Abstract:
A pressure-measuring glow plug device includes a module housing, a glow plug configured to ignite a combustion mixture in a combustion chamber of an internal combustion engine, and a pressure-measuring device. The pressure-measuring device has a pressure sensor configured to detect the pressure in the combustion chamber. The glow plug is connected to the module housing by a flexurally elastic membrane. The force acting on the glow plug in the combustion chamber is transferred to the pressure sensor, which is supported on a supporting element by a preloading force. The supporting element is fastened rigidly to the module housing by a sensor housing. The glow plug device further includes a separate loading sleeve that is connected at one end to the pressure-transferring piece and at the other end to the supporting element. The loading sleeve is configured to apply the preloading force for the pressure sensor.

Description:
This application is a 35 U.S.C. §371 National Stage Application of PCT/EP2013/058958, filed on Apr. 30, 2013, which claims the benefit of priority to Serial No. DE 10 2012 209 237.4, filed on May 31, 2012 in Germany, the disclosures of which are incorporated herein by reference in their entirety. 
     BACKGROUND 
     The disclosure relates to a pressure-measuring glow plug device for insertion into a cylinder head of an internal combustion engine having the features of the disclosure. 
     PRIOR ART 
     A pressure-measuring glow plug device of this type is known from WO 2007/096208 A1, in which a glow plug for igniting a combustion mixture of an internal combustion engine and a pressure-measuring device with a pressure sensor for detecting a combustion chamber pressure of the internal combustion engine are arranged in a housing. The glow plug is exposed to the combustion chamber pressure and, as pressure pickup, transmits the combustion chamber pressure to the pressure sensor, the pressure sensor being received between the glow plug which acts as pressure pickup and a supporting element in a sensor housing. A resiliently flexible diaphragm is arranged between the sensor housing and the glow plug which serves as pressure pickup, which diaphragm makes the required axial longitudinal movement of the glow plug for pressure transmission possible and at the same time applies the required prestressing force for the pressure sensor. As a result, the forces which act on the resiliently flexible diaphragm during the mounting of the glow and pressure-measuring module also have an effect on the prestress of the pressure sensor. 
     SUMMARY 
     The disclosure has the advantage that a glow and pressure-measuring module has been produced, in which the pressure sensor is prestressed between the pressure transmission piece and the supporting element by means of a clamping sleeve which is used in addition to the sensor housing. As a result, the prestressing force for the pressure sensor remains uninfluenced during the installation of the glow and pressure-measuring module into the housing of the pressure-measuring glow plug device. 
     Advantageous developments of the disclosure are possible as a result of the measures of the subclaims. 
     The clamping sleeve, the pressure transmission piece, the supporting element and the pressure sensor which is surrounded by it form a pre-assembled sensor unit which can be inserted into an end section of the sensor housing, which end section faces away from the combustion chamber. As a result, the sensor unit can be mounted independently of the glow and pressure-measuring module. The forces which act on the resiliently flexible diaphragm during mounting therefore do not act on the prestress of the pressure sensor. The supporting element is given its firm fixing in housing terms by the sensor housing being connected to the supporting element with an end section which faces away from the combustion chamber and being connected to the housing of the pressure-measuring glow plug device at an end section which faces the combustion chamber. As a result, the sensor unit is at the same time fixed firmly in housing terms in the sensor housing. 
     In order to exert an axial longitudinal movement for pressure transmission, the glow plug is connected to the sensor housing by means of the resiliently flexible diaphragm at an end section which faces the combustion chamber. For the transmission of force, a connecting sleeve which surrounds the glow plug at the end section which faces away from the combustion chamber and which is connected at least indirectly to the glow plug is flange-connected to the pressure transmission piece. 
     The connecting sleeve expediently forms a receiving space for a glow current contact on the glow plug side, in which receiving space the glow current contact makes contact with a glow current line. Here, the glow current line is guided through the sensor unit, the pressure transmission piece having a first leadthrough and the supporting element having a second leadthrough for this purpose, through which the glow current line is guided, it being possible for the glow current line to make contact with a high current connector which lies outside the sensor unit. 
     The components which are connected to the sensor housing form a glow and pressure-measuring module which can be inserted into the glow module housing of the pressure-measuring glow plug device as a structural unit which can be pre-assembled. The glow and pressure-measuring module is connected fixedly to the housing of the pressure-measuring glow plug device by means of a fastening point which is configured on the sensor housing, the fastening point being formed by a supporting section which is configured on the sensor housing. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       One exemplary embodiment of the disclosure is shown in the drawings and is explained in greater detail in the following description. 
       In the drawings: 
         FIG. 1  shows a sectional illustration through a section on the combustion chamber side of a pressure-measuring glow plug device according to the disclosure, 
         FIG. 2  shows an enlarged detail X in  FIG. 1 , and 
         FIG. 3  shows the enlarged detail X in  FIG. 2  in an illustration which has been rotated axially by 180°. 
     
    
    
     DETAILED DESCRIPTION 
     The pressure-measuring glow plug device which is shown in  FIG. 1  combines a conventional glow plug  20  for use in compression-ignition internal combustion engines with an additional pressure-measuring function of a pressure-measuring device  30  for detecting a combustion chamber pressure of the internal combustion engine. The pressure-measuring glow plug device comprises substantially a glow and pressure-measuring module  11  which is accommodated in a housing  13  of the pressure-measuring glow plug device, which housing  13  will be called the glow module housing in the following text, and a connector module  14  which is not shown in greater detail and is accommodated in a connector module housing  15 . Two sensor connectors  16  for the pressure-measuring device  30  and a high current connector  17  for the glow plug device  20  which lead in the connector module  14  to electrical connections (not shown) for a connector plug are formed on the connector module  14  so as to protrude into the glow module housing  13  and to be exposed there. A signal processing unit for preprocessing the signals of the pressure-measuring device  30  can be integrated into the connector module  14 . 
     The components of the glow plug device  20  for igniting the internal combustion engine and the components of the pressure-measuring device  30  for combustion chamber pressure measurement are accommodated in the glow and pressure-measuring module  11 . The glow plug device  20  comprises a glow plug  21  which protrudes out of the glow module housing  13  on the combustion chamber side, protrudes with the projecting part into the combustion chamber of the internal combustion engine and at the same time as a result forms a pressure pickup for the pressure which prevails in the combustion chamber. In the present exemplary embodiment, the glow plug  21  is a ceramic glow plug, into which an electrical heating element (not shown) is embedded. The ceramic glow plug  21  is surrounded by a metallic supporting tube  22 . The heating element (not shown) is connected via an outer contact to the supporting tube  22  in order to form one pole and is connected via an electrical connection  23  to a glow current contact  24  in order to form the other pole, the glow current contact  24  being guided out of the supporting tube  22  as a solid connector bolt such that an end section  25  which faces away from the combustion chamber is exposed. The electrical connection from the glow current contact  24  to the high current connector  17  on the connector module  12  is realized by means of a glow current line  27 . 
     Furthermore, an electrically insulating sealing element  29  is arranged between the supporting tube  22  and the glow current contact  24 . However, it is also conceivable to configure the glow plug  21  as a metallic glow tube with an embedded heating coil. 
     The pressure-measuring device  30  is accommodated within the glow module housing  13  and comprises a sensor unit  40 , a resiliently flexible diaphragm  32 , a sensor housing  33  and a connecting sleeve  34 . 
     The sensor unit  40  comprises a piezoelectric pressure sensor  41 , a pressure piece  42  on the glow plug side, a pressure piece  43  on the supporting element side, a pressure transmission piece  44 , a supporting element  45  and a clamping sleeve  46 . The clamping sleeve  46  is of flexible configuration for the purpose of the realization of an axial movement of the pressure transmission piece  44  for the transmission of force to the pressure sensor  41 . To this end, the clamping sleeve  46  is configured, for example, as a tubular spring. The pressure pieces  41 ,  42  are produced from an electrically insulating material. The pressure sensor  41  is positioned between the pressure piece  42  on the glow plug side and the pressure piece  43  on the supporting element side by means of a prestressing force which is applied by the clamping sleeve  46 . The pressure sensor  41  has two sensor lines  47  which are connected electrically to the two sensor connectors  16 . 
     The pressure transmission piece  44  and the supporting element  45  are connected by means of the resilient clamping sleeve  46  in such a way that firstly the required prestress acts on the pressure sensor  41  and that secondly the pressure transmission piece  44  can perform the axial movement which is necessary for the transmission of force to the pressure sensor  41 . As a result, the clamping sleeve  46  forms a separate clamping element for the pressure sensor  41  independently of the sensor housing  33 . For the fixed connection of the clamping sleeve  46  to the pressure transmission piece  44  and the supporting element  45 , the clamping sleeve  46  is connected at the pressure transmission piece  44  by means of a first welded seam  48  and at the supporting element  45  by means of a second welded seam  49 . As a result, the sensor unit  40  forms a structural unit which can be pre-assembled separately from the glow and pressure-measuring module  11 . 
     The sensor lines  47  are guided out of the sensor unit  40  on the connector module side. To this end, according to  FIG. 2 , two leadthroughs  51  are provided in the supporting element  45 , through which leadthroughs  51  the two sensor lines  47  are guided toward the sensor connectors  16 . 
     In order to realize the contact between the glow current contact  24  and the high current connector  17 , the glow current line  27  is guided through the sensor unit  40 . To this end, according to  FIG. 3 , the pressure transmission piece  44  has a first leadthrough  52  for leading through the glow current line  27  toward the glow current contact  24 , and the supporting element  45  has a second leadthrough  53  for leading through the glow current line  27  toward the high current connector  17 . The glow current line  27  which is guided substantially axially through the sensor unit  30  has a first 90 degree bend on the glow plug side and a second 90 degree bend on the connector side, with the result that the glow current line  27  can be guided axially through the sensor unit  40 . For contact with the glow current contact  24 , a radial bore is made in the connector-side end section  25  of the glow current contact  24 , into which radial bore the first 90 degree bend of the glow current line  27  is introduced and makes electrical contact there. 
     In order to realize the pressure transmission from the glow plug  21  to the pressure sensor  41 , the glow plug  21  is mounted axially displaceably in the glow module housing  13  by means of the resiliently flexible diaphragm  32 . Furthermore, a transmission of force takes place from the glow plug  21  to the pressure transmission piece  44  of the sensor unit  40 . To this end, the supporting tube  22  which is connected fixedly to the glow plug  21  with the connecting sleeve  34  is extended axially in the direction of the sensor unit  40  with an end section  55 . The extended end section  55  is placed on a collar which is configured on the pressure transmission piece  44  and is connected there by means of a first welded seam  56  to the pressure transmission piece  44 . The supporting tube  22  and the connecting sleeve  34  are connected fixedly by means of a second welded seam  57 . A hollow-cylindrical receiving space  58  is therefore formed within the end section  55 , in which receiving space  58  the connector-side end section  25  of the glow current contact  24  is exposed and makes contact there with the glow current line  27 . 
     In order to configure the glow and pressure-measuring module  11 , the resiliently flexible diaphragm  32  is connected to the sensor housing  33  by means of a third welded seam  59 . The sensor housing  33  is welded on the supporting element  45  by means of a fourth welded seam  61 . The second welded seam  49  for connecting the clamping sleeve  46  and the fourth welded seam  61  for connecting the sensor housing  33  are configured on different diameters of the supporting element  45 . As a result, there is a further structural unit which can be pre-assembled with the glow and pressure-measuring module  11 , in which further structural unit the sensor unit  40  is received as a first structural unit which can be pre-assembled, and which further structural unit is inserted into the glow module housing  13  and is connected fixedly to the glow module housing  13 . It has proven expedient that an annular gap  36  is formed between the outer wall of the connecting sleeve  34  and the inner wall of the sensor housing  33 , and between the outer wall of the clamping sleeve  34  and the inner wall of the sensor housing  33 . The annular gap  36  serves to provide a friction-free spacing for the axial displacement of the connecting sleeve  34  and the resilient clamping sleeve  34  relative to the sensor housing  33  which is fixed in housing terms. 
     In order to fasten the glow and pressure-measuring module  11  in the glow module housing  13 , an outer supporting section  64  is configured on the sensor housing  33 , which outer supporting section  64  is adapted by way of its external diameter to the internal diameter of the glow module housing  13 . The supporting section  64  forms a connecting point on the sensor housing  13 , to which the sensor housing  33  on the glow module housing  13  is connected by means of a further welded seam  62 . The further welded seam  62  and the third welded seam  59  are of circumferential configuration for sealing purposes. 
     The prestress for the pressure sensor  41  is therefore applied by the clamping sleeve  46  and not by the spring force of the resiliently flexible diaphragm  32 . As a result, the prestress for the pressure sensor  41  can be set outside the glow and pressure-measuring module  11  on the pre-assembled sensor unit  40 . As a result, the prestress of the pressure sensor  41  is not influenced by the spring force of the resilient diaphragm  32  or by the following assembly steps during the insertion of the glow and pressure-measuring module  11  into the glow module housing  13 . 
     The pressure which prevails in the combustion chamber and exerts a pressure force on the glow plug  21  which acts as pressure pickup causes the glow plug  21  with the supporting tube  22  and the connecting sleeve  34  to perform an axial movement along the longitudinal axis of the pressure-measuring glow plug device, on account of the resiliently flexible diaphragm  32 , with respect to the glow module housing  13  which is fastened fixedly in the cylinder head. The pressure force acts on the pressure transmission piece  44  and the latter presses via the first pressure piece  42  on the pressure sensor  41  on account of the resilient action of the clamping sleeve  46 , which pressure sensor  41  is supported via the second pressure piece  43  on the supporting element  45  which is connected fixedly to the sensor housing  33  and is fixed as a result.