JPH02658Y2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a piezoelectric pickup device for an internal combustion engine that is attached to a cylinder wall or the like of an internal combustion engine to electrically detect knocking or the like occurring within the engine using a piezoelectric element.

A mounting case is fixed to the cylinder wall of an internal combustion engine, and a piezoelectric element is placed on the bottom of the internal cavity, and a weight is sequentially placed on top of the piezoelectric element and connected to the bottom of the internal cavity. A non-resonant piezoelectric pickup device is known in which knocking is detected by causing distortion in the piezoelectric element due to the acceleration vibration of the weight caused by knocking, and generating an output signal.

By the way, in a conventional piezoelectric pickup device for an internal combustion engine, as shown in Figs. 1 and 2, a molding material such as a rubber-like soft epoxy resin is placed in the inner space b of a mounting case a in order to suppress spurious noise and maintain confidentiality. e
was filled to directly cover the circumferences of the piezoelectric element c and the weight d. For this reason, there was a drawback that sensor characteristics were significantly affected by changes in rubber elasticity due to temperature, particularly by hardening of the molding material at low temperatures.

In addition, as shown in Fig. 2, if the lid f has a sealed structure in which the upper opening of the inner space b is shielded, the volume change of the molding material e cannot be tolerated, so the expansion force of the resin at high temperatures causes the above-mentioned An extra load was applied to the piezoelectric element c and the weight d, which adversely affected the temperature characteristics. That is, both of the structures shown in FIGS. 1 and 2 had the disadvantage of poor temperature characteristics.

The present invention is aimed at eliminating the above-mentioned drawbacks of the conventional technology, and is a metal mounting device with a male screw protruding from the lower surface for screwing into the cylinder wall of an internal combustion engine, and an inner cavity provided in the main body. A piezoelectric element is sequentially placed on the bottom surface of the inner cavity of the case, and a weight is sequentially placed on top of the piezoelectric element and connected to the bottom surface of the inner cavity, and the periphery of the weight is covered with an elastic covering. The piezoelectric element is filled with a molding material, and the elastic covering absorbs the effects of hardening and volume changes of the molding material, thereby preventing the effects on the top surface of the piezoelectric element.

An embodiment of the present invention will be described with reference to FIG.

Reference numeral 1 denotes a mounting case which is attached to a cylinder wall s of an internal combustion engine by screwing a male screw 2 formed on the lower surface thereof, and a screw hole 4 provided on the lower surface of an inner space 3 which is open at the upper side. , by screwing the lower end of the mounting screw 5, the mounting screw 5 is erected in the inner space 3.

Reference numeral 6 denotes a ring-shaped piezoelectric element having a through hole 7 formed in the center and electrodes on the upper and lower surfaces, and two piezoelectric elements are mounted on the mounting screw 5 with an electrode plate 8 interposed between them. Fit and ride on the lower surface of the inner cavity 3. Furthermore, an annular weight 9 having the same outer diameter as the piezoelectric element 4 is disposed on the piezoelectric elements 6 by screwing a female screw 10 formed on its inner surface into the threaded rod 5. As a result, the weight 9 is mounted on the piezoelectric elements 6, 6.

Reference numeral 12 denotes an elastic covering of a sky cylinder made of foamed silicone rubber, foamed chloroprene rubber, or other elastic material, which is a main part of the present invention, and its inner diameter is the same as the outside of the piezoelectric elements 6, 6 and weight 9. Match the diameter,
It is placed over the piezoelectric element 6 and weight 9 at the top. At this time, in order to enable electrical connection between the electrode plate 8 and the conductive wire 15 described later, the lower end of the elastic covering 12 is made to be slightly above the electrode plate 8.

However, the piezoelectric elements 6 and the weight 9 may be entirely covered by forming a hole for signal extraction at the lower edge of the elastic covering 12. In this case, since the side peripheral surfaces of the piezoelectric elements 6, 6 are also covered, the effects of changes in hardness and expansion and contraction of the molding material 16 can be more effectively prevented.

After connecting the conductive wire 15 supported by the holding fitting 14 fitted to the inner surface of the upper end of the mounting case 1 to the electrode plate 8, a molding material 16 of epoxy, silicone, etc. is placed in the inner space 3. Fill it with. In this installed state, the electrode formed on the upper surface of the upper piezoelectric element 6 contacts the bottom surface of the inner cavity 3 via the weight 9 and the screw rod 5, and the electrode provided on the lower surface of the lower piezoelectric element 6 contacts the bottom surface of the inner cavity 3. The body is grounded by being electrically connected to the main body of the mounting case 1, respectively, and the output voltage generated in the piezoelectric elements 6, 6 is taken out from the electrode plate 8 via a conductive wire 15.

FIG. 4 is a graph comparing the characteristics at low temperatures between the value x of the embodiment described above and the value y of the conventional device shown in FIG. 1. At a low temperature of -40°C, the piezoelectric constant g ₃₃ = 17.1×10 ^-3 Vm/N, outer diameter 10φ,
The conventional device shown in FIG. 1 and the embodiment device shown in FIG. 3 are constructed using two pieces of lead zirconate titanate with an inner diameter of 5φ and a thickness of 3 mm as piezoelectric elements, and a constant acceleration of 1G (acceleration of gravity) is achieved. The relationship between the frequency and the output voltage was measured.

As a result, in the conventional device, the value of the output voltage varies considerably depending on the frequency. However, in the case of the device of the above embodiment, the change in output voltage was gradual as the frequency increased. From this, the present invention has found that even if the molding material 16 hardens at low temperatures, the elastic covering 12 can alleviate this effect.

Even in the case of the sensor in which the inner space 3 was sealed with a lid, the characteristics at high temperatures did not deteriorate. From this, it can be seen that even if the mold material 16 expands due to high temperature, the elastic covering 12 absorbs the expansion and prevents it from affecting the piezoelectric element 6, weight 9, etc. Ta.

As clarified by the description of the above embodiments, the present invention covers the weights 9 which are sequentially placed and fixed on the bottom surface of the inner cavity 3 of the metal mounting case 1 with the elastic covering 12. The elastic covering 12 absorbs the effects of changes in hardness and expansion and contraction of the molding material 16 filled in the inner cavity 3, and can alleviate the effects on the top surface of the piezoelectric element 6, thereby improving the temperature characteristics of the piezoelectric element 6. It has an excellent effect of significantly improving the

[Brief explanation of the drawing]

1 and 2 are vertical side views of a conventional knock sensor, FIG. 3 is a vertical side view of an embodiment of the present invention, and FIG. 4 is a graph showing temperature characteristics at low temperatures. 1; Mounting case, 3; Inner space, 6; Piezoelectric element,
9; Weight, 12; Elastic covering, 16; Mold material.

Claims (1)

[Scope of utility model registration request] A metal mounting case has a male screw protruding from its lower surface to be screwed into the cylinder wall of an internal combustion engine, and has an inner cavity in its main body, and a piezoelectric element is mounted on the bottom of the inner cavity.
An internal combustion engine characterized in that weights are successively placed on the upper part and connected to the bottom surface of the inner cavity, the periphery of the weights is covered with an elastic covering, and the inner cavity is further filled with a molding material. Piezoelectric pickup device.