FLUID MACHINERY

Abstract: The present invention relates to a fluid machinery for generating a pressure by rotating an impeller with a motor. The fluid machinery has a frequency converter (F) for supplying electric power to the motor, a detector for detecting a frequency and a current value, and a program for specifying in advance the relationship between the frequency and the current value. A frequency and a current value in an actual operation are compared with the specified program, and the frequency generated by the frequency converter (F) is varied so that an operating point of the fluid machinery approaches the specified program.

Description: Technical Field The present invention relates to a fluid machinery, and more particularly to a fluid machinery which includes a centrifugal pump arranged to easily provide constant-flow-rate characteristics suitable for a circulation pump, and an axial-flow pump arranged to easily provide constant-pump-head characteristics suitable for a water supply pump. Background Art Heretofore, centrifugal pumps have been used as cold or hot water circulation pumps in heating or cooling applications. Important factors to be taken into account in this heating or cooling applications are as follows: 1 ○ Even if a required flow rate is known, since there is a slight difference between a calculated pipe-induced loss and an actual pipe-induced loss, the fluid flow rate needs to be adjusted by a valve at site. In this case, the fluid flow suffers an energy loss commensurate with a loss caused by the valve. 2 ○ when the pipe-induced loss increases due to aging of the pipe, or clogging of the valve caused by foreign matter, the flow rate is reduced. Therefore, it is necessary to adjust the flow rate periodically by the valve or the like. 3 ○ Because no means for measuring the flow rate is generally available at site, it is necessary to know the pressure with a pressure gage or the like and estimate the flow rate based on a pump characteristic curve. However, this process is low in accuracy. Conventional techniques for solving the above problems are set forth as follows: 1 ○ A signal from an electromagnetic flowmeter is processed by a control console, and the opening of a solenoid-operated valve is controlled. Since this process is expensive and accompanied by a loss caused by the valve, its energy-saving effect is small. 2 ○ A signal from an electromagnetic flowmeter is sent to a frequency converter for operating the pump at variable speeds. This process has an energy-saving effect, but is expensive. 3 ○ The pump has a rotational speed selecting knob which is used to change Q - H characteristics of the pump and also to meet a required flow rate in combination with a valve. This process is effective to reduce an energy loss due to the resistance imposed by the valve, but is not effective to stabilize the flow rate. If there is an increase in the pipe-induced loss, then, the flow rate needs to be adjusted each time the pipe-induced loss increases. EP-A-0 584 713 discloses a method for controlling an electric motor driving a centrifugal pump having a diameter ratio D1/D2 less than approximately 1/2 and a varying fluid flow-through, the motor being connected to a supply mains through a power-control device. An electrical measuring signal is produced, being proportional to the current drawn by the motor or by the power-control device, and based on the known characteristics of the motor and the pump, the electrical measuring signal is processed so as to produce a control signal, being used as an input signal to the power-control device. The electrical measuring signal is processed in such a manner, that the control signal causes the delivery pressure of the pump to be substantially constant over a large variation interval for the fluid flow-through. EP-A-0 644 333 discloses a pump control system which has a pump unit composed of a turbo pump, a motor for operating the turbo pump, and a frequency/voltage converter for generating a frequency and a voltage to energize the motor. The rotational speed of the turbo pump is varied in order to equalize the current of the motor to a constant current irrespective of the head of the pump. The pump can be operated to take fully advantage of the current capacity of the motor. US-A-4 511 312 discloses a method and apparatus for driving the impeller in a turbo-type liquid pump operating at relatively low power and relatively high delivery head by means of an a.c. motor. The motor is driven from a static inverter which operates at an operating frequency of 100-1000 Hz. This enables high specific speed impellers to be used, and therewith provides a considerable increase in the efficiency and capacity of the pump at unchanged motor sizes. US-A-4 629 116 discloses an electric-motor-driven circulating pump for heating systems which reduces power consumption of the motor, whereby the reduction ensues by means of periodic interruption of a line feed by means of electronic switch means so that switch-on and pause intervals follow one another. The switch means interrupt or close current flow at a zero-axis crossing of the voltage of the line feed. Disclosure of Invention In view of the above problems, it is therfore an object of the present invention to provide a fluid machinery such as a centrifugal pump or the like which requires no special auxiliary facilities and supplies a stable flow rate at all times regardless of changes in the resistance imposed by the pipe. Another object of the present invention is to provide a fluid machinery such as an axial-flow pump which generates a constant pump head even when the flow rate varies, and is suitable for use as a water supply pump. In order to achieve the above object, a pump assembly is provided as set forth in claim 1. Preferred embodiments of the present invention may be gathered from the dependent claims. Specifically, claim 1 is directed to a pump assembly comprising a canned motor pump and a frequency converter (inverter) mounted an a pump casing. That is, the pump assembly is defined as an inverter-mounting-type pump. Conventionally, the frequency converter (inverter) is provided in the control panel provided separately from the pump. According to the present invention, the frequency converter is mounted an the pump to form an integral pump assembly. The program for specifying the relationship between the frequency and the current valve is required for each pump. Because the frequency converter incorporating such program is mounted an the pump, components required for each pump can be concentrated on the pump. Thus, it is possible to simplify the structure of the control panel and share the same type of control panel for controlling other types of pumps. Brief Description of Drawings FIGS. 1A and 1B are diagrams illustrative of a basic concept of a fluid machinery according to the present invention; FIG. 2 is a diagram illustrative of a basic concept of a fluid machinery according to the present invention; FIG. 3 is a cross-sectional view of a pump assembly suitable for embodying the present invention; and FIG. 4 is a circuit diagram of a frequency converter in the present invention. Best Mode for Carrying Out the Invention An embodiment of a fluid machinery according to the present invention will be described below. FIGS. 1A and 1B are diagrams illustrative of a basic concept of a fluid machinery according to the present invention. FIG. 1A is a diagram showing the relationship between the flow rate (Q) and pump head (H) of a centrifugal pump which is an example of the fluid machinery, and FIG. 1B is a diagram showing at an enlarged scale an encircled area I(b) in FIG. 1A. In FIG. 1A, the horizontal axis represents the flow rate ratio, and the vertical axis represents the pump head ratio. A motor for actuating the centrifugal pump has an inverter and a plurality of knobs (selecting means) for selecting a desired flow rate. The motor comprises a three-phase induction motor, for example. In FIGS. 1A and 1B, it is assumed that two sets of an inverter frequency (Hz) and a current (A (ampere)) are stored in a memory as follows: Knob A A = 0.001 × Hz 2 ··· flow rate ratio 0.7 Knob B A = 0.0014 × Hz 2 ··· flow rate ratio 1.0 Now, it is assumed that the knob B is selected. At this time, the pipe exhibits a resistance curve 2 ○ in FIG. 1A. When the pump is actuated, it is operated at a frequency of 100 Hz (6000 rpm) that has been stored beforehand. The operating point is at a point α1 of intersection (100 Hz - 15 A) between the Q-H curve and the resistance curve 2 ○. At this operating point, the current value is larger than the stored current A = 0.0014 × Hz 2 (A = 0.0014 × 100 2 = 14A), meaning that the current value is excessively large for the frequency of 100 Hz. The inverter then decelerates the pump to equalize the current to A = 0.0014Hz 2 , i.e., operates the pump at a reduced frequency. It is assumed that the pump is operated at 90 Hz as a result of the deceleration. The operating point is now at a point β1 of intersection (90 Hz - 10 A) between the Q-H curve and the resistance curve 2 ○. At this operating point, the current value is smaller than the stored current A = 0.0014Hz 2 (A = 0.0014 × 90 2 = 11.34 A), meaning that the current value is excessively small for the frequency of 90 Hz. The inverter then accelerates the pump to equalize the current to A = 0.0014Hz 2 , i.e., operates the pump at an increased frequency. As a consequence, the pump is operated at a point γ1 where A = 0.0014 × 95 2 ≒ 12.5 A (95 Hz - 12.5 A). Therefore, the pump is operated at a flow rate of the selected knob B. According to this process, the pump is operated at a constant flow rate with a minimum amount of consumed electric power required, regardless of the magnitude and variations of the resistance imposed by the pipe. The process is thus optimum for a circulation pump. A true point δ, representing a flow rate and a pump head that are really necessary, in FIG. 1A is an operating point where a most suitable quantity of heat is supplied when the pump is used to circulate hot water. This point may possibly deviate slightly from a calculated operating quantity of heat because a margin is introduced for calculations. In order to solve the above problem, more types (e.g., about 8 types, rather than the two types of A, B shown in FIG. 1A) that can be selected by the flow rate selecting knob for the inverter may be employed. The foregoing description is directed to the example of a centrifugal pump where the shaft power (consumed electric power and current value) increases as the flow rate increases at a constant rotational speed (constant frequency (Hz)). FIG. 2 is a diagram illustrative of a process of controlling, under a constant pressure, an axial-flow pump where the shaft power decreases as the flow rate increases at a constant rotational speed (constant frequency (Hz)). In FIG. 2, the horizontal axis represents the flow rate ratio, and the vertical axis represents the pump head ratio. In FIG. 2, it is assumed that one set of an inverter frequency (Hz) and current (A (ampere) in an inverter is stored in a memory as follows: A = 0.0012 × Hz 2 ··· flow rate ratio 0.75 The pipe has a resistance curve 1 ○ in FIG. 2. when the pump is actuated, it is operated at a frequency of 100 Hz (6000 rpm) that has been stored beforehand. The operating point is at a point α2 of intersection (100 Hz - 14 A) between the Q-H curve and the resistance curve 1 ○. At this operating point, the current value is larger than the stored current A = 0.0012 × Hz 2 (A = 0.0012 × 100 2 = 12A), meaning that the current value is excessively large for the frequency of 100 Hz. The inverter then decelerates the pump to equalize the current to A = 0.0012Hz 2 , i.e., operates the pump at a reduced frequency. It is assumed that the pump is operated at 90 Hz as a result of the deceleration. The operating point is now at a point β2 of intersection (90 Hz - 9 A) between the Q-H curve and the resistance curve 1 ○. At this operating point, the current value is lower than the stored current A = 0.0012Hz 2 (A = 0.0012 × 90 2 = 9.72 A), meaning that the current value is excessively small for the frequency of 90 Hz. The inverter then accelerates the pump to equalize the current to A = 0.0012Hz 2 , i.e., operates the pump at an increased frequency. As a consequence, the pump is operated at a point where A = 0.0012 × 95 2 ≒ 11 A (95 Hz - 11 A), i.e., under a selected pressure. According to this process, the pump is operated under a constant pressure (pump head) with a minimum amount of consumed electric power required, regardless of the magnitude and variations of the resistance imposed by the pipe. The process is thus optimum for a water supply pump. According to the present invention, as shown in FIGS. 1A, 1B, and 2, since the pump alone is capable of maintaining a flow rate or a pressure at a constant level without using an electromagnetic flowmeter or a pressure gage (or a pressure sensor), the user is not required to have special auxiliary facilities and to perform any operation such as an operation for adjusting any valves. FIG. 3 shows a pump assembly suitable for embodying the present invention. The pump assembly comprises a full-circumferential-flow-type canned motor pump in which a fluid being handled flows around a motor. The full-circumferential-flow-type canned motor pump according to the illustrated embodiment comprises a pump casing 1, a canned motor 6 housed in the pump casing 1, and an impeller 8 fixed to an end of a main shaft 7 of the canned motor 6. The pump casing 1 comprises an outer pump casing barrel 2 and a suction casing 3 and a discharge casing 4 which are connected respectively to opposite ends of the outer pump casing barrel 2. The suction casing 3 is joined to the outer pump casing barrel 2 by welding, and the discharge casing 4 is joined to the outer pump casing barrel 2 by flanges 61, 62. Each of the outer pump casing barrel 2, the suction casing 3, and the discharge casing 4 is made of sheet metal such as stainless steel. The canned motor 6 comprises a stator 13, an outer motor frame barrel 14 disposed around the stator 13, a pair of side motor frame plates 15, 16 welded to opposite open ends of the outer motor frame barrel 14, and a can 17 fitted in the stator 13 and welded to the side motor frame plates 15, 16. A rotor 18 rotatably disposed in the stator 13 is shrink-fitted over the main shaft 7. An annular space (flow passage) 40 is defined between the outer motor frame barrel 14 and the outer pump casing barrel 2. An inverter (frequency converter) F is fixedly mounted on an outer surface of the outer pump casing barrel 2 which confines the fluid to be pumped around the motor. The inverter F is housed in a case 20 which accommodates a flow rate indicator and a flow rate selecting knob. A guide member 11 for guiding the fluid radially inwardly is held by the side motor frame plate 15 of the canned motor 6. The impeller 8 is housed in an inner casing 12 that is fixed to the guide member 11. A seal member 13 is disposed around the guide member 11. A liner ring 51 is mounted on an inner end of the guide member 11 and held in sliding contact with a front face (inlet mouth) of the impeller 8. The inner casing 12 is substantially dome-shaped, and covers an end of the main shaft 7 of the canned motor pump 6. The inner casing 12 has a guide device 12a comprising guide vanes or a volute for guiding the fluid discharged from the impeller 8. The inner casing 12 also has an air vent hole 12b defined in a distal end thereof. Bearings that are used comprise plain bearings made of silicon carbide, and all the bearings are disposed in a space defined between the motor rotor 18 and the impeller 8. The bearings are lubricated by liquid handled by the pump. A bearing bracket 21 is made of cast stainless steel. Stationary radial bearings 22, 23 are shrink-fitted in axially opposite ends of the bearing bracket 21, and are prevented from rotating by a synthetic resin injected from their outer circumferential surfaces. The stationary radial bearings 22, 23 have axial ends held in sliding contact with respective rotatable thrust bearings 24, 25. The rotatable thrust bearings 24, 25 and rotatable radial bearings 26, 27 are fixedly mounted on the main shaft 7 by a impeller locking nut 29 with the impeller 8 and a distance piece 28 interposed therebetween. operation of the full-circumferential-flow-type canned motor pump shown in FIG. 3 will briefly be described below. The fluid drawn from the suction casing 3 flows into the annular flow passage 40 defined between the outer motor frame barrel 14 and the outer pump casing barrel 2, passes through the annular flow passage 40, and is guided into the impeller 8 by the guide member 11. The fluid discharged from the impeller 8 flows through the guide device 12a, and is discharged from the discharge casing 4. An embodiment of the frequency converter in the present invention will be described below with reference to FIG. 4. In FIG. 4, the fluid machinery such as a pump is denoted by M, and the frequency converter is denoted by F. If a three-phase AC electric energy is supplied to the frequency converter F, then the frequency converter F includes a converter section comprising a rectifying circuit 41 for converting an alternating current into a direct current and a smoothing capacitor 42 for smoothing a rectified voltage, and a three-phase inverter 43 for converting the direct current into an alternating current. To the converter section, there are connected an auxiliary power supply 44 and a voltage detector 45 which detects a DC voltage of the converter section. The frequency converter F also has a controller 46 which stores the relationship between generating frequencies and current values. The controller 46 outputs a PWM signal to drive the three-phase inverter 43. A current detecting sensor 48 is connected to an output terminal of the three-phase inverter 43. A current detected by the current detecting sensor 48 is converted by a current detector 47 into a signal which is supplied to the controller 46. The three-phase inverter 43 has output terminals connected to the motor 6, which is associated with a temperature sensor 49. The controller 46 comprises a ROM which stores a function for specifying a generating frequency and a current, a CPU for comparing a signal from the current detector 47 with settings stored in the ROM, performing arithmetic operations, and outputting a PWM signal, and a control IC. The frequency converter F has the controller 46, and can store time which the frequency converter has outputted. If the pump is operated according to the above constant flow-rate control process, then the frequency converter F is capable of detecting the flow rate of the fluid delivered by the pump from moment to moment. The frequency converter F also has a calculating function. Thus, the frequency converter F can indicate an integrated flow rate, in addition to a flow rate from moment to moment. The pump assembly can therefore be used as a flowmeter. Furthermore, using a memory function of the frequency converter F, the pump assembly can be automatically operated to perform a task of delivering a certain amount (e.g., 1 m 3 ) of water for an every certain period of time (e.g., 24 hours) for a certain number of successive days (e.g., 5 days), stop performing the task for a certain number of successive days ( e.g. , 2 days), and perform the task for a certain number of successive days (e.g., 5 days). This process is suitable for limiting the amount of water supply per day for water saving purposes, and has an advantage that it can automatically supply water without the need for any special ancillary facilities. As described above, the present invention provides a fluid machinery such as a centrifugal pump which needs no special ancillary facilities, but can supply a fluid at a stable rate at all times, regardless of changes in the resistance imposed by the pipe. According the present invention, there is also provided a fluid machinery such as an axial-flow pump which is capable of generating a constant pump head regardless of changes in the flow rate. Industrial Applicability The present invention is preferably applicable to a fluid pump including a centrifugal pump which can easily provide constant-flow-rate characteristics suitable for a circulation pump, and an axial-flow pump which can easily provide constant-pump-head characteristics suitable for a water supply pump.

Claims: A pump assembly comprising: a canned motor pump comprising a pump casing (1), a canned motor (6) housed in said pump casing, and an impeller fixed to a main shaft (7) of said canned motor; a frequency converter (F) for supplying electing power to said motor, said frequency converter being mounted on an outer surface of said pump casing; a detector for detecting a frequency and a current value; and a program provided in said frequency converter for specifying in advance the relationship between the frequency and the current value; wherein a frequency and a current value in an actual operation are comparedwith the specifiedprogram, and the frequency generated by said frequency converter is varied to equalize the current value generated by said frequency converter to the specified program. A pump assembly according to claim 1, wherein a flow rate of said pump is controlled so as to be substantially constant by said frequency converter. A pump assembly according to claim 1, wherein a generated pressure of said pump is controlled so as to be substantially constant by said frequency converter. A pump assembly according to claim 1, wherein the frequency (Hz) and the current value (A) are related by a unique function and programmed. A pump assembly according to claim 4, wherein the relationship between said frequency (Hz) and said current value (A) is expressed by A = KHz n (where K and n represent positive constants). A pump assembly according to claim 5, wherein said frequency converter has means for changing values of K and n. A pump assembly according to claim 1, wherein said canned motor pump comprises a full-circumferential-flow-type canned motor pump in which a fluid being handled flows around a motor, and said frequency converter is mounted on said outer surface of said pump casing which confines the fluid to be pumped around said motor. A pump assembly according to claim 7, wherein said pump assembly has a function for multiplying time outputted from said frequency converter by the value of the constant flow rate for thereby calculating the flow rate. A pump assembly according to claim 8, wherein said frequency converter has an indicator for the flow rate. A pump assembly according to claim 8, wherein by using a memory function of said frequency converter, said pump assembly can be automatically operated to perform a task of delivering a certain amount of water for an every certain period of time for a certain number of successive days, stop performing the task for a certain number of successive days, and perform the task for a certain number of successive days.

Inventors: IIJIMA KATSUJI, KOBAYASHI MAKOTO, MIYAKE YOSHIO, MIYAZAKI YOSHIAKI, UWAI KEITA, YAGI KAORU, YAMAMOTO MASAKAZU, IIJIMA, KATSUJI, KOBAYASHI, MAKOTO, MIYAKE, YOSHIO, MIYAZAKI, YOSHIAKI, UWAI, KEITA, YAGI, KAORU, YAMAMOTO, MASAKAZU
Applicants: EBARA CORP, EBARA CORPORATION
Application year: 1998
Main classification: F04D15
IPC codes: F04D15