Pressure sensor for measuring the pressure of a measuring medium

Abstract

The invention relates to a pressure sensor (1) for detecting the pressure of a measuring medium, in particular for detecting a pressure in a hydrogen-operated system, comprising a sensor housing (10) with a closed housing interior (9) and a pressure sensor element (7), wherein a circuit substrate (8) electrically connected to the pressure sensor element (7) is arranged in the housing interior (9). It is proposed to arrange a separate heating element (12) in the sensor housing (10), wherein the heating element (12) is suitable and designed to heat the circuit substrate (8) locally and is in particular designed to heat the circuit substrate (8) to a temperature above -40°C when the ambient temperature of the pressure sensor (1) is less than -40°C.

Description

Prior ArtVarious types of pressure sensors for detecting the pressure of a measurement medium are known in the prior art.For example, EP 1 518 099 B1 describes a pressure sensor which has a two-part sensor housing made of a hexagon serving as a housing base part and a housing cover part placed thereon with an electrical connection integrated in the housing cover part. The hexagon forms a metallic base plate which is provided with a central aperture. A metallic pressure connector provided with a feed channel, the outer jacket of which may be provided with a screw thread, is welded onto the base plate. The supply duct is introduced into the pressure connector, for example, as a through bore. A metallic pressure measuring cell with a blind hole-like inner recess is welded onto the pressure connector as the actual pressure sensor element. The small hole-like inner recess continues the supply channel and ends at a thin movable membrane of the pressure measuring cell. The side of the pressure measuring cell facing away from the inner recess is provided with a sensor circuit which detects a bending of the membrane resulting from a pressurization of the feed channel, so that the pressure of a measuring medium can be detected. The two-part sensor housing encloses a closed housing interior, into which the pressure measuring cell with the sensor circuit is inserted through the central opening of the hexagon. The sensor circuit can be bonded to a circuit substrate in the housing interior, which is bonded to the side of the hexagon facing the housing interior. The circuit substrate is contacted with connector pins of the housing cover part via electrically conductive spring elements.Such pressure sensors are used, for example, as high-pressure sensors in various motor vehicles in direct diesel or gasoline injection systems.Disclosure of the InventionThe invention proposes a pressure sensor for detecting the pressure of a measurement medium, in particular for detecting a pressure in a system operated with hydrogen, comprising a sensor housing having a closed housing interior and a pressure sensor element, wherein a circuit substrate electrically connected to the pressure sensor element is arranged in the housing interior. According to the invention, it is proposed that a separate heating element is arranged in the sensor housing, wherein the heating element is suitable and designed to locally heat the circuit substrate.A separate heating element is understood to mean a heating element which is provided to heat the circuit substrate to a target temperature. The separate heating element is therefore not any current-carrying conductor track, but a component which is implemented exclusively for heating purposes and is suitable and designed for heating the circuit substrate locally to a predeterminable temperature value.The circuit substrate can be a circuit substrate provided with electrical and / or electronic components. The circuit substrate can be, for example, a printed circuit board or a ceramic substrate, which can be equipped with passive electrical components, such as, for example, resistors, coils or capacitors, and / or with active electronic components, such as, for example, an IC, and also with contact elements.The pressure sensor may be suitable for detecting the pressure of a fluid measurement medium. The measurement medium can be liquid or gaseous. Without being limited thereto, the actual pressure sensor element can be designed, for example, similarly to EP 1 518 099 B1, as a metallic pressure measuring cell with a deflectable membrane, which is provided with a sensor circuit on a side facing the housing interior.A temperature sensor element for detecting an internal temperature of the pressure sensor is understood to mean a temperature sensor element which detects a temperature on or in a component of the pressure sensor. The temperature sensor element can be designed, for example, as an NTC. In contrast to the combined pressure and temperature sensors known in the prior art, in which the pressure and the temperature of the measurement medium are detected, the temperature sensor element does not detect an external temperature, but rather a temperature present within the pressure sensor. In order to be influenced as little as possible by the heating power of the heating element, it is expedient to arrange the temperature sensor element as far away as possible from the heating element in the pressure sensor. This can be achieved, for example, by arranging the temperature sensor element such that it detects, for example, the temperature in a metallic pressure connection of the pressure sensor connected to the sensor housing of the pressure sensor.Advantages of the InventionThe pressure sensor according to the invention has the advantage that it is also well suited in particular for hydrogen applications. The pressure sensors of the prior art described above are not suitable for use conditions below -40° C. This is due to the fact that the standard electronic components of the circuit substrate are limited by the manufacturers to a temperature application range above -40° C. If such pressure sensors are used for hydrogen applications, they are suitable for the field of application above -40° C., but due to the physical properties of the hydrogen, the measurement medium and, due to the thermal coupling, all the add-on components adjoining the measurement medium, including one or more pressure sensors, can also assume temperatures below -40° C.The pressure sensor according to the invention is advantageously also suitable for media temperatures below -40° C. At the same time, the circuit substrate can nevertheless be equipped with inexpensive standardized electronic components which can be used in an area of use above -40° C. According to the invention, this is achieved by a separate heating element which is suitable and designed for locally heating the circuit substrate with the electronic components.In particular, the heating element is designed to heat the circuit substrate to a temperature above -40° C. or higher at an ambient temperature of the pressure sensor or a temperature of the measurement medium of less than -40° C.The heating element is here advantageously integrated into the pressure sensor, so that no external heating is required. The dimensions and the installation space of the pressure sensor are advantageously not larger than in the case of the conventional pressure sensors described at the beginning, which are used in motor vehicle technology.The heating element can be arranged in such a way that the circuit substrate with the electrical and / or electronic components arranged thereon is locally heated. In this case, it is possible to prevent other parts of the pressure sensor from being heated up to a great extent. In a construction in which the circuit substrate has an inner recess into which the pressure sensor element engages, it can be achieved, for example, through the gap between the circuit substrate and the pressure sensor element that a sensor circuit arranged on the pressure sensor element and facing the housing interior is not heated, or is almost not heated, by the heating element.Advantageous embodiments and further developments of the invention make possible the features contained in the dependent claims.Advantageously, only one additional connecting line is required for connecting a heating current signal to the heating element. The circuit is closed by a ground line.The pressure sensor preferably further comprises a temperature sensor element which detects an internal temperature of the pressure sensor at a point remote from the heating element, in particular a temperature in a pressure connection of the pressure sensor connected to the sensor housing. The internally measured temperature of the pressure sensor can advantageously be used as a controlled variable for the control and / or regulation of a heater current signal of the heating element.For this purpose, an electronic control and / or regulating circuit can advantageously be provided, which applies a heating current signal to the heating element as a function of a temperature signal of the inner temperature sensor element.The electronic control and / or regulating circuit can be arranged in a simple and inexpensive manner either in an external control device or else in the housing interior of the pressure sensor, in particular on the circuit substrate.The heating element can be formed in a simple manner as a heating conductor track which is arranged in the vicinity of or in the circuit substrate.For example, it is possible to integrate the heating conductor track as an inner conductor track into the circuit substrate, so that the heating conductor track is surrounded on all sides by the circuit substrate. The integration of a further conductor track into a circuit substrate provided with conductor tracks, such as a printed circuit board or a ceramic multilayer substrate, can be produced at low cost and without great additional outlay.Alternatively or additionally, it is also possible to arrange the heating conductor track on the surface on a side of the circuit substrate facing the housing interior.It is also possible for the sensor housing to have a base plate to which the circuit substrate is adhesively bonded by means of an adhesive. This base plate can be a metallic hexagon, for example. In this case, the heating conductor track can also be integrated into the adhesive, for example, between the circuit substrate and the base plate. For this purpose, for example, a double-sided adhesive tape can be used, so that the heating element is bonded under the circuit carrier and at the same time the circuit substrate is bonded to the base plate.Brief Description of the DrawingsPossible embodiments of the invention are explained below with reference to the attached figures. In the drawing, the following are shown: FIG. 1 shows a cross section through a first exemplary embodiment of a pressure sensor according to the invention, FIGS. 2a to 2c show different exemplary embodiments for the arrangement of a heating element in or on the circuit substrate of the pressure sensor from FIG. 1, FIG. 3 shows an enlarged detail from FIG. 1, FIG. 4 shows an embodiment for controlling the heating element of the pressure sensor according to the invention, FIG. 5 shows a further embodiment for controlling the heating element of the pressure sensor according to the invention.Embodiments of the InventionFIG. 1 shows a cross section through a first exemplary embodiment of a pressure sensor 1 according to the invention. The pressure sensor is advantageously suitable for medium temperatures below -40° C. and can be used in a hydrogen-operated system, for example a fuel cell system, for detecting the pressure of a hydrogen-containing, fluid measurement medium.The pressure sensor 1 has a sensor housing 10. The sensor housing 10 comprises a metallic base plate 4, the circumferential wall 5 of which is designed, for example, as a hexagon 5, and a housing cover part 2 which is placed on the base plate 4 and has an electrical connection integrated in the housing cover part 2. The base plate 4 has a central aperture 41 (FIG. 3 ) which penetrates the base plate 4. Between the base plate 4 and the housing cover part 2 a closed housing interior 9 is formed. The housing cover part 2 can be formed as an injection molded part made of plastic with a metal frame 3 injected therein and manufactured as a deep-drawn part. The metal frame 3 can be welded onto the base plate 4 in a circumferential manner. The housing cover part 2 is provided with contact elements 22 injected therein, the first ends 21 of which are exposed to the outside on a plug part of the housing cover part 2 and the second ends 23 of which, facing away from the first ends 21, are exposed to the housing interior 9. On the side of the base plate 4 facing away from the housing cover part 2, a metallic pressure connection 6 is welded on. The pressure connection 6 can be provided with a screw thread 62 for fastening the pressure sensor 1 in a mounting opening of a line provided with the measurement medium. The pressure connection 6 has a continuous feed duct 61 for the measurement medium, which is designed, for example, as a bore. A pressure sensor element 7, for example, in the form of a metallic pressure measuring cell, is welded onto the end of the pressure connection 6 facing the base plate 4. The pressure sensor element 7 can have a blind hole-like inner recess 72, which continues the supply channel 61. The supply channel 61 ends at a movable metallic diaphragm of the pressure sensor element 7. For temperature compensation of the measuring bridge, an additional measuring element for the temperature, e.g. an NTC, can be provided, which detects a temperature in the vicinity of the pressure sensor element.As shown in FIG. 3, the pressure sensor element 7 welded onto the pressure connection 6 projects through the aperture 41 of the base plate 4 into the housing interior 9, wherein the aperture 41 is closed by the welded-on pressure connection 6. A circuit substrate 8, which is embodied for example as a printed circuit board and is provided with electronic components not shown in FIGS. 1 and 3, is arranged in the closed housing interior 9. The circuit substrate 8 can be bonded to the base plate 4 for example via an adhesive 81, in particular an adhesive layer or double-sided adhesive film. The circuit substrate 8 has a central inner recess 82, in which the pressure sensor element 7 engages. The sensor circuit 71 on the side of the pressure sensor element 7 facing the housing interior 9 is electrically connected to the circuit substrate 8, for example, via bonding wire connections 83. The circuit substrate 8 can have contact areas which are electrically conductively connected to the second ends 23 of the contact elements 22 via electrical contact springs 87.According to the invention, the pressure sensor 1 shown is provided with a separate heating element 12. This heating element 12 is preferably arranged on or on the circuit substrate 8, wherein the heating element 12 is suitable and configured to locally heat the circuit substrate 8. In particular, the heating element 12 is designed and suitable for heating the circuit substrate 8 completely or partially to a temperature above -40° C. at an ambient temperature of the pressure sensor 1 below -40° C. The heating element 12 can be formed, for example, as a heating conductor track 12 ain or on the circuit substrate 8.FIGS. 2a to 2c show different embodiments for arranging the heating conductor track 12a in or on the circuit substrate 8. It is possible, for example, to form the heating conductor track 12 as an inner conductor track in the circuit substrate 8, as is illustrated in FIG. 2 a. In this case, the heating conductor track 12a is surrounded on all sides by the circuit substrate 8.In the embodiment of FIG. 2 b, the heating conductor track 12 ais integrated between the circuit substrate 8 and the base plate 4 in an adhesive 81. In this case, the heating conductor track 12a adheres to the underside of the circuit substrate 8. At the same time, the circuit substrate 8 is bonded to the base plate 4 by means of the adhesive 81, which can be, for example, a film that is adhesive on both sides.In the embodiment variant of FIG. 2 c, it is provided, similar to FIG. 1 or 3, to arrange the heating conductor track 12 aon the circuit substrate 8 in the housing interior 9. The heating conductor track 12a is thus arranged as a conductor track on the surface of the circuit substrate 8. There, the heating conductor path 12 acan be designed, for example, as a meander or as a circumferential, non-closed circular ring or in another shape.The heating element 12 is advantageously arranged in such a way that direct local heating of the circuit substrate 8 is possible without the entire pressure sensor having to be heated. The local heating of the circuit substrate 8 to a temperature value above -40° C. can be effected in particular in such a way that the pressure sensor element 7 or its sensor circuit 71 is not heated or is only slightly heated by the heating element 12.As can also be seen in FIG. 3, the pressure sensor 1 can furthermore have, in particular, a temperature sensor element 11. The temperature sensor element 11 can be designed, for example, as an NTC resistor and can be electrically contacted to the circuit substrate 8. The temperature sensor element 11 can, for example, pass through a bore in the base plate 11 by means of connecting lines and engage with its temperature-sensitive measuring element, for example a sensor pellet, in a receiving opening of the pressure connector 6. This ensures that the temperature sensor element 11 detects an internal temperature of the pressure sensor 1 at a point remote from the heating element 12, which is not influenced, or is influenced only to an extremely slight extent, by the heating element 12.FIGS. 4 and 5 show different exemplary embodiments for driving the heating element 12 in the pressure sensor 1. Reference numeral 100 denotes an external control device which is connected to the pressure sensor 1. As shown in FIG. 4, the pressure sensor 1 can be connected to the control device via a supply connection V and a ground connection Ms. The pressure sensor 1 transmits the detected pressure signal P of the pressure sensor element 7 and the temperature signal T of the temperature sensor element 11 to the control device 100. The control device 100 can have an electronic control and / or regulating circuit 91, to which the temperature signal T and, if appropriate, further system parameters a1, a2and a3 present in the control device, such as, for example, the temperature of a tank of the measurement medium, are fed as input variables. The electronic control and / or regulating circuit 91 can form a heating current signal S 1 as a function of at least the temperature signal T, which heating current signal is supplied to the heating element 12 of the pressure sensor 1 via the contact elements 22, the contact spring 87 and the interconnect connections of the circuit substrate 8. The heating element 12 is also connected to the control device by a ground connection Mh via the contact elements 22, so that a closed circuit through the heating element 12 is possible. Since the second electrical terminal of the heating element 12 is a ground terminal, the heating element 12 requires the heating current signal S 1 as the only control signal.FIG. 5 shows a further exemplary embodiment for controlling the heating element 12 in the pressure sensor 1. In addition to the supply terminal V, the ground terminal Ms of the circuit substrate 8 and the ground terminal Mh of the heating element 12, a connecting line is provided on which the control device 100 transmits an uncontrolled supply signal S 2 for the heating element 12 to the pressure sensor 1. The electronic control and / or regulating circuit 91 forms from the uncontrolled supply signal S2 and the temperature signal T the regulated heating current signal S1, which is fed to the heating element 12. The second terminal of the heating element 12 is the ground terminal Mh. The electronic control and / or regulating circuit 91 can be arranged on the circuit substrate 8.References included in the specificationThis list of documents cited by the applicant has been produced in an automated manner and is only included for the better information of the reader. The list is not part of the German patent application or utility model application. The DPMA does not take any adhesion for any faults or omissions.Patent Literature citedEP 1 518 099 B1 [0002, 0007]

Claims

Pressure sensor (1) for detecting the pressure of a measurement medium, in particular for detecting a pressure in a system operated with hydrogen, comprising a sensor housing (10) having a closed housing interior (9) and a pressure sensor element (7), wherein a circuit substrate (8) electrically connected to the pressure sensor element (7) is arranged in the housing interior (9), characterized in that a separate heating element (12) is arranged in the sensor housing (10), wherein the heating element (12) is suitable and designed to locally heat the circuit substrate (8).Pressure sensor (1) according to Claim 1, characterized in that the heating element (12) is designed to heat the circuit substrate (8) to a temperature above -40°C at an ambient temperature of the pressure sensor (1) of less than -40°C.Pressure sensor (1) according to Claim 1 or 2, characterized in that the pressure sensor (1) furthermore has a temperature sensor element (11) which detects an internal temperature of the pressure sensor (1) at a point remote from the heating element (12), in particular a temperature in a pressure connection (6) of the pressure sensor (1) connected to the sensor housing (10).Pressure sensor (1) according to Claim 3, characterized in that an electronic control and / or regulating circuit (91) is provided which applies a heating current signal (S1) to the heating element (12) as a function of a temperature signal (T) of the temperature sensor element (11).Pressure sensor (1) according to Claim 4, characterized in that the electronic control and / or regulating circuit (91) is arranged in an external control unit (100) or in the housing interior (9) of the pressure sensor (1), in particular on the circuit substrate (8).Pressure sensor (1) according to one of the preceding claims, characterized in that the heating element (12) is designed as a heating conductor track (12a).Pressure sensor (1) according to Claim 6, characterized in that the heating conductor track (12a) is integrated into the circuit substrate (8) as an inner conductor track and is surrounded on all sides by the circuit substrate.Pressure sensor (1) according to Claim 6, characterized in that the heating conductor track (12a) is arranged on the circuit substrate (8) in the housing interior (9).Pressure sensor (1) according to Claim 6, characterized in that the sensor housing (10) has a base plate (4) to which the circuit substrate (8) is adhesively bonded by means of an adhesive (81), and in that the heating conductor track (12a) is integrated into the adhesive (81) between the circuit substrate (8) and the base plate (4).Pressure sensor (1) according to one of the preceding claims, characterized in that the circuit substrate (8) has an inner recess (82), in which the pressure sensor element (7) engages, wherein a sensor circuit (71) arranged on the pressure sensor element (7) and facing the housing interior (9) is not heated or is almost not heated by the heating element (12).

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