are first and second compressing units, and the first and
second compressing units are positioned on opposite sides of the
gear box, connected with each other by a mutual impeller shaft, and
share a common pinion gear provided on the mutual impeller
shaft.
3. The method of claim 1, wherein each impeller is rotated at about
100,000 to 200,000 rpm.
4. The method of claim 1, wherein the induction motor is a two-pole
induction motor.
5. The method of claim 1, wherein the inverter includes a rectifier
unit for converting the commercial AC power to DC power and an
inverter unit for converting the DC power to the AC power having a
desired frequency greater than 60 Hz and less than 200 Hz.
6. The method of claim 1, further comprising the step of
maintaining a discharge pressure of the high speed compressor at a
predetermined discharge value.
7. The method of claim 6, wherein the discharge pressure of the
high speed compressor is maintained at the pre-determined discharge
value by adjusting the output frequency of the inverter by means of
the frequency controller.
8. The method of claim 6, wherein the pre-determined discharge
value is about 7 kg/cm.sup.2.
9. The method of claim 1, wherein each compressing unit produces
compressed air, and further comprising the step of indirectly
cooling the compressed air.
10. The method of claim 2, wherein each compressing unit produces
compressed air, and further comprising the step of indirectly
cooling the compressed air.
11. The method of claim 10, wherein the step of indirectly cooling
the compressed air comprises providing intercooler means between
the first compressing unit and the second compressing unit, and
providing aftercooler means at an outlet of the second compressing
unit.
Description
BACKGROUND OF THE INVENTION
1. Technical Field
The present invention relates to a turbo compressor which is
rotated by an induction motor via a speed-up gear mechanism, and
more particularly to a turbo compressor which is rotated at a high
but mechanically safe speed and which can be operated independently
of a frequency of a commercial power source applied to the
induction motor.
2. Background Art
Generally a high speed compressor includes a plurality of
scroll-and-impeller sets (or a plurality of compressing units)
connected in series. Each scroll-and-impeller set or compressing
unit includes a scroll and an impeller rotatably placed in the
scroll. A high speed compressor including two compressing units is
generally called a two-stage compressor. The air is introduced into
a first compressing unit and compressed therein. The compressed air
is then introduced to a second compressing unit. In this manner,
the air is successively compressed through the in-series connected
compressing units and ultimately discharged from the last
compressing unit.
A high speed compressor also has a gear box and a bull gear
rotatably provided in the gear box. The compressing units are
generally mounted on an outer surface of the gear box. A drive
shaft extends from the bull gear out of the gear box and is driven
by an induction motor. The drive shaft is directly connected with
the induction motor.
Each impeller has a shaft extending into the gear box and a pinion
gear is mounted on a free end of the shaft. The pinion gears of the
impellers mesh with the bull gear inside the gear box. It should be
noted that a single pinion gear may mesh with the bull gear inside
the gear box if only two compressing units are mounted on the gear
box and the two impellers share a common shaft and a common pinion
gear.
The bull gear is a large gear as compared with the pinion gears in
diameter and number of teeth. The bull gear is connected with the
induction motor via the drive shaft. Accordingly, the impellers are
driven by the induction motor via the full gear and pinion
gears.
In order to raise a rotational speed of the impellers, the
large-diameter bull gear and the small-diameter pinion gears are,
directly engaged with each other like a planetary gear set. This is
a one-stage speed-up mechanism.
Conventionally, a commercial power source is used for actuation of
the induction motor. A frequency of the commercial power source is
generally different from country to country or from region to
region. Therefore, the rotational speed of the induction motor also
differs depending upon a place where the induction motor is used.
For example, when a two-pole induction motor is driven in a 60 Hz
region, a rotational speed meter reads 3,600 rpm whereas when it is
driven in a 50 Hz region, the rotational speed meter indicates
3,000 rpm.
A speed-up ratio by the bull gear and each pinion gear is generally
about twenty times since a gear ratio between the pinion gear and
the bull gear is about 1/20. Therefore, a maximum speed of the
impeller reaches about 60,000-72,000 rpm.
Consequently, performances of the high speed compressor vary with a
frequency of an available commercial power source.
In the meantime, a compact high speed compressor has been desired
in the art. In order to reduce dimensions of the high speed
compressor without degrading its performances, it is necessary to
rotate each impeller at a higher speed such as some 100,000
rpm.
To raise the impeller rotational speed, the speed-up ratio and/or
the motor rotational speed should be increased. Employing a larger
bull gear and/or smaller pinion gears results in an increased
speed-up ratio. In addition, using a two-stage speed-up mechanism
can also raise the impeller rotational speed.
However, it is practically impossible to raise a gear ratio between
the bull gear and the pinion gear while employing a one-stage
speed-up mechanism. This is because if there is substantial
difference between the two gears in dimension, the gear diameter of
the bull gear becomes too large with respect to its gear tooth
height and width so that mechanically appropriate meshing cannot be
expected between the bull gear and the pinion gears as long as
these gears are manufactured with ordinary tolerance. It is
generally said that the practically feasible maximum speed-up ratio
(or reciprocal of the gear ratio) is thirty times.
If a two-stage speed-up structure is utilized, the speed-up ratio
at each stage can be reduced. However, an intermediate gear is
needed, so that the overall speed-up mechanism becomes complicated
and larger. This is contrary to the above-mentioned object, i.e.,
size reduction of a high speed compressor.
The rotational speed of the motor is determined by a frequency of a
commercial power source since the induction motor is used. Thus,
the rotational speed of the motor cannot be raised.
Another concern is that a discharge pressure of the high speed
compressor becomes higher than a designed value in winter since an
air temperature becomes lower in winter and therefore an air
density is higher in winter than in summer. Consequently, the motor
should bear a greater load in winter. To avoid this, conventionally
an inlet valve of the high speed compressor is throttled.
SUMMARY OF THE INVENTION
One object of the present invention is to provide a high speed
compressor which can be rotated at a high rotational speed while
ensuring a mechanically proper engagement between a bull gear and a
pinion gear and which can exhibit predetermined performances
regardless of a frequency of an available commercial power
source.
According to one aspect of the present invention, there is provided
a high speed compressor which comprises: a gear box; two
compressing units supported on opposite lateral walls of the gear
box, each compressing unit including a scroll and an impeller
rotatably housed in the scroll, each impeller having an impeller
shaft extending into the gear box and jointed with the other
impeller shaft at its end such that the impellers share a common
shaft; a pinion gear mounted on the common impeller shaft; a bull
gear supported in the gear box and engaged with the pinion gear, a
rotation center axis of the bull gear being coaxial to a center
axis of the gear box; a drive shaft extending from the bull gear
out of the gear box along the center axis of the gear box; an
induction motor connected with the drive shaft for causing the
impellers to rotate by way of the bull gear and the pinion gear;
and an inverter connected with the induction motor at its one end
and with a commercial power source at the other end for converting
an A.C. power of the commercial power source into an A.C. power
having a desired frequency and feeding it to the induction motor
for actuation of the induction motor.
The gear ratio between the pinion gear and the bull gear may be
about 1/10 to 1/30. The induction motor may be a two-pole motor.
The inverter may have a rated output frequency of about 60 to 200
Hz. Each impeller may be rotated at 60,000 to 200,000 rpm so that
the high speed compressor of the invention functions as a compact
but high performance high speed compressor.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
FIG. 1 illustrates a high speed compressor according to the present
invention, shown partly in section and, without an intercooler and
an aftercooler;
FIG. 2 illustrates a perspective view of two compressing units of
the high speed compressor shown in FIG. 1, together with the
intercooler and aftercooler but without a gear box; and
FIG. 3 is a graph illustrating characteristics of the high speed
compressor shown in FIG. 1.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Now, a preferred embodiment of the present invention will be
described with reference to the accompanying drawings.
Referring to FIG. 1, a high speed compressor 10 is a
two-stage-compression type compressor and includes two compressing
units 12 and 13. The first compressing unit 12 and the second
compressing unit 13 are symmetrically located on opposite side
walls of a gear box 11 respectively near an upper end of the gear
box 11.
The first compressing unit 12 includes a first scroll 15 attached
to the upper left side wall of the gear box 11 and a first impeller
18 rotatably supported by the gear box 11 and rotatably housed in
the first scroll 15. An external air is introduced into the first
compressing unit 12 in an axial direction of the first impeller 18
(from the left in FIG. 1) and compressed by the first impeller 18
upon rotation of the first impeller 18 as a centrifugal force is
applied to the air. Similarly, the second compressing unit 13
includes a second scroll 16 mounted on the upper right side wall of
the gear box 11 and a second impeller 19 rotatably supported by the
gear box 11 and rotatably housed in the second scroll 16. The
compressed air from the first compressing unit 12 is introduced to
the second compressing unit 13 and another centrifugal force is
applied to the air by the second impeller 19 to further compress
the air.
The first and second impellers 18 and 19 have a common shaft 22 or
these two impellers are connected to each other by a first driven
shaft 22. The first driven shaft 22 horizontally extends through an
upper portion of the gear box 11 and is rotatably supported by a
pair of bearings 21 fitted in openings formed in the opposite upper
side walls of the gear box 11. A pinion gear 23 is provided on the
first driven shaft 22 at its midpoint.
A drive shaft 30 horizontally extends through a center portion of
the gear box 11 along a horizontal center axis of the gear box. A
second pair of bearings 31 buried in opposite center walls of the
gear box 11 support the drive shaft 30. The drive shaft 30 extends
beyond the right second bearing 31 and out of the gear box 11. A
bull gear 32 is provided on the drive shaft 30 inside the gear box
11. The bull gear 32 meshes with the pinion gear 23.
The bull gear 32 is a large-diameter gear having a large number of
teeth. The pinion gear 23 is a small-diameter gear having a small
number of teeth. A gear ratio between the large gear and the small
gear is between 1/10 and 1/30.
A free end of the drive shaft 30 is connected to an induction motor
35 via a coupling 33.
The illustrated induction motor 35 is a two-pole induction motor.
This motor 35 is driven by an inverter 40. The inverter 40 includes
a rectifier element 41 having diodes and an inverter element 42
having transistors. A single- or three-phase commercial A.C. power
source 43 of 60 or 50 Hz is converted to a D.C. power by the
rectifier element 41 and undergoes a smoothing operation. The
resulting D.C. power is on/off controlled by the transistors of the
inverter element 42 to output a PWM (Pulse Width Modulated) wave
and in turn an A.C. power having a desired frequency.
A frequency controller 44 is connected to the inverter 40 to
control the output frequency of the inverter by switching on/off
the transistors of the inverter element 42. A current detector 45
is also connected with the inverter 40 to detect a current flowing
in the inverter 40.
The inverter 40 generates an A.C. power having a frequency of 60 to
200 Hz and supplies it to the induction motor 35. It should be
noted that the inverter 40 can change the output frequency between
0 Hz and 120 Hz at intervals of, for example, 0.1 Hz.
The illustrated bull gear 32 and pinion gear 23 are smaller than
conventional ones in diameter respectively. This is because the
rotational speed of each of these gears is higher than a
conventional design. By reducing the gear diameter, the peripheral
speed of the gear is suppressed or maintained at an appropriate
value and therefore a mechanical safety of the high speed
compressor is ensured. If the peripheral speed is raised, the
centrifugal force also becomes larger. The large centrifugal force
may result in breakage of the gears 23 and 32 and/or other parts of
the high speed compressor or malfunctioning of the high speed
compressor 1.
In the illustrated embodiment, a load of the induction motor 35 is
designed to be below 200 kW and a discharge pressure at the last
compressing unit of the high speed compressor is designed to be 7
kg/cm.sup.2.
Referring now to FIG. 2, it is understood that the high speed
compressor of the invention is provided with a water-cooling-type
air coolers (i.e., intercooler 51 and aftercooler 52).
Between the first compressing unit 12 and the second compressing
unit 13, provided is an intercooler 51. An aftercooler 52 connects
to an outlet of the second compressing unit 13 via a tube 59.
Cooling water tubes 54 and 55 extend into and from each of the
intercooler 51 and the aftercooler 52 so that the compressed air is
indirectly cooled by the cooling water flowing through these water
tubes.
An external air is sucked into the first compressing unit 12 from
an air intake opening 56 and compressed therein. Upon compression,
the air temperature rises. This compressed hot air is introduced to
the intercooler 51 through a first outlet tube 57 and cooled
therein. After that, the air is introduced into the second
compressing unit 13 by an inlet tube 58 and compressed therein. The
compressed air is then introduced to the aftercooler 52 by the
second outlet tube 59 and cooled therein. The cooled and compressed
air is ultimately supplied from an outlet tube 53 to a particular
unit which needs the compressed air.
Now, operations of the high speed compressor will be described.
Referring back to FIG. 1, the inverter 40 outputs a two-phase A.C.
power having a frequency of 60-200 Hz to the induction motor 35
using the frequency controller 44.
The induction motor 35 is a bipolar motor and rotates at a speed of
3,600-12,000 rpm. The bull gear 32 directly connected to the
induction motor 35 also rotates at a high speed, i.e., 3,600-12,000
rpm. The gear ratio of the pinion gear 23 to the bull gear 32 is
about 1/10-1/30. As a result, the speed of the impellers 18 and 19
connected to the pinion gear 23 is increased about 10-30 times and
reaches about 60,000-200,000 rpm.
The inverter 40 inverts a commercial A.C. power to a D.C. power and
converts it to an A.C. power having an desired frequency.
Therefore, the high speed compressor of the invention is not
influenced by the frequency of the commercial power source.
Specifically, regardless of the commercial power source frequency
being 50 or 60 Hz, the high speed compressor can use the same gears
and the same motor.
Since the impellers 18 and 19 rotate at a very high speed such as
60,000 to 200,000 rpm and the diameters of the bull gear 32 and
pinion gear 23 are reduced respectively as compared with the
conventional ones, both size reduction and rotational speed
increase are achieved.
The rated output frequency of the inverter 40 is 60 to 200 Hz. It
should be noted, however, that its frequency is adjustable at
intervals of predetermined Hz (e.g., 0.1 Hz) and therefore
performances of the high speed compressor are also adjustable.
Referring to FIG. 3, illustrated is relationship between suction
volume and planned (or designed) shaft power of the high speed
compressor and that between suction volume and planned pressure
increase.
In this embodiment, a planned pressure is 100% when discharge
pressure is, for example, 7 kg/cm.sup.2 and a planned flow rate
(suction volume) at this discharge pressure is 100%. The point "p"
represents a design point of when the discharge pressure is 100%
and the suction volume is 100% with a condition that an inlet valve
opening degree of the high speed compressor is 100%. The point "w"
is a design point of when a shaft power under the same condition
takes a 100% designed value. Then, the relationship between the
volume and the pressure draws a characteristic curve 70 and the
shaft power change draws a straight line 71.
The design point "p" is plotted under another condition that the
intake air temperature is a designed value (e.g., 25.degree. C.).
If the atmospheric temperature rises to, for example, 35.degree. C.
in summer, the air density drops so that the characteristic curve
70 shifts downward as indicated by the dotted curve 72. If the
atmospheric temperature drops to, for instance, 5.degree. C. in,
winter, the air density rises about 10% and accordingly the
characteristic curve shifts upward as indicated by the curve
73.
Therefore, the load of the high speed compressor 1 varies with the
intake air conditions. In particular, the discharge pressure is
high in winter so that the high speed compressor 1 is operated
under an excessive load condition.
To cope with this, the current detector 45 is used to detect the
current of the inverter 40 for determination of the load of the
induction motor 35. If the detected current is beyond a limit
value, the frequency controller 44 causes the output frequency of
the inverter 40 to drop. Upon this controlling operation by the
controller 44, the rotational speed of the induction motor 35 is
decelerated, the load on the induction motor 35 is lightened and
the high speed compressor 1 is driven according to the
characteristic curve 70 which passes through the design point "p",
i.e., the volume (intake air flow rate) and the pressure of the
high speed compressor take the most desirable values.
Conventionally, the rotational speed of the induction motor is
fixed and not adjustable, and the load change due to the change of
the intake air condition is coped with by adjusting the opening
degree of the intake valve. In the present invention, on the other
hand, the rotational speed of the induction motor itself is also
adjustable so that the load change is coped with by the induction
motor rotational speed adjustment and/or the intake valve opening
degree adjustment.
Incidentally, the high speed compressor is usually operated by one
of two control methods: one is a constant pressure and non surge
control method in which a discharge pressure is maintained
independently of volume change and the other is a load and no load
control method in which the high speed compressor is turned on and
off when the volume changes.
Conventionally, these control methods are carried out by adjusting
the opening degree of the inlet valve. However, the valve opening
degree control only adjusts the intake air flow rate: it does not
control the performances or capability of the high speed
compressor. Accordingly, a drive range in the volume/pressure graph
is very limited. In the present invention, the frequency control is
added to the conventional control (i.e., intake valve opening
degree control) so that the drive range or control range in the
volume/pressure graph is considerably broadened. Further, switching
to the no load operation from the load operation can be done in an
easier manner.
During the pressure-constant control, conventionally the opening
degree of the inlet valve of the high speed compressor is adjusted
in order to maintain the discharge pressure when the volume changes
(or when consumed air flow rate changes). If the valve opening
degree is adjusted, both the volume and pressure change. The inlet
valve opening degree adjustment results in larger change in volume
than in pressure. Contrarily, the frequency of the power source to
the induction motor is adjusted by the inverter 40 in the present
invention. The frequency adjustment can change the pressure without
substantial change of the volume. Specifically, the pressure varies
with square of rotational speed and the volume is proportional to
the rotational speed so that larger change occurs in pressure than
in volume. In the present invention, therefore, the inverter 40 is
mainly utilized to keep the discharge pressure at a constant value
when the volume change is small whereas the intake valve is mainly
utilized when the volume change is large.
During the load condition of the non-load/load drive mode, the high
speed compressor is operated according to the curve 70 of FIG. 3.
During the non-load condition, the inlet valve is throttled to a
15% opening degree from a 100% opening degree until the discharge
pressure approaches the atmospheric pressure and the shaft power of
the high speed compressor drops to 10%. In this case, the
rotational speed of the high speed compressor is also decelerated
by the inverter 40 for smooth and easy shifting to the non-load
condition from the load condition.
In the foregoing, the high speed compressor of a two-stage
compression type is described. However, it should be noted that the
present invention may be applied to a three-stage compression type
and a four-stage compression type. Further, the illustrated
induction motor is a two-pole motor, but it may be a motor having
three poles or more.
* * * * *