DE102012202058A1 - Diaphragm for combustion chamber pressure sensor - Google Patents

Abstract

The invention relates to a pressure measuring device for an internal combustion engine, in particular for determining a combustion chamber pressure. The pressure measuring device comprises a housing (10) in which a sensor membrane (19, 20) is accommodated. This separates a pressure chamber (24) from a cavity (22). The sensor membrane (19, 20) comprises a pressurized surface (27) and seals the housing (10) against the pressure to be measured. The pressurized surface (27) of the sensor membrane (20) is located between a first deflection point (32) and a second deflection point (38) of the sensor membrane (20), each in reduced second and third wall thicknesses (34, 40) with respect to a first Wall thickness (28) of the sensor membrane are executed.

Description

State of the art

DE 10 2006 057 627 A1 refers to a pressure measuring device. This serves for arrangement in the combustion chamber of an internal combustion engine. The pressure measuring device has a housing, a force transmission element, which projects at a chamber-side opening of the housing partially out of the housing and a pressure sensor. This is arranged in an interior of the housing. In this case, the pressure sensor is in operative connection with the force transmission element. Furthermore, a membrane is provided, which seals the interior of the housing in which the pressure sensor is arranged opposite the chamber-side opening. The diaphragm, which is preferably formed as a metal diaphragm, has a power transmission portion oriented in an axial direction of the power transmission member. In addition, the pressure sensor is in operative connection with the force transmission element by means of the force transmission section of the diaphragm. As a result, at least a partial compensation thermally induced changes in length of the membrane, which are caused for example by hot fuel gases and can lead to periodic impairments of the pressure measurement by means of the pressure sensor.

DE 10 2007 049 971 A1 refers to a glow plug. A glow plug is used for arrangement in a chamber of an internal combustion engine. The glow plug has a housing, a rod-shaped heating element, which partially protrudes from the housing and a pressure sensor, which is arranged in an inner space of the housing. In this case, the pressure sensor is on the one hand in operative connection with the rod-shaped heating element to detect a conditional on the pressure prevailing in the chamber pressure of the heating element for determining the pressure prevailing in the chamber. On the other hand, the pressure sensor is supported on a fixing element connected to the housing. A spring diaphragm seals the interior of the housing relative to the chamber of the internal combustion engine. The spring diaphragm is designed as an S-shaped spring diaphragm. By means of this embodiment, in particular a pressure-balanced design can be achieved, so that the accuracy of a pressure measurement by means of the pressure sensor is improved.

Within a combustion chamber pressure sensor, the membrane is required to seal the interior of the sensor against the combustion chamber. Due to their temperature and their aggressive chemical properties, penetrating media in particular destroy the components of the sensor module and the electronics within a very short time. At the same time, the membrane should withstand the stresses during sensor operation. The burdens are mainly the cyclic loads of the pressure change (several hundred million load cycles per lifetime) as well as the high level of the average temperature.

Presentation of the invention

According to the invention, the membrane made of metallic material, which can be used in a combustion chamber pressure sensor, designed so that a minimization of the wall thickness of the membrane made of metallic material can be achieved, the minimization of the wall thickness, in particular in a transition region between pressurized membrane surface and adjacent Areas is realized. Furthermore, by maximizing the distance between the transition regions between the pressurized membrane surface and the transition regions, it can be achieved that the membrane proposed according to the invention is sufficiently limp in order not to hinder the path of the pressure signal to be measured supercritically. The membrane obstructs the path of the pressure signal to be measured by the membrane receives a portion of the pressure signal to be measured and does not forward to a measurement sensor, such as a piezoelectric sensor. If only a reduced pressure signal is forwarded to the measuring sensor system, measurement results of the sensor system are subject to inaccuracies due to an interference with a signal noise. In case of a critical obstruction of the path of the pressure signal to be measured inaccuracies due to signal noise can not be reliably compensated. The bending slackness is achieved by maximizing a radial distance between the two deflection points (diameter approx. 7 mm to diameter approx. 4.5 mm). On the other hand, the wall thicknesses in the area of the deflections are minimized as far as the strength of the component allows. The wall thickness is for example in the range of an outer deflection only a few tenths mm, in particular 0.2 mm, while the wall thickness can be at an internal deflection or at a radius of 0.2 to 0.35 mm. The two aforementioned deflection points create a kind of "hinge" around which the membrane winds.

Advantages of the invention

Advantageously, the membrane proposed according to the invention, in particular suitable for use in combustion chamber pressure sensors, has a minimal thermal shock effect, by means of which the measuring accuracy of the combustion chamber pressure sensor is reduced. This is realized by having a constricted area on the outside Deflection is formed extended, so that the membrane is given the opportunity to work in this area and sideways dodge. The lateral deflection of the membrane made of metallic material significantly reduces the thermal shock effect. For example, an extension of the constricted area by about 2 mm in the thermal shock effect already significantly. With otherwise the same geometry a further extension of the constricted area would lead to a further reduction of the thermal shock effect, however, which preclude requirements with respect to the sensor length.

Furthermore, the lateral deflection of the membrane of further dimensions of the membrane, in particular transition radii and the position of Dichtverschweißungen influenced. By optimizing the elongation of the constricted region, taking into account the other parameters which influence the lateral deflection of the membrane, the design of the membrane with respect to the thermal shock can be further optimized.

Furthermore, the combustion chamber pressure sensor according to the invention provides a possibility of minimizing the portion of the pressure signal that is not forwarded by the membrane to the measurement sensor system. The measurement sensor operates in operation at a high level of the recorded pressure forces, whereby a distinction of pressure force changes of signal noise is facilitated. The combustion chamber pressure sensor according to the invention has improved measurement accuracy.

Short description of the drawing

With reference to the drawing, the invention will be described below in more detail.

It shows:

1 and 2 Representations of previously used sensor membranes,

3 a longitudinal section through a combustion chamber pressure sensor according to the invention

4 2 shows a schematic half section through a combustion chamber pressure sensor with a sensor membrane proposed according to the invention according to a first embodiment variant,

5 a section through an inventively proposed sensor membrane of the first embodiment,

6 a second embodiment of the inventively proposed sensor membrane in the assembled state and

7 a section through the inventively proposed sensor membrane in its second embodiment.

Embodiments of the invention

The 1 and 2 show a sensor membrane according to the prior art.

The 1 and 2 it can be seen that a sensor membrane 19 symmetrical to its axis of symmetry 18 is formed and a membrane lateral surface 26 having. The sectional view according to 2 it can be seen that the sensor membrane 19 according to the prior art in a first wall thickness 28 is executed.

3 shows a longitudinal section of an embodiment of a combustion chamber pressure sensor according to the invention. The combustion chamber pressure sensor comprises a housing 10 into which a pressure pin 58 is included, the one pressure room 24 is facing. The pressure pin 58 takes pressure forces out of the pressure chamber 24 and sets the action of the compressive force in a movement along an axis 18 around. Between the pressure pin 58 and the housing 10 is a cavity 22 educated. Further, along the axis 18 behind the pressure pin 58 a measuring sensor 59 arranged by the pressure pin 58 taken axial movement and converted into a measuring signal. This takes the pressure pin 58 Pressure forces from the pressure chamber 24 and directs the pressure forces along an internal force path 60 via a compensation body 4 to the measuring sensor 59 , Furthermore, the pressure pin 58 with a Viton seal 5 provided and to a Glühstromleitung 3 connected the pressure pin 58 , which can be designed as a glow tube, supplied with electrical energy. Furthermore, the combustion chamber pressure sensor comprises 3 a sensor membrane 20 in the cavity 22 between the case 10 and the pressure pin 58 is included. The sensor membrane 20 is substantially Z-shaped and lies with a combustion chamber-facing end of the pressure pin 58 at. The sensor membrane is located at the end facing away from the combustion chamber 20 on a lateral surface 12 the inside of the case 10 at. The sensor membrane is located at a combustion chamber-remote end to a sensor housing 6 at. Furthermore, the housing 10 at a combustion chamber-facing end as a cone 16 educated. The sensor membrane 20 is by means of sealing welds 63 with the housing 10 , the sensor housing 6 and the pressure pin 58 connected. At the sealing weld 63 containing the sensor membrane 20 with the pressure pin 58 connects, branches from the pressure pin 58 absorbed compressive force in the inner and an outer force path 60 . 61 , The proportion of compressive force along the outer force path 61 is forwarded, runs to a fixation 2 that go along the axis 18 behind the measuring sensor 59 is arranged. Furthermore, the outer force path branches 61 at the sealing weld 63 containing the sensor membrane 20 with the housing 10 combines. It branches off from the outer power path 61 one from the case 10 absorbed power 62 from. During operation of the combustion chamber pressure sensor is an area 27 the sensor membrane 20 the temperature and pressure effect from the pressure chamber 24 immediately exposed. Alternatively, the pressure pin 58 also be designed as a glow tube.

In the illustration according to 4 a half section through a combustion chamber pressure sensor is shown, which includes a sensor membrane in its first embodiment according to the invention.

4 shows that a case 10 a combustion chamber pressure sensor is formed symmetrically to its axis. A lateral surface of the housing 10 the combustion chamber pressure sensor is denoted by reference numerals 12 designated. The housing 10 is in a housing wall thickness 14 executed. The housing 10 includes a cone 16 and a sensor membrane 20 , The sensor membrane 20 separates a cavity 22 from a pressure room 24 within which the pressure to be measured is present.

When in the cavity 22 The sensor system accommodated in the combustion chamber pressure sensor is, for example, a piezoelectric sensor system which converts the pressure signal into an electrical signal.

The inventively proposed sensor membrane 20 includes a pressurized surface, also compare position 27 in 5 ,

As shown in the illustration 4 shows, is the sensor membrane 20 essentially procure Z-shaped and senses the pressures prevailing in the combustion chamber of an internal combustion engine. To do this, make sure the sensor membrane 20 possible loads of pressure change over several hundred million load cycles per lifetime for the high level of average temperature endures, without failing.

By means of the sensor membrane 20 becomes the cavity 22 opposite the pressure chamber 24 sealed pressure, while ensuring that the sensor membrane 20 is sufficiently limp in order not to hinder the path of the pressure signal to be measured supercritically.

The representation according to 5 is a cut through the in 4 to be taken in the mounted state shown sensor membrane in its first embodiment.

The representation according to 5 shows that the sensor membrane 20 Z-shaped and is constructed symmetrically to its axis. The membrane lateral surface is denoted by reference numerals 26 designated. The length of the membrane lateral surface 26 influences the mechanical behavior of the sensor membrane 20 and their bending slackness. The length of the membrane lateral surface 26 is preferably between 0 mm and 2 mm.

From the sectional view according to 5 shows that the inventively proposed sensor membrane 20 in its first embodiment in the area where it is the cavity 22 limited, in a first wall thickness 28 is trained. As shown in the illustration 5 can be seen further, takes the wall thickness of the sensor membrane 20 below a paragraph 30 different values. So lies in the outlet of the paragraph 30 towards the pressure room 24 seen, a first turning point 32 on an inner surface 46 the sensor membrane 20 , The sensor membrane 20 points in an area on the lateral surface 12 the combustion chamber pressure sensor 10 is applied, a first wall thickness 28 on, which is between 0.2 mm and 1.0 mm. At the first turning point 32 - here in the illustration according to 4 formed as a radius on the inner circumferential surface 46 - takes the material of the sensor membrane 20 a second wall thickness 34 at. This second wall thickness 34 is on the order of 0.15 mm to 0.4 mm. At the first turning point 32 closes a pressurized area 27 the sensor membrane 20 which is substantially perpendicular to the axis of symmetry 18 the sensor membrane 20 is oriented. At a second turning point 38 has the sensor membrane 20 a diameter jump and goes into a constricted area 50 above. At the second turning point 38 has the material of the sensor membrane 20 also a reduced, here a third reduced wall thickness 40 on. The reduced second wall thickness 34 and the reduced third wall thickness 40 can be identical, ie lying in the range between 0.15 mm and 0.4 mm; However, there is also the possibility of the two mentioned reduced wall thicknesses 34 respectively. 40 different from each other. Furthermore, the thickness of the sensor membrane 20 on the pressurized surface 27 preferably between 0.2 mm and 0.4 mm.

From the illustration according to 5 also shows that the two deflection points 32 and 38 in which the sensor membrane proposed according to the invention has targeted weakenings, at a radial distance 42 are arranged relative to each other. This means that the two deflection points 32 . 38 act as a "hinge" in which the pressurized area 27 the sensor membrane 20 not between the two deflection points 32 . 38 twists. By maximizing this radial distance 42 between the first deflection point 32 and the second turning point 38 can achieve in an advantageous manner that the membrane design of the sensor membrane 20 has the required Biegeschlaffheit so as not to obscure the path of the pressure signal to be measured supercritically. This bending slackness is in addition to maximizing the radial distance 42 by minimizing the wall thickness in the area of the deflection points 32 and 38 or the pressurized area 27 the sensor membrane still supported. Furthermore, lies between the deflection 32 and 38 with respect to the axis 18 a radial distance 42 with a size of 0.75 mm to 1.25 mm.

In the 5 sectional sensor membrane 20 for determining the combustion chamber pressure at a combustion chamber pressure sensor, for example, is preferably made of a high-strength material, in particular steel 1.4542. In general, the sealing of the sensor interior, ie the cavity takes place 22 the combustion chamber pressure sensor thereby, through the sensor membrane 20 itself and by a Dichtverschweißung with sealing cone housing a combustion chamber pressure sensor or a glow plug.

In the illustration according to 6 a second embodiment of the present invention proposed sensor membrane is shown in the installed state.

The representation according to 6 can be seen that in this embodiment of a combustion chamber pressure sensor of the cavity 22 in which the sensitive piezoelectric measuring sensor is housed, through the sensor membrane 20 in Z-shape from the acted upon by the combustion chamber pressure space 24 is disconnected. From the illustration according to 5 shows that the here in Z-shaped sensor membrane 20 also the two deflection points 32 and 38 having. Between the two deflection points 32 and 38 of which the first turning point 32 radially outside and the second deflection point 38 positioned radially inward, which runs the pressure chamber 24 essentially limiting pressurized area 27 , From the illustration according to 5 shows that the wall thickness, which in 5 illustrated second embodiment of the inventively proposed sensor membrane 20 has, below the paragraph 30 in a reduced, substantially uniform wall thickness 56 passes. As 5 further shows, is an extension 52 that are in a set range 50 (see illustration according to 7 ) connects to a push pin 58 at. 7 shows a section through the in 5 in the assembled state shown second embodiment of the present invention proposed sensor membrane.

As 7 shows and also 5 can already be seen, takes the wall thickness of the sensor membrane 20 below the paragraph 30 a substantially uniform, reduced wall thickness 56 at. In the area of the diameter transition 58 the sensor membrane 20 , within which the diameter of the sensor membrane 20 starting from the first deflection point 32 on the second radially outer second deflection 38 passing, the sensor membrane tapers 20 in a constricted area 50 , The constricted area 50 represents an extension 52 This extension 52 is a few millimeters, for example, preferably 2 mm. By this extension 52 can the thermal shock effect that the sensor membrane 20 in operation is minimized. This represents the extension 52 an area where thermal expansion due to thermal shock can be absorbed. In this case, the thermal expansion occurring as a result of thermal shock of the sensor membrane 20 on a combustion chamber-facing side and a combustion chamber-remote side of the sensor membrane 20 different in the short term.

By in the constricted area 50 planned extension 52 For example, the sensor membrane proposed according to the invention can work in this area, ie deviate laterally, which leads to a significant reduction in the thermal shock effect. The extension 52 in the constricted area 50 is located, allows a reduction of the thermal shock effect to 0.54 bar. The length of the extension 52 further influences in interaction with other dimensions of the sensor membrane 20 the effect of a thermal shock on the accuracy of the combustion chamber pressure sensor. Such dimensions can the transition radii 54 and / or the location of seal welded joints. By concerted variation of the length of the extension 52 in the constricted area 50 as well as the transition radii 54 , can further optimize the thermal shock effect of only 0.3 bar at the same time reduced Einschnürlänge, ie when shortening the extension 52 be achieved.

The inventively proposed sensor membrane in the two based on the 3 to 7 described variants is characterized in that they both the cavity 22 in which the piezoelectrically operating measuring sensor is accommodated, shields and seals against the high pressures occurring, and due to its design with the targeted weakening zones at the deflection points 32 and 38 coped with several hundred million pressure load changes at the high temperatures that occur. In particular, the sensor membrane proposed according to the invention is 20 according to the described two embodiments so sufficiently limp formed that the path of the pressure signal to be measured is not hindered, on the one hand also by minimizing the wall thickness to the reduced second and third wall thicknesses 34 respectively. 40 according to the first embodiment or on the reduced uniform wall thickness 56 is due to the second embodiment. Furthermore, the bending slackness of the sensor membrane proposed according to the invention in the two variants described above is supported by the fact that the two counted wall thickness weakenings represent deflection points 32 . 38 are arranged offset radially to each other, ie at a radial distance 42 are positioned with respect to each other.

The wall thicknesses, ie the reduced second wall thickness 32 , the reduced third wall thickness 40 as well as the reduced uniform wall thickness 56 are in the area of the deflection points 32 . 38 minimized as far as the strength of the component sensor membrane allows.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 102006057627 A1 [0001]
• DE 102007049971 A1 [0002]

Claims (12)

Pressure measuring device for an internal combustion engine, in particular for determining a combustion chamber pressure with a housing ( 10 ), in which a sensor membrane ( 19 . 20 ), which has a pressure chamber ( 24 ) of a cavity ( 22 ) and the one pressurized surface ( 27 ), wherein the sensor membrane ( 19 . 20 ) the housing ( 10 ) seals against the pressure to be measured, characterized in that the pressurized surface ( 27 ) of the sensor membrane ( 20 ) between a first deflection point ( 32 ) and a second deflection point ( 38 ), each in reduced wall thickness ( 34 . 40 ) with respect to a first wall thickness ( 28 ) of the sensor membrane ( 20 ) are executed. Pressure measuring device according to claim 1, characterized in that the reduced second and third wall thicknesses ( 34 . 40 ) are identical. Pressure measuring device according to claim 1, characterized in that the reduced second and third wall thicknesses ( 34 . 40 ) are different from each other. Pressure measuring device according to one of the preceding claims, characterized in that the deflection points ( 32 . 38 ) in the sensor membrane ( 20 ) at a radial distance ( 42 ) are arranged to each other. Pressure measuring device according to one of the preceding claims, characterized in that the first wall thickness ( 28 ) of the sensor membrane ( 20 ) is up to 1.0 mm, preferably between 0.2 mm and 1.0 mm. Pressure measuring device according to one of the preceding claims, characterized in that the reduced second and third wall thicknesses ( 34 . 40 ) are between 0.15 mm and 0.4 mm. Pressure measuring device according to one of the preceding claims, characterized in that the sensor membrane ( 20 ) a constricted area ( 50 ). Pressure measuring device according to the preceding claim, characterized in that the constricted area ( 50 ) an extension ( 52 ), starting from the pressurized surface ( 27 ) in the direction of the pressure chamber ( 24 ). Pressure measuring device according to one of the preceding claims, characterized in that the extension ( 52 ) starting from the second deflection point ( 38 ) of the sensor membrane ( 20 ). Pressure measuring device according to one of the preceding claims, characterized in that the extension ( 52 ) is several millimeters, in particular 2 mm. Pressure measuring device according to one of the preceding claims, characterized in that the extension ( 52 ) for receiving different thermal expansions on a combustion chamber-facing side and a combustion chamber side facing away from the sensor membrane ( 20 ) is designed to reduce the thermal shock effect. Pressure measuring device according to one of the preceding claims, characterized in that the extension ( 52 ) taking into account further dimensions of the sensor membrane ( 20 ) has a length for reducing the thermal shock effect.

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