SHORT DESCRIPTION OF THE DRAWINGS
In the following the invention is explained in more detail by referring to the drawings.
The Figures show:
FIG. 1 a schematic sectional representation of a sealing system according to the prior art;
FIG. 2 another schematic sectional representation of a sealing system according to the prior art;
FIG. 3 a schematic sectional representation of a high-pressure sensor according to the present invention;
FIG. 4 a detailed representation of a sealing system of the high-pressure sensor according to the present invention
- a) in an unbraced state, and
- b) in a braced state;
FIG. 5 a detailed representation of an alternative sealing system of the high-pressure sensor according to the present invention
- a) in an unbraced state, and
- b) in a braced state.
WAYS OF PRACTICING THE INVENTION
FIG. 1 shows a schematic perspective view of a conical sealing according to the prior art. The arrow P denotes the respective pressure arising during a measurement. Within a housing 2 there is shown an inner part 3 engaging therewith and braced therewith by means of a thread which has an outwardly facing cone. This cone relies on a corresponding opposite cone at the housing 2 thereby forming a sealing portion 8. Since the cone at the inner part 3 is clearly more elastic than the housing 2 a relative movement between the components mentioned may occur resulting in wear and eventually in leakiness of the sealing portion 8.
FIG. 2 shows another sealing system according to the prior art. This system has an intermediate part 18 between an inner part 3 and a housing 2.
FIG. 3 shows a high-pressure sensor 1 according to the invention. It comprises a housing 2 as well as an inner part 3 attached by means of a shaft 4 to a projection 6 at the housing 2 under an applied clamping force. In this example the clamping force has been achieved by means of a thread. Other possibilities comprise welding the housing 2 to the inner part 3. The interior 19 of the inner part 3 may accommodate a sensor element sealed against the pressure chamber 21 by a membrane 20.
The sealing area 22 of the high-pressure sensor 1 according to the invention is shown in more detail in FIG. 4. FIG. 4a represents the shaft 4 of the inner part 3 as well as the housing 2 with its projection 6 in an unbraced state. The shaft 4 has an end face 5 as well as an inner surface 9 and an outer surface 10. The housing 2 has a supporting surface 7 as well as an inner surface 11 and an outer surface 12.
In contrast to the prior art according to FIG. 1 the angles α, β of the conical sealing are oriented in different directions. I.e. particularly the supporting surface 7 is arranged in an acute angle α with respect to the inner surface 11 of the projection. It may be contemplated to embody the end face 5 on the shaft 4 in a planar manner, perpendicularly to the direction of pressure. The end face 5, however, is preferably arranged in an obtuse angle β to the inner surface 9 of the shaft 4 as represented in this embodiment. Preferably, an open angle of about 1-2° remains between the end face 5 and the supporting surface 7. The acute angle α and the obtuse angle β mentioned above are together less than or equal to 1800. Preferably, the sum of these two angles α and β is between 170 and 180°.
According to the invention, the acute angle α of the projection should be between 45 and 70°, preferably between 60 and 70°. Accordingly, according to the invention the obtuse angle β of the shaft should be between 110 and 135°, preferably between 110° and 120°.
FIG. 4
b shows the shaft 4 of the inner part 3 as well as the projection 6 of the housing 2 in a braced state. This bracing has been generated by a clamping force acting on the housing 2 and the inner part 3 as indicated by the arrows in FIG. 4a. Due to this clamping force, the end face 5 fits closely to the supporting surface 7 at least along a sealing line 8.
This clamping force results in deformations and distortions of individual regions of the housing 2 and the inner part 3. Thus, due to the mutual pressure the inner surface 11 of the projection is pushed in an inward direction, while simultaneously the end portion of the shaft 4 and in particular its inner surface 9 and outer surface 11 are pushed in an outward direction. According to the invention, the shaft 4 is now supported by the housing 2. Preferably, projection 6 is provided with an undercut 14 so that the outer surface of the shaft 10 is able to move somewhat into the region of the undercut 14. Thereby, a second contact is created between the housing 2 and the inner part 3 at the outer surface 12 of the projection near a region where the undercut 14 begins. Along this support line 13 the shaft 4 rests on the housing 2. Because it rests on the housing 2 the shaft 4 is firmly tightened within the projection 6. If a high pressure is applied to the sensor the shaft 4 is unable to move further to the outside and thereby increases the pressure onto this support line 13. Concomitantly, the pressure acts on the inner surface 11 of the projection thereby further increasing the sealing effect.
The support line 13 from the shaft 4 to the housing 2 can be embodied as a second sealing zone if all perimeters of both components 2, 3 lack notches in the area of the support line 13.
As an alternative solution to the undercut 14, the edge between the outer surface of the shaft 10 and the end face 5 of the shaft 4, as shown in FIG. 5, can be provided with a flattening 24. Both versions as shown in FIG. 4 and FIG. 5 result in the definition of the support line 13 as a second sealing zone when a pressure is applied. Due to the definition of this sealing zone as edge or line, a high pressure per surface is assured. By contrast, the pressure per surface of an undefined, two-dimensional shaped sealing zone would be lower and the thereby achieved sealing unsafe. The undercut 14 and/or the flattening 24 serve different functions. Upon application of the clamping force the volume in the region between the two sealing zones is decreased generating a pressure which counteracts the clamping force. The higher the volume the smaller is the pressure. Without an undercut 14 or a flattening 24 the volume is very small; namely it is limited by the angle opening of 180°-α-β between the support surface 7 and the end face 5 since in this case the support line 13 meets the corner of the outer end face 5. Secondly, the undercut 14 or a flattening 24 ensure further engagement of the shaft 4 with the housing 2 thereby increasing the tightening.
A ventilation channel 15 as shown in FIG. 3 can be provided in the area of the undercut 14 or a flattening 24 to the surrounding 17 in order to avoid the building up of pressure upon application of the clamping force. This ventilation channel 17 can extend directly across the housing 2. Alternatively, the shaft 4 or the projection 6 may have a notch along their outer surface 10 or 12, respectively, serving as a ventilation channel 15.
Since upon application of the clamping force the inner surfaces 9, 11 of shaft and projection are displaced relatively to each other they may be adapted accordingly. Advantageously in an unbraced state the inner surface 11 of the projection is positioned more to the outside than the inner surface 9 of the shaft. By the displacement described of the components upon application of the clamping force the two inner surfaces 9, 11 are pushed closer to each other.
On the other hand it may be advantageous that in an unbraced state the inner surface 11 of the projection is located more inside than the inner surface 9 of the shaft. By this it can be avoided that upon application of a clamping force the sharp edge between the support surface 7 and the inner surface 11 of the projection notches into the end face 5 of the inner part 3 thereby preventing the desired relative movement between end face and support surface.
An advantage of the above-mentioned sealing system is the uniform rigidity of the inner wall in the area of the sealing region 22 due to the fact that the shaft 4 rests on the housing 2. In the embodiment of the prior art according to FIG. 1 the shaft 4 of the inner part 3 is softer than the portion of the housing 2 onto which the pressure to be measured directly acts. This can be prevented by means of the support 13 in the embodiment according to the invention. Also, this does not create relative movements between the inner part 3 and the housing 2 thus decreasing the scuffing tendency along the contact line.
The direction of the seal surface 13 is in the direction the pressure to be measured affects the inner part 3 and/or the shaft 4. This provides a seal which increases with increasing pressure, but without providing extra load on the pressure capsule, thus providing good strain isolation for the pressure capsule from the external strains in the pressure containment housing.
Another particular embodiment relates to the materials of the housing 2 and the inner part 3. Preferably, these components should be composed of different materials or of materials of different hardness. This also reduces scuffing, in particular this prevents cold welding at the sealing line 7 and at the support line 13. Such cold welding is inconvenient particularly if the final clamping force or pre-tension has not yet been applied. Preferably, the inner part 3 is rather harder because this prevents the sharp edge between the support surface 7 and the inner surface 11 of the projection to notch into the end face 5 of the inner part 3 upon application of the clamping force which would prevent the desired relative movement between end face 5 and support surface 7.
According to the invention, a high-pressure sensor 1 is equipped with a sealing system of the above-mentioned type. Specifically for sensors having an inner diameter 23 of at least 10, preferably at least 15 mm such sealing systems are advantageous because conventional solutions often fail in the case of such big sensors. This is particularly true for oil-filled piezo-resistive high-pressure sensors provided with a silicon chip.
LIST OF DESIGNATIONS
1 high-pressure sensor
2 housing
3 inner part
4 shaft
5 end face
6 projection
7 support area
8 sealing line
9 inner surface of the shaft
10 outer surface of the shaft
11 inner surface of the projection
12 outer surface of the projection
13 support line
14 undercut
15 ventilation channel
16 inner diameter
17 surrounding
18 intermediate part
19 interior of inner part
20 Membrane
21 pressure chamber
22 sealing area
23 inner diameter
24 flattening
- α angle between support surface and inner surface of the projection
- β angle between end face and inner surface of the shaft
Patent Application
20080028862
