JPH0318904Y2 - - Google Patents

Description

[Detailed description of the invention] (Field of industrial application) This invention relates to a mounting structure for a pressure sensor in which a pressure element that detects the pressure in the combustion chamber of an internal combustion engine and converts it into an electrical signal is incorporated inside a gasket. It is.

(Prior Art) In order to understand the combustion mechanism of an internal combustion engine, it is necessary to know the magnitude of the internal pressure and changes in pressure over time.

Conventionally, when trying to measure the pressure inside a cylinder,
It is necessary to make a hole in the cylinder wall to create a pressure receiving surface, and while drilling holes in the cylinder wall is fine for air-cooled engines, it is problematic for water-cooled engines.
There is a problem in that the temperature distribution at the cylinder head differs from the actual temperature distribution due to the opening of the hole.

Recently, in order to incorporate a pressure-receiving surface into the ignition plug as a method for measuring without drilling holes, a prototype was created that combined a pressure pickup and a ignition plug into one, but this also depends on the actual conditions. There are different difficulties. Furthermore, with the method of picking up the discharge state by electromagnetic induction using a coil, it is not possible to directly know the pressure inside the cylinder.

As a means of solving these problems, we have developed a pressure sensor mounting structure that uses a gasket-type pressure sensor in which a piezoelectric element is enclosed in an annular metal case, and that is installed between the cylinder head and the spark plug to measure combustion pressure. is being produced.
(Special Publication 41-5154).

(Problems to be solved by the invention) There are many accidents in which such pressure sensors are affected by severe vibrations, resulting in element cracks or gas leaks. It was thought that this could be improved by using an annular plate made of soft metal such as Cu or Al for the surface. (Public Application No. 59-143859).

However, when we further investigated the hardness of this annular plate, we found that if it is too hard or too soft, element cracking and gas leakage are likely to occur.

(Means for solving the problem) The present invention uses an annular plate made of metal with a hardness of H _V 50 to H _V 270 when installing a gasket type pressure sensor on the spark plug mounting seat surface or cylinder head seat surface. This solves the problems of the prior art.

(Embodiment) In the embodiment of the present _invention , as shown in Fig. 1, a spark plug 1 _is attached to an engine head 2. Sensor 4 is installed.
5 is a lead wire for taking out the output of the sensor 4.

For example, as shown in FIG. 2, the sensor used here includes a laminate 11 consisting of an annular internal electrode 12, piezoelectric elements 13, 13 disposed above and below it, and outer electrodes 14, 14, inside an annular metal case 16. The output lead wire 5 connected to the internal electrode 12 is housed in the metal case 1.
This is a gasket type pressure sensor led out from one end of the gasket. A protective member 6 for the lead wire 5 is composed of a metal cylindrical portion 7 and a rubber boot 8, and is fitted into a plug hole of the cylinder head.

Now, when such a pressure sensor is installed as shown in FIG. 1, tests were conducted with various hardnesses of the annular plate, and unexpected findings were obtained as shown in FIG. 3.

That is, when the hardness was 50 _HV to 270 _HV , no defects occurred at all, but when the hardness was less than 50 _HV , cracking of the element was observed, and the lower the hardness, the higher the defect occurrence rate. Moreover, when the temperature exceeds 270H _V , gas leakage is observed, and the failure rate increases rapidly as the hardness increases.

The qualification conditions for the above examination are as follows.

Element cracking: Checked for cracks after tightening 5 times at 6 kg/m.

Gas leakage: When tightened at 2.5 kg and pressurized to 15 kg/cm ² , if there was a gas leak of 1 c.c./min or more, it was considered defective.

(Effect of the invention) When the invention is used, the hardness is H _V 50 as an annular plate.
Since the gasket-type pressure sensor is mounted using ~H _V 270 metal, highly reliable pressure detection can be performed without cracking the sensor element or gas leakage.

[Brief explanation of the drawing]

Figure 1 is a partial vertical sectional view showing an example of the mounting structure of the gasket type pressure sensor of the present invention, Figure 2 is a partial vertical sectional view showing an example of the gasket type pressure sensor, and Figure 3 is the hardness of the annular plate. It is a graph showing the relationship between and the defective occurrence rate. 1... Spark plug, 2... Engine head, 3... Annular plate, 4... Sensor.

Claims (1)

[Scope of utility model registration request] A gasket type pressure sensor in which a piezoelectric element is enclosed in an annular metal case is installed between the cylinder head and the spark plug to detect combustion pressure.In the pressure sensor installation part, the pressure sensor is attached to the seat surface of the spark plug's mounting bracket. Or, a gasket type pressure sensor mounting structure characterized in that it is fastened to the cylinder head via an annular plate made of metal having a hardness of _HV 50 to _HV 270 on one side of the cylinder head seating surface.