JPS6242345Y2 - - Google Patents

Description

[Detailed description of the invention] This invention is a piezoelectric pressure sensor for internal combustion engines that is inserted in the form of a washer into the engine bolt that connects the cylinder block and cylinder head, and outputs an electrical signal in response to fluctuations in cylinder pressure. This relates to a sensor, and the drawings will be explained below.

In Fig. 1, 1 and 1' are a pair of ring-shaped piezoelectric elements made of piezoelectric ceramics such as lead zirconate titanate and lead titanate, which are connected via the same ring-shaped terminal plate 2 so that they are electrically parallel. and face each other. 3 and 3' are ring-shaped pressure plates and pressure receiving plates made of soft metal such as aluminum that are in contact with the outer surfaces of the piezoelectric elements 1 and 1' facing each other with the terminal plate 2 in between; It increases the mechanical strength of ' and equalizes the distribution of compressive stress applied during tightening. 4, 4' are the piezoelectric elements 1,
1' and an insulating layer thinly coated on the inner and outer circumferential surfaces of the terminal plate 2 to prevent the terminal plate 2 from coming into contact with an inner case and an outer case, which will be described later, and causing a short circuit. 5 and 5'
are the inner and outer circumferential surfaces of the piezoelectric elements 1 and 1' whose inner and outer circumferential surfaces are covered with insulating layers 4 and 4', the terminal plate 2, and the pressure plate 3 and pressure receiving plate 3' that are in contact with the upper and lower surfaces of the piezoelectric elements, respectively. A metal inner case and an outer case fitted with the edges 5a, 5b and 5'a of the upper and lower opening surfaces.
5'b is bent so as to engage the outer edges of the pressure plate 3 and the pressure receiving plate 3', thereby joining the laminate together. Reference numeral 6 denotes a conduit protruding from one side of the outer case 5' so as to surround the protruding piece 2a of the terminal plate, and 7 has one end inserted into the conduit 6 and the protruding piece 2a of the terminal plate.
The configuration up to this point is approximately the same as the conventional one, except for the signal carrying lead wire connected to a.

Such a piezoelectric pressure sensor is inserted with a washer type into any one bolt (indicated by a chain line N) among a large number of engine bolts that fasten the cylinder block and cylinder head, and the hexagonal head of the bolt N is inserted into the bolt. The piezoelectric element is installed under a constant compressive stress between part N' and the cylinder head surface (indicated by the chain line M), and the compressive stress changes in response to fluctuations in the cylinder pressure. 1 and 1', which can be extracted from the signal carrying lead wire 7 and supplied to an external engine control circuit device.

However, in the conventional pressure sensor mentioned above, the hexagonal head N' of the engine bolt and the cylinder head surface M
In addition, since the outer surfaces of the pressure plate 3 and the pressure receiving plate 3', which are exposed from the upper and lower surfaces of the sensor, are in contact with each other almost entirely, the heat conduction area is large, and as a result, high-temperature engine heat is transmitted to the piezoelectric element 1. , 1', or deteriorate the electrical performance of the piezoelectric element and the metal terminal plate 2, which comes into contact with it.
A large shear strain was generated between the pressure plate 3 and the pressure receiving plate 3' due to the difference in thermal expansion, and the piezoelectric elements 1 and 1' were sometimes damaged.

In order to solve the above-mentioned problems, the present invention has annular protrusions 3 on the outer surfaces of the pressure plate 3 and the pressure receiving plate 3', respectively.
a, 3'a (see Fig. 2A) or a plurality of small protrusions arranged at equal intervals, 3b..., 3'b... (see Fig. 2B).

However, when the piezoelectric pressure sensor according to the present invention is inserted into an engine bolt, the outer surfaces of the pressure plate 3 and the pressure receiving plate exposed from the upper and lower surfaces of the sensor are connected to the hexagonal head N' of the bolt and the cylinder head surface M.
However, only the protrusions 3a, 3'a or 3b..., 3'b..., which have a small contact area, come into contact with the protrusions 3a, 3'a, or 3b..., 3'b..., and most of them face each other through a gap (air) with a small thermal conductivity.
Heat transfer from the engine is reduced, so the performance of the piezoelectric element will not deteriorate or be damaged due to the high-temperature engine heat as in the past. Demonstrates outstanding effectiveness.

Although this proposal is directed to a piezoelectric pressure sensor in which a pair of ring-shaped piezoelectric elements, a terminal plate, a pressure plate, and a pressure receiving plate are covered by an inner case and an outer case, the present invention is not limited to this. A piezoelectric element that is easily inserted into an engine bolt in the form of a washer and generates an electrical signal due to fluctuations in the pressure inside the cylinder, and a piezoelectric element that is reinforced from the top and bottom surfaces and is used to equalize the distribution of compressive stress during tightening. The present invention can be applied to an embodiment including a pressure plate and a pressure receiving plate.

[Brief explanation of the drawing]

Figure 1A is a front cross-sectional view of a piezoelectric pressure sensor to which the present invention is applied, Figure B is a planar cross-sectional view taken along line A--A in Figure A, and Figure 2A is a similar processing method to that used in Figure 1. A perspective view of a pressure plate (and a pressure receiving plate), FIG. 1B is a perspective view of a pressure plate (and a pressure receiving plate) according to another embodiment. 1, 1'... Piezoelectric element, 3... Pressure plate, 3'...
Pressure receiving plate, 3a, 3'a, 3b, 3'b...protrusion, N
... Engine bolt, N' ... Hexagonal head, M ... Cylinder head surface.

Claims (1)

[Scope of utility model registration request] The engine bolt is inserted between the hexagonal head of the engine bolt and the cylinder head surface, and is installed under a certain compressive stress, and outputs an electric signal in response to fluctuations in cylinder pressure, and at least a piezoelectric element is used. In a pressure sensor equipped with a metal pressure plate and a pressure receiving plate that sandwich the same between the upper and lower surfaces, the heat conduction area between the hexagonal head of the engine bolt and the cylinder head surface is reduced on the outer surfaces of the pressure plate and the pressure receiving plate, respectively. A piezoelectric pressure sensor for internal combustion engines characterized by having a protrusion.