WO2023001638A1

WO2023001638A1 - Filter monitoring system

Info

Publication number: WO2023001638A1
Application number: PCT/EP2022/069487
Authority: WO
Inventors: Arnaud LECLERC; Romain LIAUTARD; Joel HERNANDEZ; Pascal FERRAT
Original assignee: Sensirion Ag
Priority date: 2021-07-23
Filing date: 2022-07-12
Publication date: 2023-01-26
Also published as: DE202021103938U1

Abstract

The invention relates to a filter monitoring system (1) for monitoring the state of a filter (4) in a fluid channel (20), in particular an HVAC fluid channel, which is located in a vehicle, having a differential pressure sensor (10). The filter monitoring system (1) is designed to be arranged on the fluid channel (20) such that the differential pressure sensor (10) ascertains the pressure difference ∆P between the pressure (P1) of a channel fluid (2) flowing through the fluid channel (20) in a fluid channel (20) region (21) located downstream of the filter (4) and the pressure (P0) of a surrounding fluid (3) in a region (30) outside of the fluid channel (20).

Description

TITLE

FILTER MONITORING SYSTEM

TECHNICAL AREA

The present invention relates to a filter monitoring system for monitoring the condition of a filter in a fluid channel.

STATE OF THE ART

Filters are often essential for removing particles from fluids, including gases and liquids. Air filters, for example, are essential parts of HVAC (heating, ventilation, air conditioning) systems, while fuel filters are used in burners and engines, among other things.

Clogging of such a filter usually has undesirable consequences, such as increased energy consumption, overheating and/or other damage.

It is therefore desirable to detect the clogging of a filter at an early stage in order to initiate cleaning or replacement of the filter in good time.

Many systems for monitoring the condition of a filter are known in the prior art.

For example, US 7,594,960 B2 discloses a system for monitoring the condition of an air filter. The system includes a mechanical force measuring device located on the downstream side of the filter. The filter flexes in response to flow through the filter, thereby exerting a force on the force measuring device, the force increasing as the filter becomes clogged.

US 9,120,043 B2 discloses a filter life sensor within a air treatment system. The air handling system includes an airflow inlet, an airflow outlet, and a filter disposed between the airflow inlet and the airflow outlet. The filter sensor assembly includes a bypass connecting the airflow inlet to the airflow outlet and a dielectric vibration sensor adjacent the bypass. A stream of air flowing through the bypass causes the frequency and amplitude of the vibration to increase.

US 2006/0259273 A1 discloses a filter monitoring system that uses a differential pressure sensor to provide a continuous signal output proportional to a pressure drop across a filter element. A system that monitors a pressure drop across a filter is also disclosed in WO 2015/078672 A1.

In such monitoring systems, a first pressure port is upstream of the filter element and a second pressure port is downstream of the filter element. Particles can therefore penetrate through the first pressure connection into the differential pressure sensor and contaminate it, which can impair the function of the differential pressure sensor. The problem is particularly acute with dynamic differential pressure sensors, which measure differential pressure by monitoring fluid flow through a sensor channel. Dynamic differential pressure sensors quickly become inoperable when particles pass through the sensor channel. It may therefore be necessary to use static differential pressure sensors instead of dynamic differential pressure sensors. However, static differential pressure sensors capable of detecting sufficiently small pressure differences are relatively expensive.

PRESENTATION OF THE INVENTION

In a first aspect, it is an object of the present invention to specify a filter monitoring system that prevents contamination of the differential pressure sensor, enables simple system integration and does not hinder replacement and cleaning of the filter.

This object is achieved by a filter monitoring system according to claim 1. Further embodiments are specified in the dependent claims.

A filter monitoring system for monitoring the condition of a filter in a fluid duct, in particular an HVAC fluid duct, which is in a vehicle can be located, having a differential pressure sensor, the filter monitoring system being designed to be arranged on the fluid duct in such a way that the differential pressure sensor detects a pressure difference between a pressure of a duct fluid flowing through the fluid duct in an area of the fluid duct located downstream of the filter and a pressure of an ambient fluid determined in an area outside the fluid channel.

The fact that a pressure difference between the pressure of the channel fluid in an area of the fluid channel located downstream of the filter and the pressure of the ambient fluid in an area outside of the fluid channel is determined prevents particles from an area located upstream of the filter from entering the differential pressure sensor reach and contaminate it. The latter would be the case, for example, in an arrangement which would provide for a determination of a pressure difference between the pressure of the channel fluid in a region of the fluid channel located downstream of the filter and the pressure of the channel fluid in a region of the fluid channel located upstream of the filter. In addition, the proposed filter monitoring system enables a particularly simple arrangement on the fluid channel, since only a single access opening is required in a boundary wall of the fluid channel.

The differential pressure sensor preferably has a first pressure connection and a second pressure connection, the first pressure connection and the second pressure connection being located outside the fluid channel when the filter monitoring system is arranged as intended on the fluid channel. Furthermore, the filter monitoring system preferably comprises a housing which protrudes into an access opening in a boundary wall of the fluid channel. The housing preferably has a connecting channel which fluidically connects the first pressure connection to the region of the fluid channel located downstream of the filter. In addition, the housing preferably connects the second pressure connection fluidically to the environment, i.e. to the area outside the fluid channel in which the ambient fluid is located.

Ideally, the filter monitoring system has a protective filter which is arranged in such a way that the ambient fluid can only get through the protective filter from the area outside the fluid channel into the second pressure connection of the differential pressure sensor. Such a protective filter can prevent particles from the ambient fluid from getting into the differential pressure sensor. In contrast to the flow rate of the channel fluid through the filter in the fluid channel, the ambient fluid has a very low flow rate through the protective filter, as a result of which the dirt filter is only slightly and slowly soiled.

The differential pressure sensor is preferably a dynamic differential pressure sensor having a sensor channel extending between the first pressure port and the second pressure port, wherein the differential pressure sensor can be configured to determine the pressure differential between the first pressure port and the second pressure port by sensing fluid flow through measures the sensor channel, the sensor fluid flow being caused by the pressure difference between the pressure of the surrounding fluid and the pressure of the channel fluid.

The sensor channel has a cross-sectional area that is orders of magnitude smaller than the cross-sectional area of the fluid channel through which the channel fluid flows, e.g. by at least a factor T000 smaller. Accordingly, the flow rate through the sensor channel is orders of magnitude smaller than the flow rate through the fluid channel.

The filter monitoring system is preferably designed such that the first pressure connection of the differential pressure sensor extends perpendicularly to a longitudinal direction of the fluid channel or a flow direction of the channel fluid defined thereby, when the filter monitoring system is arranged as intended on the fluid channel. In particular, the housing of the filter monitoring system can be designed in such a way that it accommodates the differential pressure sensor in a corresponding orientation.

The differential pressure sensor is preferably designed in a design in which the second pressure connection extends parallel to the first pressure connection, with the first pressure connection and the second pressure connection both pointing in the direction of the fluid channel when the filter monitoring system is arranged on the fluid channel as intended. The housing of the filter monitoring system can accordingly be designed to accommodate a differential pressure sensor of this design. Such an arrangement of the pressure connections is widespread in differential pressure sensors. If the filter monitoring system provides for such an arrangement of the pressure connections (which e.g a corresponding design of the housing is required), commercially available differential pressure sensors can be used. As a result, the costs of the filter monitoring system can be further reduced.

The housing can have a sealing surface which is designed to rest on an outside of a boundary wall of the fluid channel. The housing can also have a connecting device, via which connecting device the housing can be connected to the boundary wall of the fluid channel. This connection device can in particular be a bayonet connection. The connecting device can have an anti-rotation pin, which is designed to engage in a recess on the outside of the boundary wall, as a result of which the filter monitoring system is prevented from accidental rotation.

The differential pressure sensor may be attached to a circuit board held within the housing of the filter monitoring system. The housing can in particular comprise a first housing part and a second housing part. The first housing part can be used to connect the differential pressure sensor to the fluid channel. For this purpose, the first housing part can protrude into the access opening in the boundary wall of the fluid channel and have the above-mentioned connecting channel, which fluidically connects the first pressure connection to the area of the fluid channel located downstream of the filter. In addition, the first housing part preferably connects the second pressure connection fluidically to the environment, i.e. to the area outside the fluid channel in which the ambient fluid is located. Furthermore, the first housing part can have the above-mentioned sealing surface and the connecting device, via which connecting device the first housing can be connected to the boundary wall of the fluid channel.

The second housing part, on the other hand, can serve to protect the printed circuit board. For this purpose, the second housing part can have a receptacle for the printed circuit board. The circuit board can be held in the receptacle by a holding device to prevent it from accidentally falling out. The second housing part, the printed circuit board with the differential pressure sensor and the first housing part can preferably be connected to one another in such a way that the first pressure connection of the differential pressure sensor is plugged into the connecting channel of the first housing part and that the second pressure connection is located opposite a housing opening in the first housing part , through which an exchange of the surrounding fluid can take place. Ideally, the housing opening in the first housing part is spanned by the protective filter, wherein the protective filter can optionally be clamped in the first housing part by a removable protective filter holder. The protective filter can optionally also be designed as a removable filter membrane, which makes cleaning or replacement easier.

The printed circuit board can have a plug connection on a side opposite the differential pressure sensor, with the second housing part surrounding this plug connection in such a way that a guide for a counterpart to the plug connection is thereby formed. A plug connection with 3 contact pins, for example, is particularly suitable for implementing a LIN interface. Connectors with 4 contact pins - e.g. for an I2C interface - are also conceivable.

The pressure difference determined by the differential pressure sensor depends on the one hand on the flow rate of the channel fluid through the filter and accordingly on the degree of clogging of the filter, but on the other hand the determined pressure difference is also dependent on the absolute pressure of the surrounding fluid.

Since the absolute pressure of the ambient fluid is often difficult or impossible to control, such as in the case of the absolute pressure of the ambient air in a vehicle, it is desirable to be able to determine this absolute pressure of the ambient fluid. The pressure difference determined by the differential pressure sensor can be compensated with regard to the absolute pressure of the surrounding fluid in such a way that a compensated parameter results which indicates the degree of clogging of the filter independently of the pressure of the surrounding fluid and thus enables a reliable and precise status signal to be output.

The filter monitoring system can therefore have an absolute pressure sensor for determining the absolute pressure of the surrounding fluid. This absolute pressure sensor is preferably arranged inside the housing, but can also be located outside the housing.

Instead of the absolute pressure sensor or in addition to the absolute pressure sensor, the filter monitoring system can have an interface for receiving GPS data from which the absolute pressure of the surrounding fluid can be determined. The filter monitoring system can also have an interface for receiving a signal from an engine control unit of the vehicle, it being possible to determine the absolute pressure of the ambient fluid from the signal.

A method for determining the state of a filter in a fluid duct, in particular an HVAC fluid duct in a vehicle, can therefore have the following steps:

In a first step, predefined parameters can be set, which lead to a known flow rate of the channel fluid. In particular in the case of an HVAC system in a vehicle, the predefined parameters can be, for example, default states of windows, HVAC flaps or an HVAC fan.

In a second step, the pressure difference can be determined using a filter monitoring system which has a differential pressure sensor, the filter monitoring system being designed to be arranged on the fluid duct in such a way that the differential pressure sensor detects a pressure difference between a pressure of a duct fluid flowing through the fluid duct in a downstream of the filter Located area of the fluid channel and a pressure of an ambient fluid determined in an area outside of the fluid channel.

In a third step, which preferably takes place at the same time as the second step, the absolute pressure of the ambient fluid can optionally be determined using an absolute pressure sensor, GPS data or a signal from an engine control unit.

In a fourth step, a parameter that is compensated with regard to the absolute pressure can optionally be determined from the pressure difference and from the absolute pressure. The filter monitoring system can have a signal processing device which is designed to calculate such a parameter.

This parameter can then optionally be compared with a reference value in a fifth step. This reference value can be stored in a table, for example, which is stored in the signal processing device, for example.

The method can also have a reference measurement step, in which a reference value for said predefined parameters is determined after inserting a new or freshly cleaned filter in the fluid channel.

In a sixth step, a status signal can optionally be output, which indicates to what extent the determined parameter deviates from the reference value and/or whether the filter should be replaced or cleaned. It is advantageous that the absolute pressure of the surrounding fluid is used in such a method only to compensate for atmospheric fluctuations and thus has to be determined with significantly less accuracy than if the absolute pressure of the surrounding fluid had to be measured explicitly to determine the pressure difference. In this way, simple and inexpensive absolute pressure sensors can be used to determine the absolute pressure of the ambient fluid in said method.

In a second aspect, it is an object of the present invention to provide an HVAC system in which the clogging state of a filter is easily monitored.

The HVAC system includes a fluid passage and a filter disposed in the fluid passage. The HVAC system also has a filter monitoring system of the type mentioned above, the filter monitoring system being attached to the fluid duct in such a way that the differential pressure sensor detects a pressure difference between a pressure of a duct fluid flowing through the fluid duct in an area of the fluid duct located downstream of the filter and a pressure of a Ambient fluids determined in an area outside of the fluid channel.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the invention are described below with reference to the drawings, which are for explanation only and are not to be interpreted as restrictive. In the drawings show:

Figure 1 shows, in a highly schematic manner, a prior art filter monitoring system;

Fig. 2 is a graph showing the dependency of the pressure drop across a filter on the flow rate for a new filter and for a clogged filter;

3 shows, in a highly schematic manner, a filter monitoring system according to a first embodiment of the present invention;

Fig. 4 is a detailed sectional view of the first embodiment of the present invention;

5 shows an embodiment of a differential pressure sensor in a perspective view; FIG. 6 shows the structure of the filter monitoring system of FIG. 4 in a perspective exploded view;

FIG. 7a is a first perspective view of the filter monitoring system of FIG. 4; FIG. 7b is a second perspective view of the filter monitoring system of FIG. 4; Fig. 7c is a perspective view of the second housing part of the

Filter monitoring system of Figure 4 including a printed circuit board to which a differential pressure sensor is attached;

8a in a highly schematic manner a filter monitoring system according to a second embodiment of the present invention;

8b in a highly schematic manner a filter monitoring system according to a third embodiment of the present invention;

8c in a highly schematic manner a filter monitoring system according to a fourth embodiment of the present invention;

9 is a flow chart illustrating a method according to an embodiment of the present invention.

DESCRIPTION OF PREFERRED EMBODIMENTS

State of the art filter monitoring system

Figure 1 shows, in a highly schematic manner, a prior art filter monitoring system. A filter 4 is arranged in a fluid channel 20 . The filter 4 is fastened in the fluid channel 20 in a fluid-tight manner, so that a channel fluid 2 flows through the filter 4 . The filter 4 spans the cross section of the fluid channel 20 in order to stop particles from the channel fluid 2 .

A differential pressure sensor 10 has a first pressure port 11 located downstream of the filter 4 and a second pressure port 12 located upstream of the filter 4. The first pressure port 11 is exposed to the static fluid pressure Pi downstream of the filter 4, while the second pressure port 12 is exposed to the static fluid pressure P2 upstream of the filter 4 is exposed. The differential pressure sensor 10 measures the pressure drop ÄP=P2-Pi across the filter 4.

The pressure drop DR depends on the flow rate Q of the channel fluid 2 through the fluid channel 20, but at a given flow rate Q also on the degree of contamination of the filter 4, as shown schematically in FIG. A cleaner filter 4 results in a lower one Pressure drop DR as a dirty filter 4. The degree of contamination of the filter 4 can thus be monitored by measuring the pressure drop DR. In particular, for a given flow rate Q, a difference d can be formed between the pressure drop across the (potentially) clogged filter DR _n and a reference measurement of the pressure drop across a clean filter DR _d , ie d = DR _n - DR _d , and a warning signal can be triggered , this difference d should exceed a specified threshold.

Filter monitoring system according to a first embodiment

Figure 3 shows a filter monitoring system 1 according to a first embodiment of the present invention in a highly schematic manner. Instead of the fluid pressure P2 upstream of the filter 4, the second pressure connection 12 of the differential pressure sensor 10 is exposed to a pressure Po of an ambient fluid 3 in a region 30 outside of the fluid channel 20 . Since the first pressure connection 11 is exposed to the pressure Pi downstream of the filter 4, the differential pressure sensor 10 now determines the pressure difference DR=Ro-Ri. The attachment of such a filter monitoring system 1 to a fluid channel 20 is simplified in contrast to the arrangement in FIG.

FIG. 4 illustrates the first embodiment of the present invention in a sectional view. It should be noted that the dimensions of the fluid channel 20 and the filter 4 are not drawn to scale compared to the dimensions of the filter monitoring system 1 in FIG. In particular, the fluid duct can be an HVAC duct in a vehicle, which typically has a cross-section in the range of, for example, 400 to 800 cm ² . The filter monitoring system 1 comprises a housing, the housing having a first housing part 40 and a second housing part 50 . The housing shown in FIG. 4 preferably has an extent of less than 5 cm in all spatial directions. When the filter monitoring system 1 is arranged as intended (i.e. as shown here) on the fluid duct 20, the first housing part 40 protrudes into an access opening 22 in a boundary wall 24 of the fluid duct 20, with the first housing part 40 having a sealing surface 42 which is on the outside of the Fluid channel 20 rests. The first housing part 40 also has a connecting device 43 , in particular a bayonet connection as shown here, via which the first housing part 40 is connected to the fluid channel 20 . An anti-rotation pin 44 engages in a recess 23 on the outside of the fluid channel 20, thereby preventing the filter monitoring system from accidental twisting. The differential pressure sensor 10 is attached to a printed circuit board 60 which is surrounded by the second 50 housing part. The second housing part 50, the printed circuit board 60 with the differential pressure sensor 10 and the first housing part 40 are connected to one another in such a way that the first pressure connection 11 of the differential pressure sensor 10 is inserted in a plug-like manner into a connecting channel 41 of the first housing part 40, with the connecting channel 41 connecting the first pressure connection 11 of the differential pressure sensor 10 fluidically connects to a region 21 of the fluid channel 20 located downstream of the filter. A sealing ring 55 extending around the first pressure connection 11 ensures a tight insertion of the first pressure connection 11 into the connecting channel 41. The printed circuit board 60 has a plug connection 61 (here a LIN plug) on a side opposite the differential pressure sensor 10 . The second housing part 50 surrounds this plug connection 61 in such a way that a guide 54 for a counterpart to the plug connection 61 is formed. The connecting channel 41 and the first pressure connection 11 are arranged perpendicularly to a longitudinal direction of the fluid channel 20 or a flow direction of the channel fluid 2 defined thereby (see arrow in Figure 4) when the filter monitoring system is arranged on the fluid channel 20 as intended here. The second pressure port 12 runs parallel to the first pressure port 11 and, like the first pressure port, points in the direction of the fluid channel. The second pressure connection is also opposite a housing opening 46 in the first housing part 40 . A protective filter 52 spans this housing opening 46 in the first housing part 40, the protective filter 52 being clamped here by a removable protective filter holder 53 in the first housing part. In this case, the ambient fluid 3 passes through the protective filter 52 from an area 30 located outside the fluid channel 20 into the second pressure connection 12.

In the preferred embodiment illustrated here, the differential pressure sensor 10 is a dynamic differential pressure sensor having a sensor channel 13 that extends between the first pressure port 11 and the second pressure port 12, the differential pressure sensor 10 being configured such that a pressure difference DR between the first pressure port 11 and the second pressure port 12 by measuring a sensor fluid flow 14 through the sensor channel 13 . The sensor fluid flow 14 is caused by the differential pressure between the pressure Po of the surrounding fluid 3 and the pressure Pi of the channel fluid 2 . If the pressure Pi is lower than the pressure Po, which is generally the case as long as the duct fluid 2 is sucked in by a fan arranged downstream of the filter, the sensor fluid flow 14 has the values indicated by the dashed arrow in Figure 4 specified direction.

FIG. 5 shows an embodiment of the differential pressure sensor 10 in a perspective view. This embodiment corresponds to the embodiment of the differential pressure sensor 10, which can be seen in Figure 4 as part of the filter monitoring system 1 in the sectional view. The differential pressure sensor 10 has a sensor housing 15 in which the sensor channel 13 is formed. A microthermal sensor element is arranged in the sensor channel 13 . The microthermal sensor element includes a heating element, a first temperature sensor upstream of the heating element, and a second temperature sensor downstream of the heating element with respect to sensor fluid flow. To determine the sensor fluid flow through the sensor channel 13, the heating element is heated and the temperature difference between the first and second temperature sensors is determined. For a given heating power, the temperature difference in the steady state is an indicator of the sensor fluid flow through the sensor channel. Since the sensor fluid flow depends on the pressure difference between the first pressure port 11 and the second pressure port 12, the temperature difference between the first and the second temperature sensor is also an indicator of the pressure difference between these pressure ports 11,12. A control circuit is provided for supplying the heating element with current and for processing the temperature signals from the temperature sensors. The control circuit can be integrated together with the heating element and the temperature sensors on a common substrate, e.g. B. based on CMOS technology. Reference is made to EP1426740A2 for a possible structure and the mode of operation of the microthermal sensor element. The two pressure connections 11, 12 are aligned parallel to one another and extend away from the housing 15 in the same direction. A differential pressure sensor of this design is described in more detail in publication EP 3032227B1, the disclosure of which is incorporated herein by reference in its entirety. The second pressure connection 12 can, for example, also be replaced by a simple opening in the housing 15 of the differential pressure sensor. For the embodiment of the filter monitoring system of FIG. 4 it is sufficient that the differential pressure sensor has a single plug-type pressure connection.

FIG. 6 shows the structure of the filter monitoring system according to the preferred embodiment shown in FIG. 4 in a perspective exploded view. As can be seen particularly well in this exploded view, the protective filter 52 and the protective filter holder 53 are both removable in this preferred embodiment. Also clearly visible are on the outside of the first housing part 40 Locking tabs 45 which are adapted to each extend around a knob 56 mounted on an outside of the second housing part 50 when the first housing part 40 and the second housing part 50 are plugged into one another to form a snap connection.

FIGS. 7a and 7b are perspective views of the filter monitoring system 1, in which case the first housing part 40 and the second housing part 50 are plugged into one another. In the view selected in FIG. 7a, the sealing surface 42, the bayonet connection 43 and the anti-rotation pin 44 can be clearly seen. It can be seen in FIG. 7b that the second housing part forms a guide 54 for the counterpart to the plug connection 61.

FIG. 7c shows a perspective view of the second housing part 50. The second housing part has a receptacle for the printed circuit board 60. The circuit board 60 to which the differential pressure sensor 10 is attached is held by a holding device 51 in the receptacle.

Filter monitoring system according to further embodiments

FIGS. 8a to 8c show further embodiments of a filter monitoring system 1 according to the present invention, the absolute pressure Po of the surrounding fluid 3 also being determined in addition to the pressure difference DR. The filter monitoring system 1 also has a signal processing device 100, which is designed to compensate the pressure difference DR determined by the differential pressure sensor 10 with regard to the absolute pressure Po in such a way that a compensated (i.e. independent of the absolute pressure Po of the ambient fluid) parameter results.

In the second embodiment shown schematically in FIG. 8a, the filter monitoring system 1 has an absolute pressure sensor 70 for determining the absolute pressure Po of the surrounding fluid 3. This is preferably arranged inside the housing.

In the third embodiment shown schematically in FIG. 8b, the filter monitoring system 1 has an interface 101 for receiving GPS data from a GPS receiver 80, from which the absolute pressure Po of the ambient fluid 3 can be determined. In the fourth embodiment shown schematically in FIG. 8c, the filter monitoring system 1 has an interface 102 for receiving a signal from an engine control unit 90 of the vehicle, the absolute pressure Po of the ambient fluid 3 being able to be determined from the signal.

Use of the filter monitoring system

FIG. 9 shows a method for determining the condition of a filter in a fluid duct, in particular an HVAC fluid duct in a vehicle, which is based on the use of the filter monitoring system according to the second, third or fourth embodiment of the present invention. In a first step 201, predefined parameters are set, which lead to a known flow rate Q of the channel fluid. In particular in the case of an HVAC system in a vehicle, the predefined parameters can be, for example, default states of windows, HVAC flaps or an HVAC fan. In a second step 202, the pressure difference DR is determined using the differential pressure sensor in the filter monitoring system. In a third step 203, which ideally takes place at the same time as the second step 202, the absolute pressure Po of the ambient fluid is determined using an absolute pressure sensor, GPS data or a signal from an engine control unit. In a fourth step 204, a parameter compensated with regard to the absolute pressure Po is determined from the pressure difference DR and the absolute pressure Po. In a fifth step 205, this parameter is then compared with a reference value which was determined for the said predefined parameters when the filter 4 was new or freshly cleaned. This reference value can be taken from a table, for example, which can be stored in the signal processing device 100 . In a sixth step 206, a status signal is output which indicates to what extent the normalized parameter determined deviates from the reference value and/or whether the filter should be replaced or cleaned.

Filter Monitoring System Sizing Considerations

For a HVAC fluid duct in a vehicle, the differential pressure DR at a duct fluid (air in this case) flow rate of Q=300 m ³ /h with a new filter is DR=50-100 Pa, while with a clogged filter there is typically a pressure differential of DR=200-300 Pa occurs. Ideally, the differential pressure sensor is able to measure pressure differences in a measuring range of 10-300 Pa with an accuracy of 10-20 Pa to determine. In order to achieve such accuracy in this low measuring range, dynamic differential pressure sensors based on microthermal sensor elements are particularly suitable. Reference is made to EP1426740A2 for a possible structure and the mode of operation of a microthermal sensor element. Differential pressure sensors that have such microthermal sensor elements are disclosed in EP 3032227 B1.

LIST OF REFERENCE NUMBERS Filter monitoring system 44 Anti-rotation pin Channel fluid 45 Closing tabs Ambient fluid 46 Housing opening filter 50 Second housing part differential pressure sensor 52 Protective filter first pressure connection 53 Protective filter holder second pressure connection 54 Guide sensor channel 55 Sealing ring sensor fluid flow 56 Nubs sensor housing 60 Circuit board fluid channel 61 Connector connection area of the fluid channel 70 Absolute pressure sensor downstream of the filter 80 GPS receiver access opening 90 engine control unit recess 100 signal processing boundary wall device area outside the 101 interface

Fluid channel 102 interface first housing part Po pressure of the surrounding fluid connecting channel Pi pressure of the channel fluid sealing surface DR pressure difference connecting device

Claims

PATENT CLAIMS

1. Filter monitoring system (1) for monitoring the condition of a filter (4) in a fluid duct (20), in particular an HVAC fluid duct, having a differential pressure sensor (10), characterized in that the filter monitoring system (1) is designed to fluid channel (20) so that the differential pressure sensor (10) detects a pressure difference DR between a pressure (Pi) of a channel fluid (2) flowing through the fluid channel (20) in a region (21) of the fluid channel located downstream of the filter (4). (20) and a pressure (Po) of an ambient fluid (3) in a region (30) outside of the fluid channel (20).

2. Filter monitoring system according to claim 1, wherein the differential pressure sensor (10) has a first pressure connection (11) and a second pressure connection (12), the first pressure connection (11) and the second pressure connection (12) being outside the fluid channel (20). , when the filter monitoring system (1) is arranged as intended on the fluid duct (20), the filter monitoring system (1) comprising a housing which protrudes into an access opening (22) in a boundary wall (24) of the fluid duct (20), the housing having a has a connecting channel (41), which fluidly connects the first pressure port (11) to the area (21) of the fluid channel (20) located downstream of the filter (4), and wherein the housing connects the second pressure port (12) to the area (30 ) outside of the fluid channel (20) fluidically connects.

3. Filter monitoring system according to claim 2, wherein the filter monitoring system (1) has a protective filter (52) which is arranged in such a way that the ambient fluid (3) can only flow through the protective filter (52) from the area outside the fluid channel (20). (30) reaches the second pressure connection (12) of the differential pressure sensor (10).

4. Filter monitoring system according to one of claims 2 or 3, wherein the differential pressure sensor (10) is a dynamic differential pressure sensor with a sensor channel (13) between the first pressure port (11) and the second pressure port (12), wherein the differential pressure sensor (10) is configured so that it determines the pressure difference DR between the first pressure port (11) and the second pressure port (12) by a sensor fluid flow (14) through the sensor channel (13) measures, the sensor fluid flow (14) being caused by the pressure difference DR between the pressure (Po) of the surrounding fluid (3) and the pressure (Pi) of the channel fluid (2).

5. Filter monitoring system according to any one of claims 2-4, wherein the

Filter monitoring system (1) is designed in such a way that the first pressure connection (11) of the differential pressure sensor (10) extends perpendicularly to a longitudinal direction of the fluid duct (20) or a flow direction of the duct fluid (3) defined thereby, if the filter monitoring system (1) is used as intended is arranged on the fluid channel (20), and in particular the housing of the filter monitoring system (1) is designed in such a way that it accommodates the differential pressure sensor in a corresponding orientation.

6. Filter monitoring system according to any one of claims 2-5, wherein the

Differential pressure sensor (10) is designed in a design in which the second pressure connection (12) extends parallel to the first pressure connection (11), the first pressure connection (11) and the second pressure connection (12) both in the direction of the fluid channel (20) if the filter monitoring system (1) is arranged as intended on the fluid channel (20), and the housing of the filter monitoring system (1) is designed to accommodate a differential pressure sensor (10) designed in this design.

7. Filter monitoring system according to one of claims 2-6, wherein the housing has a sealing surface (42) which is designed to rest on an outside of a boundary wall (24) of the fluid channel (20), the housing having a connecting device (43), in particular a bayonet connection, via which connection device (43) the housing can be connected to the boundary wall (24) of the fluid channel (20), and wherein the connection device (43) optionally has an anti-rotation pin (44) which is designed to Recess (23) engage on the outside of the boundary wall (24).

8. Filter monitoring system according to one of claims 2-7, wherein the differential pressure sensor (10) is attached to a printed circuit board (60), the housing of the filter monitoring system (1) comprising a first housing part (40) and a second housing part (50), wherein the first housing part (40) has the connecting channel (41), which fluidly connects the first pressure connection (11) to the area (21) of the fluid channel (20) located downstream of the filter (4), the first housing part (40) second pressure connection (12) with the area (30) outside the fluid channel (20) fluidly, wherein the second housing part (50) has a receptacle for the printed circuit board (60), wherein the printed circuit board (60) is optionally supported by a holding device (51) is held in the receptacle, and wherein the second housing part (50), the printed circuit board (60) with the differential pressure sensor (10) and the first housing part (40) can be connected to one another in such a way that the first pressure port s (11) of the differential pressure sensor (10) in the connecting channel (41) of the first housing part (40) and that the second pressure connection (12) is located opposite a housing opening (46) in the first housing part (40), through which an exchange of the surrounding fluid (3) takes place.

9. Filter monitoring system according to claim 8 in combination with claim 3, wherein the housing opening (46) in the first housing part (40) is spanned by the protective filter (52), the protective filter (52) optionally being supported by a removable protective filter holder (53) in the first housing part (40) is stuck.

10. Filter monitoring system according to claim 8 or 9, wherein the printed circuit board (60) has a plug connection (61), in particular a LIN-compatible plug connection, on a side opposite the differential pressure sensor (10), and the second housing part (50) has this plug connection ( 61) so that a guide (54) for a counterpart to the plug connector (61) is formed.

11. Filter monitoring system according to one of the preceding claims, wherein the filter monitoring system (1) has an absolute pressure sensor (70) for determining the absolute pressure Po of the ambient fluid (3).

12. Filter monitoring system according to claim 11, wherein the absolute pressure sensor (70) is arranged within the housing.

13. Filter monitoring system according to one of the preceding claims, wherein the filter monitoring system (1) has an interface (101) for receiving GPS data from which the absolute pressure Po of the ambient fluid (3) can be determined.

14. Filter monitoring system according to one of the preceding claims, wherein the filter monitoring system (1) has an interface (102) for receiving a signal from an engine control unit (90) of the vehicle, wherein the absolute pressure Po of the ambient fluid (3) can be determined from the signal.

15. HVAC system, comprising: a fluid passage (20); a filter (4), which is arranged in the fluid channel (20), and a filter monitoring system (1) with a differential pressure sensor (10) according to any one of the preceding claims, wherein the filter monitoring system (1) is attached to the fluid channel (20) in such a way that the differential pressure sensor (10) detects a pressure difference DR between a pressure (Pi) of a channel fluid (2) flowing through the fluid channel (20) in a region (21) of the fluid channel (20) located downstream of the filter (4) and a pressure (Po) of an ambient fluid (3) in a region (30) outside of the fluid channel (20).

16. A method for determining the state of a filter (4) in a fluid duct (20), in particular an HVAC fluid duct in a vehicle, the method comprising:

(201) setting predefined parameters which lead to a known flow rate Q of a channel fluid (2) flowing through the fluid channel (20);

(202) Determining a pressure difference DR using a differential pressure sensor (10) of a filter monitoring system (1) according to one of the preceding claims, wherein the filter monitoring system (1) is attached to the fluid duct (20) in such a way that the differential pressure sensor (10) measures the pressure difference DR between a Pressure (Pi) of the channel fluid (2) flowing through the fluid channel (20) in an area (21) of the fluid channel (20) located downstream of the filter (4) and an absolute pressure (Po) of an ambient fluid (3) in an area ( 30) determined outside the fluid channel (20);

(203) determining the absolute pressure Po of an ambient fluid (3) in a region (30) outside the fluid channel (20);

(204) Determination of a parameter compensated with regard to the absolute pressure Po from the pressure difference DR and the absolute pressure Po;

(205) comparing the parameter with a reference value;

(206) Outputting a status signal, the status signal indicating the extent to which the determined parameter deviates from the reference value and/or whether the filter (4) should be replaced or cleaned.