JPS641613Y2 - - 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.

A metal case is fixed to the cylinder wall of an 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 to detect the occurrence of knocking.

However, the conventional structure is based on so-called body grounding, in which the ground electrode of the piezoelectric element is electrically connected to the metal case and grounded, so the metal case has a potential with respect to the true ground potential, so there is no potential difference between them. This potential difference is superimposed on the output signal generated from the piezoelectric element along with knocking, resulting in noise.

The present invention aims to eliminate the above-mentioned drawbacks, and includes an insulating plate laid on the inner bottom surface of a metal case that is fixed to the cylinder wall of an internal combustion engine, a thin metal plate on the insulating plate, and a piezoelectric element bonded on the thin plate. The metal case and the piezoelectric element are insulated by supporting a vibration sensing member having a resonant frequency approximately equal to the knocking frequency, and the upper and lower electrodes of the piezoelectric element are respectively connected to terminals insulated from the metal case. The structure is such that the piezoelectric element and the metal case are insulated by an insulating plate, and the ground electrode of the piezoelectric element is connected to a ground terminal that is separately insulated from the metal case.

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

Reference numeral 2 is a metal case having a hexagonal outer periphery with a cylindrical internal space, and a mounting screw 3 protruding from the lower surface of the metal case is screwed into a female thread provided on the cylinder wall 1 of the internal combustion engine. solidifies. An insulating plate 4 made of Bakelite or the like having an outer diameter equal to the inner diameter of the case is placed on the inner bottom surface of the case 2, and a metal support plate 5 having an outer diameter smaller than the insulating plate 4 is applied.

7 is a ring-shaped piezoelectric element 9 having electrodes 10a and 10b on the upper and lower surfaces on a disk-shaped thin metal plate 8.
It is a vibration sensing member formed by bonding two together, and its resonant frequency is made to match the knocking frequency in the frequency band of 5 to 10 kHz. The sensing member 7 has washers 13, 13 on the upper and lower surfaces of the center hole 8a of the thin plate 8.
, pass the bolt 12 through the hole, screw the space nut 14 from below, and then screw the threaded portion of the space nut 14 into the screw hole 5a provided in the center of the support plate 5. It is supported on a plate 5.

A grounding electrode plate 15 is fastened between the head of the bolt 12 and the upper washer 13.

Reference numeral 17 is an inverted cup-shaped plastic presser cover whose outer diameter is equal to the inner diameter of the metal case 2, and has a pressing stepped surface 19 on the lower edge of the circumferential wall 18 of which the outer circumferential edge of the support plate 5 is tightly fitted. At the same time, a ground terminal 20 and an output terminal 21 are inserted into the upper wall surface, the ground terminal 20 is connected to the electrode plate 15 attached to the bolt 12, and the output terminal 21 is connected to the upper surface electrode 10a of the piezoelectric element 9. Connect with.

The presser lid 17 is fitted into the internal gap of the metal case 2 by pressing the pressing step surface 19 against the support plate 5, and the thin edge 2a provided on the upper peripheral edge of the metal case 2 is swaged inward. 17 is housed in the case 2 without being able to escape.

The present embodiment has the above-mentioned configuration, and the thin metal plate 8 is insulated from the metal case 2 by the insulating plate 4 provided between the support plate 5 and the inner bottom surface of the case 2, and the ground electrode 10b on the lower surface of the piezoelectric element 9 is Said metal thin plate 8, washer 1
3 and an electrode plate 15, it is connected to a ground terminal 20 which is insulated from the metal case 2 by a presser cover 17.

To explain the operation of the above embodiment, when knocking occurs in the combustion chamber of the engine, the shock wave is transmitted to the cylinder wall 1 as mechanical vibration, and the knocking occurs in the metal case 2 screwed to the wall 1 with the mounting screw 3. A vibration approximately equal to the natural frequency of is generated.

Therefore, the vibration is transmitted to the internal vibration sensing member 7 via the insulating plate 4 and the support plate 5, and the periphery thereof swings around the bolt 12.

Since the resonant frequency of the vibration sensing member 7 is set approximately equal to the knocking frequency, it resonates,
The piezoelectric element 9 is often distorted, creating a potential difference between the upper surface electrode 10a and the lower surface electrode 10b, and this output voltage is obtained from the output terminal 21. At this time, the bottom electrode 10
Since b is not dependent on the body ground, it is a true ground potential, so an output with less noise can be obtained.

As detailed above, the present invention has a metal case 2.
An insulating plate 4 is laid on the inner bottom surface of the piezoelectric element 9, and the ground electrode 10b of the piezoelectric element 9 is connected to a ground terminal 20 insulated from the metal case 2. It is possible to prevent the influence of noise on the output signal due to the potential difference generated between other dissimilar metals and the earth electrode 10b, and there is an excellent effect that a clear output signal can be obtained and knocking detection can be performed accurately.

[Brief explanation of the drawing]

The accompanying drawings show an embodiment of the present invention, in which FIG. 1 is a longitudinal sectional side view and FIG. 2 is a sectional view taken along the line A--A in FIG. 1. 2... Metal case, 4... Insulating plate, 7... Vibration sensing member, 8... Metal thin plate, 9... Piezoelectric element, 1
0a, 10b...electrodes.

Claims (1)

[Scope of utility model registration request] An insulating plate is laid on the inner bottom surface of a metal case that is fixed to the cylinder wall of an internal combustion engine, and a resonant frequency approximately equal to the knocking frequency of the thin metal plate and the piezoelectric element bonded to the thin plate is set on the insulating plate. Knotting detection for an internal combustion engine, characterized in that a metal case and a piezoelectric element are insulated by supporting a vibration sensing member having a metal case, and upper and lower electrodes of the piezoelectric element are respectively connected to terminals insulated from the metal case. Device.