Pump assembly for delivering liquids and gases

A pump assembly for delivering liquids or gases include a pump and an electromotor for driving the pump, the speed and/or torque of the electromotor being made variable by a static frequency converter. The frequency converter can be miniaturized by highly-integrated circuits and other provisions for a sufficient emission of dissipation heat. The frequency converter is arranged inside or on the pump assembly, forming a structural unit with pump assembly, and the dissipation heat of the frequency converter is emitted by the fluid delivered or to be delivered by the pump assembly, the fluid acting as dissipator.

FIELD OF THE INVENTION 
The invention relates to a pump assembly for delivering liquids or gases, 
comprising a pump and an electromotor driving the pump, the speed and/or 
torque of said electromotor being variable by means of a static frequency 
converter. 
BACKGROUND ART 
Pumps are the most frequent machines in engineering. In technical 
literature hydraulic pumps as well as ventilators and blast engines 
working with low pressure ratios are classed as "pumps". During the 
designing of the machine there is this no need to take the compressability 
of the fluid to be delivered into consideration. 
Both the positive displacement pump as well as the fluid flow pump follow 
the known model laws, i.e. for the positive displacement pump it holds 
that P.about.n.multidot.D.sup.3 and for the fluid flow pump it holds that 
P.about.n.sup.3 .multidot.D.sup.5, where P is power, n is speed of 
rotation and D are the characteristic dimensions of the energy-transfering 
module of the machine. It is evident that the power of a positive 
displacement pump increases linear with the speed of rotation, whereas the 
power of a fluid flow pump increases with the third power of the speed of 
rotation. In the following we refer to fluid flow pumps, although the 
invention also relates to the two types of machines mentioned above. The 
model laws illustrate the effect of speed on the hydraulic power of the 
machine in question. Consequently, it is of considerable advantage with 
regard to dimensions, weight, price and often efficiency of a pump 
assembly to operate a pump at high speeds. 
When driving a pump by means of an electromotor the speed of the pump is in 
most cases directly dependent on the frequency of the main circuit. That 
is the reason why frequency converters are increasingly employed. Such a 
converter has further advantages. It allows, for example, the simultaneous 
operation of structurally equal assemblies of different speeds for the 
execution of different tasks while at the same time reducing the stock of 
spare parts. Furthermore the user is no longer forced to exactly compute 
the characteristic curve of the assembly in advance, since the 
requirements of the assembly are met substantially lossless by choosing 
the correct speed. Finally, it is possible to deliver various products in 
the same system without exchanging the assembly by simply altering the 
speed. This is often necessary in chemical plants. 
A prerequisite for providing these advantageous is the installation of 
frequency converters. Known converters have to be installed apart from the 
pump assembly, since they are bulky and expensive. The price of a 
frequency converter normally increases the price of a pump assembly 
considerably, especially in the low-power range. A further disadvantage of 
known converters is interference with the ambient due to electromagnetic 
fields generated by the cable between a frequency converter and a pump 
assembly. This is only avoidable by extensive shielding, thus further 
curtailing the mobility of the pump assembly. 
SUMMARY OF THE INVENTION 
The object of the invention is to provide a frequency-controlled pump 
assembly, especially for small and medium power outputs, said assembly 
being inexpensive and thus universally applicable, thus using the above 
advantages for a broad spectrum of applications. Moreover, the savings in 
material and energy in such pump assemblies reduce the environmental load. 
In satisfaction of the foregoing object and advantages, the above pump 
assembly is according to the invention provided with a frequency converter 
miniaturized by highly integrated circuits, arranged inside or on the pump 
assembly and forming a structural unit with said pump assembly, the 
dissipation heat of said frequency converter being emitted by the fluid 
delivered or to be delivered by the pump assembly, said fluid acting as 
dissipator. 
The power of such an assembly and also the energy losses emitted in the 
form of dissipation heat increase with the third power of the linear 
dimensions of the assembly. The surface for emitting dissipation heat to 
the ambient only increases with the second power of the linear dimensions 
of the assembly. Consequently, any heat-generating object with a 
predetermined power output has to be of a defined minimum size. On the one 
hand, said size depends on the temperature difference between the heat 
source of the object and the dissipator, i.e. either the ambient or the 
coolant, and, on the other hand, on the size of the thermal resistance of 
the flow path. The lower the thermal resistance the smaller are the 
dimensions of the assembly. 
This discourse is important for the understanding of the theoretical 
background of the invention. The field of electronics allows very small 
dimensions of assemblies if the admissible operating temperature is not 
exceeded. The temperature limit can be kept when decreasing the dimensions 
of the assembly, if dissipators of low temperatures are found and the heat 
transmission coefficient for the surface emitting the dissipation heat is 
increased. 
Installing a frequency converter in or on a pump assembly enables the use 
of the delivered fluid or the fluid to be delivered as dissipator in a 
simple way. In known, separately installed frequency converters the 
dissipation heat is emitted to the ambient air by free convection, 
whereas heat losses can now be emitted by forced convection e.g. with 
turbulent fluid flow. When cooling with water the heat transmission 
coefficient is two to three orders of magnitude above heat transmission 
coefficients in the case of free convection. 
It is often advantageous to install the frequency converter in a bypass of 
the pump instead of entirely or partially in the flow path of the fluid, 
especially when delivering hot fluids. The flow in the bypass can be used 
as coolant and dissipator for the frequency converter after emission of 
heat to the ambient. 
For rough operation the frequency converter is situated between the pump 
and the electromotor. In order to improve heat emission, ducted cooling is 
provided by means of a ventilator or the clutch between the motor and the 
pump representing a rotor. It is also possible to connect the frequency 
converter to a separate cooling system. 
A further possibility for reducing the heat resistance and improving the 
heat dissipation is, e.g. to form the frequency converter, its housing and 
the free housing space in a special way. Thus, the housing of the 
frequency converter is a capsule pressure-resistant and leakproof towards 
the ambient and at least partially provided with a filling acting as heat 
conductor for the dissipation heat emitted to the surface of the capsule. 
If high external pressures are expected, the filling can stabilize the 
shape of the capsule, while the wall of the capsule is still comparatively 
thin in order to ensure good heat transmission. Usually, the filling is a 
dielectric material, such as a pourable solid or a liquid. 
The filling can also be a pourable solid with a liquid, the latter filling 
part of the space between the solid particles for foaming a heat-pipe 
system in such a way that the liquid vaporizes where the dissipation heat 
is developed and the vapor condenses on the inner surface of the capsule 
while emitting condensation heat. The condensate can then flow back to the 
area where the dissipation heat is developed. 
The output signal of some types of frequency converters is varied by 
actuating circuit elements. These circuit elements are not easily 
accessible in encapsulated frequency converters. Consequently, said 
elements are to be indirectly actuated from the outside of the wall of the 
capsule either mechanically or electromagnetically.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
According to FIG. 1 the water to be delivered enters a stator 2 of a pump 
via a suction muff 1, flows through pump steps 3 of a pump 4, said steps 
being provided with rotors, and leaves the pump through a pressure muff 6 
in a top 5 of the pump. A motor 7 driving the pump is connected to the top 
5 of the pump by means of a connecting piece 8. The shaft ends of the 
motor and the pump as well as the clutch of the connecting piece 8 are 
covered and thus not visible. 
In this embodiment a frequency converter 9, miniaturized by means of highly 
integrated circuits, is situated in the pump stator 2. Part of the surface 
of the converter is in the flow path of the water entering the pump 4 via 
the suction muff 1. The frequency converter emits part of its dissipation 
heat to the water via a wall 10. 
FIG. 1 also illustrates a further possibility for arranging a frequency 
converter 9a (see dashed lines). In this embodiment the frequency 
converter is situated in a bypass of two pump steps 3 and cooled by means 
of a partial flow of the water delivered by the pump. Here the water 
diverted through the bypass flows through cooling channels (not shown) in 
the frequency converter and returns to the pump 4 after having absorbed 
the dissipation heat. 
Another arrangement of the frequency converter in the bypass is shown in 
FIG. 2. The inline pump assembly illustrated in FIG. 2 is well-known and 
does not require further explanation. A housing 11 of a single-step pump 
is usually provided with bores 14 and 15 at a suction muff 12 and a 
pressure muff 13 respectively for measuring the pressure difference. If a 
connection 16, preferably provided with cooling ribs 17 in a predetermined 
area, is established from the bore 15 to the frequency converter 9b and 
another connection 18 is returned to the bore 14, the frequency converter 
is situated in the bypass to the pump. In this case the frequency 
converter is also cooled by the fluid during hot water delivery, since the 
partial flow through the bypass emits most of its heat to the ambient via 
the connection 16 and the cooling ribs 17. The temperature level of the 
fluid is thus so far reduced that it can be used as coolant for the 
frequency converter. 
In the embodiment shown in FIG. 3 the frequency converter 9c is situated 
between the motor and the pump 4. A clutch 19 formed like a rotor or 
another, separately installed rotor (not shown) provides the cooling of 
the frequency converter. 
If the outer dimensions of the frequency converter are adapted to the outer 
dimensions of the stepped chambers 3, the frequency converter 9d can also 
be arranged between two pump steps 3 in the flow path of the fluid, cf. 
FIG. 3. 
With very hot fluids, it is advantageous to employ ducted cooling of the 
frequency converter, cf. FIG. 2. The connections 16 and 18 are removed and 
the bores 14 and 15 are closed off. The frequency converter 9b is 
connected to an external cooling arrangement via two connections 20 and 21 
(depicted with dashed lines). The converter is provided with a coolant 
flowing through the cooling channels of the frequency converter and 
absorbing dissipation heat, emitting the heat via the connection 21. 
FIG. 4 shows yet another embodiment of a frequency converter 9 in a 
sectional view. It includes a liquid-proof capsule made of two parts 22 
and 23 provided with a filling 24 of pourable solid stabilizing the 
capsule. The electronic equipment 26 of the frequency converter situated 
in the bottom 23 of the capsule on a support 25 is surrounded by the solid 
filling 24 and by a liquid 27 so that the frequency converter operates as 
a heat-pipe system. In the bottom part of the capsule the liquid fills the 
space between the particles of the solid and vaporizes when the 
dissipation heat is sufficiently high. The vapor rises between the 
particles of the solid and finally condenses at a wall 22 of the capsule. 
The condensate is returned to the bottom part of the capsule. 
It is known that the output signal of the frequency converter can be 
changed by actuating circuit elements. These circuit elements 28 are no 
longer accessible from the outside due to the encapsulation of the 
frequency converter. Consequently they must be actuated from the outside 
through the wall 22 of the capsule either mechanically or 
electromagnetically. The frequency converter can, for example, be 
mechanically actuated by deforming the comparatively thin wall of the 
capsule with a tool, where the circuit elements 28 are situated, for 
triggering the corresponding electronic processes. Another possibility is 
to actuate the contacts of the circuit elements by means of an 
electromagnet, thus adjusting the desired output signal of the frequency 
converter. 
Furthermore it is advantageous to provide the frequency converter with plug 
contacts 29, connected to the input and the output of the frequency 
converter on the one side and, on the other side, being slidable onto 
counter contacts for establishing a connection with the main circuit, the 
stator windings and the external sensors. 
Arranging the frequency converter within the pump or the motor results in a 
sufficient shielding to the ambient. As another consequence the usually 
long and shielded off connections to external frequency converters 
installed at a distance from the pump assembly become superfluous. 
The frequency converter is miniaturized by means of highly integrated 
circuits, field-controlled transistors being suitably used in the output 
circuit of the frequency converter. A minimum size of the frequency 
converter can especially be achieved by providing a faultless emission of 
dissipation heat according to the above description. 
It should be noted that not all parts of the frequency converter have to be 
installed inside the capsule. The capacitor 30 of the intermediate circuit 
of the frequency converter inside the capsule, cf. FIG. 4, can also be 
arranged outside the capsule, cf. FIG. 2. The same applies correspondingly 
to the inductance of the intermediate circuit, if the frequency converter 
operates with current accumulation and not with voltage accumulation. An 
external arrangement of the intermediate circuit results in a further 
miniaturization of the frequency converter. So-called direct transformers 
operating without intermediate circuits are also included in the term 
"frequency converter" of the present invention. 
The operational value determined by the output circuit of the frequency 
converter can also be controlled by internal or external signals. For this 
purpose the frequency converter is provided with internal sensors, such as 
those reacting to current, voltage or temperature, or with external 
sensors and servo components, all of them connected to the controller of 
the frequency converter. Such external sensors can react to, for example, 
pressure, flow volume and temperature of the pump assembly. External servo 
components are, for example, time components switching off and on certain 
operational modes of the frequency converter for predetermined periods of 
time.