Fluid machine with induction motor

A fluid machine system has such characteristics that the flow rate is proportional to the rotational speed, the produced pressure is proportional to the square of the rotational speed, and the shaft power is proportional to the cube of the rotational speed. The fluid machine system has a first fluid machine actuatable by an induction motor, and a second fluid machine actuatable by the induction motor for producing a flow rate of 1/K and a shaft power of 1/K of those the first fluid machine at the same rotational speed as that of the first fluid machine for generating the same pressure as that of the first fluid machine. The fluid machines having many times of design points can be operated by the same induction motor.

BACKGROUND OF THE INVENTION 
1. Field of the Invention: 
The present invention relates to a fluid machine with an induction motor, 
and more particularly to a fluid machine having many types of design 
points which can be operated by the same induction motor. 
2. Description of the Prior Art: 
Heretofore, a voltage and a frequency to be supplied to a motor are 
uniquely determined at a site where the motor is used. In order to enable 
the motor to be common use, it has been customary to provide a design 
point where shaft powers (motor outputs) are the same and to vary a flow 
rate and a produced pressure. 
FIG. 4 of the accompanying drawings shows the relationship between a flow 
rate (Q) and a head (H) of a conventional fluid machine with an induction 
motor. A pump, for example, will be described as a non-positive 
displacement fluid machine having such characteristics that the flow rate 
is proportional to the rotational speed, the produced pressure is 
proportional to the square of the rotational speed, and the shaft power is 
proportional to the cube of the rotational speed. 
A motor .alpha. is combined with a pump A at a flow rate Q and a head H, a 
motor .beta. is combined with a pump B at a flow rate (1/K)Q and the head 
H, and the motor .alpha. is combined with a pump C at the flow rate (1/K)Q 
and the head KH, thereby handling three particular points. Thus, three 
particular points are handled by two types of motors and three types of 
pumps. 
Various specifications at the particular points are shown in FIG. 4. 
With the conventional fluid machine arrangement, however, it is necessary 
to have a fluid machine available at each of the particular points, as 
shown in FIG. 4, and a motor can be shared only at the same output point. 
As a result, the number of types of design points of a fluid machine is 
enormous as compared with the number of types of motors used. 
SUMMARY OF THE INVENTION 
It is therefore an object of the present invention to provide a fluid 
machine with an induction motor which can be shared at the same torque 
point by using a frequency/voltage converter, and which can satisfy many 
particulars with few fluid machines. 
According to the present invention, there is provided a fluid machine 
system having such characteristics that the flow rate is proportional to 
the rotational speed, the produced pressure is proportional to the square 
of the rotational speed, comprising a first induction motor operable at at 
least two frequencies and rotational speeds; a first fluid machine 
mountable to an output shaft of said first induction motor for actuation 
by said first induction motor at a first of said rotational speeds, said 
first fluid machine producing a flow rate Q and a shaft power P and a 
pressure H at said first of said rotational speeds when said first 
induction motor operates at a first of said frequencies; and a second 
fluid machine mountable to an output shaft of another induction motor and 
operable at a design point specifying a flow rate of 1/K times Q and a 
shaft power of 1/K times P and the pressure H when said second fluid 
machine is actuated by said another induction motor at said first of said 
rotational speeds. The second fluid machine is also operable at a design 
point specifying a flow rate which is K.sup.-1/2 times Q, a pressure which 
is K times H, a shaft power which is K.sup.1/2 times P, and a torque which 
is equal to that of said first fluid machine when said second fluid 
machine is actuated by said first induction motor, operating at a second 
of said frequencies which is K.sup.1/2 times that of said first of said 
frequencies, at a second of said rotational speeds which is K.sup.1/2 
times that of said first of said rotational speeds. Fluid machines 
operable at different design points can therefore be operated by a given 
induction motor. 
With this arrangement, a wide range of particulars can be handled with a 
combination of few types of fluid machines and motors, and design points 
can be placed in a narrow range of specific speeds for high efficiency and 
productivity. 
The above and other objects, features, and advantages of the present 
invention will become apparent from the following description when taken 
in conjunction with the accompanying drawings which illustrate a preferred 
embodiment of the present invention by way of example.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
FIG. 1 shows a basic arrangement of a fluid machine with an induction motor 
according to the present invention. In FIG. 1, a pump, for example, is 
illustrated as a non-positive displacement fluid machine having such 
characteristics that the flow rate is proportional to the rotational 
speed, the produced pressure is proportional to the square of the 
rotational speed, and the shaft power is proportional to the cube of the 
rotational speed. 
A pump A having a rotational speed N, a pump head H, a flow rate Q and a 
shaft power P is actuated by a motor .alpha. at a frequency F and a 
voltage V. Another pump B having a rotational speed N, a pump head H, a 
flow rate (1/K)Q and a shaft power (1/K)P is actuated by a motor .beta. at 
a frequency F and a voltage V, where K is a constant flow rate or head 
nominal value. Various specifications of the pumps A, B and the motors 
.alpha., .beta. are shown in FIG. 1. 
If the pump B is coupled to the motor .alpha., then the pump B is operated 
for a flow rate K.sup.-1/2 Q, a pump head KH, a shaft power K.sup.1/2 P, a 
rotational speed K.sup.1/2N, and a torque T by the motor .alpha. at a 
frequency K.sup.1/2 F and a voltage K.sup.1/2 V. The frequency and voltage 
of the motor .alpha. can be varied by a frequency/voltage converter. 
The pump B can be shared at particular points marked by .oval-hollow., 
.DELTA. in FIG. 1 because the rotational speed can be increased by the 
frequency/voltage converter. Specifically, since the rotational speed at 
the particular point .DELTA. is K.sup.1/2 times the rotational speed at 
the particular point .oval-hollow., the flow rate becomes K.sup.-1/2 Q, 
the pump head becomes KH, and the shaft power becomes K.sup.1/2 P. K is 
preferably 1.6 or a similar value. 
The motor .alpha. shifts from a particular point marked by .quadrature. to 
the particular point .DELTA. because when the frequency increases while 
the ratio F/V of the voltage and the frequency is being constant, the 
rotational speed increases in proportion to the frequency while the torque 
T is being constant, and hence the output also increases in proportion to 
the rotational speed. 
According to the present invention, therefore, the three particular points 
can be realized by two types of motors and two types of pumps. 
In order to satisfy the particular point .DELTA. at the same rotational 
speed N as that of the particular points .oval-hollow., .quadrature., not 
only a new motor is necessary, but also a pump having a specific speed 
K.sup.-1 Ns is needed. That is, there is required a pump having a smaller 
specific speed than the pump B (specific speed K.sup.-1/2 Ns) which is 
operated at the rotational speed K.sup.1/2 N. This indicates that the 
present invention can cope with a wider range of particulars with a 
smaller range of pump specific speeds. 
Therefore, a wide range of particulars can be handled by using only pumps 
having specific speeds which are advantageous from the standpoints of pump 
performance and pump productivity, i.e., pumps having pressed impellers. 
FIG. 2 shows the arrangement shown in FIG. 1 at an enlarged scale. In FIG. 
2, four pump types A, B, C, D and four motor types "a", "b", "c", "d" are 
made available. 
Since there are ten points of intersection in FIG. 2, ten particular points 
can be realized with four pump types and four motor types. Consequently, 
many particular points can be satisfied with few fluid machines and few 
motors. 
A pump which may preferably be employed as the fluid machine with an 
induction motor according to the present invention will be described below 
with reference to FIG. 3. FIG. 3 shows in cross section a 
full-circumferential-flow pump which comprises a pump casing 1, a canned 
motor 6 housed in the pump casing 1, and a pair of impellers 8, 9 fixedly 
mounted on a main shaft 7 of the canned motor 6. The pump casing 1 
comprises an outer casing member 2, a suction casing member 3 connected to 
an axial end of the outer casing member 2 by flanges 51, 52, and a 
discharge casing member 4 connected to an opposite axial end of the outer 
casing member 2 by flanges 51, 52. Each of the outer casing member 2, the 
suction casing member 3, and the discharge casing member 4 is made of a 
pressed sheet of stainless steel or the like. 
The impeller 8 is housed in a first inner casing 10 having a return vane 
10a, the first inner casing 10 being disposed in the pump casing 1. The 
impeller 9 is housed in a second inner casing 11 having a guide device 
11a, the second inner casing 11 disposed in the pump casing 1 and 
connected to the first inner casing 10. A resilient seal 12 is interposed 
between the first inner casing 10 and the suction casing member 3. Liner 
rings 45 are mounted on radially inner ends, respectively, of the first 
and second inner casings 10, 11. 
The canned motor 6 comprises a stator 13, an outer motor frame barrel 14 
fixedly fitted over the stator 13 and securely disposed in the pump casing 
1, a pair of motor frame side plates 15, 16 welded to respective opposite 
open ends of the outer motor frame barrel 14, and a can 17 fitted in the 
stator 13 and welded to the motor frame side plates 15, 16. The canned 
motor 6 also has a rotor 18 rotatably disposed in the stator 13 and hence 
the can 17, and shrink-fitted over the main shaft 7. 
A cable housing 20 is welded to the outer motor frame barrel 14. Leads from 
coils disposed in the outer motor frame barrel 14 are extended and 
connected to a power supply cable in the cable housing 20, which is in 
turn connected to a frequency/voltage converter. 
The pump has an anti-thrust load bearing assembly and a thrust load bearing 
assembly. 
First, the anti-thrust load bearing assembly will be described below. A 
radial bearing 22 and a fixed thrust bearing 23 are mounted on a bearing 
bracket 21 near the discharge casing member 4. The radial bearing 22 has 
an end which serves as a fixed thrust sliding member. A rotary thrust 
bearing 24 serving as a rotary thrust sliding member and a thrust collar 
25 are disposed one on each side of the radial bearing 22 and the fixed 
thrust bearing 23. The rotary thrust bearing 24 is secured to a thrust 
disk 26 which is fixed to the main shaft 7 through a sand shield 27 by a 
nut 28 threaded over an externally threaded surface on an end of the main 
shaft 7. 
The bearing bracket 21 is inserted in a socket defined in the motor frame 
side plate 16 through a resilient O-ring 29. The bearing bracket 21 is 
also held against the motor frame side plate 16 through a resilient gasket 
30. The radial bearing 22 is slidably supported on a sleeve 31 which is 
fitted over the main shaft 7. 
The thrust load bearing assembly will now be described below. A radial 
bearing 33 is mounted on a bearing bracket 32 near the impeller 9, and 
slidably supported on a sleeve 34 which is fitted over the main shaft 7. 
The sleeve 34 is axially held against a washer 35 which is fixed the main 
shaft 7 through the impeller 9, a sleeve 42, and the impeller 8 by a nut 
36 threaded over an externally threaded surface on an opposite end of the 
main shaft 7. The bearing bracket 32 is inserted in a socket defined in 
the motor frame side plate 15 through a resilient O-ring 37. The bearing 
bracket 32 is also held against the motor frame side plate 15. 
Operation of the full-circumferential-flow pump shown in FIG. 2 will be 
described below. A fluid drawn into the suction casing 3 is pressurized by 
the impellers 8, 9, and oriented from a radial direction into an axial 
direction by the guide device 11a. Therefore, the fluid flows into an 
annular passage 40 defined between the outer casing member 2 and the outer 
motor frame barrel 14, and then flows through the annular passage 40 into 
the discharge casing member 4. 
From the discharge casing member 4, most of the fluid is discharged through 
a discharge port out of the pump. The remaining fluid passes behind the 
sand shield 27 into a rotor chamber in which it lubricates the bearings 
22, 23, 24, 35. Thereafter, the fluid flows through an opening 32a defined 
in the bearing bracket 32, and Joins the fluid which is discharged from 
the impeller 9. 
Generally, for a constant-torque load, i.e., for a load having a constant 
torque even when the rotational speed varies, the rotational speed can be 
controlled by varying the frequency while keeping the voltage/frequency 
ratio constant. It is known that the motor flux is constant at this time, 
and the current and the heat generated by the motor remain the same. 
One problem with the above control process is that even though the heat 
generated by the motor remains the same, the temperature of stator 
windings does not remain the same. For example, a motor with a motor 
cooling fan mounted on a shaft end thereof cannot be operated at too low a 
rotational speed because the cooling capability is lowered as the 
rotational speed decreases. If a motor structure is such that the heat 
produced by bearings affects the temperature of the stator windings, the 
temperature of the stator windings may be too high when the rotational 
speed increases. 
According to the present invention, as shown in FIG. 3, the motor is of a 
forced-cooling structure and is of the canned type. By passing a solution 
pumped by the pump into a rotor chamber, the heat produced by the rotor 
and the heat produced by the bearings are prevented from affecting the 
temperature of the stator windings. 
With the arrangement of the present invention, a wide range of particulars 
can be handled with a combination of few types of fluid machines and 
motors, and design points can be placed in a narrow range of specific 
speeds for high efficiency and productivity. 
Furthermore, a high pressure and output can be produced by a fluid machine 
by employing a frequency/voltage converter without changing outer 
configuration and dimensions of the fluid machine. Since the torque is the 
same even if the rotational speed is different, the main shaft and key 
structures may be shared. 
Although a certain preferred embodiment of the present invention has been 
shown and described in detail, it should be understood that various 
changes and modifications may be made therein without departing from the 
scope of the appended claims.