Pressure sensor with membrane and application of such a pressure sensor

Abstract

A pressure sensor with a membrane and the use of such a pressure sensor, the pressure sensor comprising: a sensor housing (3) with a longitudinal axis (A) and an inner cavity (4); a measuring element (5) arranged in the inner cavity (4) of the sensor housing (3); and a rotationally symmetrical membrane (6), the membrane having a peripheral edge portion (7), by means of which the membrane (6) is connected to the end of the pressure chamber side of the sensor housing (3) and seals the inner cavity of the sensor housing (3) on the pressure chamber side; wherein the membrane (6) also has a central pressure plunger (8) operatively connected to the measuring element (5) and a flexible annular membrane segment (9), wherein the annular membrane segment (9) connects the pressure plunger (8) to the peripheral edge portion (7) of the membrane (6); the annular membrane segment (9) is designed in cross section as a circular arc (10) with a constant material thickness and convex on the pressure chamber side.

Description

[0001] This application is a divisional application of the Chinese invention application filed on February 22, 2016 by the applicant Kistler Holding AG, with the invention name “Pressure sensor with membrane and application of such pressure sensor” and application number 201610095080.2. Technical Field

[0002] The invention relates to a pressure sensor having a membrane mounted on the pressure chamber side for measuring the pressure in a pressure chamber, in particular a combustion chamber of an internal combustion engine, and to the use of such a pressure sensor. Background Art

[0003] Pressure sensors for measuring the pressure in a pressure chamber, in particular a combustion chamber of an internal combustion engine, usually have a hollow cylindrical sensor housing in which a measuring element is arranged. The sensor housing is sealed on the pressure chamber side or combustion chamber side by a heat-resistant, flexible membrane, which separates the combustion chamber from the interior of the sensor. The membrane transmits the pressure prevailing in the combustion chamber directly or indirectly to the measuring element.

[0004] A problem that occurs in all known pressure sensors for combustion chambers or pressure chambers with large and rapid temperature fluctuations is the so-called thermal shock. Thermal expansion and mechanical stresses in the sensor and in particular in the membrane due to temperature changes in the pressure chamber can lead to more or less large measurement errors (e.g. due to membrane deformations), which are difficult to correct by calculation. Known membranes that are optimized with regard to thermal shock have a thin-walled, flat design and therefore have a limited service life. Although the service life of the membrane can be increased by using a thicker design, this in turn leads to a higher stiffness and therefore a reduction in the sensor sensitivity. At the same time, the known thicker membrane designs result in a poorer thermal shock behavior (Thermoschockverhalten) of the sensor.

[0005] Patent document US20040231425 describes pressure sensors with different membrane shapes. In order to reduce measurement errors caused by material expansion, a membrane is arranged between a pressure plunger and a fixed edge with a folded or wavy section. In this case, the upward and downward movement of the pressure plunger due to thermal expansion is reduced by providing the section with upward and downward pointing areas. In such membranes, the material thickness is usually uniform or has a maximum thickness in the middle of the pressure plunger area.

[0006] From patent document WO2010040239, a membrane for a pressure sensor is known, which comprises an outer edge and an inner pressure plunger. The outer edge and the inner pressure plunger are connected by an elastic section. Similar to patent document US20040231425, the elastic section has areas pointing upward and downward. In order to reduce the measurement errors caused by thermal expansion, it is also proposed that the material thickness of the elastic section is changed so that it has the thinnest point in the middle, and the material thickness increases continuously from this point to both sides. This produces an articulated membrane, which can better compensate for thermal expansion. However, the disadvantage is that as the membrane gradually becomes thinner, its robustness will also decrease, and therefore its service life will be reduced. Summary of the invention

[0007] The object of the present invention is to provide a pressure sensor in a pressure chamber with large pressure and temperature fluctuations with an optimum measuring accuracy or thermal shock behavior and service life under high stress conditions.

[0008] The object of the present invention is achieved by a pressure sensor having the features of the present invention. The pressure sensor for measuring the pressure in a pressure chamber, in particular a combustion chamber of an internal combustion engine, comprises: a sensor housing having a longitudinal axis and an inner cavity; a measuring element arranged in the inner cavity of the sensor housing; and a rotationally symmetrically configured membrane. The membrane has a peripheral edge portion, through which the membrane is connected to the end of the pressure chamber side of the sensor housing, in particular welded, and seals the inner cavity of the sensor housing on the pressure chamber side. The membrane also has a central pressure plunger that is effectively connected to the measuring element and a flexible annular membrane segment. The annular membrane segment connects the pressure plunger to the peripheral edge portion of the membrane. The annular membrane segment is designed in cross section as a circular arc with a constant material thickness and convex on the pressure chamber side. This convex circular arc-shaped membrane can withstand external pressure better than membranes of other geometric shapes because the pressure supports the robustness of the arc structure. Of course, this advantage can also be maintained if the arc is concave.

[0009] Preferably, the radially inner end point of the arc of uniform thickness is arranged on the pressure chamber side to be set back along the longitudinal axis in the direction toward the inner cavity relative to the radially outer end point of the arc, so that the arc can be extended without protruding out of the edge area of ​​the membrane when viewed in the axial direction A at its front end.

[0010] In fact, under the condition of rotational symmetry, these end points are respectively located on the lines of the circle.

[0011] A membrane with an arc-shaped flexible membrane segment of uniform thickness has a better force distribution than a membrane with a straight portion. This uniform force distribution on the arc reduces the stress in the membrane, which in turn has a positive effect on the robustness of the membrane and thus on the service life. By moving the radial inner end point of the arc or the surface on the pressure chamber side of the pressure plunger back, the arc can be designed at a larger angle (center angle), which further enhances the effect of the arc. In addition, the advantage of this backward movement is that for a given arc angle (center angle) (for example 90 degrees) and a given arc radius, the membrane can also have a smaller outer radius, as if the inner end point is at the same height as the outer end point. It has been confirmed by simulation that by moving the inner end point back, the thermal shock performance can also be improved, or the measurement error of the measuring element, preferably a piezoelectric or piezoresistive measuring element caused by this can be reduced.

[0012] Preferably, the peripheral edge portion of the membrane can extend out of the apex of the arc on the pressure chamber side in the direction of the longitudinal axis. The apex refers to the point of the arc that extends farthest into the pressure chamber when viewed in the longitudinal direction. In extreme cases, the apex can coincide with the outer end point, where the apex is usually between the two end points but closer to the outer end point. By moving the apex of the arc back relative to the pressure chamber in the longitudinal direction with respect to the surface of the pressure chamber side of the peripheral edge portion, a circumferential edge that is higher than the rest of the membrane is formed. Here, the arc does not extend beyond the inner wall of the pressure chamber in the installed state of the pressure sensor, and is therefore better protected under harsh conditions, especially in the combustion chamber. The surface of the peripheral edge portion can be configured horizontally perpendicular to the longitudinal axis. It has also been confirmed by simulation that the thermal shock performance of the membrane can be optimized by the peripheral edge that is higher than the arc.

[0013] The surface of the peripheral edge section can also be arranged displaced at the level of the apex or relative to the apex along the longitudinal axis in the direction toward the inner chamber. In this case, the pressure sensor preferably has a sealing cone or a protective sleeve, which seals the sensor housing relative to the combustion chamber wall and projects the apex of the arc on the pressure chamber side in the direction of the longitudinal axis of the pressure sensor, so that the membrane is arranged offset relative to the pressure chamber wall in the installed state. The sealing cone or the protective sleeve then forms a circumferential edge that is raised relative to the rest of the pressure sensor.

[0014] On the pressure chamber side, in the transition from the annular membrane segment to the peripheral edge portion, a circumferential recess, for example a U-shaped, groove-shaped or V-shaped recess, can be provided, which extends the arc further, i.e. has a larger arc angle. The recess is preferably configured so that a uniform transition without sharp edges is formed between the arc and the recess. The surface of the recess on its radial outer edge facing the pressure chamber side of the peripheral edge portion can form an obtuse angle of 90 to 160 degrees, preferably 120 to 130 degrees. Such a transition can be designed as a sharp, rounded or broken edge.

[0015] The circular arcs may enclose an angle (central angle) of 30 to 120 degrees, preferably 55 to 90 degrees. Under comparable measuring conditions, such a membrane has a higher robustness than conventional membranes.

[0016] The pressure plunger can have an undercut on the interior side in the inner extension of the circular arc, which leads to an increase in the pressure plunger surface acting on the measuring element on the interior side.

[0017] The pressure piston and / or the peripheral edge section are designed to be thicker in the direction of the longitudinal axis of the membrane than the material thickness of the circular arc, so that the annular membrane section constitutes the thinnest and therefore flexible section of the membrane.

[0018] The dimensions and quality of the membrane can be given as follows and can be achieved alone or in any combination with the above features:

[0019] The angle enclosed by the arcs of the circle with constant material thickness is 30 to 120 degrees, preferably 55 to 90 degrees.

[0020] The recess forms an obtuse angle of 90 to 160 degrees, preferably 120 to 130 degrees, at its radial outer edge with respect to the surface of the outer peripheral edge portion on the pressure chamber side.

[0021] On the interior side, tangents at the outer end points of the extension of the circular arc enclose an opening angle of 10 to 80 degrees, preferably 30 to 40 degrees, with the longitudinal axis of the sensor housing.

[0022] The ratio of the outer arc radius to the outer radius of the membrane is about 0.1 to 0.4, preferably about 0.25.

[0023] The membrane can be made, for example, of steel, an iron-based alloy, a nickel-based alloy, a cobalt-based alloy or a titanium-based alloy having high strength and high temperature resistance.

[0024] The invention also relates to the use of a pressure sensor having the above-mentioned features for measuring the pressure in the combustion chamber of an internal combustion engine. Such a pressure sensor can also be used in internal ballistics, for example in a pressure chamber, where fast and large pressure and temperature changes also occur. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The present invention will be described in detail below with reference to the embodiments and in conjunction with the accompanying drawings.

[0026] Figure 1 A cross-sectional view showing a first embodiment of a membrane of a pressure sensor according to the present invention;

[0027] Figure 2 a cross-sectional view showing a second embodiment of a membrane of a pressure sensor; and

[0028] Figure 3 A third specific embodiment of a membrane of a pressure sensor is shown in cross section.

[0029] The reference numerals are described as follows:

[0030] 1Pressure sensor

[0031] 2Pressure chamber

[0032] 3Sensor housing

[0033] 4 Inner cavity

[0034] 5. Measuring element

[0035] 6. Film

[0036] 7 Outer edge part

[0037] 8 Pressure plunger

[0038] 9 Ring membrane segment

[0039] 10 Arc

[0040] 11 recesses

[0041] 12 Pressure chamber wall

[0042] 13 central basin

[0043] 14 Undercut

[0044] 15 Inner wall

[0045] 16 Surface of the edge portion

[0046] 17 Sealing cone / protective sleeve

[0047] A longitudinal axis

[0048] P1 Radial inner end point of the arc

[0049] P2 The radial outer end point of the arc

[0050] Vertex of S1 arc DETAILED DESCRIPTION

[0051] exist Figure 1 and Figure 2 , an embodiment of a membrane 6 of a pressure sensor 1 for measuring the pressure in a pressure chamber, in particular in a combustion chamber of an internal combustion engine, is shown in a sectional view. The pressure sensor 1 comprises a hollow cylindrical sensor housing 3 with an inner cavity 4, and a measuring element 5, preferably a piezoelectric or piezoresistive measuring element, arranged in the inner cavity 4. The sensor housing 3 and the measuring element 5 are only partially shown. Other elements of the pressure sensor, such as electrical interfaces or supports for the measuring element on the sensor housing, are not shown. The pressure sensor 1 is, for example, screwed into a suitable opening in an engine block in a sealing manner or fixed in another way, for example. The inner wall 12 of the pressure chamber 2 is indicated in the figure in the region of the membrane 6 by a dashed line.

[0052] The rotationally symmetrical membrane 6 has a peripheral edge portion 7, a central pressure plunger 8 and a flexible annular membrane segment 9. The membrane is fixedly welded to the upper edge of the hollow cylindrical sensor housing 3 via the peripheral edge portion 7 and seals the inner cavity 4 of the sensor housing 3 relative to the pressure chamber 2. In the embodiment shown, the membrane and the sensor housing are connected edge to edge. Other connections (such as a circumferential seam) are also possible. The flexible annular membrane segment 9 connects the peripheral edge portion 7 to the central pressure plunger 8. The central pressure plunger 8 is effectively connected to the measuring element 5, so that the measuring element 5 detects the displacement of the pressure plunger 8 along the longitudinal axis A of the pressure sensor 1 due to the internal pressure in the pressure chamber 2.

[0053] The annular membrane segment 9 is constructed in cross section as an arc 10 which is convex on the pressure chamber side and has a vertex S1 which is the highest in the axial direction. The arc 10 has a constant material thickness and is designed to be thinner than the peripheral edge portion 7 or the central pressure plunger 8. The arc 10 defines a central pot 13 on the pressure plunger 8, which has a substantially flat bottom. Where the arc 10 is connected to the bottom of the central pot 13, the arc has a radial inner end point P1 on the pressure chamber side. The arc has a radial outer end point P2 at the connection point with the peripheral edge portion 7, wherein the inner end point P1 is set back relative to the outer end point P2 along the longitudinal axis A in the direction of the inner cavity 4. In addition, the vertex S1 of the arc 10 is preferably set lower than the surface 16 on the pressure chamber side of the peripheral edge portion 7. The surface 16 on the pressure chamber side of the peripheral edge portion 7 preferably protrudes from the arc 10 so that the surface is substantially aligned with the wall 12 of the pressure chamber 2 in the installed state of the pressure sensor 1, and the arc 10 does not extend into the pressure chamber 2. The peripheral edge portion 7 forms a peripheral edge which in this case projects above the remainder of the membrane 6 .

[0054] Depend on Figure 1 and Figure 2It can be clearly seen that, when the arc radius remains unchanged, the angle α (center angle α) enclosed by the arc 10 can be increased by moving the inner end point P1 or the bottom of the basin 13 further downward. Figure 1 In the case of Figure 2 In addition, the angle α of the arc 10 can also be increased by the design or depth of the circumferential recess 11, which is formed on the radially inwardly pointing side of the peripheral edge portion 7 on the pressure chamber side. Usually, the deepest point of the recess 11 corresponds essentially to the outer end point P2 of the arc 10.

[0055] In this embodiment, the recess 11 forms an obtuse angle γ of preferably about 135 degrees at its radial outer edge with respect to the surface 16 of the pressure chamber side of the peripheral edge part 7. A sharp edge is formed at the transition. On the inner chamber side, the tangent at the end point of the extension of the arc 10, more precisely the tangent at the transition of the annular membrane segment 9 to the peripheral edge part 7, encloses an opening angle β of about 30 degrees with the longitudinal axis A of the cylindrical sensor housing or with the inner wall 15 of the cylindrical sensor housing 3, which is parallel to the longitudinal axis A in the embodiment shown.

[0056] In such Figure 2 In the embodiment according to the invention shown, the pressure plunger 8 has an undercut 14 on the inner side, in the inner extension of the arc 10 , which leads to an increase in the surface of the pressure plunger 8 acting on the measuring element 5 on the inner side.

[0057] Different from Figure 1 and Figure 2 In the implementation method, Figure 3 In the embodiment of the membrane 6, the surface 16 of the peripheral edge portion 7 is approximately at the height of the vertex S1. This surface 16 can also be moved further toward the inner cavity 4 along the longitudinal axis A and arranged at a height between the vertex S1 and the outer end point P2. In this embodiment, the pressure sensor 1 has a sealing cone or protective sleeve 17, which protrudes from the vertex S1 on the pressure chamber side in the direction of the longitudinal axis A, so that the membrane is set back relative to the wall 12 of the pressure chamber 2.

Claims

1. A pressure sensor (1) for measuring the pressure in a pressure chamber (2), include: A sensor housing (3) having a longitudinal axis (A) and an inner cavity (4); a measuring element (5) arranged in the inner cavity (4) of the sensor housing (3); and a rotationally symmetrical membrane (6) having a peripheral edge portion (7), the membrane (6) being connected to the end of the sensor housing (3) on the pressure chamber side by means of the peripheral edge portion and sealingly closing the inner cavity of the sensor housing (3) on the pressure chamber side, wherein the membrane (6) also has a central pressure plunger (8) operatively connected to the measuring element (5) and a flexible annular membrane segment (9), the annular membrane segment connecting the pressure plunger (8) to the peripheral edge portion (7), The invention is characterized in that the flexible annular membrane section (9) is designed as a circular arc (10) with a constant material thickness and convex on the pressure chamber side when viewed in cross section. The arc forms an angle (α) of 30 to 90 degrees, The radially inner end point (P1) of the circular arc (10) on the pressure chamber side is arranged offset relative to the radially outer end point (P2) of the circular arc (10) along the longitudinal axis (A) in the direction toward the inner cavity (4), The circular arc (10) has a vertex (S1) which does not protrude into the pressure chamber (2) in the direction of the longitudinal axis (A), And the apex (S1) is arranged to be lower than the surface (16) on the pressure chamber side of the peripheral edge portion (7) in the direction of the longitudinal axis (A).

2. The pressure sensor according to claim 1, It is characterized in that The pressure chamber (2) is a combustion chamber of an internal combustion engine.

3. The pressure sensor according to claim 1, It is characterized in that The membrane (6) is made of steel, nickel-based alloy, iron-based alloy, cobalt-based alloy or titanium-based alloy.

4. The pressure sensor according to claim 1, It is characterized in that On the pressure chamber side, a circumferential recess (11) is formed in the transition of the annular membrane segment (9) to the peripheral edge section (7).

5. The pressure sensor according to claim 4, It is characterized in that The recess (11) forms an obtuse angle (γ) of 90 to 160 degrees at its radial outer edge with respect to a surface (16) on the pressure chamber side of the outer peripheral edge portion (7).

6. The pressure sensor according to claim 5, It is characterized in that The recess (11) forms an obtuse angle (γ) of 120 to 130 degrees at its radial outer edge with respect to a surface (16) on the pressure chamber side of the outer peripheral edge portion (7).

7. The pressure sensor according to any one of claims 1 to 6, It is characterized in that On the inner chamber side, a tangent line at the outer end point of the extension of the arc (10) encloses an opening angle (β) of 10 to 80 degrees with the longitudinal axis (A) of the sensor housing.

8. The pressure sensor according to claim 7, It is characterized in that On the inner chamber side, a tangent line at the outer end point of the extension of the arc (10) encloses an opening angle (β) of 30 to 40 degrees with the longitudinal axis (A) of the sensor housing.

9. The pressure sensor according to any one of claims 1 to 6, It is characterized in that The pressure plunger (8) has an undercut (14) on the inner cavity side in the inner extension of the circular arc (10).

10. The pressure sensor according to any one of claims 1 to 6, It is characterized in that The pressure plunger (8) and / or the peripheral edge section (7) are designed to be thicker than the material thickness of the circular arc (10) in the direction of the longitudinal axis (A) of the membrane (6).

11. The pressure sensor according to any one of claims 1 to 6, It is characterized in that On the pressure chamber side, centrally above the pressure piston (8), a central pot (13) is formed which is defined by the annular membrane segment (9) and has a substantially flat or circular bottom. 12 . Use of a pressure sensor according to claim 1 in a combustion chamber of an internal combustion engine or for internal ballistics.

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