JPH11264759A - Knocking detection device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance reliability and durability, by preventing a piezoelectric element from cracking due to thermal expansion force of a mold resin. SOLUTION: In assemblage of this device, a piezoelectric element 17, a terminal plate 27, an annular insulator 35, and an annular weight 36 are fitted in order into a tubular spacer 22 made of resin, and thereafter the tubular spacer 22 is fitted to a tubular base member 11 and forced into a projecting rib formed on the periphery thereof, whereby a gap 39 not allowing invasion of a mold resin is formed between the tubular base member 11 and the tubular spacer 22. Then, a conical spring washer 40 is fitted to the tubular base member 11 and fastened by a nut 15, and this is molded with the mold resin into a resin housing 12. If the mold resin having invaded inside a piezoelectric element 17 or the tubular spacer 22 made of resin is thermally expanded at the time of molding, such thermal expansion can be relieved by the gap 39 on the inner circumference side of the tubular spacer 22, and thermal expansion force acting on the piezoelectric element 17 from the inner circumferential surface side thereof can be reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a knocking detecting device for detecting knocking vibration of an engine using a piezoelectric element.

[0002]

2. Description of the Related Art As this kind of knocking detection device,
For example, Japanese Patent Application Laid-Open No. 9-138160,
As shown in Japanese Patent Publication No. 506, an annular piezoelectric element, a terminal plate for extracting an electric signal from the piezoelectric element, an annular weight, and the like are attached to the outer periphery of a metal cylindrical base member, and these are molded with a molding resin. Some are molded. This knocking detection device is used by inserting a bolt into the center of a cylindrical base member and tightening and fixing it to a cylinder block of an engine.

[0003]

In the above structure, during molding, the molten resin enters the minute gap between the metallic cylindrical base member and the annular piezoelectric element due to the injection pressure. The gap is also filled with the mold resin. The knocking detection device fixed to the cylinder block of the engine is exposed to the heat of the engine during operation of the engine and becomes high temperature, so that each member of the knocking detection device thermally expands. Since the coefficient of thermal expansion of the element (ceramic) is much larger than that of the element (ceramic), the thermal expansion force of the mold resin acts from the inner peripheral surface of the piezoelectric element every time the engine becomes hot, and this thermal expansion force acts on the piezoelectric element The tensile force comes to work. Ceramic piezoelectric elements are relatively strong in compressive force, but relatively weak in tensile force. Therefore, every time the engine temperature rises, the thermal expansion force of the mold resin from the inner peripheral surface of the piezoelectric element increases. If the piezoelectric element repeatedly acts, cracks may occur in the piezoelectric element, which causes a decrease in reliability and durability.

[0004] The present invention has been made in view of such circumstances, and accordingly, an object of the present invention is to prevent cracking of a piezoelectric element due to the thermal expansion force of a mold resin, thereby improving reliability and reliability.
An object of the present invention is to provide a knocking detection device capable of improving durability.

[0005]

According to a first aspect of the present invention, there is provided a knocking detecting device, wherein an inner periphery of an annular piezoelectric element is fitted to an outer periphery of a cylindrical spacer. The inner circumference of the cylindrical spacer is fitted to the outer circumference of the cylindrical base member, and a gap is formed between the outer circumference of the cylindrical base member and the inner circumference of the cylindrical spacer so that the mold resin does not enter. In this configuration, since the cylindrical spacer is interposed between the outer circumference of the cylindrical base member and the inner circumference of the annular piezoelectric element, the space between the cylindrical spacer and the inner circumference of the piezoelectric element is formed during molding. There is a possibility that the mold resin may enter the inside of the piezoelectric element. However, a gap is formed between the inner periphery of the cylindrical spacer and the outer periphery of the cylindrical base member so that the mold resin does not enter the inner periphery of the piezoelectric element. Even if the mold resin or the tubular spacer that has entered the tube expands thermally, the thermal expansion can be released to the gap on the inner peripheral side of the tubular spacer. This allows
The thermal expansion force acting from the inner peripheral surface side of the piezoelectric element can be reduced, the crack of the piezoelectric element can be prevented, and the reliability and durability can be improved.

By the way, in order to form a gap between the outer periphery of the cylindrical base member and the inner periphery of the cylindrical spacer so that the mold resin does not enter, the sealing property (adhesion) of the contact portion between the two members is ensured. However, if the contact area is increased, the frictional resistance when the cylindrical spacer is fitted (press-fitted) to the cylindrical base member increases, and the assemblability decreases.

In consideration of this point, a convex rib is formed on the outer periphery of the cylindrical base member or the inner periphery of the cylindrical spacer so as to extend continuously over the entire periphery. Preferably, the gap is formed. By doing so, the contact state between the convex rib and the member on the other side is close to the line contact, and the sealing property can be ensured with the minimum necessary contact area. For this reason, fitting (press-fitting) of the tubular spacer to the tubular base member becomes relatively easy, and assemblability can be improved.

Further, a positioning portion for temporarily holding the piezoelectric element in a positioning state may be formed on the cylindrical spacer. In this way, by assembling the piezoelectric element to the cylindrical spacer, the positioning of the piezoelectric element can be performed at the same time, and the assembling property can be improved. ,
Was troublesome).

Further, a terminal holding portion may be formed on the cylindrical spacer, and the terminal plate may be temporarily held by the terminal holding portion in a state where the terminal plate is overlaid on the electrode surface of the piezoelectric element. By doing so, the terminal plate can also be temporarily held by the cylindrical spacer, and the assemblability can be improved as compared with the conventional case where the terminal plate is held by a jig and assembled.

Further, a plurality of positioning portions having different sizes are formed in the cylindrical spacer, and each positioning portion is fitted into a notch formed in each of the two terminal plates. Thus, each terminal plate may be positioned. In this way, by making the sizes of the respective positioning portions different, the positional relationship between the two terminal plates and the respective positioning portions can be uniquely determined. Assembly can be prevented beforehand.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to the drawings. The tubular base member 11 is formed of a metal such as iron, and has a flange 11a at a lower end thereof. The outer periphery of the upper end of the cylindrical base member 11 and the flange 1
On the outer periphery of 1a, one or a plurality of annular grooves 13 and 14 for securing the sealing property with the resin housing 12 are formed. A screw portion 16 for tightening the nut 15 is formed on the outer periphery of the cylindrical base member 11 below the annular groove 13 at the upper end, and an annular protrusion forming a gap 39 described below is formed below the screw portion 16. The rib 37 is formed integrally.

Piezoelectric element 17 for detecting knocking vibration
Is formed in an annular shape by PZT ceramic or the like, and is polarized such that the polarization direction of the half surface A and the polarization direction of the remaining half surface B are opposite to each other. On each of the half surfaces A and B on the upper surface of the piezoelectric element 17, semi-circular upper electrodes 18 and
19 (see FIG. 3) is formed, and an annular lower surface electrode (not shown) is formed on the surface (the lower surface of the piezoelectric element 17) opposite to the upper surface electrodes 18 and 19, extending all around the surface. ing. Thereby, the two upper surface electrodes 1 of the piezoelectric element 17 are formed.
Electrical signals corresponding to knocking vibrations can be taken out from 8, 19. Flat surfaces 20 and 21 for positioning are formed on the outer peripheral surface of the piezoelectric element 17 at positions corresponding to the vicinity of the center of each of the upper electrodes 18 and 19.

The piezoelectric element 17 is fitted and held in a cylindrical spacer 22 made of resin. A flange 22a that receives the lower surface of the piezoelectric element 17 is integrally formed at the lower end of the cylindrical spacer 22, and the flange 22a insulates the lower electrode of the piezoelectric element 17 from the flange 11a of the cylindrical base member 11. Play a role. For example, at two locations on the outer periphery of the flange portion 22a of the cylindrical spacer 22, projecting piece-shaped positioning portions 23, 2 for temporarily holding the piezoelectric element 17 in a positioned state.
4 are integrally formed upwardly corresponding to the flat surfaces 20 and 21 of the piezoelectric element 17, and further, each of the positioning portions 23, 24 and 90 is formed.
° Terminal holding parts 25, 26 at different positions
Are integrally formed upward. Each terminal holder 2
Engagement claws 25a, 26a projecting in the lateral direction are integrally formed on both sides of the upper ends of the piezoelectric elements 17, 26, respectively.
The two terminal plates 27, 28 superimposed on the upper surface electrodes 18, 19, respectively, are connected to the respective terminal holders 25, 26.
Are engaged and held by the engagement claws 25a, 26a.

At the outside of the center of each of the terminal plates 27 and 28, a notch 2 into which the positioning portions 23 and 24 are fitted is provided.
9, 30 are formed. In order to reduce the contact area (insertion resistance) between each notch 29, 30 and each positioning part 23, 24, each notch 29, 30 is formed in a substantially W shape, and the center of each notch 29, 30 is formed. The top is each positioning part 2
3 and 24. Further, in order to uniquely determine the mounting position and mounting direction of the two terminal plates 27 and 28, the two positioning portions 23 and 24 (notches 29 and 30) are formed to have different widths from each other. Further, the two terminal holding portions 25 and 26 are also formed to have different widths from each other.

Each terminal plate 27, 28 is connected to each lead wire 32 by a lead terminal 31, respectively.
And a grommet (rubber stopper) 33 for waterproofing is fitted in the connection portion. The two lead wires 32 are inserted through one tube 34.

In the cylindrical spacer 22, an annular insulator 35 and an annular weight 36 made of resin are sequentially fitted on terminal plates 27 and 28, respectively. The cylindrical spacer 22 includes the piezoelectric element 17 and the terminal plate 2.
7, 28, insulator 35 and annular weight 36
Are fitted to the outer periphery of the cylindrical base member 11 in a state where the members are assembled. On the outer peripheral surface of the cylindrical base member 11, a convex rib 37 extending continuously over the entire periphery thereof is integrally formed at a position corresponding to the upper part of the inner peripheral surface of the cylindrical spacer 22. By pressing the inner peripheral surface of the spacer 22 into pressure, a gap 39 is formed between the outer periphery of the tubular base member 11 and the inner periphery of the tubular spacer 22 so that the mold resin does not enter.

The cylindrical base member 11 has a disc spring washer 40
The disc spring washer 40 is fitted on the annular weight 36.
Are superimposed on each other, and a nut 15 is
It is tightened. As a result, the annular weight 36 is attached to the terminal plate 2 by the spring force of the disc spring washer 40.
7 and 28 and press the terminal plates 27 and 28
Are brought into pressure contact with the upper electrodes 18 and 19 of the piezoelectric element 17 to electrically connect them, and a set load in the polarization direction (vertical direction) is applied to the piezoelectric element 17. The components assembled to the tubular base member 11 as described above are:
It is molded with a resin housing 12 molded with a mold resin.

Next, a procedure for assembling the knocking detection device having the above configuration will be described. First, the piezoelectric element 17 is fitted into the cylindrical spacer 22. At this time, the flat surfaces 20, 21 on the outer periphery of the piezoelectric element 17 are aligned with the positioning portions 23,
By fitting the piezoelectric element 17 into the cylindrical spacer 22, the piezoelectric element 17 is temporarily held in the cylindrical spacer 22 in a positioned state.

Thereafter, the notches 29, 30 of the terminal plates 27, 28 are fitted into the positioning portions 23, 24,
The terminal plates 27 and 28 are superimposed on the upper electrodes 18 and 19 of the piezoelectric element 17, and each terminal plate 2
The both ends of the terminals 7 and 28 are engaged with the engaging claws 25a and 26a of the terminal holding parts 25 and 26, respectively. In this case, since the two positioning portions 23, 24 (cutout portions 29, 30) are formed with different widths from each other, the assembling position of the two terminal plates 27, 28 is uniquely determined.
The erroneous mounting of the two terminal plates 27 and 28 by mistake is prevented beforehand. In the present embodiment, since the two terminal holding portions 25 and 26 are also formed with different widths from each other, the direction in which the lead wires 31 of the two terminal plates 27 and 28 are pulled out is determined in one direction.

As described above, in this embodiment, the piezoelectric element 17 and the terminal plates 27 and 28 are
By mounting the piezoelectric element 17, the positioning of the piezoelectric element 17 and the terminal plates 27 and 28 can be performed at the same time.
There is no need to assemble while positioning with a jig,
The assemblability can be improved.

In this embodiment, since the notches 29, 30 of the terminal plates 27, 28 are formed in a substantially W shape, the central tops of the notches 29, 30 correspond to the positioning portions 23, 24. It will be in contact. As a result, the contact area between each of the cutouts 29, 30 and each of the positioning portions 23, 24 is reduced, the insertion resistance is reduced, and the terminal plates 27, 28 can be easily assembled.

After assembling the terminal plates 27 and 28, the annular insulator 35 and the annular weight 36 are sequentially fitted into the cylindrical spacer 22, and then the cylindrical spacer 2 is inserted.
2 into the cylindrical base member 11 and the cylindrical spacer 22
Is brought into contact with the flange 11a of the tubular base member 11. At this time, the inner circumference of the cylindrical spacer 22 is press-fitted into the convex rib 37 of the cylindrical spacer 22 and pressed against each other, so that the outer circumference of the cylindrical base member 11 and the inner circumference of the cylindrical spacer 22 are interposed. Thus, a gap 39 is formed in which the mold resin does not enter.

Thereafter, the disc spring washer 40 is fitted into the cylindrical base member 11, and the disc spring washer 40 is superimposed on the annular weight 36. Then, the nut 15 is tightened to the screw portion 16, and the disc spring washer is mounted. Annular weight 36 with spring force of 40
Is pressed against the terminal plates 27 and 28. As a result, the terminal plates 27 and 28 are brought into pressure contact with the upper electrodes 18 and 19 of the piezoelectric element 17 to electrically connect the two, and the spring force of the disc spring washer 40 and the load of the annular weight 36 apply to the piezoelectric element 17. A set load in the polarization direction is applied.

After assembling the components to the cylindrical base member 11 as described above, the assembly is molded with a mold resin to form a resin housing 12, and a knocking detection device is manufactured. At the time of molding, there is a possibility that mold resin may enter between the cylindrical spacer 22 and the inner periphery of the piezoelectric element 17, but between the inner periphery of the cylindrical spacer 22 and the outer periphery of the cylindrical base member 11. Since the gap 39 into which the molding resin does not enter is formed, even if the molding resin or the resin-made cylindrical spacer 22 that has entered the inner peripheral side of the piezoelectric element 17 thermally expands, the thermal expansion is reduced by the cylindrical spacer 22. Can be released to the gap 39 on the inner peripheral side. This allows
The thermal expansion force acting from the inner peripheral surface side of the piezoelectric element 17 can be reduced, the cracks of the piezoelectric element 17 due to the thermal expansion force of the resin can be prevented, and the reliability and durability of the knocking detection device can be improved.

In this embodiment, the cylindrical base member 11
The convex ribs 37 are formed on the outer peripheral surface of the cylindrical base member 11 in order to form a gap 39 between the cylindrical spacer 22 and the cylindrical spacer 22. Is also good. Alternatively, by forming a concave portion on the outer peripheral surface of the cylindrical base member 11 or the inner peripheral surface of the cylindrical spacer 22, the molding resin is provided between the outer periphery of the cylindrical base member 11 and the inner periphery of the cylindrical spacer 22. May be formed so as not to enter.

In addition, the present invention relates to positioning portions 23, 24
The shape and number of the terminals, and the terminal holders 25 and 2
The shape and the number of 6 may be changed, and various changes can be made.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view of a knocking detection device according to an embodiment of the present invention.

FIG. 2 is a plan view showing a state where a terminal plate is assembled to a cylindrical spacer.

FIG. 3 is an exploded perspective view of components to be assembled to the cylindrical base member.

[Description of Signs] 11: cylindrical base member, 11a: flange, 12: resin housing, 15: nut, 17: piezoelectric element, 18, 19 ...
Top electrode, 20, 21 ... flat surface, 22 ... cylindrical spacer,
22a ... flange, 23, 24 ... positioning part, 25, 26 ...
Terminal holding part, 25a, 26a ... engaging claw part, 27,
28: Terminal plate, 29, 30: Notch, 3
1, 32: lead wire, 35: annular insulator, 36: annular weight, 37: convex rib, 39: gap, 40: disc spring washer.

Claims (5)

[Claims] 1. A knocking detection device in which an annular piezoelectric element, a terminal plate for extracting an electric signal from the piezoelectric element, and the like are assembled on the outer periphery of a cylindrical base member, and these are molded with a molding resin. With the inner periphery of the piezoelectric element fitted to the outer periphery of the tubular spacer, the inner periphery of the tubular spacer is fitted to the outer periphery of the tubular base member, and the outer periphery of the tubular base member and the tubular spacer are fitted. A knocking detecting device, wherein a gap is formed between the inner periphery of the knocking device and the inner periphery of the knocking device. 2. A convex rib extending continuously around the entire periphery of the cylindrical base member or the inner periphery of the cylindrical spacer, and the gap is formed by the convex rib. The knocking detection device according to claim 1. 3. The knocking detection device according to claim 1, wherein a positioning portion for temporarily holding the piezoelectric element in a positioning state is formed in the cylindrical spacer. 4. The cylindrical spacer is provided with a terminal holding portion for temporarily holding the terminal plate in a state of being superimposed on an electrode surface of the piezoelectric element. 3. The knocking detection device according to claim 1. 5. A plurality of positioning portions having different sizes are formed, and each positioning portion is positioned by fitting each positioning portion into a notch formed in each of two terminal plates. The knocking detection device according to claim 3, wherein