Title of Invention	A DEVICE FOR COOLING AN ELECTRIC MODULE AND A TECHNICAL APPLIANCE
Abstract	The invention relates to a device for cooling an electrical module (BG) arranged in a housing (G), comprising at least one membrane filter (MB) disposed in an air inlet (LE) of the hous- ing (B) in each case, for superficial filtering of at least dirt particles from an inflowing air for cooling the electrical module (BG), and at least one cooling means (VE) for establishing said inflowing air in the housing (G) and for discharging said filtered cooling air, the filtered cooling air having heated up on account of flowing through and/or around the module (BG), out of at least one air outlet (LA) of the housing (G). Atleast one membrane filter (MB) is configured in the form of a fine-pored membrane (MBR) of an electrically conductive material for an electromagnetic shielding of the electrical module (BG), applied to a backing material (TM).

Title of Invention

A DEVICE FOR COOLING AN ELECTRIC MODULE AND A TECHNICAL APPLIANCE

Abstract

The invention relates to a device for cooling an electrical module (BG) arranged in a housing (G), comprising at least one membrane filter (MB) disposed in an air inlet (LE) of the hous- ing (B) in each case, for superficial filtering of at least dirt particles from an inflowing air for cooling the electrical module (BG), and at least one cooling means (VE) for establishing said inflowing air in the housing (G) and for discharging said filtered cooling air, the filtered cooling air having heated up on account of flowing through and/or around the module (BG), out of at least one air outlet (LA) of the housing (G). Atleast one membrane filter (MB) is configured in the form of a fine-pored membrane (MBR) of an electrically conductive material for an electromagnetic shielding of the electrical module (BG), applied to a backing material (TM).

Full Text	Description The invention relates to an arrangement for cooling an electrical module arranged in a housing and to a technical appliance, in particular a base stations of a mobile radio system or wireless subscriber line system. In an electrically operated technical appliance, the lost power of components and modules through which current flows leads to a heating-up of the appliance. Since standard electrical components for technical appliances have only a limited admissible operating temperature range, of for example up to 70°C, they are cooled by cooling devices. These cooling devices are, for example, fans which establish an air flow in the housing, flowing around or through the electrical components and modules, and consequently bring about a discharge of the thermal output produced. During operation of the technical appliances outside enclosed spaces or in adverse conditions within enclosed spaces, adequate protection from environmental influences, such as for example dirt particles and liquids, must be additionally provided along with heat discharge. In this respect, protective regulations in accordance with the specified IP classes must be observed in order to ensure long-term functioning of the technical appliances. It is known from DE 19755944 to provide in an air inlet of a housing a membrane filter for a superficial filtering of dirt particles from inflowing cooling air and for separating out liquids. In comparison with a housing known for example from DE 19626778, with an air/air heat exchanger, which ensures complete separation of an internal cooling circuit from an external cooling circuit, adequate protection of the electrical components can be achieved for the aforementioned areas of use of the technical appliance with the corresponding protective regulations in a simple way by use of the membrane filter. At the same time, a temperature difference, required for the cooling, between the temperature of the ambient atmosphere and the temperature inside the housing is reduced. A membrane filter of this type is based, for example, on a membrane filter known for use in articles of clothing by the designation Goretex, Sympatex, etc. The membrane of the filter comprises a fine netting or knitted fabric of fibers, which permits a very small pore size. An example of a material which may be used for this is PTFE (polytetrafluoroethylene) , also known by the name Teflon. The membrane is generally provided on a backing material, such as for example polyamide, in order to achieve a certain stability and resistance of the membrane filter. In addition to the criteria with regard to protective regulations, EMC guidelines (EMC - Electromagnetic Compatibility) must also be satisfied, ensuring on the one hand protection of the electrical modules arranged in the housing of the technical appliance from electromagnetic influences from the surroundings of the appliance and on the other hand protection of the surroundings from electromagnetic radiation emanating from the electrical modules. On account of the plastic material used, the membrane filter is permeable to electromagnetic radiation and consequently does not bring about adequate shielding. Additional shielding, for example by a wire netting arranged in front of the membrane filter, is therefore necessary to satisfy the EMC guidelines. However, it is disadvantageous to provide this additional wire netting as a further element of the housing of the technical appliance and, for example, it increases the overall dimensions of the housing. Furthermore, it makes maintenance and cleaning of the membrane filter more difficult. US 5,431,974 discloses a filter arrangement for electromagnetic shielding. The filter arrangement in this case comprises an electrically conductive frame with at least one opening, a panel of porous electrically conductive material, a layer of electrically conductive adhesive and also an electrically conductive gasket material. Preferably chosen as the porous panel is from synthetic polymers which has been made electrically conductive at the surface by electrochemical processes. The invention is based on the object of specifying an arrangement for cooling and a technical appliance which, with known use of a membrane filter, permits adequate electromagnetic shielding without the specified disadvantages of the prior art. This object is achieved by the arrangement for cooling according to patent claims 1 and 2 and also the technical appliance according to patent claim 11. Advantageous developments of the invention can be taken from the dependent patent subclaims. The arrangement according to the invention for cooling an electrical module arranged in a housing has at least one membrane filter, arranged in an air inlet of the housing in each case, for a superficial filtering of at least dirt particles from inflowing cooling air for cooling the electrical module and also at least one cooling device for establishing an air flow in the housing and for discharging the filtered cooling air, heated up on account of flowing through or around the module, out of the housing from at least one air outlet. The membrane filter is characterized by having a netting of an electrically conductive material for electromagnetically shielding the electrical module. The configuration of the arrangement according to the invention has the advantage that an integration of the electrically conductive netting achieves the effect of electromagnetic shielding without an additional shielding arrangement having to be provided. Furthermore, the advantageous properties of the membrane filter are not restricted. For example, simple cleaning of the filter without prior detachment of a shielding grating is possible. As a result, the housing of the technical appliance can be provided in a very compact form. The arrangement according to the invention can be used in technical appliances with at least one electrical module, such as for example base stations of a mobile radio system or wireless subscriber line system (access network systems), traffic control devices, power supply devices or switch cabinets for a control system of industrial machines. In the same way, the arrangement according to the invention can be used, for example, in smaller electrical appliances, such as for example a portable or stationary home computer, or in electrical measuring instruments. According to a first configuration of the invention, the membrane filter additionally separates out liquids at the surface, whereby use of the technical appliance is also possible outside enclosed spaces or under adverse ambient conditions According to a second configuration, the membrane filter is provided in the form of a fine-pored membrane applied to a backing material. This configuration of the membrane filter advantageously permits individual adaptability of the backing material and/or the membrane to special conditions of use of the technical appliance. For example, a filter resistant to chemical substances, such as for example acids, can be used for technical appliances used in production. According to a third development, based on the second configuration, the electrically conductive netting is woven into the backing material of the membrane filter. As a result, a firm bonding of the netting to the backing material is advantageously achieved, one of the effects being, for example, that the stability of the membrane filter is increased. As an alternative to the third configuration, the electrically conductive netting is applied to the backing material. This configuration advantageously permits simple production of the membrane filter, the electrically conductive netting being applied to the membrane filter, for example, in an additional production step. A bonding between the netting and the backing material can be achieved, for example, by an adhesive bonding technique. According to a further alternative configuration, the electrically conductive netting is provided in the form of backing material for the membrane. By this configuration, the electromagnetic shielding is advantageously integrated directly into the membrane filter, as a result of which there are no further working steps in the production of the membrane filter. According to further alternative configurations, the membrane may be made from a PTFE material known as Teflon or from an electrically conductive material. The PTFE material is already widely used, for example for water-impermeable items of clothing, and, on account of the properties, can be flexibly adapted to a wide variety of requirements with regard to the pore size. If the membrane is produced from an electrically conductive material that has for example the same or comparable properties, it is advantageously possible to dispense with the additional electrically conductive netting. According to a further configuration, the electrically conductive material may be provided in the form of a metal, plastic or ceramic material. Plastic and ceramic materials in particular have advantageous properties in comparison with known metal materials, for example with regard to the resistance to environmental influences, strength and processability. According to a further configuration of the invention, the electrically conductive netting is electrically connected to the housing, the latter likewise being made at least partially from an electrically conductive material. Electrically conductive netting may be understood here according to the invention as meaning an additional netting, a netting used as a backing material or a membrane of electrically conductive material. The connection to the housing brings about a grounding of the membrane filter, which may alternatively also be achieved by means of a separate grounded electrical connection. According to a further configuration of the invention, the effective surface area of the membrane filter is enlarged by a periodic folding, as a result of which clogging of the filter is advantageously reduced and the maintenance intervals are increased. Furthermore, a membrane filter according to the invention is advantageously additionally arranged at the air outlet of the housing. This configuration permits, for example, a reversal of the cooling air flow in the housing, in order to free the membrane filter at the air inlet of dirt particles, without dirt particles or liquids at the same time being able to pass through the air outlet into the housing. According to a further configuration, the cooling device comprises a fan impeller driven by a motor. In this case, the motor speed, and consequently the throughput of the cooling air in the housing, for example, can be controlled in dependence on the temperature in the housing and/or on the temperature of the ambient atmosphere, with the advantageous result that a constant operating temperature of the electrical module and a constant temperature inside the housing are ensured, and consequently the service life of the electrical module is advantageously prolonged. Furthermore, the speed of the cooling device can be controlled, for example, in such a way that the admissible limiting temperatures of the electrical module are not quite exceeded, and consequently the noise emission of the arrangement is minimized by the lowest possible speed of the cooling device. The arrangement according to the invention is suitable in particular for use in technical appliances, such as for example base stations or similar outdoor installations of a mobile radio system, or wireless subscriber line system, and also in traffic control devices, radio relay devices etc. Exemplary embodiments of the invention are explained in more detail with reference to the accompanying drawings, in which: figure 1 shows a base station of a mobile radio system with the arrangement according to the invention for cooling electrical modules, in a front view, figure 2 shows the arrangement according to the invention in a side view, figure 3 shows two ways in which the membrane filter according to the invention can be provided, by way of example, and figure 4 shows a detailed representation of the membrane filter according to the invention. A prior-art technical appliance, such as for example a base station BTS of a mobile radio system or wireless subscriber line system, according to figure 1, includes a plurality of electrical modules BG. During the operation of the electrical appliance, the lost power of the individual electrical modules BG results in a heating-up effect, giving rise to the necessity for cooling in order not to exceed an admissible operating temperature of the modules. The housing G, represented in a front view, of the electrical appliance has on the end face an air inlet LE with a membrane filter MB. The overall dimensions of the air inlet LE are set, for example, in such a way that cooling air flowing in through the membrane filter MB from the ambient atmosphere of the technical appliance can flow through the electrical modules BG in each case from below, and if appropriate from the front, and consequently can bring about a cooling-down of the modules. The active surface area of the membrane filter MB, which may be larger than the air inlet LE, for example due to a fold formation, is dimensioned such that the pressure drop of the inflowing cooling air can be compensated by a cooling -device, or an adequate amount of cooling air can still flow in despite a partial clogging of the membrane filter MB by dirt particles or liquid. Figure 2 presents the described technical appliance in a side view, in order to illustrate in more detail the internal construction shown by way of example. On the left-hand side of the housing G, a frame R with the membrane filter MB is arranged in front of the air inlet LE. The additional frame R permits rapid removal of the membrane filter MB, for example for maintenance and cleaning purposes or, for replacement. At the same time, the frame R permits the described folding of the membrane filter MB. To restrict the overall dimensions of the technical appliance, the frame R may also be integrated into the housing G. The membrane filter MB is designed in the form of a surface filter, which has the special advantageous property of separating out dirt particles and liquids from the ambient atmosphere already at the surface of the membrane, whereby, for example, sensitive electronic components or circuits in the modules BG are protected from environmental influences of this type. A membrane filter MB of this type is based, for example, on a membrane filter known by the designation Goretex, Sympatex etc. for use in articles of clothing. The membrane of the filter comprises a fine netting or a knitted fabric of fibers. A very small pore size prevents any ingress of dirt particles into the membrane and consequently clogging. Nevertheless, dirt particles can be deposited on the surface of the membrane, but can be removed in a simple way. In the same way, liquids cannot pass the membrane up to a specific pressure per unit area. An example of a material used for the membrane is PTFE, also known by the name Teflon. The membrane is generally applied to a coarsely woven backing material, such as for example polyamide, in order to achieve high stability and resistance of the membrane filter MB. A special design of the membrane filter MB allows protective regulations in accordance with the IP guidelines up to, for example, IP55 to be satisfied, thereby permitting use of the technical appliance outside enclosed spaces or under adverse ambient conditions, such as occur for example in industrial production. Special selection of the membrane filter material additionally allows individual adaptation to the actual ambient conditions, such as for example resistance to acids. Known membrane filters MBR produced according to the prior art consist of materials described above which are permeable to electromagnetic waves. To satisfy EMC guidelines (EMC - Electromagnetic Compatibility), however, the housing G of the technical appliance must in the same way have an electromagnetic shielding in the region of the air inlet LE. This is generally achieved by a wire grating attached in front of the air inlet LE and electrically connected to the housing. According to the invention, on the other hand, the electromagnetic shielding is achieved by a special configuration of the membrane filter MB, whereby, for example, the maintenance and cleaning of the membrane filter MB is simplified. The possible configurations are presented below in Figures 3a and 3b. The cooling of the electrical modules BG by a direct flow of cooling air through the housing G has the advantage of a necessary temperature difference tending toward zero between the temperature of the ambient atmosphere or the temperature of the inflowing cooling air and the temperature inside the housing G, whereby the operation of the electrical modules BG is safeguarded even at a temperature of the ambient atmosphere of, for example, +7 0°C, which corresponds to the limiting temperature of the components, reduced by the degree of internal heating-up. A cooling device VE, which is arranged for example in the upper region of the rear housing wall, sucks in the air heated up as it flows through or around the electrical modules BG and discharges it to the ambient atmosphere through an air outlet LA. Used as cooling devices VE are, for example, one or more fans, which produce an air flow. Cooling by means of natural convection is not adequate for reliable operation of the modules BG below the limiting temperature if a strong heating-up of the modules BG occurs on account of a high internal lost power. To control the temperature inside the housing G, the speed of the fan is automatically controlled. To acquire parameters for this control, temperature sensors which permanently determine the temperatures of the inflowing cooling air and the atmosphere inside the housing G may be provided, for example in the region of the air inlet LE and at various points inside the housing G. In this automatic control, the throughput of the cooling air in the housing G is changed by means of the speed of the fan of the cooling device VE in order to obtain, for example, a constant temperature inside the housing G independently of the temperature of the ambient atmosphere. A constant operating temperature of the modules BG has positive effects, for example on the service life of the electronic components and the high-performance circuits. In addition, constantly keeping the speed of the cooling device VE low, on condition that the limiting temperature of the components is not exceeded, makes it possible to minimize the noise emission of the technical appliance. Furthermore, the automatic control makes it possible to dispense with the operation of the cooling device VE initially during cold starting of the appliance, to heat up the modules BG quickly to the desired operating temperature, and to carry out further automatic control of the cooling device VE only once this operating temperature has been reached, to maintain the operating temperature. During maintenance of the technical appliance, it is possible, for example by a reversal of the direction of rotation or a change in the blade setting of the fan impeller of the cooling devices VE, for the air flow in the housing G to be reversed, whereby cooling air flows into the housing through the air outlet LA and is led out through the membrane filter MB. As this happens, dirt particles deposited on the surface of the membrane filter MB are dislodged, and consequently a cleaning of the membrane filter MB is achieved. This cleaning operation may also be initiated, for example, by a permanent measuring process of the air throughput in dependence on the speed of the cooling arrangement VE, when it falls below a fixed value, the measured ratio indicating the degree of soiling of the membrane filter MB. In this case, a membrane filter MB is advantageously likewise arranged in the air outlet LA, so that no dirt particles or liquid can get into the housing G even when the air flow is reversed. Arranging the modules BG in such a way that they are spaced apart from one another makes it possible for a flow to take place through and/or around the modules BG. According to a known type of design, the modules BG comprise, for example, a module frame with electronic components and high-performance circuits located therein. The module frames are provided with ventilation slits, through which cooling air can reach the components and circuits. Within the scope of the invention, modules BG are understood as also meaning all the electrical devices of a technical appliance. These are to include, for example, printed-circuit boards provided in a personal computer and also peripheral units, such as for example hard disks. The arrangement of figure 2 has in the spaces between the individual modules BG and also below the lowermost and above the uppermost module BG air-directing devices, which have the task of distributing cooling air flowing in through the membrane filter MB evenly over the base area of the respective module BG, so that a homogeneous flow through the entire module BG occurs. Furthermore, the air-directing devices may be used for the mutual electromagnetic shielding of the modules BG with regard to satisfying the EMC regulations. Figure 3a and figure 3b each show a membrane filter MB according to the invention in a sectional representation. A prior-art membrane filter MB comprises a coarsely woven and stable backing material TM with a membrane MBR of a fine knitted fabric or filament applied thereto. According to the invention, as shown in figure 3a, a netting GT of an electrically conductive material is incorporated into the backing material TM. This conductive material may, for example, be woven in directly during the production of the backing material TM, and, in a way corresponding to figure 1 and figure 4, produce for example a lattice- shaped structure referred to as Ripstock. The advantage of weaving-in is to be seen in the fact that the still very fine-pored surface prevents particles from becoming lodged on the netting and consequently clogging the membrane filter MB. A metal, plastic or ceramic is used as the electrically conductive material, it also being possible to take into consideration the use of all materials exhibiting the desired properties in the future. The electrically conductive netting GT is connected to frame or grounded. This may take place by a connection of the netting GT to the housing, provided that the latter likewise consists at least partially of an electrically conductive material. According to figure 3b, the electrically conductive netting GT is applied to the carrier material TM and physically connected to it. Further variants according to the invention of the construction of the membrane filter MB, according to which the backing material TM or the membrane MBR itself consists of an electrically conductive material, are not represented in the figures. In these latter configurations, it is possible to dispense with an additional electrically conductive netting, thereby- further simplifying the construction and production of the membrane filter MB. In figure 4, the membrane filter MB, arranged in a frame R, is shown with an electrically conductive netting GT. In an enlargement of a detail at the bottom, the structure of the membrane filter MB is presented in a plan view. The membrane MBR, comprising a knitted fabric of individual thin filaments and permitting a very small pore size, can be seen clearly. Arranged over the membrane MBR is the netting GT of electrically conductive material, with a relatively great distance between the individual members of the netting GT. The dimensioning of the netting takes place, for example, in such a way that on the one hand a smallest possible surface of the membrane filter MB is sealed by the netting GT, on the other hand adequate electromagnetic shielding and stability of the membrane filter MB are achieved. The structure of the electrically conductive netting GT indicated in figure 1 and figure 4 is shown by way of example and can, within the scope of the invention, also take the form of any of a large number of known further structures. WE CLAIM 1. A device for cooling an electrical module (BG) arranged in a housing (G), comprising at least one membrane filter (MB) deposed in an air inlet (LE) of the housing (G) in each case, for superficial filtering of at least dirt particles from an inflowing air for cooling the electrical module (BG), and at least one cooling means (VE) for establishing said inflowing air in the housing (G) and for discharging said filtered cooling air, the filtered cooling air having heated up on account of flowing through and/or around the module (BG), out of at least one air outlet (LA) of the housing (G), characterized in that the atleast one membrane filter (MB) is configured in the form of a fine-pored membrane (MBR) of an electrically conductive material for an electromagnetic shielding of the electrical module (BG), applied to a backing material (TM). 2. A device for cooling an electrical module (BG) arranged in a housing (G)/ comprising at least one membrane filter (MB), disposed in an air inlet (LE) of the housing (G) in each case, for superficial filtering of at least dirt particles from an inflowing air for cooling the electrical module (BG), and at least one cooling means (VE) for establishing said air inflowing in the housing (G) and for discharging said filtered cooling air, the filtered cooling air having heated up on account of flowing through and/or around the module (BG), out of at least one air outlet (LA) of the housing (G), characterized in that the atleast one membrane filter (MB) is configured in the form of a fine-pored membrane (MBR) applied to a backing material (TM), and in that a netting (GT) of an electrically conductive material being woven into the backing material (TM) of the membrane filter (MB) for an electromagnetic shielding of the electrical module (BG). 3. The device as claimed in claim 1 or 2, wherein the atleast one membrane filter (MB) additionally separates out liquids at the surface. 4. The device as claimed in claim 2, wherein the electrically conductive netting (GT) is provided in the form of a backing material (TM) for the atleast one membrane (MBR). 5. The device as claimed in one of claims 2 to 4, wherein the atteast one membrane (MBR) is made from a PTFE material. 6. The device as claimed in a preceding claim, wherein a metal, plastic or ceramic material is used as the electrically conductive material. 7. The device as claimed in a preceding claim, wherein the electrically conductive netting (GT) is electrically connected to the housing (G), and wherein the housing being made at least partially from an electrically conductive material. 8. The device as claimed in a preceding claim, wherein the effective surface area of the atleast one membrane filter (MB) is enlarged by a periodic folding. 9. The device as claimed in a preceding claim, wherein an additional membrane filter (MB) with an electrically conductive netting (GT) is disposed at the air outlet (LA). 10. The device as claimed in the preceding claim, wherein the cooling device (VE) is a fan impeller driven by a motor. 11. A technical appliance in particular, a base station (BTS) of a mobile radio system and/or a wireless subscriber line system comprising a device as claimed in any of claims 1 to 10. The invention relates to a device for cooling an electrical module (BG) arranged in a housing (G), comprising at least one membrane filter (MB) disposed in an air inlet (LE) of the hous- ing (B) in each case, for superficial filtering of at least dirt particles from an inflowing air for cooling the electrical module (BG), and at least one cooling means (VE) for establishing said inflowing air in the housing (G) and for discharging said filtered cooling air, the filtered cooling air having heated up on account of flowing through and/or around the module (BG), out of at least one air outlet (LA) of the housing (G). Atleast one membrane filter (MB) is configured in the form of a fine-pored membrane (MBR) of an electrically conductive material for an electromagnetic shielding of the electrical module (BG), applied to a backing material (TM).

Full Text

Description
The invention relates to an arrangement for cooling an
electrical module arranged in a housing and to a
technical appliance, in particular a base stations of a
mobile radio system or wireless subscriber line system.
In an electrically operated technical appliance, the
lost power of components and modules through which
current flows leads to a heating-up of the appliance.
Since standard electrical components for technical
appliances have only a limited admissible operating
temperature range, of for example up to 70°C, they are
cooled by cooling devices. These cooling devices are,
for example, fans which establish an air flow in the
housing, flowing around or through the electrical
components and modules, and consequently bring about a
discharge of the thermal output produced.
During operation of the technical appliances outside
enclosed spaces or in adverse conditions within
enclosed spaces, adequate protection from environmental
influences, such as for example dirt particles and
liquids, must be additionally provided along with heat
discharge. In this respect, protective regulations in
accordance with the specified IP classes must be
observed in order to ensure long-term functioning of
the technical appliances.
It is known from DE 19755944 to provide in an air inlet
of a housing a membrane filter for a superficial
filtering of dirt particles from inflowing cooling air
and for separating out liquids. In comparison with a
housing known for example from DE 19626778, with

an air/air heat exchanger, which ensures complete
separation of an internal cooling circuit from an
external cooling circuit, adequate protection of the
electrical components can be achieved for the
aforementioned areas of use of the technical appliance
with the corresponding protective regulations in a
simple way by use of the membrane filter. At the same
time, a temperature difference, required for the
cooling, between the temperature of the ambient
atmosphere and the temperature inside the housing is
reduced.
A membrane filter of this type is based, for example,
on a membrane filter known for use in articles of
clothing by the designation Goretex, Sympatex, etc.
The membrane of the filter comprises a fine netting or
knitted fabric of fibers, which permits a very small
pore size. An example of a material which may be used
for this is PTFE (polytetrafluoroethylene) , also known
by the name Teflon. The membrane is generally provided
on a backing material, such as for example polyamide,
in order to achieve a certain stability and resistance
of the membrane filter.
In addition to the criteria with regard to protective
regulations, EMC guidelines (EMC - Electromagnetic
Compatibility) must also be satisfied, ensuring on the
one hand protection of the electrical modules arranged
in the housing of the technical appliance from
electromagnetic influences from the surroundings of the
appliance and on the other hand protection of the
surroundings from electromagnetic radiation emanating
from the electrical modules.
On account of the plastic material used, the membrane
filter is permeable to electromagnetic radiation and

consequently does not bring about adequate shielding.
Additional shielding, for example by a wire netting
arranged in front of the membrane filter, is therefore
necessary to satisfy the EMC guidelines. However, it
is disadvantageous to provide this additional wire
netting as a further element of the housing of the
technical appliance and, for example, it increases the
overall dimensions of the housing. Furthermore, it
makes maintenance and cleaning of the membrane filter
more difficult.
US 5,431,974 discloses a filter arrangement for
electromagnetic shielding. The filter arrangement in
this case comprises an electrically conductive frame
with at least one opening, a panel of porous
electrically conductive material, a layer of
electrically conductive adhesive and also an
electrically conductive gasket material. Preferably
chosen as the porous panel is from synthetic polymers
which has been made electrically conductive at the
surface by electrochemical processes.
The invention is based on the object of specifying an
arrangement for cooling and a technical appliance
which, with known use of a membrane filter, permits
adequate electromagnetic shielding without the
specified disadvantages of the prior art. This object
is achieved by the arrangement for cooling according to
patent claims 1 and 2 and also the technical appliance
according to patent claim 11. Advantageous
developments of the invention can be taken from the
dependent patent subclaims.
The arrangement according to the invention for cooling
an electrical module arranged in a housing has at least
one membrane filter, arranged in an air inlet of the

housing in each case, for a superficial filtering of at
least dirt particles from inflowing cooling air for
cooling the electrical module and also at least one
cooling device for establishing an air flow in the
housing and for discharging the filtered cooling air,
heated up on account of flowing through or around the
module, out of the housing from at least one air
outlet. The membrane filter is characterized by having
a netting of an electrically conductive material for
electromagnetically shielding the electrical module.
The configuration of the arrangement according to the
invention has the advantage that an integration of the
electrically conductive

netting achieves the effect of electromagnetic
shielding without an additional shielding arrangement
having to be provided. Furthermore, the advantageous
properties of the membrane filter are not restricted.
For example, simple cleaning of the filter without
prior detachment of a shielding grating is possible.
As a result, the housing of the technical appliance can
be provided in a very compact form.
The arrangement according to the invention can be used
in technical appliances with at least one electrical
module, such as for example base stations of a mobile
radio system or wireless subscriber line system (access
network systems), traffic control devices, power supply
devices or switch cabinets for a control system of
industrial machines. In the same way, the arrangement
according to the invention can be used, for example, in
smaller electrical appliances, such as for example a
portable or stationary home computer, or in electrical
measuring instruments.
According to a first configuration of the invention,
the membrane filter additionally separates out liquids
at the surface, whereby use of the technical appliance
is also possible outside enclosed spaces or under
adverse ambient conditions
According to a second configuration, the membrane
filter is provided in the form of a fine-pored membrane
applied to a backing material. This configuration of
the membrane filter advantageously permits individual
adaptability of the backing material and/or the
membrane to special conditions of use of the technical
appliance. For example, a filter resistant to chemical
substances, such as for example acids, can be used for
technical appliances used in production.

According to a third development, based on the second
configuration, the electrically conductive netting is
woven into the backing material of the membrane filter.
As a result, a firm bonding of the netting to the
backing material is advantageously achieved, one of the
effects being, for example, that the stability of the
membrane filter is increased.
As an alternative to the third configuration, the
electrically conductive netting is applied to the
backing material. This configuration advantageously
permits simple production of the membrane filter, the
electrically conductive netting being applied to the
membrane filter, for example, in an additional
production step. A bonding between the netting and the
backing material can be achieved, for example, by an
adhesive bonding technique.
According to a further alternative configuration, the
electrically conductive netting is provided in the form
of backing material for the membrane. By this
configuration, the electromagnetic shielding is
advantageously integrated directly into the membrane
filter, as a result of which there are no further
working steps in the production of the membrane filter.
According to further alternative configurations, the
membrane may be made from a PTFE material known as
Teflon or from an electrically conductive material.
The PTFE material is already widely used, for example
for water-impermeable items of clothing, and, on
account of the properties, can be flexibly adapted to a
wide variety of requirements with regard to the pore
size. If the membrane is produced from an electrically
conductive material that has for example the same or
comparable properties, it is advantageously possible to
dispense with the additional electrically conductive
netting.

According to a further configuration, the electrically
conductive material may be provided in the form of a
metal, plastic or ceramic material. Plastic and
ceramic materials in particular have advantageous
properties in comparison with known metal materials,
for example with regard to the resistance to
environmental influences, strength and processability.
According to a further configuration of the invention,
the electrically conductive netting is electrically
connected to the housing, the latter likewise being
made at least partially from an electrically conductive
material. Electrically conductive netting may be
understood here according to the invention as meaning
an additional netting, a netting used as a backing
material or a membrane of electrically conductive
material. The connection to the housing brings about a
grounding of the membrane filter, which may
alternatively also be achieved by means of a separate
grounded electrical connection.
According to a further configuration of the invention,
the effective surface area of the membrane filter is
enlarged by a periodic folding, as a result of which
clogging of the filter is advantageously reduced and
the maintenance intervals are increased.
Furthermore, a membrane filter according to the
invention is advantageously additionally arranged at
the air outlet of the housing. This configuration
permits, for example, a reversal of the cooling air
flow in the housing, in order to free the membrane
filter at the air inlet of dirt particles, without dirt
particles or liquids at the same time being able to
pass through the air outlet into the housing.

According to a further configuration, the cooling
device comprises a fan impeller driven by a motor. In
this case, the motor speed, and consequently the
throughput of the cooling air in the housing, for
example, can be controlled in dependence on the
temperature in the housing and/or on the temperature of
the ambient atmosphere, with the advantageous result
that a constant operating temperature of the electrical
module and a constant temperature inside the housing
are ensured, and consequently the service life of the
electrical module is advantageously prolonged.
Furthermore, the speed of the cooling device can be
controlled, for example, in such a way that the
admissible limiting temperatures of the electrical
module are not quite exceeded, and consequently the
noise emission of the arrangement is minimized by the
lowest possible speed of the cooling device.
The arrangement according to the invention is suitable
in particular for use in technical appliances, such as
for example base stations or similar outdoor
installations of a mobile radio system, or wireless
subscriber line system, and also in traffic control
devices, radio relay devices etc.
Exemplary embodiments of the invention are explained in
more detail with reference to the accompanying drawings, in
which:
figure 1 shows a base station of a mobile radio system
with the arrangement according to the
invention for cooling electrical modules, in
a front view,
figure 2 shows the arrangement according to the
invention in a side view,
figure 3 shows two ways in which the membrane filter

according to the invention can be provided,
by way of example, and

figure 4 shows a detailed representation of the
membrane filter according to the invention.
A prior-art technical appliance, such as for example a
base station BTS of a mobile radio system or wireless
subscriber line system, according to figure 1, includes
a plurality of electrical modules BG. During the
operation of the electrical appliance, the lost power
of the individual electrical modules BG results in a
heating-up effect, giving rise to the necessity for
cooling in order not to exceed an admissible operating
temperature of the modules.
The housing G, represented in a front view, of the
electrical appliance has on the end face an air inlet
LE with a membrane filter MB. The overall dimensions
of the air inlet LE are set, for example, in such a way
that cooling air flowing in through the membrane filter
MB from the ambient atmosphere of the technical
appliance can flow through the electrical modules BG in
each case from below, and if appropriate from the
front, and consequently can bring about a cooling-down
of the modules. The active surface area of the
membrane filter MB, which may be larger than the air
inlet LE, for example due to a fold formation, is
dimensioned such that the pressure drop of the
inflowing cooling air can be compensated by a cooling
-device, or an adequate amount of cooling air can still
flow in despite a partial clogging of the membrane
filter MB by dirt particles or liquid.
Figure 2 presents the described technical appliance in
a side view, in order to illustrate in more detail the
internal construction shown by way of example. On the
left-hand side of the housing G, a frame R with the
membrane filter MB is arranged in front of the air
inlet LE. The additional frame R permits rapid removal
of the membrane filter MB, for example for maintenance

and cleaning purposes or, for replacement. At the same
time,

the frame R permits the described folding of the
membrane filter MB. To restrict the overall dimensions
of the technical appliance, the frame R may also be
integrated into the housing G.
The membrane filter MB is designed in the form of a
surface filter, which has the special advantageous
property of separating out dirt particles and liquids
from the ambient atmosphere already at the surface of
the membrane, whereby, for example, sensitive
electronic components or circuits in the modules BG are
protected from environmental influences of this type.
A membrane filter MB of this type is based, for
example, on a membrane filter known by the designation
Goretex, Sympatex etc. for use in articles of clothing.
The membrane of the filter comprises a fine netting or
a knitted fabric of fibers. A very small pore size
prevents any ingress of dirt particles into the
membrane and consequently clogging. Nevertheless, dirt
particles can be deposited on the surface of the
membrane, but can be removed in a simple way. In the
same way, liquids cannot pass the membrane up to a
specific pressure per unit area.
An example of a material used for the membrane is PTFE,
also known by the name Teflon. The membrane is
generally applied to a coarsely woven backing material,
such as for example polyamide, in order to achieve high
stability and resistance of the membrane filter MB.
A special design of the membrane filter MB allows
protective regulations in accordance with the IP
guidelines up to, for example, IP55 to be satisfied,
thereby permitting use of the technical appliance
outside enclosed spaces or under adverse ambient
conditions, such as occur for example in industrial
production. Special selection of the membrane filter
material additionally allows

individual adaptation to the actual ambient conditions,
such as for example resistance to acids.
Known membrane filters MBR produced according to the
prior art consist of materials described above which
are permeable to electromagnetic waves. To satisfy EMC
guidelines (EMC - Electromagnetic Compatibility),
however, the housing G of the technical appliance must
in the same way have an electromagnetic shielding in
the region of the air inlet LE. This is generally
achieved by a wire grating attached in front of the air
inlet LE and electrically connected to the housing.
According to the invention, on the other hand, the
electromagnetic shielding is achieved by a special
configuration of the membrane filter MB, whereby, for
example, the maintenance and cleaning of the membrane
filter MB is simplified. The possible configurations
are presented below in Figures 3a and 3b.
The cooling of the electrical modules BG by a direct
flow of cooling air through the housing G has the
advantage of a necessary temperature difference tending
toward zero between the temperature of the ambient
atmosphere or the temperature of the inflowing cooling
air and the temperature inside the housing G, whereby
the operation of the electrical modules BG is
safeguarded even at a temperature of the ambient
atmosphere of, for example, +7 0°C, which corresponds to
the limiting temperature of the components, reduced by
the degree of internal heating-up.
A cooling device VE, which is arranged for example in
the upper region of the rear housing wall, sucks in the
air heated up as it flows through or around the
electrical modules BG and discharges it to the ambient
atmosphere through an air outlet LA. Used as cooling
devices VE are, for example, one or more fans, which

produce an air flow. Cooling by means of natural
convection is not adequate for reliable operation of
the modules BG below the limiting temperature if a
strong heating-up of the modules BG occurs on account
of a high internal lost power.
To control the temperature inside the housing G, the
speed of the fan is automatically controlled. To
acquire parameters for this control, temperature
sensors which permanently determine the temperatures of
the inflowing cooling air and the atmosphere inside the
housing G may be provided, for example in the region of
the air inlet LE and at various points inside the
housing G. In this automatic control, the throughput
of the cooling air in the housing G is changed by means
of the speed of the fan of the cooling device VE in
order to obtain, for example, a constant temperature
inside the housing G independently of the temperature
of the ambient atmosphere. A constant operating
temperature of the modules BG has positive effects, for
example on the service life of the electronic
components and the high-performance circuits. In
addition, constantly keeping the speed of the cooling
device VE low, on condition that the limiting
temperature of the components is not exceeded, makes it
possible to minimize the noise emission of the
technical appliance. Furthermore, the automatic
control makes it possible to dispense with the
operation of the cooling device VE initially during
cold starting of the appliance, to heat up the modules
BG quickly to the desired operating temperature, and to
carry out further automatic control of the cooling
device VE only once this operating temperature has been
reached, to maintain the operating temperature.
During maintenance of the technical appliance, it is
possible, for example by a reversal of the direction of
rotation or a change in the blade setting of the fan

impeller of the cooling devices VE, for the

air flow in the housing G to be reversed, whereby
cooling air flows into the housing through the air
outlet LA and is led out through the membrane filter
MB. As this happens, dirt particles deposited on the
surface of the membrane filter MB are dislodged, and
consequently a cleaning of the membrane filter MB is
achieved. This cleaning operation may also be
initiated, for example, by a permanent measuring
process of the air throughput in dependence on the
speed of the cooling arrangement VE, when it falls
below a fixed value, the measured ratio indicating the
degree of soiling of the membrane filter MB. In this
case, a membrane filter MB is advantageously likewise
arranged in the air outlet LA, so that no dirt
particles or liquid can get into the housing G even
when the air flow is reversed.
Arranging the modules BG in such a way that they are
spaced apart from one another makes it possible for a
flow to take place through and/or around the modules
BG. According to a known type of design, the modules
BG comprise, for example, a module frame with
electronic components and high-performance circuits
located therein. The module frames are provided with
ventilation slits, through which cooling air can reach
the components and circuits. Within the scope of the
invention, modules BG are understood as also meaning
all the electrical devices of a technical appliance.
These are to include, for example, printed-circuit
boards provided in a personal computer and also
peripheral units, such as for example hard disks.
The arrangement of figure 2 has in the spaces between
the individual modules BG and also below the lowermost
and above the uppermost module BG air-directing
devices, which have the task of distributing cooling
air flowing in through the membrane filter MB evenly
over the base area of the respective module BG, so that

a homogeneous

flow through the entire module BG occurs. Furthermore,
the air-directing devices may be used for the mutual
electromagnetic shielding of the modules BG with regard
to satisfying the EMC regulations.
Figure 3a and figure 3b each show a membrane filter MB
according to the invention in a sectional
representation. A prior-art membrane filter MB
comprises a coarsely woven and stable backing material
TM with a membrane MBR of a fine knitted fabric or
filament applied thereto. According to the invention,
as shown in figure 3a, a netting GT of an electrically
conductive material is incorporated into the backing
material TM. This conductive material may, for
example, be woven in directly during the production of
the backing material TM, and, in a way corresponding to
figure 1 and figure 4, produce for example a lattice-
shaped structure referred to as Ripstock. The
advantage of weaving-in is to be seen in the fact that
the still very fine-pored surface prevents particles
from becoming lodged on the netting and consequently
clogging the membrane filter MB. A metal, plastic or
ceramic is used as the electrically conductive
material, it also being possible to take into
consideration the use of all materials exhibiting the
desired properties in the future. The electrically
conductive netting GT is connected to frame or
grounded. This may take place by a connection of the
netting GT to the housing, provided that the latter
likewise consists at least partially of an electrically
conductive material.
According to figure 3b, the electrically conductive
netting GT is applied to the carrier material TM and
physically connected to it. Further variants according
to the invention of the construction of the membrane
filter MB, according to which the backing material TM
or the membrane MBR itself consists of an electrically

conductive material, are not represented in the
figures. In these

latter configurations, it is possible to dispense with
an additional electrically conductive netting, thereby-
further simplifying the construction and production of
the membrane filter MB.
In figure 4, the membrane filter MB, arranged in a
frame R, is shown with an electrically conductive
netting GT. In an enlargement of a detail at the
bottom, the structure of the membrane filter MB is
presented in a plan view. The membrane MBR, comprising
a knitted fabric of individual thin filaments and
permitting a very small pore size, can be seen clearly.
Arranged over the membrane MBR is the netting GT of
electrically conductive material, with a relatively
great distance between the individual members of the
netting GT. The dimensioning of the netting takes
place, for example, in such a way that on the one hand
a smallest possible surface of the membrane filter MB
is sealed by the netting GT, on the other hand adequate
electromagnetic shielding and stability of the membrane
filter MB are achieved. The structure of the
electrically conductive netting GT indicated in figure
1 and figure 4 is shown by way of example and can,
within the scope of the invention, also take the form
of any of a large number of known further structures.

WE CLAIM
1. A device for cooling an electrical module (BG) arranged in a housing (G),
comprising at least one membrane filter (MB) deposed in an air inlet (LE)
of the housing (G) in each case, for superficial filtering of at least dirt
particles from an inflowing air for cooling the electrical module (BG), and
at least one cooling means (VE) for establishing said inflowing air in the
housing (G) and for discharging said filtered cooling air, the filtered
cooling air having heated up on account of flowing through and/or around
the module (BG), out of at least one air outlet (LA) of the housing (G),
characterized in that the atleast one membrane filter (MB) is configured in
the form of a fine-pored membrane (MBR) of an electrically conductive
material for an electromagnetic shielding of the electrical module (BG),
applied to a backing material (TM).
2. A device for cooling an electrical module (BG) arranged in a housing (G)/
comprising at least one membrane filter (MB), disposed in an air inlet (LE)
of the housing (G) in each case, for superficial filtering of at least dirt
particles from an inflowing air for cooling the electrical module (BG), and
at least one cooling means (VE) for establishing said air inflowing in the
housing (G) and for discharging said filtered cooling air, the filtered
cooling air having heated up on account of flowing through and/or around
the module (BG), out of at least one air outlet (LA) of the housing (G),
characterized in that the atleast one membrane filter (MB) is configured in
the form of a fine-pored membrane (MBR) applied to a backing material
(TM), and in that a netting (GT) of an electrically conductive material
being woven into the backing material (TM) of the membrane filter (MB)
for an electromagnetic shielding of the electrical module (BG).
3. The device as claimed in claim 1 or 2, wherein the atleast one membrane
filter (MB) additionally separates out liquids at the surface.

4. The device as claimed in claim 2, wherein the electrically conductive
netting (GT) is provided in the form of a backing material (TM) for the
atleast one membrane (MBR).
5. The device as claimed in one of claims 2 to 4, wherein the atteast one
membrane (MBR) is made from a PTFE material.
6. The device as claimed in a preceding claim, wherein a metal, plastic or
ceramic material is used as the electrically conductive material.
7. The device as claimed in a preceding claim, wherein the electrically
conductive netting (GT) is electrically connected to the housing (G), and
wherein the housing being made at least partially from an electrically
conductive material.
8. The device as claimed in a preceding claim, wherein the effective surface
area of the atleast one membrane filter (MB) is enlarged by a periodic
folding.
9. The device as claimed in a preceding claim, wherein an additional
membrane filter (MB) with an electrically conductive netting (GT) is
disposed at the air outlet (LA).
10. The device as claimed in the preceding claim, wherein the cooling device
(VE) is a fan impeller driven by a motor.
11. A technical appliance in particular, a base station (BTS) of a mobile radio
system and/or a wireless subscriber line system comprising a device as
claimed in any of claims 1 to 10.
The invention relates to a device for cooling an electrical
module (BG) arranged in a housing (G), comprising at least one
membrane filter (MB) disposed in an air inlet (LE) of the hous-
ing (B) in each case, for superficial filtering of at least dirt
particles from an inflowing air for cooling the electrical module
(BG), and at least one cooling means (VE) for establishing said
inflowing air in the housing (G) and for discharging said
filtered cooling air, the filtered cooling air having heated up
on account of flowing through and/or around the module (BG), out
of at least one air outlet (LA) of the housing (G). Atleast one
membrane filter (MB) is configured in the form of a fine-pored
membrane (MBR) of an electrically conductive material for an
electromagnetic shielding of the electrical module (BG), applied
to a backing material (TM).

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Patent Number

225455

Indian Patent Application Number

IN/PCT/2001/01040/KOL

PG Journal Number

46/2008

Publication Date

14-Nov-2008

Grant Date

12-Nov-2008

Date of Filing

05-Oct-2001

Name of Patentee

SIEMENS AKTIENGESELLSCHAFT

Applicant Address

WITTELSBACHERPLATZ 2, D-80333 MUNICH

Inventors:

#	Inventor's Name	Inventor's Address
1	REECK, GUIDO	KLEISTRASSE 9A, D-85521 OTTOBRUNN
2	HOEFER, BRUNO	NEUFELDSTRASSE 11A, D-82140 OLCHING

PCT International Classification Number

H05K 9/00

PCT International Application Number

PCT/DE00/01077

PCT International Filing date

2000-04-07

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1	199 16 594.7	1999-04-13	Germany