JP4904221B2 - Sensor assembly - Google Patents

Description

  The present invention relates to a sensor assembly including a piezoelectric element that outputs an electrical signal corresponding to an applied load when a load is applied in a direction orthogonal to a surface direction.

Some sensor assemblies include an optical fiber as a sensor element that detects the amount of displacement of the vehicle body. The optical fiber is sandwiched between a bumper reinforcement and a bumper cover.
When a load acts on the bumper cover, the load is transmitted to the optical fiber through the bumper cover, and the optical fiber is deformed by the transmitted load.
When the optical fiber is deformed, the amount of light passing through the optical fiber changes, and a collision is detected based on the changed amount of light (see, for example, Patent Document 1).
JP 2005-263038 A

Incidentally, in order to accurately detect a collision with the sensor assembly of Patent Document 1, it is necessary to suitably deform the optical fiber in accordance with the load at the time of the collision.
However, when the load at the time of collision is applied to a portion that is removed from the optical fiber, it is conceivable that the portion of the bumper cover that is removed from the optical fiber is deformed by the applied load.

When the deformed portion comes into contact with the bumper reinforcement, it is considered that the load is directly transmitted from the bumper cover to the bumper reinforcement, and the load is not efficiently transmitted to the optical fiber.
For this reason, it is difficult to accurately detect the load at the time of collision by suitably deforming the optical fiber (that is, the sensor element) corresponding to the load at the time of collision.

  An object of the present invention is to provide a sensor assembly capable of accurately detecting a load at the time of a collision.

Invention, elongated piezoelectric element outputting an electric signal corresponding to the load weight to be input in a direction perpendicular to the plane direction is provided on the bumper beam which constitutes a part of a vehicle body according to claim 1 A sensor assembly capable of detecting the load by the piezoelectric element , wherein the bumper beam extends in a vehicle body width direction, and the piezoelectric element is sensitive when a load is applied in a predetermined direction along the surface direction. The width of the vehicle body is such that the sensitivity is kept low when a load is applied in a direction perpendicular to the predetermined direction, and the longitudinal direction of the piezoelectric element is the direction orthogonal to the predetermined direction. It is characterized by matching with the direction .

Here, the piezoelectric element has a characteristic that sensitivity is high when a load is applied in a predetermined direction along the plane direction, and sensitivity is suppressed low when a load is applied in a direction orthogonal to the predetermined direction.
Hereinafter, in order to facilitate understanding of the invention, a predetermined direction is referred to as a “sensitivity direction”, and a direction orthogonal to the predetermined direction is referred to as a “non-sensitivity direction”.

Because of this characteristic, when the piezoelectric element is curved and deformed with respect to the sensitivity direction, a load is applied in a predetermined direction and an electric signal is output.
On the other hand, in order to accurately detect the load input by the piezoelectric element, when the piezoelectric element is pressed / pressed by applying a load in a direction orthogonal to the surface direction of the piezoelectric element, It is preferable to detect only the signal.
Therefore, in claim 1, the longitudinal direction of the piezoelectric element is made to coincide with the insensitive direction.

  According to a second aspect of the present invention, a piezoelectric film made of polyvinylidene fluoride is used as the piezoelectric element. When the piezoelectric element is provided on a long object, the longitudinal direction of the piezoelectric element coincides with the longitudinal direction of the long object. It was made to be characterized.

Here, when a load acts on the long object in a direction perpendicular to the longitudinal direction, the long object is bent and deformed at both ends of the long object at fulcrums (reference points). When the long object is bent and deformed, the piezoelectric element included in the long object is also bent and deformed following the long object.
Therefore, when the sensitivity direction of the piezoelectric element is matched with the longitudinal direction of the long object, a load is applied in the sensitivity direction of the piezoelectric element and an electric signal is output.

For this reason, when a load is applied in a direction orthogonal to the surface direction of the piezoelectric element and the piezoelectric element is pressed / pressed, it becomes difficult to detect only the electric signal generated by the pressing / pressing. It cannot be detected with high accuracy.
Therefore, in claim 2, when the piezoelectric element is provided on the long object, the longitudinal direction of the piezoelectric element (that is, the insensitive direction) is made to coincide with the longitudinal direction of the long object.

In the invention according to claim 1, the longitudinal direction of the piezoelectric element is made to coincide with the insensitive direction. Therefore, even when the piezoelectric element is curved and deformed in the longitudinal direction, the piezoelectric element does not output an electrical signal based on the deformation in the longitudinal direction.
As a result, when a load is applied in a direction perpendicular to the surface direction of the piezoelectric element to press / press the piezoelectric element, it becomes possible to detect only the electric signal generated by the compression / press, Can be detected with high accuracy.

  In the invention according to claim 2, a piezoelectric film made of polyvinylidene fluoride is used as the piezoelectric element. Since polyvinylidene fluoride can be easily thinned, the entire sensor can be made thinner and smaller.

Furthermore, when the piezoelectric element is provided on the long object, the longitudinal direction of the piezoelectric element (that is, the insensitive direction) is matched with the longitudinal direction of the long object.
Therefore, when a piezoelectric element is pressed / pressed by a load acting in a direction perpendicular to the surface direction of the piezoelectric element, even if the piezoelectric element is curved and deformed following a long object, the compression / pressing occurs. It is possible to detect only the electrical signal thus generated, and it is possible to accurately detect the load generated by the collision.

  The best mode for carrying out the present invention will be described below with reference to the accompanying drawings. In the present embodiment, an example in which the sensor assembly 10 is assembled to the front bumper beam 13 of the vehicle will be described. However, the present invention can be applied to other long objects.

FIG. 1 is a perspective view showing a sensor assembly according to the present invention, and FIG. 2 is an exploded perspective view showing the sensor assembly according to the present invention.
The sensor assembly 10 includes a front bumper beam 13 attached to the left and right front side frames 11, 12, a first member 14 attached to the front bumper beam 13, and a first member 14 disposed between the first member 14 and the front bumper beam 13. Two members 15 and a sensor element unit 16 supported by the second member 15 are provided.

The front bumper beam 13 is a member that constitutes a part of the vehicle body 18 by being attached to the front end portions 11 a and 12 a of the left and right front side frames 11 and 12.
The front bumper beam 13 is formed in a substantially sun-shaped cross section, and is provided at the central portion 21 extending in the vehicle body width direction, the left inclined portion 22 provided at the left end of the central portion 21, and the right end of the central portion 21. It is a long object provided with the right inclined part 23.

In the front wall 25 of the front bumper beam 13, a plurality of insertion holes 27 are formed at a predetermined interval at the center in the vertical direction.
Further, a plurality of upper locking holes 28 are formed at predetermined intervals in the vicinity of the upper side of the front wall 25 of the front bumper beam 13.
Furthermore, a plurality of lower locking holes 29 are formed at predetermined intervals in the vicinity of the lower side of the front wall 25 of the front bumper beam 13.

The first member 14 includes a belt-shaped beam cover 31 extending along the front wall 25 of the front bumper beam 13, and the back surface 31 a of the beam cover 31 has an insertion portion 33..., Upper and lower mounting portions 34. Load transmitting portions 36 and 37 are provided, respectively.
The insertion portion 33, the upper and lower attachment portions 34, 35, and the upper and lower load transmission portions 36, 37 will be described in detail with reference to FIGS.

The second member 15 is a belt-like member that is interposed between the first member 14 and the front bumper beam 13 and extends along the front wall 25 of the front bumper beam 13.
The second member 15 is bonded (supported) to the front wall 25 of the front bumper beam 13 with, for example, a double-sided adhesive tape (not shown).

In the second member 15, a plurality of positioning holes 41 are formed at predetermined intervals in the central portion in the vertical direction.
The second member 15 includes an upper projecting piece 42 on the upper side, a lower projecting piece 43 on the lower side, and a sensor support surface 44 between the upper and lower projecting pieces 42 and 43.

The upper projecting piece 42 is a part projecting from the upper side toward the front of the vehicle body. The lower projecting piece 43 is a part projecting from the lower side toward the front of the vehicle body.
The sensor support surface 44 is a surface that supports the sensor element unit 16.
The positioning hole 41 will be described in detail with reference to FIGS.

  The sensor element unit 16 includes a laminate 46 formed in a strip shape along the sensor support surface 44, a plurality of upper sensor elements (piezoelectric elements) 47 embedded along the upper side of the laminate 46, and the lower side of the laminate 46. It is a long object provided with a plurality of lower sensor elements (piezoelectric elements) 48 embedded therein.

In the laminate 46, a plurality of fitting holes 51 are formed at predetermined intervals in the center portion in the vertical direction.
The upper and lower sensor elements 47 and 48 are strip-shaped (long-shaped) elements extending in the lateral direction.
The sensor element unit 16 is provided on the front bumper beam 13 via the second member 15 by being bonded (supported) to the sensor support surface 44 of the second member 15 with, for example, a double-sided adhesive tape (not shown). ing.

3 is a sectional view taken along line 3-3 in FIG. 1, and FIG. 4 is an exploded view of FIG.
In the second member 15, bosses 53 (see also FIG. 2) are formed at predetermined intervals in the center of the surface 15 b in the vertical direction, and positioning holes 41 are formed in the bosses 53, respectively. The plurality of positioning holes 41 are through holes.
A sensor support surface 44 is formed between the upper and lower projecting pieces 42 and 43 on the surface 15 b of the second member 15. The height dimension of the sensor support surface 44 is H1.

In the sensor element unit 16, the height dimension of the laminate 46 is set to H2. The height dimension H2 of the laminate 46 is set to be slightly smaller than the height dimension H1 of the sensor support surface 44.
An upper sensor element 47 is embedded in the vicinity of the upper side 46 a of the laminate 46. The upper sensor element 47 is provided on the upper side of the insertion portion 33.
A lower sensor element 48 is embedded in the vicinity of the lower side 46 b of the laminate 46. The lower sensor element 48 is provided below the insertion portion 33.

Piezoelectric films are used as the upper and lower sensor elements 47 and 48. That is, the upper and lower sensor elements 47 and 48 are distorted when a load in a direction orthogonal to the surface direction of each sensor element 47 and 48 is input (acted), and the generated distortion amount (input load) is increased. It is an element that outputs an electric signal correspondingly.
Thereby, an electric signal corresponding to the input (acting) load can be output.
The upper and lower sensor elements 47 and 48 will be described in detail with reference to the upper sensor element 47 in FIGS. 5A and 5B.

Here, the fitting hole 51 of the laminate 46 is fitted to the boss 53 in a state where the sensor element unit 16 is bonded to the sensor support surface 44 with a double-sided adhesive tape (not shown).
Thereby, the sensor element unit 16 is positioned at a predetermined position by the plurality of bosses 53.

Further, the upper and lower sides 46 a and 46 b of the sensor element unit 16 are positioned at predetermined positions by the upper and lower projecting pieces 42 and 43.
Thereby, the sensor element unit 16 can be reliably positioned with respect to the second member 15 at a predetermined position.

The first member 14 is provided on the front side of the vehicle body of the sensor element unit 16.
The upper mounting portion 34 of the first member 14 is an elastically deformable locking member that extends toward the rear of the vehicle body from the vicinity of the upper side 31b on the back surface 31a of the beam cover 31.
The upper mounting portion 34 is provided with a locking claw 56 facing upward at the tip of the protruding piece 55.
The locking claw 56 is a part that prevents the protruding piece 55 from slipping out from the upper locking hole 28 toward the front of the vehicle body by locking to the periphery of the upper locking hole 28 of the front bumper beam 13.

  The lower attachment portion 35 of the first member 14 is a member that is vertically symmetrical with the upper attachment portion 34, and the same reference numerals are given to the respective constituent portions and the description thereof is omitted.

The upper load transmission portion 36 of the first member 14 is continuously formed on the back surface 31a of the beam cover 31 near the lower portion of the upper mounting portion 34 from the left end 31d to the right end 31e (see FIG. 2) of the beam cover 31. Has been.
The upper load transmission portion 36 is a bulging portion that bulges toward the rear of the vehicle body (that is, toward the upper sensor element 47), and is provided above the insertion portion 33.
Specifically, the upper load transmission portion 36 is disposed between the upper mounting portion 34 and the insertion portion 33.

The lower load transmission portion 37 of the first member 14 is a member that is vertically symmetrical with the upper load transmission portion 36, and is provided below the insertion portion 33.
Specifically, the lower load transmission portion 37 is disposed between the lower mounting portion 35 and the insertion portion 33.
Hereinafter, the same reference numerals as the constituent parts of the upper load transmitting part 36 are given to the constituent parts of the lower load transmitting part 37 and the description thereof is omitted.

The insertion portion 33 of the first member 14 is a columnar protrusion that extends from the center in the vertical direction toward the rear of the vehicle body on the back surface 31 a of the beam cover 31.
The insertion portion 33 is a member that can penetrate the positioning hole 41 of the second member 15 and can penetrate the insertion hole 27 of the front bumper beam 13.

By penetrating the insertion portion 33 into the positioning hole 41, the first member 14 and the second member 15 can be relatively positioned with respect to the vertical direction by the positioning portion 30.
Accordingly, the contact surface 36 a of the upper load transmission unit 36 can be opposed to the upper sensor element 47, and the contact surface 37 a of the lower load transmission unit 37 can be opposed to the lower sensor element 48.

FIG. 5A is a perspective view showing a sensor element of a sensor assembly according to the present invention, and FIG. 5B is a diagram showing a molecular structure of the sensor element according to the present invention.
Since the upper and lower sensor elements 47 and 48 are the same sensor element, the upper sensor element 47 will be described and the description of the lower sensor element 48 will be omitted.
A normal piezoelectric film is used as the upper sensor element 47 shown in FIG. An example of this piezoelectric film is polyvinylidene fluoride (PVDF).
Since this PVDF can be easily thinned, the entire sensor can be made thinner and smaller.

PVDF is deformed in a predetermined direction (d31 direction) along the plane direction on the molecular structure (—CH ₂ CF ₂ —) shown in FIG. 5B, and a direction orthogonal to the plane direction (d33 direction). It has the property of causing polarization due to the change of the dipole moment with respect to deformation.
On the other hand, this PVDF has a characteristic that, in the deformation in the direction (d32 direction) perpendicular to the predetermined direction along the plane direction, the structural symmetry is maintained, so that polarization due to the dipole moment does not occur.
The predetermined direction (d31 direction) along the surface direction is the above-described “sensitivity direction”.
The direction (d32 direction) orthogonal to the predetermined direction along the surface direction is the above-described “insensitive direction”.

That is, the upper sensor element 47 generates a voltage (polarization voltage) by causing polarization due to a change in the dipole moment when compression / pressing is applied in a direction orthogonal to the surface direction.
Further, when a tensile force acts in the sensitivity direction, the upper sensor element 47 generates polarization due to a change in the dipole moment and generates a voltage (polarization voltage) (high sensitivity).
On the other hand, even if a tensile force acts in the non-sensitivity direction, the upper sensor element 47 does not generate polarization due to the dipole moment, and thus does not generate voltage (polarization voltage) (low sensitivity).

Incidentally, the sensor element unit 16 shown in FIG. 2 is a long object formed in a long dimension in the vehicle body width direction (that is, in the left-right direction) and in a short dimension in the vertical direction.
Therefore, when a load is applied in a direction orthogonal to the surface direction of the sensor element unit 16, the left and right end portions are bent and deformed in a direction orthogonal to the longitudinal direction of the sensor element unit 16 with the fulcrum (reference) as a fulcrum.
Hereinafter, the bending deformation in the direction orthogonal to the longitudinal direction of the sensor element unit 16 is referred to as “longitudinal deformation”.

When the sensor element unit 16 is deformed in the longitudinal direction, the upper sensor element 47 (see FIG. 5A) is similarly curved and deformed (longitudinal deformation) in the longitudinal direction with reference to the left and right end portions 47a and 47b. .
The upper sensor element 47 deformed in the longitudinal direction has a longer overall length than the upper sensor element 47 before deformation. That is, when the upper sensor element 47 is deformed in the longitudinal direction, a tensile force in the insensitive direction acts on the upper sensor element 47.

On the other hand, the sensor element unit 16 is formed with a short vertical dimension. Therefore, even when a load is applied in a direction orthogonal to the surface direction of the sensor element unit 16, the sensor element unit 16 curves in a direction orthogonal to the short direction with the upper and lower sides serving as fulcrums (references). Does not deform.
Hereinafter, the bending deformation in the direction orthogonal to the short direction of the sensor element unit 16 is referred to as “short direction deformation”.

Therefore, the upper sensor element 47 (see FIG. 5A) does not deform in the lateral direction with respect to the upper and lower sides 47c and 47d.
That is, when a load is applied in a direction perpendicular to the surface direction of the sensor element unit 16, the upper sensor element 47 shown in FIG. 5A can secure a state in which no tensile force acts in the sensitivity direction.

Here, in order to detect only the load at the time of collision by the upper sensor element 47, when the upper sensor element 47 is pressed / pressed with a pressing force acting in a direction orthogonal to the surface direction, It is necessary to detect only the electric signal generated by pressing.
Therefore, the longitudinal direction of the upper sensor element 47 shown in FIG.
Therefore, the upper sensor element 47 does not generate a voltage even when a tensile force F1 is applied in the long direction, but generates a voltage when a tensile force F2 is applied in a direction orthogonal to the long direction (short direction). To do.

However, as described above, when a load is applied in a direction orthogonal to the surface direction of the sensor element unit 16, the upper sensor element 47 is not deformed in the short direction.
Therefore, even when a load is applied in a direction orthogonal to the surface direction of the upper sensor element 47 to press / press the upper sensor element 47, even when the upper sensor element 47 is curved and deformed following the sensor element unit 16. Only the electric signal generated by this compression / pressing can be detected, and the load generated by the collision can be detected with high accuracy.

Next, the operation of the sensor assembly 10 will be described with reference to FIGS.
FIG. 6 is a diagram illustrating an example in which a load is applied to the first member of the sensor assembly according to the present invention.
A load F3 acts on the first member 14 from the front side of the vehicle body as shown by an arrow. The load F3 is a load orthogonal to the surface direction of the upper and lower sensor elements 47, 48.
Here, the contact surface 36 a of the upper load transmission portion 36 and the contact surface 37 a of the lower load transmission portion 37 are in contact with the sensor element unit 16.
A part of the load F3 is transmitted to the upper load transmission portion 36 as indicated by an arrow A. On the other hand, the remainder of the load F3 is transmitted to the lower load transmitting portion 37 as indicated by an arrow B.

The contact surface 36 a of the upper load transmitting portion 36 faces the upper sensor element 47. Further, the contact surface 37 a of the lower load transmitting portion 37 faces the lower sensor element 48.
Therefore, the load transmitted to the upper load transmitting portion 36 acts in a direction orthogonal to the surface direction of the upper sensor element 47, and the upper sensor element 47 can be favorably pressed / pressed.

Similarly, the load transmitted to the lower load transmitting portion 37 acts in a direction perpendicular to the surface direction of the lower sensor element 48, and the lower sensor element 48 can be favorably pressed / pressed.
Thereby, the load F3 can be made to act on the upper and lower sensor elements 47 and 48 efficiently.
Hereinafter, of the upper and lower sensor elements 47, 48, the upper sensor element 47 will be described, and the description of the lower sensor element 48 will be omitted.

FIGS. 7A and 7B are diagrams illustrating an example in which a load is applied to the upper sensor element according to the present invention.
In (a), when a load acts on the upper and lower sensor elements 47 and 48, a pressing force can be applied to the upper and lower sensor elements 47 and 48.
When a load is applied to the upper and lower sensor elements 47 and 48, the sensor element unit 16 is deformed in the longitudinal direction rearward of the vehicle body with the left and right end portions 16a and 16b serving as fulcrums (references) as indicated by imaginary lines.
On the other hand, since the sensor element unit 16 has a short vertical dimension, the sensor element unit 16 does not deform in the lateral direction rearward of the vehicle body with the upper and lower sides 16c and 16d serving as fulcrums (reference).

In (b), the sensor element unit 16 is deformed in the longitudinal direction with the left and right end portions 16a and 16b as fulcrums (references), so that the upper sensor element 47 is also rearward of the vehicle body with respect to the left and right end portions 47a and 47b. Deforms in the longitudinal direction.
The upper sensor element 47 deformed in the longitudinal direction has a total length L longer than that of the upper sensor element 47 before deformation.

Here, the upper sensor element 47 has the longitudinal direction of the upper sensor element 47 (that is, the insensitive direction) aligned with the longitudinal direction of the sensor element unit 16 as a long object. Therefore, even if the total length L of the upper sensor element 47 is increased, the upper sensor element 47 does not generate a voltage.
Thus, the upper sensor element 47 detects only the pressing force that compresses / presses the upper sensor element 47, that is, only the load at the time of collision, acting in a direction orthogonal to the surface direction of the upper sensor element 47. It can be output as an electric signal, and the load at the time of collision can be detected with high accuracy.

In the above embodiment, the front bumper beam 13 is exemplified as a long object. However, the present invention is not limited to this, and the present invention can be applied to other long objects such as a rear bumper beam.
Furthermore, it is also possible to apply to long objects other than vehicles.

  The sensor assembly of the present invention is suitable for application to an automobile including a piezoelectric element that outputs an electrical signal corresponding to a load in a direction orthogonal to the surface direction.

It is a perspective view which shows the sensor assembly which concerns on this invention. It is a disassembled perspective view which shows the sensor assembly which concerns on this invention. FIG. 3 is a sectional view taken along line 3-3 in FIG. 1. FIG. 4 is an exploded view of FIG. 3. (A) is a perspective view which shows the sensor element of the sensor assembly which concerns on this invention, (b) is a figure which shows the molecular structure of the sensor element which concerns on this invention. It is a figure explaining the example which the load acted on the 1st member of the sensor assembly concerning the present invention. It is a figure explaining the example which the load acted on the upper sensor element which concerns on this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Sensor assembly , 13 ... Front bumper beam (bumper beam), 18 ... Vehicle body , 47 ... Upper sensor element (piezoelectric element), 48 ... Lower sensor element (piezoelectric element), F3 ... Load.

Claims (2)

Elongated piezoelectric element outputting an electric signal corresponding to the load weight to be input in a direction perpendicular to the plane direction is provided in the bumper beam constituting a part of the vehicle body, the load at the piezoelectric element A detectable sensor assembly comprising:
The bumper beam extends in the vehicle width direction,
The piezoelectric element is
Sensitivity is high when a load is applied in a predetermined direction along the surface direction, and sensitivity is low when a load is applied in a direction orthogonal to the predetermined direction,
A sensor assembly characterized in that a longitudinal direction of the piezoelectric element coincides with a vehicle body width direction which is a direction orthogonal to the predetermined direction. As the piezoelectric element, a piezoelectric film made of polyvinylidene fluoride is used,
The sensor assembly according to claim 1, wherein when the piezoelectric element is provided on a long object, the longitudinal direction of the piezoelectric element is made to coincide with the longitudinal direction of the long object.

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