Spark Plug With a Pressure Measuring Device

The invention relates to a spark plug with a pressure measuring device claim. In a known spark plug the pressure measuring device which is mounted within the spark plug housing is separated from the insulator and also from the combustion chamber by a thin walled inserted element. Therefore, the housing itself has only a relative thin outer wall and in view of the separate insert element the structure of the spark plug is expensive and complicated. In view of the inserted element the pressure measuring device reacts relatively sluggishly.

It is therefore an object of the present invention to provide a spark plug in which a pressure measuring device is immediately connected with a pressure chamber.

In keeping with these objects and with others which will become apparent hereinafter, one feature of the present invention resides, briefly stated, in a spark plug with a pressure measuring device in which a housing of the spark plug has an eccentrically arranged longitudinal opening which forms in the housing a housing part with a thicker wall, and a pressure measuring device is arranged in this housing part.

In such construction the pressure measuring device is directly connected with the pressure chamber. Thus, the pressure measuring device has a relative low reaction time and can therefore rapidly measure low pressure fluctuations. Since the pressure measuring device is fixedly mounted in a bore in the housing of the spark plug it has a great resistance against vibration. In other words it cannot change its position under the action of loads which occur during operation and therefore cannot cause any erroneous measurements. In view of the unsymmetric disposition of the center bore with the insulation element no outer structural changes of the housing of the spark plugs are required, so that the spark plug can be installed without any problems in hitherto known arrangements.

The novel features which are considered as characteristic for the invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.

One exemplified embodiment of the invention is illustrated in the drawing and is explained in more detail in the following.

FIG. 1 shows a longitudinal section of a spark plug in accordance with one embodiment of the present invention; and FIG. 2 shows the same section of the spark plug in accordance with another embodiment of the invention with FIG. 1.

A spark plug has a housing 10 with an eccentrically arranged longitudinal bore 12. The housing 10 can be screwed in customary manner with the assistance of an outer thread 13, into a motor block. The housing 10 is provided at its end facing the combustion chamber with a measuring electrode 14. An insulating element 15 is arranged in the longitudinal bore 12 and has an insulator tip 16 which faces the measuring electrode 14. Furthermore, the insulating element 15 is provided with a central longitudinal bore 18 for accommodating a connecting bolt 43 shown in dotted and a center electrode 19. The center electrode 19 and the measuring electrode 14 together form the spark path for the spark plug 11.

As a result of the eccentrical mounting of the longitudinal bore 12 the housing is provided with one housing part 20 having another housing part 21 having thick wall and a thin wall. In the housing part 20 with the thicker wall a pocket bore 22 is formed extending parallel to the longitudinal bore 12, a step bore 24 is provided at a bottom 23 of the pocket bore 22. The step bore 24 extends transversely to the pocket bore 22 and has a portion 25 of a smaller diameter, which in the area of the insulator foot tip 16 opens into a breathing chamber 26 of spark plug 11. An obliquely extending bore. An obliquely extending bore 28 is formed the area of approximately in a compression and heat shrinking zone 27 of the housing 10 and opens into the pocket bore 22.

A pressure sensor 31 is mounted in the step bore 24 and used for measuring the combustion pressures in the combustion chamber. This may be a customary known sensor with piezoelectric elements or also with piezo ceramic piezoresistive or electrodynamic elements. The pressure sensor 31 is in direct operating connection with the combustion chamber by means of the portion 25 of step bore 24. The electrical lines of the pressure sensor 31 lead to the outside through the pocket bore 24 and the bore 28 and to an evaluation device, not shown. A resistor 41 is mounted in the longitudinal bore 18 between the connecting bolt 43 and the center electrode 19.

In the embodiment shown in FIG. 2 the same parts are designated with the same reference numbers. A step bore 34 is formed in the housing part 20 with the thicker wall, parallel to the longitudinal bore 12 and is connected with bore 28. The bore portion 35 with the smaller diameter is directed toward the combustion chamber. A membrane 37 which is in operative connection with the pressure sensor 31 is mounted on a shoulder 36 of the step bore 34. As in the exemplified embodiment in accordance with FIG. 1, it can again be provided with piezoelectric, piezoresistive or electrodynamic elements. A sleeve like extension part 38 engages the pressure sensor 31 and maintains the pressure sensor 31 in its position. The extension part 38 is mounted in the step bore 34 by means of a screw 39. For obtaining interference free signals of the pressure sensor 31 a resistor suppressor is mounted between the connecting bolt and the center electrode 19.

It is important that the longitudinal bore 12 is formed eccentrically, so that the housing part 20 with a thicker wall is provided for of the pressure sensor 31.

The function of a spark plug is sufficiently known and is therefore not discussed in detail.