JPH06207866A - Load detector - Google Patents

Abstract

PURPOSE:To furnish a load detector which enables improvement of precision and reliability by reduction of a change in characteristics due to temperature and the deterioration with time, improvement of productivity by facilitation of manufacture and improvement of a detecting precision by an increase in an output sensitivity. CONSTITUTION:A resistance element is formed of a resistor thick film formed on a strain generating body 6a by baking, while a connection constituting a Wheatstone bridge circuit is formed of a conductor thick film 6d formed on the strain generating body 6a by baking, and the strain detecting direction of the resistor thick film 6c1 in one opposite set in the Wheatstone bridge circuit is made a load detecting direction. The strain detecting direction of the resistor thick film 6c2 in the other opposite set is made to intersect the load detecting direction, and cut parts 6j and 6k for avoiding transmission of a load input are formed in the strain generating body 6a in the part wherein the resistor thick film 6c2 of which the strain detecting direction is made to intersect the load detecting direction is provided.

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 resistance element has a gauge factor of about 2 at most and the output voltage is small, the output sensitivity to the load input is low, and therefore a high amplification factor is required and the detection accuracy is deteriorated.

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 capable of increasing the output sensitivity and 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. In the Wheatstone bridge circuit, the strain detection direction of one of the opposing resistor thick films is set as the load detection direction, and the connection is formed by a conductor thick film formed by firing the wire into a strain-generating body. The strain detection direction of the resistor thick film of the other set is the direction intersecting the load detection direction, and the strain thick direction of the strain generating element of the strain generating element is the direction intersecting the load detection direction. Load on the flexure element It was formed with the structure of the notch for avoiding the transmission of input.

[0010]

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 without load 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, if there is a load input to the flexure element,
One of the sets of resistor thick films, whose strain detection direction is the load detection direction, acts to increase the output voltage of the Wheatstone bridge circuit by decreasing the resistance value, whereas the strain detection direction is the load detection direction. In the other set of resistor thick film that is in the direction intersecting with, the gauge factor is high (about
In the case of 2.6 or more), the resistance value of the Wheatstone bridge circuit will be reduced and the output voltage of the Wheatstone bridge circuit will be reduced.

However, according to the present invention, in order to avoid the transmission of the load input to the strain element in the portion where the one set of the resistor thick film is provided, the strain detection direction being the direction intersecting the load detection direction, That is, by adopting a configuration in which each of the cutouts that avoids the occurrence of distortion is formed, it is possible to prevent the output voltage from decreasing due to the decrease in resistance value.

Therefore, a large output voltage can be obtained on the basis of a large change in resistance value in one set of resistor thick films whose strain detection direction is the load detection direction, and thus high output sensitivity to a load input can be obtained. The detection accuracy is improved.

[0015]

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 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 drawing, 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 detecting device 6 will be described with reference to FIG. 1 which is a perspective view showing the load detecting device 6 and FIG. 3 which is a development view showing an outer peripheral surface of the load detecting 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 perpendicular to the load detection direction are alternately formed at substantially equal intervals, and each of these resistors is formed. a thick film _{6c (6c 1, 6c 2,} 6c 3, 6c 4), connected to the conductor thick film 6d is formed 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 and two circumferential (horizontal) resistor thick films 6c
_The connection state is such that ₂ , 6c ₄ face each other.

The axial (vertical) resistor thick film 6c
₁ , 6c ₃ are made of a material having a particularly high gauge factor K _f v (7 to 10), while circumferential (lateral) resistor thick film 6c
_{Also for 2} and 6c ₄ , the gauge factor K _f h ₀ is at least 2.6 or more.

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.

Then, 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 and 6d and the terminals 6e, 6f, 6g and 6h are formed by firing an inorganic material. The resistance values of the resistor thick films 6c ₁ , 6c ₂ , 6c ₃ , 6c ₄ are R ₁ , R ₂ , R ₃ and R ₄ , respectively.

Further, at the upper end opening edge portion of the strain-generating body 6a, in the axial extension line portion of the position where the circumferential (lateral) resistor thick films 6c ₂ and 6c ₄ are provided, that portion is formed. Are formed with notches 6j and 6k for eliminating one of the pressure receiving surfaces, and these notches 6j and 6k are provided in respective circumferential directions (lateral directions).
The strain is prevented from being generated in the strain element 6a portion where the resistor thick films 6c ₂ and 6c ₄ are provided, that is, the load input to each circumferential (lateral) resistor thick film 6c ₂ and 6c ₄ is performed. By avoiding the transmission, the resistance value is prevented from changing (decreasing).

Next, the operation will be described.

The procedure for manufacturing the load detecting device 6 of the present embodiment will be described. First, a cylindrical strain element 6a having notches 6j and 6k formed in the upper end opening edge portion thereof in a state of facing each other in the diametrical direction. The insulating thick film 6b is baked on the outer peripheral surface of the.
Next, including the terminals 6e, 6f, 6g, and 6h, the conductor thick film 6
b. Finally, each resistor thick film 6c is baked at a predetermined position. It should be noted that although printing is performed on the strain-generating body 6a during firing, since the strain-generating body 6a has a cylindrical shape, for example, printing by spraying as described in JP-A-2-151701 is performed. By the way, when the flexure element has a planar shape or is processed into a cylindrical shape after printing, at the time of this printing, for example, Japanese Patent Publication No. 55-5292.
Screen printing as described in Japanese Patent No. 4 can be used.

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 temperature change or the like (to prevent zero point drift), the output voltage under no load may be changed. 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.

[0027]

[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).

[0030]

[Formula 2]

[0031]

[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 6c ₂ , Original strain detection direction (circumferential direction) in 6c ₄
Shows the gauge factor of.

Therefore, the resistance value change amount dRv of the vertical resistance thick films 6c ₁ and 6c ₃ is calculated by the following equation (5), and the circumferential (horizontal) resistance thick films 6c ₂ and 6c ₄ can be calculated. 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 values of the axial (vertical) resistor thick films 6c ₁ and 6c ₃ decrease 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.

[0037] _{dRh = {K f h 0 -2} (1 + 0.3)} Rh · ε v = {K f h 0 -2.6} Rh · ε v ········ (7) the 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 v of the axial (vertical) resistor thick films 6c ₁ and 6c ₃ is set to 7 to 10, and the circumferential direction (lateral direction) is set. ) Since the gauge factor K _f h _{0 of the} resistor thick films 6c ₂ and 6c ₄ is also set to a value of 2.6 or more, if there is a load input to the strain element 6a, the axial (vertical) resistor thick films will be 6c ₁ and 6c
_{In the case of 3} , the resistance value changes in the decreasing direction to act in the direction of increasing the output voltage e ₀ of the Wheatstone bridge circuit, whereas in the circumferential direction (transverse direction) of the resistor thick film 6
In c ₂ and 6c ₄ , the resistance value changes in the decreasing direction, so that the output voltage e ₀ acts in the decreasing direction.

However, in this embodiment, the strain generating element 6a in the portion where the circumferential (lateral) resistor thick films 6c ₂ and 6c ₄ are provided has a circumferential (lateral) resistor thick film 6c ₂ and 6c. _Four
To avoid the transfer of load inputs to, ie,
Notches 6j and 6k are formed to avoid the occurrence of strain, and the resistance value does not change (decrease) even when a load is applied to the flexure element 6a.

Therefore, a large voltage e ₀ can be obtained as the output of the Wheatstone bridge circuit based on a large resistance value change (decrease) in the axial (vertical) resistor thick films 6c ₁ and 6c ₃ . High output sensitivity with respect to load input can be obtained and detection accuracy can be improved.

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, according to the resistor thick film 6c, a gage factor higher than a general metal strain gage factor can be obtained by appropriately selecting the material, and thereby the output sensitivity to a load input is obtained. The cutout portion formed in the strain body 6a can change (decrease) the resistance value of the circumferential (lateral) resistor thick films 6c ₂ and 6c ₄ that can increase the output voltage e ₀ and can be increased. By avoiding 6j and 6k, 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, whereby the detection accuracy can be improved. It has the characteristics of

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 notch portion for avoiding the transmission of the load input is formed in the upper end opening edge portion which is one pressure receiving surface of the flexure element, but the pressure receiving surface and the circumferential (lateral) resistor are formed. It may be formed in a lateral hole shape in the strain-generating body at an intermediate position between the thick film and the firing portion.

[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 ratio higher than that of a general metal strain gauge, and it is possible to improve the detection accuracy.

In addition, in the Wheatstone bridge circuit, the strain detection direction of the resistor thick film of one of the opposing pairs is set as the load detection direction, and the strain detection direction of the resistor thick film of the other pair of opposing pairs is set as the load detection direction. In addition to the direction that intersects with the strain detection direction, the strain detection body is formed with a notch for avoiding the transmission of the load input in the portion where the thick resistor film is provided. This makes it possible to prevent a decrease in the output voltage due to a decrease in the resistance value of one set of resistor thick films in which the strain detection direction intersects the load detection direction. It is possible to obtain a large output voltage based on a large change in the resistance value of the resistor thick film of the set, and thereby a high output sensitivity to a load input can be obtained and the detection accuracy can be improved. Effect is obtained that it becomes.

[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 6j notch 6k notch

Claims (1)

[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 resistance 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 in the Wheatstone bridge circuit, one pair of resistors facing each other is formed. The strain detection direction of the body thick film is the load detection direction,
A resistor thick film is provided in which the strain detection direction of the other pair of resistor thick films that face each other is a direction that intersects the load detection direction, and the strain generation direction of the strain element is a direction that intersects the load detection direction. A load detecting device characterized in that a notch portion for avoiding transmission of a load input is formed in a part of the flexure element.