JPH06207865A - Load detector - Google Patents

Abstract

(57) [Abstract] [Purpose] A load detection device capable of improving the accuracy and reliability by reducing the change in characteristics due to temperature and deterioration over time, improving the productivity by facilitating the manufacturing, and improving the detection accuracy. Offer. [Structure] A flexure element 6a which is distorted by a load input,
A load detecting device provided with four resistance elements provided on the strain-generating body 6a and having a resistance value that changes in accordance with the amount of strain, and a wire connecting each resistance element so as to form a Wheatstone bridge circuit. At the resistance element,
Of the resistor thick films 6c ₁ and 6c ₃ of _one pair facing each other in the Wheatstone bridge circuit. The strain detection direction is set to the load detection direction, the gauge ratio is set to a large value (7 to 10), and the strain detection direction of the opposite pair of resistor thick films 6c ₂ and 6c ₄ is orthogonal to the load detection direction. In addition to the direction, the gauge factor was set to be small (1.5 to 2.0).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a load detecting device for detecting a load.

[0002]

2. Description of the Related Art Conventionally, as a load detecting device, for example, one shown in FIG. 5 is known. The load detecting device 61 includes a cylindrical strain generating body 61 a and the strain generating body 6 a.
Resistance elements 61b attached to the outer peripheral surface of 1a at equal intervals
And a connection wire 61c for connecting the resistance element 61b so as to form a Wheatstone bridge circuit.

In the load detecting device 61, when a load is applied to the strain generating body 61a, the strain generating body 61a is compressed and deformed according to the load. Along with this, the resistance element 61b attached to the strain generating body 61a is also distorted, and the electric resistance value changes. Then, the output voltage of the Wheatstone bridge circuit changes according to the change of the resistance value, so that the load is detected by detecting the change of the output voltage. Incidentally, as such a load detecting device, Japanese Patent Laid-Open No. 62-50
The one described in Japanese Patent No. 601 is known.

By the way, in order not to change the zero point of the Wheatstone bridge circuit due to the influence of the temperature of the resistance element 61b as described above (so that the zero point drift = 0), the Wheatstone bridge circuit is under no load. It is preferable to set the resistance value of each resistance element 61b so that the output voltage e _{0 of 0} becomes 0.

[0005]

However, since the conventional load detecting device has a structure in which the resistance element is adhered to the flexure element, the change in the characteristics of the adhesive material to which the resistance element is adhered due to the temperature change. There is a problem that the accuracy and reliability of load detection are deteriorated due to deterioration with time and the like, and that productivity is poor.

Further, if it is attempted to set the output voltage at no load to 0 so that zero-point drift does not occur, it is necessary to accurately measure the resistance value of each resistance element in advance, which also takes time and production. The problem of poor sex arises.

Further, since the gauge factor of the resistance element is about 2 at most and the output voltage is small, the sensitivity is low.
There is a problem that a high amplification factor is required and the detection accuracy deteriorates.

The present invention has been made in view of the above problems, and it is possible to improve the accuracy and reliability by reducing the change in characteristics due to temperature and the deterioration over time, and to improve the productivity by facilitating the manufacture. It is an object of the present invention to provide a load detection device that is capable of improving the detection accuracy.

[0009]

In order to achieve the above object, a load detecting device of the present invention comprises a strain-generating body which is distorted by a load input and a resistance which is provided on the strain-generating body according to the strain amount. In a load detecting device including four resistance elements whose values change, and a connection in which each resistance element is connected so as to form a Wheatstone bridge circuit, the resistance element obtained by firing the resistance element into a flexure element. Formed with a film, the connection is formed with a conductor thick film fired into a strain-generating body, and the strain detection direction of one pair of resistor thick films facing each other in the Wheatstone bridge circuit is the load detection direction, and The gauge ratio is set to be large, the strain detection direction of the other pair of resistor thick films facing each other is set to the direction intersecting the load detection direction, and the gauge ratio is set to be small.

Further, in the load detecting device according to claim 2,
In the load detecting device according to the first aspect, the gauge ratio of one set of the resistor thick film in which the strain detecting direction is the direction intersecting the load detecting direction is set to 2.6 or less.

[0011]

When the load detecting device of the present invention is manufactured, the resistor thick film is fired at a predetermined position of the strain generating body, and the resistor thick film is connected so as to form a Wheatstone bridge circuit. The conductor thick film is fired.

The resistance value of the thick resistor film thus formed when no load is applied can be arbitrarily set by, for example, trimming. Further, since each thick film is fired, it is stable in temperature and hardly changes with time.

Further, the resistor thick film can obtain a higher gauge ratio than a general metal strain gauge by properly selecting the material thereof, thereby improving load detection accuracy.

When there is a load input to the strain-generating body, the resistance value of one set of resistor thick films whose strain-detecting direction is the load-detecting direction is decreased and the output voltage of the Wheatstone bridge circuit is increased. In this case, a large output voltage can be obtained by a large change in resistance value due to a large gauge factor.

On the other hand, in the other set of resistive element thick films in which the strain detection direction is the direction intersecting the load detection direction, depending on the value of the gauge factor, the direction in which the resistance value changes, that is, the Wheatstone bridge circuit The direction in which the output voltage increases or decreases may be reversed, but the amount of change in the resistance value with respect to the load input is small from the strain detection direction, and since the gauge factor is also small, it acts in the direction to decrease the output voltage. But the amount is small. Therefore, a large value can be obtained as the output voltage of the Wheatstone bridge circuit, which can improve the load detection accuracy.

Further, in the load detecting device according to claim 2,
When there is a load input to the flexure element, the resistance value also increases in the direction that increases the output voltage of the Wheatstone bridge circuit even in one set of resistor thick films whose strain detection direction intersects the load detection direction. With this,
The output voltage for the load input can be further increased.

Therefore, the output sensitivity is increased and the load detection accuracy can be further improved.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A load detecting device according to an embodiment of the present invention will be described with reference to the drawings. First, the configuration will be described.

FIG. 2 is a cross-sectional view showing an upper mount portion of a suspension to which the load detecting device according to the embodiment of the present invention is applied. In the figure, 1 is an upper mount, and its outer shell 1a is supported by a vehicle body 2. There is. Further, a screw portion 3a provided at the upper end of the strut rod 3 of the strut ST is inserted into the bottom portion of the inner shell 1b of the upper mount 1 from below, and the nut 5 is inserted through the spacer 4 on the insertion end side of the screw portion 3a. The strut rod 3 is mounted on the upper mount 1 by screwing and tightening. Further, a load detection device 6 for detecting a load applied to the suspension is interposed between the bottom portion of the inner shell 1b and the end portion 3b of the strut rod 3 facing the inner shell 1b. It is tightened by the nut 5. In the figure, 7 is a bumper bar,
Reference numeral 8 is a suspension spring, and 9 is a receiving member with which the upper ends of the bumper bar 7 and the suspension spring 8 are engaged.

Next, the load detection device 6 will be described with reference to FIG. 1 which is a perspective view showing the load detection device 6 and FIG. 3 which is a development view showing the outer peripheral surface of the load detection device 6.

As shown in FIG. 1, the load detecting device 6 is
It has a cylindrical flexure element 6a. Then, on the outer peripheral surface of the strain generating body 6a, two axial direction (vertical direction) resistor thick films 6c ₁ and 6c ₃ whose strain detecting direction is the load detecting direction are formed.
And two circumferential (lateral) resistor thick films 6c ₂ and 6c ₄ whose strain detection direction is orthogonal to the load detection direction are alternately formed at substantially equal intervals, and Each resistor thick film 6c (6c ₁ , 6c ₂ , 6c ₃ , 6c ₄ )
The conductor thick film 6d is formed by connecting so as to form a Wheatstone bridge circuit as shown in FIG. That is, two axial (vertical) resistor thick films 6c ₁ and 6c
₃ pairs, and 2 circumferential (lateral) resistor thick films 6
The connection is such that c ₂ and 6c ₄ face each other.

The axial (vertical) resistor thick film 6c
₁ , 6c ₃ are made of a material having a large gauge factor K _f v (7 to 10), while circumferential (lateral) resistor thick films 6c ₂ , 6
c ₄ is formed of a material having a small gauge factor K _f h ₀ (1.5 to 2.0).

The terminal 6 is provided in the middle of the thick conductor film 6d.
e, 6f, 6g, 6h are formed, the power source E is connected to the terminals 6e, 6g, and the terminals 6f, 6h have an output voltage e _0.
It is connected to an external device as an output terminal for taking out.

On the outer peripheral surface of the strain-generating body 6a, the resistor thick film 6c, the conductor thick film 6d and the terminals 6 are formed.
An insulating thick film 6b is formed on portions other than e, 6f, 6g and 6h. The thick films 6b, 6c, 6d and the terminals 6e, 6f, 6g, 6h are formed by firing an inorganic material as a raw material. In addition, each resistor thick film 6
The resistance values of c ₁ , 6c ₂ , 6c ₃ and 6c ₄ are R
₁ , R ₂ , R ₃ and R ₄ .

Next, the operation will be described.

The procedure for manufacturing the load detecting device 6 of this embodiment will be described. First, the insulating thick film 6b is baked on the outer peripheral surface of the flexure element 6a. Next, the terminals 6e, 6f, 6g,
The conductor thick film 6d including 6h is fired. Finally, each resistor thick film 6c is baked at a predetermined position. When firing,
Printing is performed on the flexure element 6a. Since the flexure element 6a has a cylindrical shape, printing is performed by spraying as described in, for example, Japanese Patent Laid-Open No. 2-151701. By the way,
When the flexure element has a planar shape or when it is processed into a cylindrical shape after printing, screen printing such as that described in Japanese Patent Publication No. 55-52924 is used for this printing. You can

By the way, in the load detecting device 6, in order to prevent the output voltage e _{0 under} no load from changing due to a temperature change or the like (to prevent zero point drift), the output voltage under no load. Is preferably set to 0. In this case, the resistance value of each resistor thick film 6c is R ₁ = R
₄ and R ₂ = R _3, and the resistance values of the resistor thick films 6c are R ₁ = R ₄ and R ₂ = R ₃ during firing.
If not, the resistance value is corrected by providing slits or grooves by laser processing or the like to the predetermined resistor thick film 6c so that the above resistance value is obtained. In this way, since the resistance value can be easily corrected by the post-processing, it does not take time for manufacturing.

The output voltage e _O of the Wheatstone bridge circuit shown in FIG. 4 can be obtained by the following equation.

[0029]

[Formula 1] That is, when a compressive load is applied in the axial direction of the flexure element 6a,
Distortion occurs in proportion to the load on the flexure element 6a, also by its strain, each resistor thick film _{6c 1, 6c 2, 6c 3} , 6c 4
Since the resistance values R ₁ , R ₂ , R ₃ , and R ₄ of the output voltage change, the output voltage e _O proportional to the load can be obtained.

The axial (vertical) resistor thick film 6c
_1, the resistance value R when the 6c ₃ the compressive load is applied
Circumferential direction (lateral direction) changes so that ₁ and R ₃ become smaller
If the resistance thick films 6c ₂ and 6c ₄ change so that their resistance values R ₂ and R ₄ increase when a compressive load is applied,
A large value can be obtained as the output voltage e _O.

The flexure element 6a when a compressive load is applied
Axial (longitudinal) resistor thick films 6c ₁ and 6c due to distortion of
The gauge factor K _f v of ₃ is calculated by the following equation (2), and the gauge factor K _f h in the load detection direction (axial direction) of the circumferential (lateral) resistor thick films 6c ₂ and 6c ₄ is , Can be obtained by the following equation (3).

[0032]

[Formula 2]

[0033]

[Formula 3] In the above equation, ν is Poisson's ratio, ε _v is axial (longitudinal) strain, and ρ is specific resistance.

The above equation (3) can be transformed into the following equation (4).

K _f h = K _f h ₀ -2 (1 + ν) (4) In the above equation, K _f h ₀ is the circumferential (lateral) resistor thick film 6c. The gauge ratios in the original strain detection direction (circumferential direction) in ₂ , 6c ₄ are shown.

Therefore, the axial (vertical) resistor thick film 6c is formed.
The resistance value variation dRv of ₁ and 6c ₃ is obtained by the following equation (5), and the circumferential direction (lateral direction) resistor thick films 6c ₂ and 6c ₄
The resistance change amount dRh can be calculated by the following equation (6).

DRv = K _f v · R _v · ε _v (5) dRh = K _f h · R h · ε _v = {K _f h ₀ -2 (1 + ν)} R h · ε _v (6) In the above formula, Rv is an initial resistance value of the axial (vertical) resistor thick films 6c ₁ and 6c ₃ , and Rh is a circumferential (horizontal) resistance. The initial resistance values of the body thick films 6c ₂ and 6c ₄ are shown.

According to the above equation (6), when a compressive load is applied, the resistance value of the axial (vertical) resistor thick films 6c ₁ and 6c ₃ decreases from the initial value, and the circumferential (lateral) Direction) Regarding the resistance values of the resistor thick films 6c ₂ and 6c ₄ , it can be seen that the increase or decrease in the resistance value depends on the gauge factor K _f h ₀ . That is, since the Poisson's ratio ν is approximately 0.3, applying this value to the above equation (6) gives the following equation (7)
become that way.

DRh = {K _f h ₀ -2 (1 + 0.3)} Rh.ε _v = {K _f h ₀ −2.6} R h ・ ε _v ... (7) The above equation (7) ), The circumferential direction (lateral direction) resistor thick film 6c
The resistance values R ₂ and R ₄ of ₂ , 6c ₄ have a gauge factor K _f h ₀ of 2.6.
In the following cases, the compressive load increases the initial value, and when the gauge factor K _f h ₀ is 2.6 or more, the compressive load decreases the initial value.

Therefore, in this embodiment, as described above, the gauge ratio K _f h ₀ of the circumferential (lateral) resistor thick films 6c ₂ and 6c ₄ is set to 1.5 to 2.0, which is 2.6 or less. , The axial (longitudinal) resistor thick films 6c ₁ and 6c ₃ are set to have a gauge factor K _f v of 2.6 or more, which is 7 to 10, so that the Wheatstone bridge receives a compressive load input to the strain element 6a. A large output voltage e ₀ can be obtained as a circuit, that is, the output sensitivity with respect to the load input becomes high.

As described above, in the load detection device 6 of the embodiment, the insulator thick film 6b, the resistor thick film 6c, the conductor thick film 6d and the respective thick films of the inorganic material are printed and fired. Since the terminals 6e to 6h are formed, the adhesion to these strain generating bodies 6a is very stable with respect to temperature, the characteristic change due to temperature is unlikely to occur, and it has high reliability even with deterioration over time. In addition, printing and firing have markedly higher productivity, as compared with the conventional method of attaching a resistor to form a Wheatstone bridge circuit.

Further, in forming the Wheatstone bridge circuit, in setting the resistance value of each resistor thick film 6c to a predetermined resistance value, conventionally, resistors having that resistance value were individually selected. On the other hand, in the case of the present embodiment, even if the resistance value is not set at the time of firing, it can be corrected by a simple process, which also improves the productivity.

Further, when the material of the resistor thick film 6c is properly selected, a gage factor higher than a general metal strain gage factor can be obtained, which can enhance the output sensitivity to a load input. , A large (7 to 10) axial (longitudinal) resistor thick film 6c _{1 having} a large gauge factor K _f v,
And 6c _3, Do (1.5 to 2.0) smaller the gauge factor K _f h ₀ circumferential direction (lateral direction) that was crossed constitute a Wheatstone bridge circuit in a state of placing the resistor thick film 6c _2, and 6c ₄ alternately Thus, a large output voltage e ₀ can be obtained as the output of the load detection device 6 with respect to the load input, and the output sensitivity is further increased, which makes it possible to improve the detection accuracy. .

The embodiment has been described above with reference to the drawings, but the specific structure is not limited to this embodiment, and the present invention can be applied even if there is a design change or the like within the scope not departing from the gist of the present invention. included.

For example, in the embodiment, the flexure element is formed in a cylindrical shape, but it may be in any other shape.

[0046]

As described above, in the load detecting device of the present invention, the resistance element and the wiring are formed by the resistor thick film and the conductor thick film which are fired in the strain generating body, and therefore the resistance is increased. Compared to sticking each element to each strain element, the productivity is significantly improved. The adhesion between each thick film and the strain element is temperature stable, and the characteristics change with temperature. The resistance of the thick film of the resistor can be set arbitrarily by trimming, so that the zero point can be easily set. To be

Further, by appropriately selecting the material of the resistor thick film, it is possible to obtain a gauge factor higher than that of a general metal strain gauge, and it is possible to improve the detection accuracy.

Furthermore, in the Wheatstone bridge circuit, the strain detection direction of the resistance thick film of one pair facing each other is set as the load detection direction, and the gauge factor thereof is increased to make the resistance thick film of the other pair of resistance thick films of the opposite pair. By making the strain detection direction intersect with the load detection direction and making the gauge factor small, the output sensitivity to the load input is increased, which makes it possible to further improve the load detection accuracy. Is obtained.

Further, in the load detecting device according to the second aspect, particularly, the gauge ratio of one set of the resistor thick film in which the load detecting direction is the direction intersecting the strain detecting direction is set to 2.6 or less. Thus, the resistance value can be increased in the direction of increasing the output voltage of the Wheatstone bridge circuit with respect to the load input, and thus the output voltage with respect to the load input can be further increased.

[Brief description of drawings]

FIG. 1 is a perspective view showing a load detection device according to an embodiment of the present invention.

FIG. 2 is a cross-sectional view showing an upper mount portion of a suspension to which the embodiment apparatus is applied.

FIG. 3 is a development view of an outer peripheral surface showing an apparatus according to an embodiment.

FIG. 4 is a circuit diagram showing a bridge formed on the outer peripheral surface of the device of the embodiment.

FIG. 5 is a perspective view showing a conventional load detection device.

[Explanation of symbols]

 6 load detector 6a strain element 6b insulating thick film 6c resistor thick film 6d conductor thick film

Claims (2)

[Claims] 1. A flexure element which is distorted by a load input,
In a load detecting device provided with four resistance elements, which are provided on the strain-generating body, and whose resistance value changes in accordance with the amount of strain, and a connection line in which these resistance elements are connected so as to form a Wheatstone bridge circuit. , The resistor element is formed of a resistor thick film that is fired into a strain generating body, and the connection is formed of a conductor thick film that is fired into a strain generating body, and one pair of resistors that face each other in the Wheatstone bridge circuit is formed. The strain detection direction of the thick film is set to the load detection direction, the gauge ratio is increased, and the strain detection direction of the opposing pair of resistor thick film is set to the direction intersecting the load detection direction and the gauge A load detection device characterized by a small rate. 2. The load detecting device according to claim 1, wherein the gauge ratio of one set of the resistor thick film in which the strain detecting direction is a direction intersecting the load detecting direction is set to 2.6 or less.