JPS6033376Y2 - Notking sensor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a sensor for detecting vibrations in an engine of an automobile, and more particularly to a vibration sensor for detecting knocking that generates an output according to the frequency of knocking vibrations caused by abnormal combustion in the engine.

Under certain operating conditions of the engine, a fire that occurs at the ignition part in the cylinder spontaneously ignites before it propagates to the unburned part at the end, causing the mixed gas in the cylinder to temporarily and rapidly burn. If knocking occurs due to
This is not desirable as smooth driving is not possible and fuel consumption is wasted.

Generally, the ignition timing of an engine is advanced to be optimal for the operating condition, but advancing the ignition timing tends to cause knocking, so if knocking occurs, it is necessary to delay the ignition timing, and knocking A sensor is required to detect the phenomenon.

It is known that the cylinder internal pressure and the engine body, where the knocking phenomenon occurs, cause abnormal vibrations.While the vibration frequency during normal engine operation has a frequency component of several tens to several hundred Hz, the vibration frequency when knocking occurs The vibration frequency component has a frequency component of approximately 5 to 10 KHz, and varies somewhat depending on the type of engine and the rotation speed.

FIG. 1 shows a structural diagram of a conventionally proposed piezoelectric single resonance knocking sensor.

In the figure, a piezoelectric ceramic plate 1 is arranged on the inner bottom surface of a bottomed cylindrical metal holder 3 equipped with a mounting screw 31 on the bottom surface, and a weight 2 is placed on it by fitting it into a shallow recess provided on the bottom surface. ing.

Further, a leaf spring 4 is inserted into a recess provided on the upper surface of the weight 2, and the leaf spring 4 is pressed into contact with a conductive support 6 inserted through an insulating plate 5 which also serves as a cover plate.

This sensor is designed to resonate at the knocking vibration frequency component by selecting the leaf spring constant and the weight of the weight 2.

However, this method has the disadvantage that it is difficult to keep the spring constant constant and therefore it is difficult to keep the resonant frequency constant.

FIG. 2 shows a piezoelectric vibration sensor for detecting minute vibrations having low frequency components, in which bending vibration of a metal plate 7 is detected by a piezoelectric ceramic 8 bonded to the root portion.

However, although it is easy to adjust the resonant frequency with this method,
The disadvantage is that the lead wire extraction part has poor vibration and shock resistance and cannot withstand engine vibrations.

The present invention was devised in view of these drawbacks, and it is an object of the present invention to provide a highly reliable piezoelectric knocking sensor that has a simple structure, good vibration resistance and impact resistance.

That is, the sensor according to the present invention constructs a unimorph vibrator by joining a piezoelectric ceramic plate with electrodes on both sides and polarized in the thickness direction and a metal plate, and a piezoelectric plate near the center of the unimorph vibrator. The unimorph resonator is characterized in that the electrode surface of the unimorph is supported in pressure contact with a conductor via a conductive soft elastic body, and the periphery of the unimorph vibrator is covered with the insulating soft elastic body.

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 3 shows an embodiment of the present invention, and parts corresponding to those in FIG. 1 are given the same numbers.

A unimorph resonator is constructed by bonding a thin metal plate 10 of the same or slightly larger shape to a piezoelectric ceramic plate 9 having electrodes on both sides and polarized in the thickness direction.

3 is a metal cylindrical holder with a bottom, and screws 3 are installed on the outside of the bottom to fix this to the cylinder block (engine body).
1, and a conductive support column 32 protrudes from the inner bottom surface of the holder 3 to support the center of one surface of the unimorph vibrator.

Reference numeral 6 denotes a conductive support pillar for supporting the center of the other surface of the unimorph vibrator, and also serves as a connection terminal with the outside.

The cover plate 5 of the holder 3 is made of an insulating material, and a support column 6 passes through a hole in the center.

The unimorph vibrator is supported at its center by applying appropriate pressure to support columns 6 and 32, respectively, through conductive soft elastic bodies 11a and 11b such as conductive rubber having an appropriate area.

Note that the conductive elastic body 11 is only on the free electrode surface side of the piezoelectric ceramic 9.
a may be interposed.

In addition, the unimorph resonator includes insulating soft elastic bodies (for example, sponge, rubber) 12a and 12b that are in contact with the inner wall of the holder 3.
By forming the soft elastic bodies 12a and 12b into an appropriate shape, the center position of the unimorph resonator can be easily determined during assembly.

Vibrations generated by the engine are transmitted to the sensor through the threaded portion 31, causing the entire sensor to vibrate.

The unimorph oscillator inside the blade also causes bending vibration, producing an output voltage corresponding to the vibration.

In particular, when the external vibration matches the resonant frequency of the unimorph resonator, the output voltage becomes extremely large.

Therefore, by selecting the material, dimensions, etc. of the unimorph vibrator, this resonance frequency can be set to a knocking vibration frequency component that corresponds to the engine type.

As described above, according to the present invention, since the unimorph vibrator is supported by pressure via the conductive soft elastic body,
Compared to the method of connecting lead wires to the unimorph resonator by soldering, vibration and shock resistance are significantly improved.

Further, by using a soft elastic body having an appropriate shape for determining the center position of the unimorph vibrator, assembly is easy.

Furthermore, according to the present invention, since the central part of the unimorph vibrator is supported, a high-output sensor with good vibration balance and good S/N ratio can be obtained.

Figure 4 shows the characteristics of a vibration sensor prototyped using a disk-shaped unimorph vibrator according to the present invention and set at a center frequency of 7K H2. It shows the sensor output voltage Vp-p.

It can be understood that a sufficiently large output voltage can be obtained near the operating point.

If a wide bandwidth is required depending on the application, the Q of resonance can be lowered by increasing the support area of the unimorph resonator or by changing the material of the soft elastic body covering the unimorph resonator to provide a damping effect. Bye.

As described above, since the sensor according to the present invention has a simple structure, it is easy to assemble and can be mass-produced at low cost.

Furthermore, since a large output signal can be obtained in terms of performance, a knocking sensor with an excellent S/N ratio can be obtained.

[Brief explanation of the drawing]

1 and 2 are structural diagrams showing an example of a conventional 7-piece sensor, FIG. 3 is a sectional view showing the structure of an embodiment of the present invention, FIG. 4 is a characteristic diagram thereof, and FIG. The figure shows an example of the connection. In the figure, 1, 8, 9: piezoelectric ceramic, 2: weight, 3:
metal holder, 5: insulating cover plate, 6: conductive support, 7.
10: metal plate, lla, llb: conductive soft elastic body, 12
a, 12b: Insulating soft elastic body.

Claims (1)

[Scope of utility model registration request] A unimorph resonator is constructed by bonding a piezoelectric ceramic plate with electrodes on both sides and polarized in the thickness direction and a metal plate, and the unimorph resonator is placed in a housing with the center part of the resonator surrounded by a conductive soft material. This toss knocking sensor is characterized by being pressure-supported by a conductive column via an elastic body, and having its peripheral portion covered with an insulating soft elastic body.