JPS58218621A - Piezoelectric resonance type knock sensor for internal combustion engine - Google Patents

Abstract

PURPOSE:To execute easily the adjustment and to obtain a good output, by making a ring plate closely adhere to one face or both faces of a metallic plate to which a ring-like piezoelectric element is sticking, and adjusting by size of its diameter so that the resonance frequency accords with the knocking frequency. CONSTITUTION:A piezoelectric resonance type knock sensor consists of a vibration detecting member 4 fitted through a bolt 9 to a supporting plate 2 fixed by a holding cover 3 in a case 1. The detecting member 4 consists of a metallic plate formed by joining a ring-like piezoelectric element 6 to the upper face, a ring plate 7 for adjusting the resonance frequency and an electrode 8 which are placed on its upper face, and a ring plate 7 which is made to press-contact with the lower face, and is fixed to the supporting plate 2 through the bolt 9 and a space nut 10. The resonance frequency is adjusted so as to accord with the knocking frequency by using the ring plate 7 of a large diameter and the ring plate of a small diameter in case when the resonance frequency is made high, and in case when it is made low, respectively. Accordingly, the adjustment is executed easily.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a piezoelectric resonance knock sensor that is fixed to a cylinder of an internal combustion engine and used to detect the occurrence of knocking within the cylinder.

A knock sensor consists of a vibration sensing member made by integrally bonding a piezoelectric element to one side of a thin metal plate, and supported in a case for mounting on an engine.The resonance frequency of the vibration sensing member is determined by the knocking vibration. It is necessary to substantially match the frequency of the wave, and if such frequency adjustment is made well, knocking occurs and the outer periphery of the piezoelectric element curves vertically and vibrates, inducing maximum output.

Therefore, since the resonance frequency of the vibration sensing member is mainly determined by the outer diameter of the piezoelectric element, the shape of the piezoelectric element is designed and fired based on a certain formula so as to match the knocking frequency of a predetermined engine.

Incidentally, even in engines of the same type and model, the knock vibration frequency varies depending on variations in engine components and operating conditions. Furthermore, the resonant frequency varies somewhat depending on how the vibration sensing member is supported. For this reason, the shape of the piezoelectric element is mass-produced based on the above design and the same shape is applied to the same engine, so when a knock sensor is installed in each engine and tested, the vibration sensing member There may be a discrepancy between the resonant frequency of the engine and the knocking frequency, making it impossible to obtain a desirable output. In this case, refiring piezoelectric elements with different outer diameters and replacing them is expensive and complicated, and is practically impossible.

The purpose of the present invention is to easily match such frequency deviations, by integrally bonding an annular piezoelectric element to one surface of a thin metal plate, and making its resonant frequency approximately match the knock vibration frequency of the engine. The vibration sensing member is supported at its center by a support bolt inserted into the center of the thin metal plate in an engine mounting case,
A ring plate for adjusting the resonant frequency is fitted onto one or both sides of the central portion of the thin plate and is closely fitted to the support bolt, and by changing the outer diameter of the ring plate, the resonance of the vibration sensing member can be adjusted. It is designed to adjust the frequency.

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

Reference numeral 1 denotes a concave case, and a mounting bolt 1a is provided protruding from the center of the outer bottom surface to be screwed into the cylinder wall of the engine. A support plate 2 is placed on the inner bottom surface of the case 1.

Reference numeral 3 denotes an insulating presser lid in the shape of an inverted cup whose outer diameter is equal to the inner diameter of the case 1, and the lower end edge of its circumferential wall is tightly fitted to the outer circumferential edge of the support plate 2.

The case 1, the support plate 2, and the presser cover 3 are
They are integrally connected by caulking inward a thin edge 1b provided at the opening edge.

Reference numeral 4 denotes a vibration sensing member made by bonding an annular piezoelectric element 6 to the upper surface of a thin metal plate 5 having a through hole in the center, and a ring for adjusting resonance frequency on two sides of the through hole of the thin metal plate 5. The plate 7 and the electrode plate 8 are brought into contact with the ring plate 7 on the lower surface, the bolt 9 is passed through the through hole, the space nut 10 is screwed, and the tip of the bolt is screwed into the inner bottom surface of the case 1. By doing so, the vibration sensing member 4 is supported within the case 1.

By tightening the space nut 10, the upper and lower ring plates 7, 7 form a thin plate 5 between the nut and the head of the bolt 9.
is in close contact with the The ring plate 7 may be provided on only one side if necessary.

The output terminal 11 and the ground terminal 12 are inserted into the presser cover 3, and the output terminal 11 is fixed above the piezoelectric element 6.'
The ground terminal 12 is connected to the electrode plate 8, which is connected to the lower electrode 6b, at the pole 6a.

In the knock sensor constructed as described above, when knocking occurs, the outer circumferential portions of the thin metal plate 5 and the piezoelectric element 6 are bent vertically around the bolt 9 due to vibration, creating a potential difference in the element 6, and an output is generated from the output terminal 11. A signal is generated.

At this time, when the resonance frequency of the vibration sensing member 4 and the knocking frequency match, the piezoelectric element is well distorted and reaches the maximum output.

In this embodiment, the resonance frequency is adjusted and matched by the ring plate. Here, in order to examine the effect of the ring plate 7 in the knock sensor having the above configuration, several types of annular piezoelectric elements 6 with different inner diameters were used.
Ring plates 7 having different outer diameters are applied to the resonance frequency f of the vibration sensing member 4. was measured. As a result, the results shown in the graph of FIG. 2 were obtained.

The experimental conditions and results will be described below.

Materials and shapes of commonly used parts> ◎Materials and shapes of thin metal plates: Nickel alloy Outer diameter i15.6 * Inner diameter i29!
5 Thickness io, 2mm ◎Material and shape material of piezoelectric element; titanic acid (TiO2), zirconic acid (ZrO2)
PZ7 ceramics made by sintering lead (, pb), outer diameter + 15.2 g, inner diameter i7z, 9 doors, 11 g thickness io,
25mm ◎Ring plate thickness i 1, 00mm Inner diameter: 2 (Experimental method) It is known that the resonance frequency fO changes depending on the thickness and shape of the thin metal plate 5 and the outer diameter and thickness of the piezoelectric element 6. It is being Therefore, keeping these things constant as described above, ring plates 7 with different outer diameters are placed in close contact with the upper and lower surfaces of the thin metal plate 5 for piezoelectric elements of several types of inner diameters (7 doors, 9 doors, 11 gates). The above-mentioned sensor was constructed, and each sensor was connected to a frequency measuring device, and the resonant frequency was read using an oscilloscope.

<Results> For each sensor, it was found that the resonance frequency increased as the outer diameter of the ring plate 7 increased.

Based on the above-mentioned knowledge, the present invention is based on the above-mentioned knowledge, and the ring plate 7 is closely attached to one or both sides of the thin metal plate 5. When the resonance frequency is to be raised, a ring plate 7 with a large diameter is used, and when the resonance frequency is to be lowered, a ring plate 7 with a small diameter is used. Since the ring plate 7 is used to adjust the resonant frequency to match the knocking frequency, the adjustment is extremely easy and the resonant frequency can be maintained at an optimum value. Piezoelectric element 6
It has excellent effects such as being able to distort well and produce good output.

[Brief explanation of drawings]

FIG. 1 is a longitudinal sectional view showing an embodiment of the present invention, and FIG. 2 is a graph of experimental results. 4; Vibration sensing portion 5; Metal thin plate 6; Piezoelectric element 7; Ring plate (7)

Claims (1)

[Claims] A vibration sensing member, which is made by integrally adhering an annular piezoelectric element to one surface of a thin metal plate and whose resonance frequency approximately matches the knock vibration frequency of the engine, is inserted into the center of the thin metal plate within a case for mounting the engine. A ring plate for adjusting the resonant frequency is fitted on one or both sides of the thin plate central portion by fitting the ring plate closely around the supporting bolt. Features a piezoelectric resonance knock sensor for internal combustion engines.