Patent Publication Number: US-2005126297-A1

Title: Pressure sensor element having an integrated sealing surface

Description:
TECHNICAL AREA  
      Pressures or forces are often measured using piezoresistive sensor elements. These sensor elements utilize the deformation of a surface by forces and/or pressures acting on this surface as the measuring effect. For this reason, it is necessary to decouple deformations from the sensor element which are not related to the pressure to be measured, such as installation-related stresses and thermal expansions.  
     BACKGROUND INFORMATION  
      Publication DE 38 11 311 C1 relates to a pressure sensor for detecting pressure in the combustion chamber of internal combustion engines. The housing of the pressure sensor is closed off from the combustion chamber via a pressure-sensitive diaphragm. A rod is joined at its first end with the pressure-sensitive diaphragm, and its second end rests against at least one piezoelectric crystal. The transmission of force to the at least one piezoelectric crystal takes place via gapless material bonding without mechanical preload. The connection of the diaphragm with the housing is formed by a welded joint, whereby all boundary surfaces of the components following the second end of the rod are joined with the aid of an adhesive connection.  
      Publication DE 40 22 783 A1 also relates to a pressure sensor for detecting pressure in the combustion chamber of internal combustion engines. A hybrid is composed of a piezoelectric material. The electronic components of an electrical evaluation circuit are located on the hybrid. Furthermore, contact surfaces are imprinted on the hybrid. The hybrid is located directly between a rod and a counter-bearing of a pressure sensor. The electronic components and the contact surfaces are joined with the aid of simple standard bonding wires. As a result, the pressure sensor according to DE 40 22 783 A1 is particularly compact.  
      Publication DE 195 38 854 C1 also relates to a pressure sensor for detecting pressure in the combustion chamber of internal combustion engines. A rod is located in a bore of a housing, the rod resting with one end against a diaphragm which closes off the opening of the bore. With one end, the rod acts on the measuring element, producing a measuring signal that is proportional to the pressure in the combustion chamber. The shape of the rod, the surface of the end of the rod and the measuring element, and the particular materials are matched with each other such that a nearly error-free introduction of pressure is possible.  
      Publication DE 44 19 138 A1 relates to a high-temperature pressure sensor, in the case of which deflection is induced within a diaphragm section when the pressure of a high-temperature fluid acts on the compression spring surface of the diaphragm section. The deflection is transferred via pressure transmission parts to a deflection detection part that generates an electrical signal in response to the pressure received. The diaphragm section has a recessed section in its center. The recessed section extends symmetrically around a central axis of the diaphragm section. One end of the pressure transmission part is brought in contact with the recessed section at a central point. A conical section in the diaphragm has a thickness that is not greater than the thickness of an exterior circumferential section or the thickness of a central base section. A thermal insulation panel can be provided on the diaphragm to protect the surface of the diaphragm section from the thermal radiation of the high-temperature fluid.  
      Piezoresistive sensor elements that are used to detect pressures and forces utilize the deformation induced by the acting forces and/or pressures as the measuring effect. For this reason, the deformations of the sensor element that can occur when it is installed, for instance, must be kept to a minimum. For this reason, the fixing thread of a sensor and its sealing surface must be located as far away from the sensor element as possible and be mechanically decoupled therefrom to the greatest extent possible.  
     ADVANTAGES OF THE INVENTION  
      In the embodiment of a sensor element having an integrated sealing surface proposed according to the present invention, a particularly compact sensor that performs many functions using one component is realized. One advantage of the sensor proposed according to the present invention is that it enables pressure detection while also permitting the pressure sensor to be sealed off from the pressurized measuring medium with the housing into which the sensor element having an integrated sealing surface proposed according to the present invention is screwed. The pressure measuring function and the sealing function are achieved by one and the same sensor element, and it is ensured that the sealing function does not negatively affect the pressure measuring function via deformation of the sensor element.  
      The integrated sealing surface allows the sensor element to be markedly reduced in size in terms of the overall size of the entire sensor. It is further possible to move the sensor diaphragm close to the measuring volume, even in very cramped installation conditions, which is not easily possible with the sensors having piezoresistive measuring elements known from the related art. 
    
    
     DRAWING  
      The invention will be described in greater detail below with reference to the drawing.  
       FIG. 1  shows a section through a welded sensor element known from the related art,  
       FIG. 2  shows a top view of the sensor element known from the related art according to the depiction in  FIG. 1 ,  
       FIG. 3  shows a perspective view of the sensor element proposed according to the present invention, and  
       FIG. 4  shows a cross section through the sensor element proposed according to the present invention, according to the depiction in  FIG. 3 . 
    
    
     DESCRIPTION OF THE EXEMPLARY EMBODIMENTS  
      The depiction according to  FIG. 1  shows a sensor element known from the related art.  
      The sensor element shown in  FIG. 1  includes a sensor body  1  on which a piezoresistive pressure sensor element  2  is mounted. Sensor body  1  is welded via a weld  7  with a plug on which a fixing thread  3  is formed, the fixing thread being spatially separated from sensor body  1 . A sealing cone  4  is located on the lower end of the plug, below fixing thread  3 . The plug has a through-bore  5  extending through it, the through-bore being closed off by a sensor diaphragm  6  of piezoresistive pressure sensor element  2 . The pressure sensor known from the related art and shown in  FIG. 1  has a relatively great overall height in order to mechanically decouple sealing cone  4 —into which the sealing forces are introduced—from sensor body  1 .  
       FIG. 2  shows a top view of the sensor element according to the depiction in  FIG. 1  and known from the related art.  
      In the top view according to  FIG. 2 , it is clear that a plurality of piezoresistive measuring elements  8  are installed on the top side of sensor diaphragm  6  of piezoresistive pressure sensor element  2 . When through-bore  5  (refer to  FIG. 1 ) is acted upon with pressure, sensor diaphragm  6  is deformed. The pressure acts on piezoresistive measuring elements  8  mounted on the top side of sensor diaphragm  6  and a signal corresponding to the pressure is produced.  
      The depiction according to  FIG. 3  is a perspective view of the sensor element having an integrated sealing surface designed according to the present invention.  
      A sensor element  10  having an integrated sealing surface has a first end face  11  and a second end face  12 . First end face  11  includes an opening from which a hollow space  30  extends to act upon a sensor diaphragm (not shown in  FIG. 3 ) provided at second end face  12 . Hollow space  30  is limited by an inner wall  18  of sensor element  10 . A sealing cone  15  is formed on first end face  11  of sensor element  10  having an integrated sealing surface. Sealing cone  15  is formed by a sealing surface  16  that extends in the shape of a cone, starting from first end face  11  in the direction of second end face  12  of sensor element  10  having an integrated sealing surface.  
      The depiction according to  FIG. 4  is a cross section through the sensor element having an integrated sealing surface according to the present invention and shown in  FIG. 3  in a perspective view.  
      Sensor element  10  having an integrated sealing surface is a rotationally symmetrical component having a symmetrical configuration relative to axis of symmetry  14 . According to the depiction in  FIG. 4 , sealing cone  15 —starting at first end face  11  of the sensor element—is formed directly on the sensor body of sensor element  10 . The slant, the cone angle with which sealing surface  16  of sealing cone  15  extends relative to first end face  11  of the sensor element, is labeled with reference numeral  17 . Cone angle  17  is preferably in the range from 30° to 60°. Hollow space  30 , limited by inner wall  18 , of sensor element  10  having an integrated sealing surface according to the depiction in  FIG. 4  is limited by sensor diaphragm  13 . A diaphragm inner side  19  faces hollow space  30 , while a diaphragm outer side  20  is second end face  12  of sensor element  10  having an integrated sealing surface. Piezoresistive measuring elements  8  are located on the top of membrane outer side  20 .  
      A decoupling groove  21  extending in the direction of inner wall  18  of sensor element  10  is provided above a force introduction region  23  on the outside of sensor element  10  according to the depiction in  FIG. 4 . Sensor element  10  having an integrated sealing surface includes an annular surface  24  in force introduction region  23 . The sensor element may be welded with a tubular sleeve at this annular surface in the circumferential direction, for example, via which the necessary forces may be introduced to achieve a seal in the region of sealing cone  15 . Sealing surface  16  of sealing cone  15  is designed such that only minimal moment which may deform sensor membrane  13  is produced by the sealing forces introduced via annular surface  24  in force introduction region  23 .  
      By forming decoupling groove  21  with a groove depth  22 , the deformations in the lower region of sensor element  10 , i.e., below decoupling groove  21 , are not transmitted to the upper region toward sensor diaphragm  13  equipped with piezoresistive measuring elements  8 . Decoupling groove  21  is formed with a groove depth  22  and a groove width  25 . To ensure the best possible mechanical decoupling of force introduction region  23  from the region in which piezoresistive measuring elements  8  of sensor element  10  having an integrated sealing surface  16  are located, groove depth  22  is configured with the largest possible groove depth  22  and the largest possible groove width  25 . The design of groove depth  22  and groove width  25  is optimized in an individualized manner, so that both the mechanical stability of sensor element  10  having an integrated sealing surface  16  against the pressure inside hollow space  30  and the starting torque required to screw in sensor element  10  having an integrated sealing surface are still ensured.  
      Sensor element  10  having an integrated sealing surface according to the present invention has a first diameter  27  in its upper region according to the depiction in  FIG. 4 . The maximum diameter of sensor element  10  having an integrated sealing surface is labeled with reference numeral  28  and is located in the region where sealing surface  16  of sealing cone  15  phases out. The mean diameter of sealing surface  16  is labeled with reference numeral  29 . In comparison with the sectional view of a sensor element known from the related art shown in  FIG. 1 , the sensor element having an integrated sealing surface proposed according to the present invention has a substantially smaller overall height  26 . By integrating sealing surface  16  of sealing cone  15  in the body of sensor element  10 , the overall size of the sensor arrangement proposed according to the present invention may be markedly reduced, and its sensor diaphragm  13  may be moved close to the measuring volume, even in cramped installation conditions. This is unattainable with the embodiment of a sensor element from the related art shown in  FIG. 1  due to the large distance between sensor diaphragm  6  and sealing surface  4 . Sealing cone  4  of the sensor element known from the related art is located far behind diaphragm  6  and is separated therefrom by the overall length of the plug-shaped body.  
      Instead of decoupling groove  21  having a rounded cross section as shown in  FIG. 4 , other decoupling geometries may be formed between force introduction region  23  for generating the sealing force and sensor diaphragm  13  on second end face  12  of sensor element  10  having an integrated sealing surface. Instead of decoupling groove  21  having a U-shaped profile shown in  FIG. 4 , it could also have a semi-cylindrical groove base, or it could be configured in the shape of a slot. The geometry of decoupling groove  21  with regard to groove depth  22  and groove width  25  varies depending on the materials used and on the installation space available for sensor element  10  having an integrated sealing surface proposed according to the present invention. To obtain an optimal mechanical decoupling of sealing cone  15  at first end face  11  of sensor element  10  and sensor diaphragm  13  formed on second end face  12  of sensor element  10 , decoupling groove  21  is located as centrally as possible between first end face  11  and second end face  12 . Sensor element  10  having an integrated sealing surface proposed according to the present invention, according to  FIGS. 3 and 4 , ensures that the functions of pressure measurement 1  and sealing the pressure sensor off from the housing into which it is screwed are performed using one and the same component.    1  Translator&#39;s Note: The German states: “the functions of pressure, measurement . . . ”   
      Using a sensor tubular sleeve  31 , sensor element  10  having an integrated sealing surface  16  is located in the cylinder head of an internal combustion engine in the vicinity of the combustion chamber, for example. Sensor tubular sleeve  31  contacts, with one end face, annular surface  24  at force introduction region  23 . The end face of sensor tubular sleeve  31  facing annular surface  24  may also be connected to annular surface  24  via a bonded connection  33  indicated in  FIG. 4 . When sensor tubular sleeve  31 —which has a threaded section  32 —is screwed in, sensor element  10  having an integrated sealing surface  16  is accommodated in the cylinder head of an internal combustion engine, creating a seal at sealing cone  15 . Decoupling groove  21  ensures that sensor diaphragm  13 —on membrane outer side  20  of which piezoresistive measuring elements  8  are located—is insulated from installation-related stresses that may have a negative effect on the measurement result.  
      Sensor element  10  having an integrated sealing surface  16  depicted in  FIG. 4  may be made of stainless steel, for example, and have a diameter of nearly 5 mm. Sensor element  10  having an integrated sealing surface proposed according to the present invention may also be fabricated with a diameter of 8.6 mm and greater, for example.  
     Reference Numerals  
     
         
           1  Sensor body  
           2  Piezoresistive pressure sensor element  
           3  Fixing thread  
           4  Sealing cone  
           5  Through-bore  
           6  Sensor diaphragm  
           7  Weld  
           8  Piezoresistive measuring elements  
           10  Sensor element having an integrated sealing surface  
           11  First end face  
           12  Second end face  
           13  Sensor diaphragm  
           14  Axis of symmetry  
           15  Sealing cone  
           16  Sealing surface  
           17  Cone angle  
           18  Inner wall  
           19  Membrane inner side  
           20  Membrane outer side  
           21  Decoupling groove  
           22  Groove depth  
           23  Force introduction region  
           24  Annular surface  
           25  Groove width  
           26  Overall height of sensor element  
           27  First diameter  
           28  Maximum diameter  
           29  Mean diameter of sealing cone  
           30  Hollow space having a measuring volume  
           31  Sensor tubular sleeve  
           32  Threaded section  
           33  Bonded connection