JPH0318136B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention can be fixed to a cylinder of an internal combustion engine, etc.
The present invention relates to a method for adjusting the resonance bandwidth of a piezoelectric resonance type knock sensor used to detect the occurrence of knocking in the cylinder. A conventional piezoelectric resonance type knock sensor has the configuration shown in FIG. In the figure, 1 is 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. Reference numeral 3 denotes a concave presser lid, which is tightly fitted into the case so that its closed end closes the opening of the case and the edge of the opening presses against the periphery of the support plate. This case 1, support plate 2, and presser cover 3 are the opening edge 1b of the case.
is fixed inseparably by bending it inward and engaging the outer peripheral area of the closed end surface of the presser cover. Reference numeral 4 denotes a vibration sensing member made by integrally adhering a disk-shaped piezoelectric element 42 having the same outer diameter to one side of a thin metal plate 41. A screw shaft 5 is provided protruding from the lower surface of the center of the thin metal plate 41. The screw shaft 5 is supported in the case 1 by screwing it into the inner bottom surface of the case 1 with a space nut 6 interposed therebetween. In addition, a terminal 9 is implanted in the presser cover 3,
The terminal 9 is electrically connected to the upper surface electrode 42a of the piezoelectric element 42 via a conducting wire 10. Further, the lower surface electrode 42b is connected to the case 1 by the screw punch 5 and is grounded to the body. The vibration sensing member 4 has a resonant frequency, which is approximately determined by its outer diameter, substantially equal to the knocking vibration frequency of the engine, so that when knocking occurs, the outer periphery of the vibration sensing member 4 bends vertically and vibrates, causing the terminal 9
Maximum power is induced from . In the graph of FIG. 2 showing the relationship between the relative output dB of the piezoelectric element and the frequency of the input vibration wave, the relative output dB reaches a maximum at the resonance frequency f ₀ and decreases before and after that. Therefore, in order to obtain a good output, it is necessary to make the resonant frequency f ₀ equal to the frequency of the detected vibration wave (knocking vibration wave) as described above. On the other hand, even if the output is 3 dB lower than the maximum output x, it can be detected as an output signal. Therefore, if the frequencies corresponding to this output are f ₁ and f ₂ , It is effective if the frequency is between f ₁ and f ₂ . Here, the width of this frequency band f ₁ to _{f 2} is referred to as the resonance band width BW. Incidentally, even in engines of the same type and model, the knock vibration frequency varies depending on variations in engine components and operating conditions, and as a result, the resonance bandwidth
If the BW is narrow and the knock vibration frequency deviates from the width, the output will drop and sufficient detection will not be obtained. Furthermore, if the resonance bandwidth BW is too wide, vibration waves caused by various causes other than knocking are generated in the engine, and these vibration waves are also detected, making it impossible to obtain accurate detection. Therefore, the resonance bandwidth BW needs to be optimized to suit the usage conditions. The present invention relates to a method of optimally adjusting the resonance bandwidth in response to the above-mentioned requirements, in which a circular hole is arranged in the center of a piezoelectric element concentrically with the outer shape, and the inner diameter of the circular hole is The resonance bandwidth of the vibration sensing member is adjusted by making it smaller when increasing the resonance bandwidth and increasing it when decreasing the resonance bandwidth. That is, the present inventor has developed a piezoelectric element 4 having the same outer diameter and having a circular hole a formed concentrically with the outer diameter.
A large number of piezoelectric elements 42' are prepared with different inner diameters of the circular holes a, and as shown in FIG. 3, each piezoelectric element 42' is
The vibration sensing member 4' is bonded to the upper surface of a thin metal plate 41' having a through hole in the center, and a ring plate 7a and an electrode plate 8 are mounted on the upper surface of the through hole, and a ring plate 7b is mounted on the lower surface. Insert the bolt (shaft) into the through hole.
5' and case 1 via space nut 6.
The output terminal 9a supports the vibration sensing member 4' in the case 1 by screwing into the inner bottom surface of the output terminal 9a, and the upper surface electrode 42'a of the piezoelectric element is implanted in the holding lid 3.
Next, the lower electrodes 42'b were similarly connected to the ground terminal 9b to form knock sensors, and the resonance bandwidth BW, resonance frequency _f0 , and output electron _VR were measured for each sensor. As a result, as shown in the graph of FIG. 5, it was found that the resonant frequencies f ₀ were almost the same, and only the resonant bandwidths BW were different. The conditions for such experiments will be described. <Material and shape of parts used> ◎Material and shape of thin metal plate Material: Nickel alloy Outer diameter: 15.6φ Inner diameter: 2φ Thickness: 0.2mm ◎Material and shape of piezoelectric element Material: Titanic acid (TiO ₂ ) Zircon Acid (ZrO ₂ ) PZT ceramics made by sintering lead (PB) Outer diameter: 15.2φ Thickness: 0.25mm ◎Ring plate shape Outer diameter: 3.4mm Inner diameter: 2mm Thickness: 1.00mm <Experimental method> Resonance It is known that the frequency f ₀ changes depending on the thickness and shape of the thin metal ring plate and the outer diameter and thickness of the piezoelectric element. Therefore, we configured the sensor shown in Figure 4 by keeping these values constant as shown above and varying only the inner diameter of the piezoelectric element.We measured the resonance frequency f ₀ (kHz) for each sensor by using a frequency measuring device, and measured it using an oscilloscope. , the relative output of the resonant frequency f ₀
We read the frequency width (resonance band width BW) corresponding to the output that is 3 dB lower than dB and the output voltage (V _R ). <Experimental result>

[Table] The above numerical values are shown graphically in FIG. This result shows that as the inner diameter becomes smaller, the resonance frequency f ₀ (kHz) hardly changes, but the resonance band BW (Hz) increases. It is also shown that the output voltage V _R gradually decreases, but not significantly. From this, by changing the inner diameter, we can change the resonance band width BW (Hz) without changing the resonance frequency f ₀ .
I understand that it is possible to change. The reason for this is not clear, but the vibration of the vibration sensing member is composed of various bending modes, but when the inner diameter is made smaller, secondary resonance becomes apparent and the resonance bandwidth becomes smaller.
It is considered that BW may increase. Based on the above findings, the present invention provides a piezoelectric element 42'
By forming a circular hole a in the hole a, the resonance bandwidth BW is arbitrarily selected.If the frequency variation of knocking vibration waves is large, the inner diameter is made small, and if it is small, other detection methods are used. In order to prevent unnecessary vibration waves from being detected together with the detected vibration waves, by forming each with a larger inner diameter, it is possible to extremely easily generate the optimum resonance bandwidth BW, and furthermore, such a resonance band Even by adjusting the width, there is an excellent effect that the resonant frequency f ₀ hardly changes. In addition, when the resonance bandwidth of the present invention is applied, the following additional effects are produced by forming the circular hole a. That is, since the center of the thin metal plate 41' is exposed, the vibration sensing member 4' can be supported in the case 1 by screwing the bolt 5' as shown in FIG. The screw punch 5 can be easily attached without requiring troublesome work such as attaching the screw punch 5 to the lower surface of the screw 41 by brazing or the like. Further, since the thin plate 41 has higher flexibility than the piezoelectric element 42', the thin plate a at the center exposed from the circular hole a can be bent well, and the piezoelectric element 42' can be curved better than before. produces high output. This can be seen from the fact that the smaller the diameter of the circular hole a, the lower the output voltage V _R becomes. Furthermore, a piezoelectric element 42' and a thin metal plate 4
1' has a different coefficient of thermal expansion, and cracks may occur in the piezoelectric element 42' at the junction between the piezoelectric element 42' and the thin plate 41 due to temperature changes in the outside air. Since the damage is reduced, the damage is prevented as much as possible.

[Brief explanation of drawings]

Fig. 1 is a vertical side view of a conventional knock sensor, Fig. 2 is a graph showing the relationship between relative output and frequency of input vibration wave, and Fig. 3 is a longitudinal side view of a knock sensor to which the present invention is applied. , FIG. 4 is a plan view of the piezoelectric element, and FIG. 5 is a graph showing experimental results according to the present invention. 4, 4'; Vibration sensing member, 41, 41'; Metal thin plate, 42, 42'; Piezoelectric element, a; Circular hole.

Claims (1)

[Scope of Claims] 1. A vibration sensing member made by integrally adhering a disc-shaped piezoelectric element to one surface of a thin metal plate and making its resonance frequency substantially match the knock vibration frequency is protruded downward from the center of the thin metal plate. A circular hole is arranged in the center of the piezoelectric element concentrically with the outer shape, and the inner diameter of the circular hole is set to increase the resonance bandwidth. The resonant bandwidth of a piezoelectric resonant sensor for an internal combustion engine is characterized in that the resonant bandwidth of a vibration sensing member is optimally adjusted by setting the resonant bandwidth to a small value when decreasing the resonant bandwidth, and increasing the resonant bandwidth when the resonant bandwidth is decreased. Adjustment method.