DE102006045924B4 - Pressure measuring device for motor vehicle applications - Google Patents

Abstract

A pressure measuring device (110) for detecting the pressure of a fluid medium (120), comprising at least one pressure measuring cell (122) accommodated in a sensor assembly (112) with an inner tube (134) for receiving the pressure of the fluid medium (120), and a probe assembly ( 114) with an outer tube (118) which can be introduced into the fluid medium (120), wherein the inner tube (134) projects into a pressure measuring channel (136) of the outer tube (118) which can be brought into communication with the fluid medium (120), wherein 134) and outer tube (118) at least one sealing ring (166) is provided, characterized in that the at least one sealing ring (166) as material a fluorosilicone rubber, in particular FVMQ, wherein the at least one sealing ring (166) in a source space (164 ), wherein the pressure measuring channel (136) is configured substantially cylindrical with a widening (160), wherein the inner tube (134) is substantially cylindrical with fit or insignificant gigas of smaller diameter than the pressure measuring channel (136) is designed, and wherein the source space (164) is limited by the expansion (160) of the pressure measuring channel (136), the outer wall of the inner tube (134) and a on the inner tube (134) pushed, essentially cylindrical spacer ring (170).

Description

State of the art

Pressure measurement devices are used in various fields of the art which are designed to measure pressure in fluid media (eg, liquids and / or gases). An important field of application is the engine and motor vehicle technology, in which pressure measuring devices of different design are used in various applications. Such pressure measuring devices are described for example in Robert Bosch GmbH (publisher): "Sensors in the motor vehicle", 2001, pages 78-85 described. However, the pressure measuring device shown below is in principle also applicable in other fields of science and technology.

In automotive engineering, such pressure measuring devices are used in particular in the intake manifold of an internal combustion engine in order to be able to measure an optimum intake pressure. For example, describe EP 0 923 717 B1 Embodiments of such pressure measuring devices, in which in addition to a pressure measuring cell, a temperature sensor is integrated in a housing. Such pressure measuring cells, as shown for example in the publication "sensors in the motor vehicle" described above, are based on different measuring principles. For example, the deformation of a sensor membrane in the pressure measuring cell can be measured by the pressure of the fluid medium. However, other measuring principles are used.

Those of the prior art, such as EP 0 923 717 B1 Known devices are optimized for the measurement of relatively non-critical gases (such as intake air) or flammable liquids such as fuel. Accordingly, the problem of sealing the pressure measuring devices which are introduced into the fluid medium (for example in the form of plug-in sensors) plays a comparatively small role relative to the exterior space. In applications for measuring the pressure of liquid fuel is thereby exploited in particular that the liquid fuels existing sealing elements, such as O-rings, swell, which additionally enhances the sealing effect.

However, in addition to the applications described above, the market for CNG vehicles, especially CNG-fueled vehicles, is experiencing an increasing recovery. Especially in CNG applications, however, it has been found that the sealing of pressure measuring devices, which are introduced, for example, into a pressure accumulator (eg a natural gas rail) plays a special role. In this case, working pressures of about 10 bar are typically used. Since natural gas is a significant source of danger, special demands are placed on such seals, which make themselves felt in particular in conditions for corresponding certifications.

It plays on the one hand a role that existing sealing elements are no longer exposed to the above-described swelling process by the contact with liquid fuels, which would additionally promote the seal. Another problem in the gas operation, especially in CNG operation, is the often required gas decompression, which often leads to a strong temperature reduction in the field of pressure measuring device and their seals. While conventional fuel pressure sensors and pressure sensors in the intake pipe usually only have to withstand temperatures down to about -30 ° C, this gas-related temperature reduction causes a range of application down to -40 ° C. Accordingly, suitable pressure gauges for such applications, which are also said to be suitable for cold countries, must demonstrate sufficient life, tightness, functionality and load capacity down to -40 ° C. The usual, known pressure measuring devices and their seals meet these requirements so far only inadequate.

Disclosure of the invention

There is therefore proposed a pressure measuring device for detecting the pressure of a fluid medium, which avoids the disadvantages of the pressure measuring devices described above. The proposed pressure measuring device is particularly designed for use in measuring a gas pressure of an explosive and / or combustible gas in a motor vehicle, such as for measuring a natural gas pressure in CNG vehicles. However, other applications are conceivable.

The proposed pressure measuring device is modular and has a sensor assembly with a pressure measuring cell received therein with an inner tube for receiving the pressure of the fluid medium, and a probe assembly with an insertable into the fluid medium outer tube. For example, reference may be made to the above-described prior art for the structure of the pressure measuring cell. However, other types of pressure cells can be used. For example, the pressure measuring device may be designed as a plug-in sensor, wherein the probe assembly as plug part in the fluid medium, for example, a natural gas rail, can be inserted.

In addition to the sealing of this introduced into the fluid medium outer tube relative to a wall of the fluid receiving medium container (which will be described further below) in particular the sealing of the probe assembly relative to the sensor assembly plays a crucial role. A basic idea of the present invention is to optimize this "inner" seal. Numerous simulations and tests have been performed for this purpose in order to improve the sealing and assembly dimensioning and material selection.

Accordingly, the pressure measuring device is designed such that the inner tube of the pressure measuring cell protrudes into a can be brought into communication with the fluid medium measuring channel of the outer tube. This protrusion can be kept to a minimum, for example to a few tenths of a mm. Alternatively, however, a Hineinragen over a longer distance is conceivable.

In this case, at least one sealing ring is provided between the inner tube and the outer tube, for example an O-ring, for example an O-ring with a circular cross-section, which seals the probe assembly with respect to the sensor assembly. In this respect, the pressure measuring device largely corresponds to the devices known from the prior art, such as the EP 0 923 717 B1 known pressure measuring device. As described above, these known pressure measuring devices have only insufficient sealing properties for use in pressurized gases, in particular CNG. Thus, it turns out that the usual sealing rings used in such pressure measuring devices, which are typically made of fluoropolymer rubber (FKM, Viton), do not withstand the tests usual for CNG at temperatures as low as -40 ° C. At such loads, the materials used exhibit shrinkage effects, embrittlement and other aging effects.

Surprisingly, however, it has been shown that fluorosilicone rubber as the material for the at least one sealing ring meets all the requirements of the automotive industry, even at temperatures as low as -40 ° C. Endurance tests, cycle tests and elevated temperature storage tests have been performed which have demonstrated the suitability of this material. Fluorosilicone rubber is particularly available under the name "FVMQ".

These test results are all the more surprising since fluorosilicone rubbers are not usually considered for such applications. This is due in particular to the fact that fluorosilicone rubbers are known to be very soft materials, which tend to deliquesce and easily deform and are therefore usually not believed to withstand the described mechanical stresses and thermal stresses.

In order to further improve the sealing of the probe assembly with respect to the sensor assembly using fluorosilicone rubbers, a geometry and mechanical design of the pressure measuring device was optimally adapted to these materials. Thus, it has proven particularly advantageous if the at least one sealing ring is received in a source space. In this case, the pressure measuring channel is configured substantially cylindrical with a widening facing the sensor module, in particular a substantially cylindrical widening. The inner tube is also configured substantially cylindrical and is fitted in the pressure measuring channel or has a slightly smaller (in particular not more than 1/10 mm) smaller diameter than the pressure measuring channel. The source space for receiving the at least one sealing ring is advantageously limited by the widening of the pressure measuring channel, the outer wall of the inner tube and a pushed onto the inner tube, substantially cylindrical spacer ring. By "substantially", slight deviations from the cylindrical shape can be understood, for example, slightly (preferably not more than 5 °) conical courses and / or bevels at the edges. The spacer ring may for example be designed such that it is supported on its end facing away from the outer tube to a component of the sensor assembly, such as an electronic circuit board.

In order to avoid that the soft sealing ring material is mechanically damaged under pressure, in an advantageous embodiment of the source space has been optimized in its geometry. Thus, it has in particular been found, if, in the case of the above-described cylindrical configuration of inner tube, pressure measuring channel, widening and spacer ring, the differences in diameter of adjacent components in a range between 0.05 mm and 0.2 mm, preferably at approximately 0, 1 mm. This configuration of the diameter differences, ie an optimization of the choice of the maximum gap occurring in the region of the source space, causes on the one hand the largest possible bearing surface is present to exert pressure on the sealing ring and thus deform it for optimum and uniform sealing. On the other hand, the gaps are chosen small enough that the fluorosilicone rubber can not penetrate into them, which would permanently damage the sealing ring.

Furthermore, it has been shown that an optimization of the height of the at least one source space, that is to say the extension along the longitudinal extension of the inner tube, can also be carried out for the use of fluorosilicone rubber. It has been shown that a height of the source space in an area between 1, 1 and 1.5 times the cord diameter of the sealing ring, preferably a height of about 1.25 times the cord diameter, an optimal Sealing effected. This optimization is especially true if a transverse compression of the at least one sealing ring (due to the thickness of the source space perpendicular to the longitudinal extent of the inner tube) to 70% to 90%, ideally 80% occurs.

These embodiments have proved to be particularly advantageous when very "small" sealing rings are used. By "small" is meant a dimensioning of the at least one sealing ring, in which the ratio between the inner diameter of the sealing ring and the cord diameter is between 0.7 and 1.1, preferably 0.9. Due to their special geometry, such sealing rings cause particular problems in practice since they are usually difficult to compress and have unfavorable deformation properties. The above-described use of fluorosilicone rubber, advantageously in combination with one of the described Quellraumgeometrien, however, leads even with such "small" sealing rings to an optimal, even at low temperatures to -40 ° C, reliable and stable seal.

In addition to the described at least one sealing ring which serves to seal between the probe assembly and the sensor assembly, as described above, at least one additional sealing ring for sealing the outer tube (for example, with respect to a housing of a natural gas rail) may be provided. This sealing ring, which is referred to below as an outer sealing ring, may also preferably comprise as a material a fluorosilicone rubber, in particular FVMQ. Although the sealing behavior of this at least one outer sealing ring is not critical in the same way as for the at least one sealing ring between probe assembly and sensor assembly due to the larger ratio between inner diameter and cord diameter described above. The above-described advantages of using the fluorosilicone rubber, in particular its excellent sealing and low-temperature properties, ie the fact that this material remains soft and deformable even at -40 ° C., allow its application to be advantageous also for the at least one outer sealing ring.

In a further advantageous embodiment, the pressure measuring device is wholly or partly made of plastic. For example, conventional thermoplastic materials such as polyamides (eg PA-66) with or without filling (for example glass fiber fillings) can be used in the automotive industry.

In this case, the at least one sealing ring, and optionally the at least one outer sealing ring, is preferably arranged in a region in which there is no separating seam of the plastic. This can be achieved by optimizing the tool geometry during injection molding. The separating seam could negatively influence the sealing properties of the at least one sealing ring or of the at least one outer sealing ring. This is particularly noticeable in the above-described use of the soft fluorosilicone rubber, wherein the fluorosilicone rubber could even be damaged by the cut seam under certain circumstances.

In a further advantageous embodiment, the sensor assembly and the probe assembly are not, as for example EP 0 923 917 B1 known, glued together, but are joined together by a sealing and Halteklebung. This facilitates the installation of the pressure measuring device considerably.

list of figures

Embodiments of the invention are illustrated in the drawings and explained in more detail in the following description.

• 1A eine Schnittdarstellung eines Ausführungsbeispiels einer erfindungsgemäßen Druckmessvorrichtung;
• 1B eine vergrößerte Detaildarstellung des Dichtbereichs A der Druckmessvorrichtung gemäß 1A;
• 2A eine perspektivische Explosionsdarstellung der Komponenten der Druckmessvorrichtung gemäß 1A; und
• 2B eine perspektivische Darstellung der Druckmessvorrichtung gemäß 1A im zusammengebauten Zustand.

Show it:

• 1A a sectional view of an embodiment of a pressure measuring device according to the invention;
• 1B an enlarged detail of the sealing area A of the pressure measuring device according to 1A ;
• 2A an exploded perspective view of the components of the pressure measuring device according to 1A ; and
• 2 B a perspective view of the pressure measuring device according to 1A in the assembled state.

Embodiments of the invention

In 1A is an embodiment of the pressure measuring device according to the invention 110 shown in section. The pressure measuring device 110 For example, it may be partially configured in multi-component injection molding technology and is designed for use in CNG applications. Accordingly, the pressure measuring device 110 a sensor assembly to be located outside of a natural gas rail 112 and a probe assembly 114 on, which partially in the form of a plug-in sensor in the Erdgasrail 116 which is in 1A is indicated, pluggable. The probe assembly has an outer tube 118 on which into the natural gas 120 protrudes.

In the sensor assembly 112 is a pressure measuring cell 122 recorded, which is constructed, for example, on the type of pressure measuring cells described in the above prior art. The pressure measuring cell 122 which is in a sensor housing 124 is fitted, has electrical connections 126 with which the pressure measuring cell 122 on a circuit board 128 is plugged. On the circuit board 128 are in 1A not shown) conductor tracks and contacts arranged, with which the pressure measuring cell 122 is contacted electrically. About electrical connections 130 in the form of tabs is the circuit board 128 with a plug 132 connected, so that a power supply and reading the measurement signals is possible.

Furthermore, the pressure measuring cell has 122 via an inner tube 134 which passes through a hole in the circuit board 128 is guided, which is cylindrical in its outer and inner diameter and which in a, also cylindrically configured, pressure measuring channel 136 in the outer tube 118 is plugged in. This is how the pressure measuring cell stands 122 with the natural gas 120 in conjunction and can be pressurized.

As can still be seen, the outer tube has 118 next to the pressure measuring channel 136 another temperature sensor recording 138 into which a temperature sensor 140 is introduced. For example, this temperature sensor may be 140 to act a semiconductor sensor element, such as an NTC resistor. The temperature sensor 140 is about a Fixierklebung 142 in the temperature sensor holder 138 fixed. About electrical connections 144 is the temperature sensor with the plug 134 and / or the circuit board 128 connected and can be powered and / or read.

The probe assembly 114 is by means of a sealing and Halteklebung 146 , whose function will be further explained below, with the sensor assembly 112 connected. Furthermore, the outer tube 118 , at the step-like transition between temperature sensor recording 138 and inlet opening of the pressure measuring channel 136 , circumferentially with an insertion bevel 148 fitted. This insertion bevel 148 allows easy insertion of the outer tube 118 in the natural gas trail 116 , For sealing between outer tube 118 and natural gas trail 116 the outer tube has an annular groove 150 on which is also equipped with rounded edges, and in which an outer sealing ring 152 is introduced. As described above, as a material for this outer sealing ring 152 also preferably fluorosilicone rubber (FVMQ) is used. The ring groove 150 is injection molding technology designed so that it has no sharp-edged seam, which the outer sealing ring 152 could damage.

A special role in the pressure measuring device according to the invention 110 according to 1A plays the sealing area between the sensor assembly 112 and probe assembly 114 which is in 1A labeled with the letter A and which in detail in 1B is shown. So is in the detail in 1B to realize that the outer tube 118 in its upper, in the sensor assembly 112 protruding end a neck 154 having. In this area of the neck 154 is the outer tube 118 circumferentially with a narrowing 156 provided with a rounded shoulder 158 ends. Inside this socket is the outer tube 118 , which is in the area of its measuring channel 136 a diameter D _M having, with a widening 160 provided, which is also cylindrical and which have a diameter D _A which is larger than the diameter D _M , At the transition between measuring channel 136 and expansion 160 is an insertion bevel 162 provided, which is an insertion of the inner tube 134 into the measuring channel 136 allows.

The inner tube is also cylindrical and has an outer diameter D _I which is preferably about 1/10 mm smaller than the inner diameter D _M of the measuring channel 136 , Between inner tube 134 and outer tube 118 forms in the area of expansion 160 a source space 164 in which a sealing ring 166 made of silicone rubber is introduced. The sealing ring 166 has a cord diameter D _S on, which is about the inner diameter D _D of the sealing ring 166 equivalent. This inner diameter D _D is dimensioned slightly smaller than the outer diameter D _I of the inner tube 134 so that the sealing ring 166 when pushed onto the inner tube 134 is stretched. Furthermore, the sealing ring 166 in his cord diameter D _S greater than the thickness D _Q of the source room 164 , which is half the difference between the outside diameter D _I of the inner tube 134 and the diameter D _A the expansion 160 calculated. For the thickness ratios, reference is made to the above description.

The expansion 160 has a radius at its lower shoulder 168 on. This radius 168 intended to prevent material of the sealing ring 166 penetrates into a corner, which may be one Damage to the soft sealing ring 166 could lead.

At its upper end becomes the source space 164 limited by a substantially cylindrical spacer ring 170 , which has an inner diameter D _R which in turn is about 1/10 mm larger than the outer diameter D _I of the inner tube 134 , The spacer ring 170 is symmetrical at its inner edges (for easier assembly) with chamfers 172 equipped, which allows easier sliding on the inner tube 134 enable.

The inner tube 134 is through a hole 174 the circuit board 128 plugged. After pushing on the spacer ring 170 on the inner tube 134 the spacer ring is supported 170 at its upper end on the circuit board 128 from. Below is the sealing ring 166 on the inner tube 134 deferred, so will, due to the smaller diameter D _D of the sealing ring 166 opposite the inner tube diameter D _I , the distance ring 170 fixed. Subsequently, the outer tube from below 118 with his neck 154 on the sealing ring 166 deferred, whereby this is compressed and the source space 164 completely or partially fills. It is usually the source space 164 such that a certain play for the movement of the outer tube 118 remains in order to be able to absorb pressure surges. At the latest after a few pressure surges, the outer tube becomes 118 However, it must be pushed into its widest possible upper position, and there is a maximum deformation of the sealing ring 166 occur. For a relief of pushing on the neck 154 on the sealing ring 166 is the neck 154 inside, ie in the area of expansion 160 , at its upper peripheral edge with an insertion bevel 176 fitted.

The illustrated arrangement, which the sealing ring 166 made of fluorosilicone rubber and the optimal dimensioning of the source space described above 164 , has been proven in practice to be reliable down to the -40 ° C range to provide a seal between the probe assembly 114 and the sensor assembly 112 to enable. In this way it prevents natural gas through the measuring channel 136 , along the outer wall of the inner tube 134 , through the source room 164 in the area of the circuit board 128 and from there further into the area outside the pressure measuring device 110 can get.

In the 2A and 2 B are perspective views of the pressure measuring device 110 shown, where 2A an exploded view before assembly and 2 B shows an assembled state.

So is in the exploded view in 2A , which also shows the assembly at the same time, to recognize that the sensor assembly 112 designed as a monolithic two-component injection-molded component, with two holes 178 about which the pressure measuring device 110 with the natural gas trail 116 can be connected (for example by screwing). Furthermore, the sensor assembly 112 the connector already described above 132 on.

In the sensor assembly 112 is the pressure measuring cell 122 with their electrical connections 126 placed on the circuit board 128 is plugged. It is between pressure measuring cell 122 and sensor housing 124 an additional fixing adhesive 180 brought in.

The inner tube 134 the pressure measuring cell 122 gets through the hole 174 in the circuit board 128 pushed. Subsequently, the spacer ring 170 deferred, followed by the sealing ring 166 , Also the electrical connections 144 of the temperature sensor 140 be with the corresponding connectors of the connector 132 in the sensor assembly 112 soldered. Subsequently, the temperature sensor 140 put on, and it is added adhesive.

Now the probe assembly 114 with the thus prepared sensor assembly 112 connected. For this purpose, as described above, the inner tube 134 in the pressure measuring channel 136 pushed in, causing the in 1B described seal is produced. Furthermore, the temperature sensor 140 in the temperature sensor receptacle 138 inserted and there by means of Fixierklebung 142 held. Typically, the temperature sensor receptacle 138 , Again, by means of a two-component injection molding, made of particularly thermally conductive plastic, such as metal and / or graphite-filled plastic, for example, again polyamide. As in 2A to recognize, points the probe assembly 114 a base plate 182 on which at the sensor assembly 112 is applied. Subsequently, this base plate 182 by means of the sealing and Halteklebung 146 with the housing of the sensor assembly 112 connected. Finally, the outer sealing ring 152 in the ring groove 150 of the outer tube 118 pushed. After this assembly is the pressure measuring device 110 ready for use. It should be noted that the assembly steps described above can also be performed in a different order than the sequence shown, or, for example, also in partially parallel execution of the method steps.

In 2 B is the pressure measuring device 110 shown again in assembled form. It can be clearly seen again that the outer tube 118 acts as a plug-in sensor, as already in 1A was described, and that the sensor assembly 112 by means of the holes 178 on the natural gas trail 116 (see 1A) can be attached. The plug 132 is executed at an acute angle to the horizontal, to facilitate contact with the pressure measuring device 110 in the natural gas trail 116 mounted pressure measuring device 110 to enable.

Claims (9)

A pressure measuring device (110) for detecting the pressure of a fluid medium (120), comprising at least one pressure measuring cell (122) accommodated in a sensor assembly (112) with an inner tube (134) for receiving the pressure of the fluid medium (120), and a probe assembly ( 114) with an outer tube (118) which can be introduced into the fluid medium (120), wherein the inner tube (134) projects into a pressure measuring channel (136) of the outer tube (118) which can be brought into communication with the fluid medium (120), wherein 134) and outer tube (118) at least one sealing ring (166) is provided, characterized in that the at least one sealing ring (166) as material a fluorosilicone rubber, in particular FVMQ, wherein the at least one sealing ring (166) in a source space (164 ), wherein the pressure measuring channel (136) is configured substantially cylindrical with a widening (160), wherein the inner tube (134) is substantially cylindrical with fit or insignificant ügig smaller diameter than the pressure measuring channel (136) is configured, and wherein the source space (164) is limited by the expansion (160) of the pressure measuring channel (136), the outer wall of the inner tube (134) and a on the inner tube (134) pushed, essentially cylindrical spacer ring (170). Pressure measuring device (110) according to the preceding claim, characterized in that the source space (164) for minimizing damages of the fluorosilicone rubber has at least one of the following configurations: - the difference between inner diameter of the spacer ring (170) and outer diameter of the inner tube (134) is in Range between 0.05 and 0.2 mm, preferably 0.1 mm; - The difference between the inner diameter of the pressure measuring channel (136) and the outer diameter of the inner tube (134) is in the range between 0.05 and 0.2 mm, preferably at 0.1 mm; - The difference between the inner diameter of the pressure measuring channel (136) and outer diameter of the spacer ring (170) is in the range between 0.05 and 0.2 mm, preferably at 0.1 mm. Pressure measuring device (110) according to one of the two preceding claims, characterized in that the at least one source space (164) has a height along the longitudinal extent of the inner tube (134), which is in the range between 1.1 times and 1.5 times. times the cord diameter of the sealing ring (166) is, preferably at 1.25 times the cord diameter. Pressure measuring device (110) according to one of the three preceding claims, characterized in that the at least one source space (164) has a thickness perpendicular to the longitudinal extension of the inner tube (134), which is in the range between 70% and 90% of the cord diameter of the sealing ring (166). , preferably at 80% of the cord diameter. Pressure measuring device (110) according to one of the preceding claims, characterized in that the at least one sealing ring (166) has a ratio between inner diameter and cord diameter between 0.7 and 1.1, preferably at 0.9. Pressure measuring device (110) according to one of the preceding claims, characterized by at least one on the outside of the outer tube (118) applied outer sealing ring (152), wherein the at least one outer sealing ring (152) preferably as a fluorosilicone material, in particular FVMQ having. Pressure measuring device (110) according to one of the preceding claims, characterized in that the pressure measuring device (110) is wholly or partly made of plastic and that the at least one sealing ring (166), and optionally the at least one outer sealing ring (152), in an area without Dividing seam of the plastic is arranged. Pressure measuring device (110) according to one of the preceding claims, characterized in that the sensor assembly (112) and the probe assembly (114) by a sealing and Halteklebung (146) are interconnected. Use of a pressure measuring device (110) according to one of the preceding claims for measuring a gas pressure of an explosive and / or combustible gas (120) in a motor vehicle, in particular for measuring a natural gas pressure in gas-powered motor vehicles.

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