BRIEF DESCRIPTION OF THE DRAWINGS
The invention will be further described below, with reference to the enclosed drawings, wherein
FIG. 1 shows a state-of-the-art pressure measuring probe in a sectional view;
FIG. 2 a glow plug with integrated pressure sensor according to the invention in a sectional view;
FIG. 3 an enlarged detail III from FIG. 2;
FIG. 4 detail III rotated by 90°;
FIG. 5 a second variant of the invention in a sectional view;
FIG. 6 a detail VI from FIG. 5;
FIG. 7 a third variant of the glow plug according to the invention in a sectional view; and
FIG. 8 an enlarged detail VIII of the variant of FIG. 7.
DETAILED DESCRIPTION OF THE DRAWINGS
The state-of-the-art pressure measuring probe shown in FIG. 1 has already been discussed in the introduction.
The glow plug 1 shown in FIGS. 2 to 4 has an integrated pressure sensor 2 while remaining fully functional as a glow plug. The pressure sensor 2 is used for measuring the pressure in the combustion chamber 3 of an internal combustion engine (not further shown), the glow plug 1 being inserted into a glow plug bore 4, which is provided with a conical seat 5. Departing from a sealing cone 7, which fits the conical seat 5, the shell 6 of the glow plug 1 has a slender section 9, with diameter <5 mm, extending towards the combustion chamber. The section 9 adjacent to the combustion chamber terminates in the rounded tip 10 of the glow plug 1, which protrudes slightly into the combustion chamber 3. In the first variant according to FIG. 2 to 4 a piezoelectric pressure sensor 2a is used, which is located without cooling in the section 9 of the glow plug 1 adjacent to the combustion chamber. In contrast to the state of the art, pressure on the pressure sensor 2a is applied in radial direction, i.e. normal to the axis 1′ of the glow plug 1, and in all variants of the invention the glow coil 8 of the glow plug 1 passes towards the tip 10 of the glow plug 1 either along the side the pressure sensor 2a or through the pressure sensor 2b, 2c (see FIGS. 5 to 8).
The piezoelectric pressure sensor 2a is placed in a radial through-bore 16 of the section 9 of the glow plug 1 adjacent to the combustion chamber between two opposing membranes 14. As can be seen from FIGS. 3 and 4 the glow coil 8 passes by the piezoelectric pressure sensor 2a as it goes towards the tip 10 of the glow plug. This results in a very compact assembly having diameter <5 mm in the area of the pressure sensor.
The piezoelectric pressure sensor 2a essentially consists of the small measuring tube 15 closed at both ends by membranes 14, which is inserted into the radial bore 16 and whose longitudinal axis 15′ is at a right angle to the longitudinal axis 1′ of the glow plug. Two or more strip-shaped measuring elements 17 may be placed between the membranes 14, the smaller sides of the measuring elements 17 contacting the membranes 14 and the transversal piezoeffect being utilized. Variants of this arrangement are possible, in which a plurality of disk-shaped measuring elements forming an element stack are placed in the small measuring tube 15.
In the embodiment shown a plane pick-up electrode 18 is provided between a pair of piezoelectric measuring elements 17, with at least one signal lead 19 exiting through an opening 20 in the wall of the small measuring tube 15. Via spring elements 27 the other sides of the measuring elements 17 are in electrically conductive contact with the small measuring tube 15 and thus with the glow plug shell 6. It would also be possible to provide signal leads for both electrodes of the measuring elements 17.
The signal leads are preferably located in the interior of the glow plug 1 protected by a thin guiding tube 28.
In a second embodiment, as shown in FIGS. 5 and 6, a preferably cylindrical membrane 21 is provided in the section 9 of the glow plug 1 adjacent to the combustion chamber, on whose inner side a high-temperature resistant strain gauge 22 is applied. In this way a DMS-pressure sensor 2b is realized, with the glow coil 8 passing towards the tip of the glow plug 1 through the cylindrical interior space 23 bounded by the strain gauge 22. This will also permit very small diameters in a range <5 mm, while providing full functionality.
Finally in a third embodiment, as shown in FIGS. 7 and 8, a preferably cylindrical membrane 21 is provided in the section 9 of the glow plug 1 adjacent to the combustion chamber, which together with a distanced electrically conductive counter-surface 24 forms a capacitive pressure sensor 2c. In this variant the glow coil 8 may pass towards the tip of the glow plug 1 through the interior space 25 bounded by the counter-surface 24. The capacitive pressure sensor 2c has annular insulating elements 26 at both ends of the cylindrical membrane 21, which hold the cylindrical counter-surface 24 at a defined distance to the cylindrical membrane 21.
Patent Application
20070245805
