JPS641616Y2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a knocking detection device that electrically detects knocking in an internal combustion engine using a piezoelectric element.

The mounting case is fixed to the cylinder wall of the internal combustion engine,
A knocking detection device is known in which a vibration sensing member made of a piezoelectric element is attached to the inner bottom surface with bolts or the like, and when knocking occurs, the piezoelectric element resonates to generate an output signal and detect the occurrence.

However, in the conventional structure, the mounting case was made of metal because the earth electrode of the piezoelectric element was electrically connected to the case and grounded as a so-called body ground. For this reason, as shown in FIG.
is made of a synthetic resin material because it is necessary to insulate the terminal c from the case a, and therefore the cover d and the case a are made of different materials and cannot be welded or otherwise applied. After fitting the lid d into the circumferential groove e on the inner periphery of the case a, the lid d is fixed inside the case a by crimping the thin edge f formed on the inner edge of the case a inward. There is a need to. For this reason, it is necessary to form a thin edge f, which complicates the molding of the case a, and since the case is constantly subjected to shocks due to the vibrations of the cylinder,
Caulking using the thin edge f may cause loosening, causing rattling of the lid and causing disconnection between the terminal c and the vibration sensing member b.

Furthermore, since the case is made of metal, the device is heavy and expensive.

Furthermore, conventional methods have relied on body grounding, and since the metal case has a potential with respect to the true ground potential, a potential difference is generated, and this potential difference is superimposed on the output signal from terminal c, causing noise. be.

The purpose of this invention is to eliminate the above-mentioned drawbacks, and the mounting case is made of synthetic resin and has a male screw protruding from the bottom surface to be screwed into the cylinder wall of an internal combustion engine, and an inner cavity with the top open. A vibration sensing member made of a material and using a piezoelectric element is provided on the inner bottom surface of the case, and a lid body made of an insulating synthetic resin holds an output terminal and a ground terminal connected to the upper and lower electrodes of the piezoelectric element. By adhering the side wall of the lid to the inner surface of the case, it is fixed in the mounting case, and by forming the mounting case from a synthetic resin material, it has compatibility with the synthetic resin lid. In addition, by making it possible to bond by means such as ultrasonic welding, high frequency welding, thermal welding, or adhesive coating, it is possible to make a strong connection without using caulking means, and the weight of the device can be reduced. In addition to being inexpensive, damage caused by body grounding is eliminated by insulating the cylinder wall with the mounting case and connecting the grounding electrode of the piezoelectric element to the grounding terminal inserted into the lid.

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

Reference numeral 2 denotes a mounting case with a hexagonal outer periphery, which has a cylindrical inner cavity and a mounting groove surface 3 formed on the inner periphery side, and has a cylinder wall 1 of an internal combustion engine on its lower surface.
A male screw 4 is provided protrudingly to be screwed into the female screw provided in the.

The mounting case 2 is molded from a synthetic resin material.

7 is a vibration sensing member formed by bonding a ring-shaped piezoelectric element 9 having electrodes 10a and 10b on the upper and lower surfaces on a disk-shaped metal thin plate 8, and whose resonance frequency is set in a frequency band of 5 to 10 kHz. Match the knocking frequency in . An insertion hole 8a is formed in the center of the thin plate 8, and washers 11, 11 are installed on the upper and lower surfaces of the hole.
The above-mentioned vibration sensing is achieved by placing the bolt 12 through the hole, screwing the space nut 13 from below, and then tightly screwing the threaded part into the screw hole 6 provided on the inner bottom surface of the case 2. The member 7 is consolidated onto the inner bottom surface 5. A grounding electrode plate 15 is fastened between the head of the bolt 12 and the upper washer 11.

16 is a ground terminal 18 and an output terminal 1 on the upper wall surface.
9 is inserted and its lower end faces the inner cavity of the case 2, and its outer diameter is equal to the inner diameter of the mounting groove surface 3 in the mounting case, and the groove surface 3 The side wall 16a is fitted to connect the ground terminal 17 to the electrode plate 15 and the output terminal 18 to the output side electrode 10a of the piezoelectric element 9, respectively. The joint surface between the side wall 16a of the lid 16 and the case 2 is bonded by ultrasonic welding, high frequency welding, thermal welding, adhesive application, etc., and the lid 16 is fixed in the case 2. Do it like this.

The operation of the above embodiment will be explained.

When knocking occurs in the engine combustion chamber, the shock wave propagates to the cylinder wall 1 as a mechanical vibration, and the mounting case 2 screwed to the wall 1 with a male screw 4 generates a vibration approximately equal to the frequency unique to the knocking. will occur. Therefore, the vibration is transmitted to the vibration sensing member 7 inside the case 2 via the bolt 12, and the bolt 1
2 and its periphery swings. Since the resonant frequency of the vibration sensing member 7 is set approximately equal to the knocking frequency, the member 7 resonates and the piezoelectric element 2 is well distorted, creating a potential difference between the output electrode 10a and the ground electrode 10b. A signal voltage is available at output terminal 18. At this time, the earth electrode 10
Since b is not dependent on the body ground, it is a true ground potential, and an output signal with less noise can be obtained.

FIG. 4 shows a second embodiment of the present invention, in which a disc-shaped thin metal plate 8' has a diameter equal to the outer diameter of the lid body 16,
A vibration sensing member 7' having a disk-shaped piezoelectric element 9 bonded to the upper surface thereof is provided on the inner bottom surface of the case 2, and the outer peripheral edge of the thin plate 8' is connected to the lid body 16.
It is clamped and fixed between the side wall 16a of the case 2 and the lower surface of the mounting groove surface 3 of the case 2.

Furthermore, a bonding film 2a is formed on the upper part of the synthetic resin case 2 by plastically deforming the resin, thereby making the inside of the case 2 more watertight.

The vibration sensing member 7a of this embodiment is peripherally held, and when knocking occurs, its center portion curves up and down, causing distortion in the piezoelectric element 2 and generating an output signal. In the case where the vibration sensing member 7a is clamped between the lid 16 and the lower surface of the mounting groove surface 3, if the lid 16 is fixed by the conventional caulking action, the clamping may loosen due to vibration and cause knocking. However, in this embodiment, since the lid body 16 and the case are reliably bonded, this drawback is eliminated.

As clarified in the above description, in the present invention, since the mounting case 2 is made of a synthetic resin material, the synthetic resin lid body 1 is fitted into the case 2.
6, it is possible to use adhesive means such as ultrasonic welding, high frequency welding, or adhesive application, so that the lid body 16 can be securely fixed to the case 2, and its inner space can be made watertight. Since the case 2 is insulated from the cylinder wall 1, it is possible to easily provide a grounding method that does not rely on body grounding.Furthermore, the case 2 can be easily molded, and is cheaper and lighter than conventional equipment. It has excellent effects such as.

[Brief explanation of drawings]

Fig. 1 is a longitudinal side view of the conventional device, Fig. 2 is a longitudinal side view of the first embodiment, Fig. 3 is a sectional view taken along line A-A in Fig. 2, and Fig. 4 is a longitudinal side view of the second embodiment. It is a diagram. 2... Mounting case, 7... Vibration sensing member, 9...
...Piezoelectric element, 16...Lid, 16a...Side wall, 1
8, 19...terminal.

Claims (1)

[Scope of utility model registration request] A knocking detection device for an internal combustion engine, comprising: a mounting case made of synthetic resin and having a male screw protruding from its underside for screwing into a cylinder wall of an internal combustion engine and an internal hollow portion open at the top; a vibration sensing member using a piezoelectric element provided on the inside bottom surface of said case; and an insulating synthetic resin lid body holding an output terminal and an earth terminal connected to upper and lower electrodes of said piezoelectric element, which is fixed inside said mounting case by bonding the side walls of said lid body to the inside surface of the case.