Differential pressure sensor

Description

[0001] The present invention relates to a differential pressure sensor for measuring the pressure in an exhaust gas duct of a heat engine and a method of manufacturing such a sensor.

[0002] Such a differential pressure sensor is used in the exhaust gas systems of internal combustion vehicles. For example, it can be used to measure a pressure difference at two different points in an exhaust line, such as before and after a particulate filter.

[0003] Prior art differential pressure sensors comprise a protective housing having a cavity in which is housed a ceramic or resin printed circuit board (PCB) as in document DE102007057903A1 on which is mounted a pressure sensitive element.

[0004] The ceramic circuit board includes an opening closed by the pressure sensitive element and electronic components electrically connected to the pressure sensitive element.

[0005] The protective housing includes a first pressure inlet communicating with a first surface of the pressure-sensitive element and a second pressure inlet communicating with a second surface of the pressure-sensitive element. These two surfaces of the pressure-sensitive element are hermetically isolated.

[0006] The pressure sensitive element is in contact with the exhaust gases which is a hot and acidic environment that can damage and foul the surface of the pressure sensitive element. A gel is therefore provided to protect this surface.

[0007] Prior art differential pressure sensors include a ceramic circuit board because the latter is resistant to this aggressive environment.

[0008] The differential pressure sensor includes a connector for connecting it to an electronic control device. The ceramic printed circuit board is connected to the electrical contacts of this connector by means of electrical connections. These electrical connections are separated from the pressure-sensitive element by a protective wall to protect them from the aggressive environment.

[0009] Other prior art differential pressure sensors alternatively include a gel covering the electrical connections to protect them from the harsh environment.

[0010] The problem with prior art differential pressure sensors is that they are expensive due to the use of ceramic printed circuit boards. In addition, the protective wall of some of these differential pressure sensors does not completely protect the electrical connections. Some of the exhaust gases manage to pass through this wall.

[0011] The invention therefore aims to overcome these drawbacks of the prior art by proposing a less expensive differential pressure sensor with equivalent resistance to attacks from exhaust gases.

[0012] The invention also aims to provide a simpler method of manufacturing a differential pressure sensor, comprising fewer manufacturing steps.

[0013] The invention relates to a differential pressure sensor for measuring the pressure in an exhaust gas duct of a heat engine, comprising: a pressure-sensitive element, a printed circuit comprising an opening closed by the pressure-sensitive element and electronic components electrically connected to the pressure-sensitive element by means of electrical connections, and a protective housing comprising a cavity in which the printed circuit and the pressure-sensitive element are housed, said protective housing comprising a first pressure inlet and a second pressure inlet.

[0014] According to the invention, the printed circuit is an epoxy resin printed circuit, and the pressure sensor comprises a solid material partially filling the cavity of the protective housing and coating the printed circuit so as to insulate its external surface from exhaust gases and to form two pressure paths isolated from each other by the solid material, including a first pressure path connecting the first pressure inlet to the lower surface of the pressure-sensitive element and a second pressure path connecting the second pressure inlet to the upper surface of the pressure-sensitive element, the solid material is an epoxy resin, the differential pressure sensor comprises a sensitive element support comprising a shell supported by the printed circuit and comprising an upper opening and a lower opening closed by the pressure-sensitive element,said lower opening being extended by a tube inserted into the opening of the printed circuit.

[0015] Alternatively, the tube extends partially through the solid material.

[0016] Alternatively, the sensitive element holder envelope contains a gel to protect the upper surface of the pressure sensitive element.

[0017] Alternatively, the protective housing includes a cover having a channel including a first end in fluid communication with the first pressure inlet of the protective housing and a second end connected to the tube of the sensitive element holder so as to form the first pressure path.

[0018] Alternatively, the second pressure inlet of the protective housing is in fluid communication with the upper opening of the sensitive element support housing so as to form the second pressure path.

[0019] The invention thus provides a differential pressure sensor comprising an epoxy resin printed circuit which is less expensive than those of the prior art using a ceramic printed circuit.

[0020] This differential pressure sensor is also more resistant to the external environment composed of exhaust gases and in which pressure measurements are made.

[0021] The invention also relates to a method of manufacturing a differential pressure sensor as defined above.

[0022] According to the invention, the method comprises the following steps: providing a protective housing comprising a cavity, a first pressure inlet and a second pressure inlet, arranging an epoxy resin printed circuit in the cavity of the protective housing, said printed circuit comprising an opening closed by the pressure-sensitive element, injecting a resin into the cavity of the protective housing to form a solid material partially filling the cavity of the protective housing and coating the printed circuit so as to insulate its external surface from the exhaust gases and to form two pressure paths isolated from each other by the solid material, including a first pressure path connecting the first pressure inlet to the lower surface of the pressure-sensitive element and a second pressure path connecting the second pressure inlet to the upper surface of the pressure-sensitive element.

[0023] The differential pressure sensor comprises a sensitive element holder having a shell supported by the printed circuit, an upper opening and a lower opening closed by the pressure sensitive element. The lower opening is extended by a tube inserted into the opening of the printed circuit.

[0024] The method then comprises, before the step of injecting a resin into the cavity of the protective housing, a step of closing the protective housing by a cover comprising a channel comprising a first end in fluid communication with the first pressure inlet of the protective housing and a second end. The second end is fitted into the tube of the sensitive element support so as to form the first pressure path.

[0025] Alternatively, during the resin injection step, the cavity of the protective housing is filled with resin up to the vicinity of the first end of the channel without covering it and up to the vicinity of the upper opening of the casing without covering it.

[0026] The invention thus provides a method of manufacturing a simpler differential pressure sensor comprising fewer manufacturing steps.

[0027] The features of the invention will be described in more detail with reference to the accompanying drawings in which: there figure 1 is a schematic representation of a differential pressure sensor according to the invention; the figure 2 is an external view of this differential pressure sensor; the figure 3 represents a protective housing after the step of providing this housing, according to the manufacturing method of the sensor of the invention; the figure 4 represents an epoxy resin printed circuit inserted into the cavity of the protective housing after the step of arranging this circuit in the cavity; the figure 5 represents the protective housing closed by a cover after the step of closing the housing by this cover; the figure 6 represents the printed circuit board coated with a solid material after the step of injecting a resin into the cavity of the protective housing.

[0028] There figure 1 schematically represents a differential pressure sensor 1 for measuring a pressure difference in an exhaust gas duct of a heat engine, according to the invention.

[0029] This differential pressure sensor 1 comprises a pressure sensitive element 2 and a printed circuit 3 made of epoxy resin comprising an opening 4 closed by the pressure sensitive element 2. The printed circuit 3 comprises electronic components not shown electrically connected to the pressure sensitive element 2 by means of electrical connections 5 and 27. The printed circuit 3 is preferably a printed circuit commonly called FR4 PCB (“Flame Resistant 4 Printed Circuit Board”) which is an epoxy resin composite reinforced with fiberglass.

[0030] The differential pressure sensor 1 comprises a protective housing 6 comprising a cavity 7 in which the printed circuit 3 and the pressure-sensitive element 2 are housed. The protective housing 6 comprises a first pressure inlet 8 and a second pressure inlet 9, as shown in the figure 2 .

[0031] The protective housing 6 comprises one or more fixing elements 30 on which the printed circuit 3 is fixed. The fixing elements 30 also make it possible to center the printed circuit 3 in the protective housing 6.

[0032] The differential pressure sensor 1 comprises a solid material 10 partially filling the cavity 7 of the protective housing 6 and coating the printed circuit 3 so as to insulate its external surface 11 and 32 from the exhaust gases and to form two pressure paths 12a, 12b hermetically isolated from each other by the solid material 10, including a first pressure path 12a connecting the first pressure inlet 8 to the lower surface 13 of the pressure-sensitive element 2 and a second pressure path 12b connecting the second pressure inlet 9 to the upper surface 14 of the pressure-sensitive element 2.

[0033] Solid material 10 is an epoxy resin.

[0034] The differential pressure sensor 1 comprises a sensitive element support 15 comprising a casing 16 supported by the printed circuit 3. The casing 16 has a circular or quadrilateral section, for example.

[0035] The casing 16 comprises an upper opening 17 and a lower opening 18 closed by the pressure-sensitive element 2. The pressure-sensitive element 2 is positioned inside the casing 16 and closes the opening between 12a and 12b. The sensitive element 2 is subjected to the pressure from 12a and 12b; it is this stress generated on the membrane which generates the differential pressure.

[0036] The lower opening 18 of the casing 16 is extended by a tube 19 hermetically inserted into the opening 4 of the printed circuit 3.

[0037] The tube 19 extends partially through the solid material 10 and does not pass through it completely.

[0038] The solid material 10 surrounds the envelope 16 and extends to the vicinity of its upper opening 17 so as not to block it.

[0039] The pressure sensitive element 2 can be mounted with a support 25 which is provided with a central orifice 26 communicating with the interior of the tube 19.

[0040] The envelope 16 of the sensitive element support 15 contains a gel 20 to protect the upper surface 14 of the pressure-sensitive element 2.

[0041] The differential pressure sensor 1 comprises a connector 33 for connecting it to an external electronic control device. The printed circuit 3 is connected to electrical contacts of this connector 33 by means of electrical connections which are covered by the solid material 10. This makes it possible to protect the electrical contacts at the same time as the printed circuit 3 by the same solid material 10, avoiding the use of a protective wall or gel on the electrical contacts.

[0042] The differential pressure sensor 1 comprises fixing tabs 27 for fixing the sensitive element support 15 to the printed circuit 3.

[0043] As shown in the figure 6 , the protective housing 6 comprises a cover 21 having a channel 22 comprising a first end 23 in fluid communication with the first pressure inlet 8 of the protective housing 6 and a second end 24 connected to the tube 19 of the sensitive element support 15 so as to form the first pressure path 12a.

[0044] The channel 22 is integrated into the cover 21. It is for example formed during the molding operation of the cover 21.

[0045] Alternatively, the channel 22 may be independent of the cover 21.

[0046] More specifically, the channel 22 has a “U” shape. It comprises a first portion 28 connected to the first pressure inlet 8 and projecting from the internal surface 29 of the cover 21.

[0047] The channel 22 comprises a second portion 30 connected to the first portion 28 and running along the internal surface 29 of the cover 21.

[0048] The channel 22 comprises a third portion 31 connected to the second portion 30 and projecting from the internal surface 29 of the cover 21. This third portion 31 comprises the second end 24 of the channel 22 which is fitted into the tube 19 of the sensitive element support 15.

[0049] The first portion 28 and the third portion 31 of the channel 22 are substantially perpendicular. The first portion 28 of the channel 22 is longer than the third portion 31.

[0050] The first portion 28 of the channel 22 comprises the first end 23 of the channel 22. The solid material 10 extends to the vicinity of this first end 23 so as not to block it.

[0051] The first end 23 of the channel 22 is arranged near the first pressure inlet 8.

[0052] The second pressure inlet 9 of the protective housing 6 is in fluid communication with the upper opening 17 of the casing 16 of the sensitive element support 15 so as to form the second pressure path 12b.

[0053] The invention also relates to a method of manufacturing a differential pressure sensor 1 as defined above.

[0054] The manufacturing process includes the following steps: providing a protective housing 6 comprising a cavity 7, a first pressure inlet 8 and a second pressure inlet 9, as shown in the figure 3 , arrange a printed circuit 3 made of epoxy resin in the cavity 7 of the protective housing 6. The printed circuit 3 comprises an opening 4 closed by the pressure-sensitive element 2, as shown in the figure 4 , injecting a resin into the cavity 7 of the protective housing 6 to form a solid material 10 partially filling the cavity 7 of the protective housing 6, as shown in the figure 6 The solid material 10 coats the printed circuit 3 so as to insulate its external surface 11 and 32 from the exhaust gases and to form two pressure paths 12a, 12b isolated from each other by the solid material 10, including a first pressure path 12a connecting the first pressure inlet 8 to the lower surface 13 of the pressure-sensitive element 2 and a second pressure path 12b connecting the second pressure inlet 9 to the upper surface 14 of the pressure-sensitive element 2.

[0055] The sensitive element support 15 comprises an envelope 16 supported by the printed circuit 3. The envelope 16 comprises an upper opening 17 and a lower opening 18 separated by the pressure-sensitive element 2. The lower opening 18 is extended by a tube 19 inserted into the opening 4 of the printed circuit 3.

[0056] The method comprises, before the step of injecting a resin into the cavity 7 of the protective housing 6, a step of closing the protective housing 6 with a cover 21, as shown in the figure 5 The cover 21 comprises a channel 22 comprising a first end 23 in fluid communication with the first pressure inlet 8 of the protective housing 6 and a second end 24. During this step, the second end 24 is hermetically fitted into the tube 19 of the sensitive element support 15 so as to form the first pressure path 12a.

[0057] During the resin injection step, the cavity 7 of the protective housing 6 is filled with the resin up to the vicinity of the first end 23 of the channel 22 without covering it and up to the vicinity of the upper opening 17 of the casing 16 without covering it.

[0058] Thus, the resin allows the two pressure paths 12a, 12b to be hermetically separated without blocking them.

[0059] As shown in the figure 6, during the resin injection step, the cover 21 is arranged at the bottom and the pressure inlets 8, 9 at the top relative to the vertical. In this way, the resin begins to cover the internal surface 29 of the cover 21, rises and ends up covering the entire external surface 11 and 32 of the printed circuit 3 potentially in contact with the exhaust gases. The upper surface 32 of the printed circuit 3 is covered by the resin by a few millimeters. In other words, the printed circuit 3 is entirely coated by the resin which hardens to form the solid material 10.

[0060] To inject the resin, an orifice is provided in the protective housing (not shown). The latter is plugged with the resin after the filling step.

[0061] According to one embodiment, a gel 20 is then introduced into the envelope 16 of the sensitive element support 15 to cover and protect the upper surface 14 of the pressure-sensitive element 2.

Claims

1. Differential-pressure sensor (1) for measuring the pressure in an exhaust pipe of a combustion engine, comprising: - a pressure-sensitive element (2), - a printed circuit (3) comprising an opening (4) closed by the pressure-sensitive element (2) and electronic components electrically connected to the pressure-sensitive element (2) by means of electrical connections (5), - a protective housing (6) comprising a cavity (7) in which the printed circuit (3) and the pressure-sensitive element (2) are housed, said protective housing (6) comprising a first pressure inlet (8) and a second pressure inlet (9), - the printed circuit (3) being an epoxy resin printed circuit, - the pressure sensor (1) comprising a solid material (10) partially filling the cavity (7) of the protective housing (6) and encapsulating the printed circuit (3) so as to insulate the external surface (11 and 32) thereof from the exhaust gases and so as to form two pressure pathways (12a, 12b) insulated from one another by the solid material (10), these being a first pressure pathway (12a), which connects the first pressure inlet (8) to the lower surface (13) of the pressure-sensitive element (2), and a second pressure pathway (12b), which connects the second pressure inlet (9) to the upper surface (14) of the pressure-sensitive element (2), the solid material (10) being an injected epoxy resin characterized in that it also comprises: - a sensitive-element support (15) comprising a casing (16) supported by the printed circuit (3) and comprising an upper opening (17) and a lower opening (18) which is closed by the pressure-sensitive element (2), said lower opening (18) being extended by a tube (19) inserted into the opening (4) of the printed circuit (3).

2. Differential-pressure sensor (1) according to Claim 1, characterized in that the tube (19) extends partially through the solid material (10).

3. Differential-pressure sensor (1) according to either one of Claims 1 and 2, characterized in that the casing (16) of the sensitive-element support (15) contains a gel (20) to protect the upper surface (14) of the pressure-sensitive element (2).

4. Differential-pressure sensor (1) according to any one of Claims 1 to 3, characterized in that the protective housing (6) comprises a cover (21) comprising a passage (22) comprising a first end (23) in fluidic communication with the first pressure inlet (8) of the protective housing (6) and a second end (24) connected to the tube (19) of the sensitive-element support (15) so as to form the first pressure pathway (12a).

5. Differential-pressure sensor (1) according to any one of Claims 1 to 4, characterized in that the second pressure inlet (9) of the protective housing (6) is in fluidic communication with the upper opening (17) of the casing (16) of the sensitive-element support (15) so as to form the second pressure pathway (12b).

6. Method for manufacturing a differential-pressure sensor (1) according to any one of Claims 1 to 5, characterized in that it comprises the following steps: - providing a protective housing (6) comprising a cavity (7), a first pressure inlet (8) and a second pressure inlet (9), - placing an epoxy resin printed circuit (3) in the cavity (7) of the protective housing (6), said printed circuit (3) comprising an opening (4) closed by the pressure-sensitive element (2), - injecting a resin into the cavity (7) of the protective housing (6) in order to form a solid material (10) partially filling the cavity (7) of the protective housing (6) and encapsulating the printed circuit (3) so as to insulate the external surface (11 and 32) thereof from the exhaust gases and so as to form two pressure pathways (12a, 12b) insulated from one another by the solid material (10), these being a first pressure pathway (12a), which connects the first pressure inlet (8) to the lower surface (13) of the pressure-sensitive element (2), and a second pressure pathway (12b), which connects the second pressure inlet (9) to the upper surface (14) of the pressure-sensitive element (2).

7. Method for manufacturing a differential-pressure sensor (1) according to Claim 6, the differential-pressure sensor (1) comprising a sensitive-element support (15) comprising a casing (16) supported by the printed circuit (3) and comprising an upper opening (17) and a lower opening (18) which is closed by the pressure-sensitive element (2), said lower opening (18) being extended by a tube (19) inserted into the opening (4) of the printed circuit (3), characterized in that the method comprises, before the step of injecting a resin into the cavity (7) of the protective housing (6), - a step of closing the protective housing (6) with a cover (21) comprising a passage (22) comprising a first end (23) in fluidic communication with the first pressure inlet (8) of the protective housing (6) and a second end (24), said second end (24) being fitted into the tube (19) of the sensitive-element support (15) so as to form the first pressure pathway (12a).

8. Method for manufacturing a differential-pressure sensor (1) according to Claim 7, characterized in that, during the step of injecting the resin, the cavity (7) of the protective housing (6) is filled with the resin as far as the vicinity of the first end (23) of the passage (22) without covering said end and as far as the vicinity of the upper opening (17) of the casing (16) without covering said opening.