pressure sensor

Abstract

The invention relates to a pressure sensor for detecting a combustion chamber pressure in internal combustion engines, in particular diesel, hydrogen and / or gas engines, comprising a support structure designed to protrude with its front side into a pressure measuring chamber, a connecting channel provided in the support structure and forming a connection from the front side to a rear side of the support structure, and a measuring element provided on the rear side of the support structure and enabling a conclusion to be drawn about a pressure prevailing in the region of the front side of the support structure, wherein the connecting channel comprises a front-side channel section, a central channel section and a rear-side channel section, characterized in that the central channel section has a cross-section that increases from the front side towards the rear side, in particular increases continuously,and preferably the rear channel section adjoining the central channel section has a cross-section which is smaller than the maximum cross-section of the central channel section.,

Description

[0001] The present invention relates to a pressure sensor for detecting a pressure, for example a combustion chamber pressure in internal combustion engines.

[0002] Such pressure sensors, also called pressure transducers or pressure transmitters, have been used for some time to measure the pressure in the combustion chambers of internal combustion engines, preferably for measuring the working pressures in the cylinder heads of internal combustion engines, e.g., for 2- or 4-stroke marine diesel and gas engines, etc. In this case, considerable pressures (peak pressures of up to several hundred bar) must be managed at average combustion chamber temperatures in the range of approximately 2000 to 3000 degrees Celsius, which can even exceed this at certain locations in the combustion chamber.

[0003] The reliability and accuracy of combustion pressure measurement in piston engines are critical to engine performance and longevity. Sensor failures that occur during this measurement are predominantly due to the phenomenon of overpressure. Overpressure can be caused by a number of internal engine processes, including knocking, pre-ignition, and pre-ignition. These events lead to abnormally high pressure spikes within the combustion chamber, which can damage the pressure sensors or significantly shorten their service life. Spark plug problems, such as incorrect ignition timing or a defective spark plug causing misfiring, can also lead to undesirable overpressure.

[0004] Advanced engine control based on precise cylinder pressure measurements is one method to minimize the risk of harmful overpressure. By accurately monitoring combustion pressure, such control systems can optimize engine operation and detect conditions that lead to overpressure early and adjust accordingly. However, this technology alone cannot completely eliminate the risk, especially in scenarios outside of normal operating conditions.

[0005] Given the increasing demands of engine manufacturers for performance and reliability, the development of even more robust pressure sensors is essential. These pressure sensors must not only be capable of performing precise measurements under extreme conditions, but also withstand the stresses caused by high pressure peaks. Particularly in the development of hydrogen engines, which are known for their high combustion efficiency and potentially lower emissions, significantly higher peak pressures must be expected compared to conventional gasoline or diesel engines. These increased pressures pose an additional challenge for sensor technology, as they further increase the material and design requirements for the pressure sensors.

[0006] If a conventional pressure sensor is subjected to excessive pressure, this will result in the deformable diaphragm used to detect the pressure becoming permanently bent or deformed. This will cause a zero point shift in the pressure measurement due to the affected diaphragm. In such a case, the structural damage to the diaphragm will result in a pressure value other than zero being output even though no pressure is actually acting on the diaphragm. In addition, the deformation of the measuring diaphragm caused by a pressure peak can also lead to damage to the measuring structure arranged on the measuring side of the diaphragm, for example through a circuit breaker or similar. This would result in the immediate total failure of the pressure sensor, necessitating immediate replacement.

[0007] In this context, it becomes clear that the further development of pressure sensors plays an important role in engine technology. More robust pressure sensors enable more efficient and safer engine control, thus enabling innovative drive solutions that are not only more powerful but also more environmentally friendly.

[0008] A widely used version of such a pressure sensor on the market features an axial gas flow through a channel extending from the front of the pressure sensor into the interior, which leads to a diaphragm pressure measuring cell located away from the combustion chamber. This diaphragm pressure measuring cell is available in large quantities as a cost-effective component, primarily using thin-film technology with strain gauges as the pressure measuring element.

[0009] It is the object of the present invention to overcome or mitigate the various deficiencies of conventional pressure sensors outlined above and to create a pressure sensor that is significantly more resistant to pressure peaks and can therefore also be used without problems, for example, in the field of hydrogen engines.

[0010] This object is achieved by a pressure sensor according to the invention which has all the features of claim 1. Advantageous embodiments of the pressure sensor are listed in the dependent claims.

[0011] The pressure sensor according to the invention for detecting a combustion chamber pressure in internal combustion engines, in particular diesel, hydrogen and / or gas engines, comprises a support structure which is designed such that its front side projects into a pressure measuring chamber, a connecting channel which is provided in the support structure and forms a connection from the front side to a rear side of the support structure, and a measuring element which is provided on the rear side of the support structure and enables a conclusion to be drawn about a pressure prevailing in the region of the front side of the support structure, wherein the connecting channel comprises a front-side channel section, a central channel section and a rear-side channel section.The pressure sensor is characterized in that the central channel section has a cross-section that increases from the front to the rear, in particular increases continuously, and preferably the rear channel section adjoining the central channel section has a cross-section that is smaller than the maximum cross-section of the central channel section. It will be clear to those skilled in the art that the invention also encompasses the case in which the central section undergoes one (or more) sudden, cylindrical expansion(s).

[0012] With such a pressure sensor it is possible to reduce the pressure peaks so that the load on the measuring element is lower than with conventional pressure sensors. This ultimately makes the pressure sensor according to the invention more durable and robust. The pressure peaks are reduced by the special design of the connecting channel which runs through the support structure. The middle channel section has an increasing cross-section so that the speed of a pressure wave under very high pressure as well as the force of pressure peaks acting on the measuring element are reduced. In advantageous combination with the rear channel section, whose cross-section is smaller than the maximum cross-section of the widening middle channel section, this results in even more efficient destruction orConversion of pressure energy of the pressure wave propagating in the connecting channel, whereby the unwanted pressure peaks, which are often responsible for damage to the pressure sensor or the measuring element that detects the pressure, can be mitigated.

[0013] The pressure sensor according to the invention, whose central channel section of the connecting channel has a widening cross-section from the front to the back of the support structure, acts as a low-pass filter for the pressure changes to be detected. This means that comparatively slow pressure changes, which occur, for example, during normal combustion in an internal combustion engine, are not influenced by the specific design of the connecting channel, whereas pressure peaks that are potentially damaging to the measuring element and are subject to rapid changes and reach high absolute values ​​compared to a normal pressure level are dampened. Such harmful pressure peaks can be generated, for example, during knocking combustion in an internal combustion engine.

[0014] According to a further development of the present invention, it can further be provided that the connecting channel with the front channel section, the middle channel section and the rear channel section runs in a straight line.

[0015] Accordingly, it can be provided that the connecting channel extends approximately in a straight line from the front to the back.

[0016] According to a further optional modification of the present invention, it can be provided that the front channel section, the middle channel section, and / or the rear channel section are / are designed with at least twofold rotational symmetry, preferably with at least twofold rotational symmetry to a common axis of rotation. The rotationally symmetrical design is particularly advantageous during production and assembly.

[0017] For the specific design of the connecting channel or its multiple channel sections, it is advantageous if they are designed with at least twofold rotational symmetry. A particularly advantageous design is the implementation of the connecting channel in a continuous symmetry, which can be achieved, for example, by drilling the different channel sections.

[0018] According to a further development of the present invention, it can be provided that the front channel section, the middle channel section and the rear channel section each directly adjoin one another.

[0019] Accordingly, the connecting channel can comprise a section which, viewed from the front, has the front channel section, the middle channel section and the rear channel section without any other channel sections in between.

[0020] According to a further advantageous embodiment of the present invention, it can be provided that the support structure, in particular the support structure and the measuring element, is / are made of a material which has a thermal conductivity which is at least 45 W / (m·K), preferably at least 50 W / (m·K) and according to a particularly preferred embodiment at least 55 W / (m·K).

[0021] Conventional stainless steels have a thermal conductivity in the range of 15-20 W / (m K), so the provision of the central channel section according to the invention, in which pressure energy is converted into thermal energy, can lead to adverse heating of the support structure or the measuring element connected to the support structure. A material with improved thermal conductivity compared to conventional stainless steels is advantageous in this regard, as heat dissipation occurs more quickly.

[0022] According to a further optional modification of the present invention, it can be provided that the cross section of the front channel section is smaller than the cross section of the rear channel section, preferably wherein the maximum cross section of the front channel section is smaller than the maximum cross section of the rear channel section.

[0023] This applies in particular to the cross-section of the front channel section, which directly borders the central channel end, compared to the cross-section of the rear channel section, which also directly borders the central channel section. If the front channel section and the rear channel section have a constant cross-section in the axial direction, consideration of the respective cross-sections in the directly adjacent areas of the central channel section is of course irrelevant.

[0024] Furthermore, it can also be provided that the cross-sectional contour in the transition area from the middle channel section to the rear channel section is identical or not identical.

[0025] It has been shown that the smaller cross-section of the front channel section provides particularly effective damping of unwanted pressure peaks compared to the larger cross-section of the rear channel section.

[0026] According to a further optional development of the present invention, it can be provided that the cross section of the front-side channel section corresponds to the minimum cross section of the middle channel section, preferably wherein the maximum cross section of the front-side channel section corresponds to the minimum cross section of the middle channel section.

[0027] This applies in particular to the cross-section of the front channel section, which directly borders the middle channel section. It can also be provided that the cross-sectional contour in the transition area between the front channel section and the middle channel section is identical.

[0028] According to a modification of the present invention, it can be provided that the cross section of the front channel section and / or the cross section of the rear channel section is the same over its respective length.

[0029] This results in a particularly simple design of the front channel section and / or the rear channel section, since the formation of the corresponding channel section can then be implemented, for example, using a simple drilling process.

[0030] According to a further advantageous development of the present invention, it can be provided that in the transition area from the middle channel section to the rear channel section, due to the smaller cross section of the rear channel section compared to the larger cross section of the middle channel section adjacent to the rear channel section, there is an impact surface which connects the two different cross sections of the middle channel section and the rear channel section.

[0031] This impact surface can be designed in such a way that it reflects a pressure wave propagating from the front towards the back of the supporting structure, so that pressure energy is destroyed or converted into other forms of energy (primarily heat).

[0032] Furthermore, it can be provided that the impact surface is aligned perpendicular to a rotational axis of the central channel section or forms an obtuse angle with it. The impact surface can thus lie in a plane whose normal is parallel to the rotational axis of the central channel section.

[0033] If the impact surface forms an obtuse angle with a rotation axis of the central channel section, there is an area undercut by the central channel section which, in a longitudinal sectional view, is formed at an acute angle to the rotation axis, whereby this acute angle together with the obtuse angle of the impact surface results in 180°.

[0034] According to a further development of the present invention, the cross-section can be determined by the maximum distance between two points in the cross-sectional plane. For example, in a circular channel section, the cross-section is the diameter of the circle.

[0035] According to a further advantageous embodiment of the present invention, it can be provided that the central channel section has the shape of a truncated pyramid or truncated cone, which faces with its smaller base area the front channel section and its larger base area the rear channel section, preferably wherein the central channel section has the shape of an equilateral truncated pyramid or a straight truncated cone.

[0036] It can further be provided that the smaller base area is identical to a cross section of the front-side channel section, preferably wherein the cross section of the front-side channel section does not change along its longitudinal direction.

[0037] Furthermore, it can be provided that the rear channel section is arranged in the larger base area, preferably in such a way that the rear channel section is arranged centrally in the larger base area and branches off from it.

[0038] Furthermore, it can be provided that the larger base surface is not oriented perpendicular to the longitudinal direction of the central channel section, but rather extends toward the smaller base surface and is itself formed, for example, by the lateral surface of a straight truncated cone or an equilateral truncated pyramid. In such a configuration, the larger base surface forms an obtuse angle with a rotational axis of the central channel section.

[0039] In a further optional modification of the present invention, the measuring element can be supported by the support structure and preferably arranged on the rear side of the support structure. According to the invention, the support structure and the measuring element can also be formed as a single piece, with 3D printing or a casting process being particularly suitable for production.

[0040] Furthermore, according to the present invention, it can be provided that the measuring element is a deformable membrane which stretches over the outlet region of the connecting channel, preferably wherein the membrane and a membrane carrier supporting the membrane are pot-shaped or cup-shaped and sits with the edge of the pot shape or the cup shape on the support structure and surrounds the outlet region of the connecting channel.

[0041] It can further be provided that a shielding element is provided in the connecting channel between the rear channel section and the outlet region in order to protect a region of the membrane, in particular a central region of the membrane, from a direct pressure wave from the pressure measuring chamber.

[0042] Furthermore, it can be provided that the shielding element is designed in such a way that the outlet of the pressure wave from the connecting channel occurs axially directly onto the membrane.

[0043] There is therefore no deflection of the flow direction of the pressure wave propagating from the front towards the back of the supporting structure in the connecting channel, but merely a reduction in cross-section by the shielding element.

[0044] According to a further development of the invention, the support structure can be accommodated in a pressure sensor housing having a thread on its outer circumference. This thread can serve to screw the pressure sensor into a corresponding mating thread in a recess of the combustion chamber, so that the front side of the support element protrudes into the combustion chamber.

[0045] According to a further advantageous modification of the invention, a cross-section of the front channel section can be in the range of 0.4 mm to 1 mm, preferably in the range of 0.5 mm to 0.7 mm, and most preferably in the range of 0.55 mm to 0.65 mm. Such a cross-section can be circular and / or extend over the entire length of the front section in an identical configuration.

[0046] Furthermore, according to the present invention, a cross-section of the rear channel section can be in the range of 3.5 mm to 7 mm, preferably in the range of 4 mm to 6 mm, and most preferably in the range of 4.7 to 4.9 mm. Such a cross-section can be circular and / or extend over the entire length of the rear section in an identical configuration.

[0047] Further advantages, features, and details of the invention will become apparent from the following description of the figures. These show: Fig. 1: a sectional view of a pressure sensor according to the invention, Fig. 2: a perspective view of the back of the support structure of the pressure sensor from above, Fig. 3: a diagram comparing a pressure curve in the center of the membrane during combustion in a hydrogen engine of a conventional pressure sensor with the pressure curve of a pressure sensor according to the invention, Fig. 4: a diagram showing the load curve of the membrane in comparison of a conventional pressure sensor with a pressure sensor according to the invention, Fig. 5a: a diagram illustrating the pressure curve during knocking combustion in a hydrogen engine, measured with a conventional pressure sensor, and Fig. 5b: a diagram illustrating the pressure curve during knocking combustion in a hydrogen engine, measured with a pressure sensor according to the invention.

[0048] Fig. 1 shows a sectional view of the pressure sensor 1 according to the invention. A pressure sensor housing 15 and a support structure 2 arranged in the lower region of the pressure sensor housing 15 can be seen. This support structure 2 is designed to protrude into a pressure chamber 4 so that a measuring element 7 can draw a conclusion about a pressure prevailing in the pressure chamber 4.

[0049] The support structure 2 has a front side 3 facing the pressure chamber 4. The measuring element 7 for detecting pressure is arranged on the rear side 6 of the support structure 2, opposite the front side 3. To create a connection to the measuring element 7, the support structure 2 has a connecting channel 5, which has a front channel section 8, a central channel section 9, and a rear channel section 10. The central channel section 9 is arranged between the front channel section 8 and the rear channel section 10.

[0050] An optionally provided shielding element 13 shields a center of the measuring element 7, typically implemented as a movable membrane, from a direct axial flow of a pressure wave from the pressure chamber 4.

[0051] For the desired insulation effect of pressure peaks that can occur in the combustion chamber 4 and represent an excessive stress for the measuring element 7, it is provided according to the invention that the central channel section 9 has a cross-section that increases in the direction from the front to the rear of the support structure 2, in particular increases continuously.

[0052] In the Fig. 1, the contour of the central channel section 9 corresponds to a straight truncated cone, the smaller base A1 of which is directed towards the front side 3 and the larger base A2 of which is directed towards the rear side 6.

[0053] It can also be seen that the cross section of the rear channel section 10 is smaller than the largest cross section of the middle channel section 9, so that in the transition area from the middle channel section 9 to the rear channel section 10 an impact surface 11 is formed, which serves to reflect a pressure wave which propagates at high speed from the front side 3 to the rear side 3 of the support structure through the connecting channel 5.

[0054] In addition, you can Fig. 1 that the cross section of the rear channel section 10 is larger than the cross section of the front channel section 8.

[0055] As non-limiting examples for a cross-section of the front channel section 8, a range of 0.4 mm to 1 mm, preferably 0.5 mm to 0.7 mm or 0.55 mm to 0.65 mm can be given.

[0056] For a cross section of the rear channel section 9, a range of 3.5 mm to 7 mm, preferably 4 mm to 6 mm and more preferably 4.7 mm to 4.9 mm can be specified.

[0057] In addition, Fig. 1 the measuring element 7 is designed by a membrane and a membrane carrier 14 which is designed in the shape of a pot or a cup and encloses the outlet area 12 of the connecting channel 5.

[0058] The arrangement position of the support structure 2 is shown projecting relative to the outer housing 15 at the front end of the outer housing 15 facing the pressure chamber 4, but the person skilled in the art will recognize that a recessed arrangement position of the support structure 2 in the interior of the outer housing 15 is also encompassed by the invention.

[0059] Fig. 2 shows a perspective view of a rear side 6 of the support structure 2 in which the shielding element 13 and the outlet area 12 can be seen.

[0060] Fig. Figure 3 shows recorded pressure values ​​in the center of the membrane for a rapid pressure increase from 50 bar to 270 bar. The dashed line shows the pressure values ​​for the Fig. 4, bottom left, shows the pressure sensor, which corresponds to a conventional pressure sensor and was used as a comparison example. Comparable results are also provided by a pressure sensor whose connecting channel has a constant cross-section over its entire length; therefore, for reasons of clarity, the pressure values ​​obtained with this sensor from the other comparison example have been omitted.

[0061] The continuous line shows the pressure values ​​of the pressure sensor according to the invention, which is provided with the specific design of the connecting channel 5.

[0062] It can be clearly seen that the pressure peak with the pressure sensor according to the invention is significantly less pronounced than with the conventional pressure sensor of the comparative example. Thus, the diaphragm of the conventional pressure sensor is subjected to a pressure of more than 275 bar, whereas the diaphragm of the pressure sensor according to the invention is subjected to a pressure of less than 110 bar.

[0063] Fig. 4 shows the load in Newton per square millimeter, which in the test arrangement according to Fig. 3 acts on the central region of the membrane 7. Here, too, it can be seen that the conventional pressure sensor, whose values ​​are again shown in dashed lines, has a significantly higher load in the center of the membrane than is the case with the pressure sensor according to the invention.

[0064] The Fig. 5a and Fig. 5b are also diagrams illustrating the pressure curve during a head event and were generated by a practical test on a hydrogen engine with knocking combustion.

[0065] This shows both the Fig. 5a as well as the Fig. 5b shows the peak pressure of the pressure curve, whereby it can be seen that the peak pressure of the conventional pressure sensor (283 bar) is significantly higher than the peak pressure of the pressure sensor according to the invention (219 bar).

[0066] The pressure sensor according to the invention dampens the knock vibration at its peak, while still allowing the knock-induced pressure oscillations to be clearly detected and evaluated by measurement. This is important because the detection of knock is useful for engine control purposes. List of reference symbols: 1 pressure sensor 2 Supporting structure 3 Front of the supporting structure 4 Pressure measuring room 5 connecting channel 6 Back of the supporting structure 7 measuring element 8 front channel section 9 middle canal section 10 rear channel section 11 Impact surface 12 Outlet area 13 Shielding element 14 membrane carriers 15 Pressure sensor housing X rotation axis

Claims

[1] Pressure sensor (1) for detecting a combustion chamber pressure in internal combustion engines, in particular diesel, hydrogen and / or gas engines, comprising: a support structure (2) which is designed to protrude with its front side (3) into a pressure measuring chamber (4), a connecting channel (5) provided in the support structure (2) and forming a connection from the front side (3) to a rear side (6) of the support structure (2), and a measuring element (7) which is provided on the rear side (6) of the support structure (2) and enables a conclusion to be drawn about a pressure prevailing in the area of ​​the front side (3) of the support structure (2), wherein the connecting channel (5) comprises a front channel section (8), a middle channel section (9) and a rear channel section (10), characterized by , that the central channel section (9) has a cross-section which increases from the front side (3) to the rear side (6), in particular increases continuously, and preferably the rear channel section (10) adjoining the central channel section (9) has a cross-section which is smaller than the maximum cross-section of the central channel section (9). [2] Pressure sensor (1) according to the preceding claim 1, wherein the connecting channel (5) with the front channel section (8), the middle channel section (9) and the rear channel section (10) runs in a straight line. [3] Pressure sensor (1) according to one of the preceding claims, wherein the front-side channel section (8), the middle channel section (9) and / or the rear-side channel section (10) are / is formed with at least twofold rotational symmetry, preferably with at least twofold rotational symmetry to a common axis of rotation (X). [4] Pressure sensor (1) according to one of the preceding claims, wherein the front channel section (8), the middle channel section (9) and the rear channel section (10) each directly adjoin one another. [5] Pressure sensor (1) according to one of the preceding claims, wherein the support structure (2), in particular the support structure (2) and the measuring element (7), is / are made of a material having a thermal conductivity of at least 45 W / (m·K), preferably at least 50 W / (m·K) and according to a particularly preferred embodiment at least 55 W / (m·K). [6] Pressure sensor (1) according to one of the preceding claims, wherein the cross section of the front-side channel section (8) is smaller than the cross section of the rear-side channel section (10) and / or wherein the cross section of the front-side channel section (8) corresponds to the minimum cross section of the central channel section (9). [7] Pressure sensor (1) according to one of the preceding claims, wherein the cross section of the front-side channel section (8) and / or the cross section of the rear-side channel section (10) is the same over its respective length. [8] Pressure sensor (1) according to one of the preceding claims, wherein in the transition region from the central channel section (9) to the rear channel section (10), due to the smaller cross section of the rear channel section (10) compared to the larger cross section of the central channel section (9) adjacent to the rear channel section (10), there is an impact surface (11) which connects the two different cross sections of the central channel section (9) and the rear channel section (10). [9] Pressure sensor (1) according to the preceding claim 8, wherein the impact surface (11) is aligned perpendicular to a rotation axis (X) of the central channel section (9) or forms an obtuse angle therewith. [10] Pressure sensor (1) according to one of the preceding claims, wherein the cross-section of a channel section is determined by the maximum distance between two points of the channel section in the cross-sectional plane. [11] Pressure sensor (1) according to one of the preceding claims, wherein the central channel section (9) has the shape of a truncated pyramid or truncated cone, which faces with its smaller base area (A1) the front channel section (8) and its larger base area (A2) the rear channel section (10), preferably wherein the central channel section (9) has the shape of an equilateral truncated pyramid or a straight truncated cone. [12] Pressure sensor (1) according to one of the preceding claims, wherein the measuring element (7) is carried by the support structure (2) and is preferably arranged on the rear side (6) of the support structure (2). [13] Pressure sensor (1) according to one of the preceding claims, wherein the measuring element (7) is a deformable membrane which stretches over the outlet region (12) of the connecting channel (5), preferably wherein the membrane and a membrane carrier supporting the membrane are pot-shaped or cup-shaped and sits with the edge of the pot shape or the cup shape on the support structure (2) and surrounds the outlet region (12) of the connecting channel (5). [14] Pressure sensor (1) according to the preceding claim 13, wherein a shielding element (13) is provided in the connecting channel (5) between the rear channel section (10) and the outlet region (13) in order to protect a region of the membrane, in particular a central region of the membrane, from a direct pressure wave from the pressure measuring chamber (4). [15] Pressure sensor (1) according to the preceding claim 14, wherein the shielding element (13) is designed such that the outlet of the pressure wave from the connecting channel (5) occurs axially directly onto the membrane.

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