JP2000214002A - Load sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a load sensor excellent in an anti-noise property, a temperature property, etc., and capable of detecting a load in a wide range with a high precision, improved so as to be usable as one for vehicles also. SOLUTION: Movable plates 2, 3 are arranged at prescribed intervals coaxially in a housing 1, and their displacements are opposed by coil springs 9, 15, respectively. On each backside of the movable plates 2, 3, magnets 4, 10 are fitted. In magnetic circuits formed by these magnets 4, 10 and magnetic pole pieces 5a, 5b and 11a, 11b, displacement detecting elements 6, 12 are arranged. The detecting element 6 is supported by the movable plate 3, and the detecting element 12 is supported by the housing 1 side. They are so assembled that only the coil spring 9 may deform in a region where an applied load F is small, that both coil springs 9, 15 may deform in an intermediate region, and that only the coil spring 15 may deform in a large load region.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a load sensor, and more particularly to a load sensor capable of detecting a load from a low load to a high load with high accuracy.

[0002]

2. Description of the Related Art One of conventional load sensors has been disclosed.
One is a strain gauge. The strain gauge has an electrical resistance of 1
It is constituted by bonding a metal foil of a predetermined shape having about 00 to 500 ohms to a flexure element, and converts a shape change when an external force is applied to the flexure element, that is, a mechanical quantity into electric resistance. In addition to the foil type, the strain gauge includes a resistance type using a nickel-copper alloy, and a semiconductor type using a semiconductor as a component. Strain gauges are widely used in industrial machines, for example, for detecting the pressure in the cavity of an injection molding machine.

[0003]

However, according to the conventional load sensor, noise resistance, temperature characteristics and the like are not good, so that the use of the sensor is limited, for example, it cannot be used for vehicles. Therefore, an object of the present invention is to provide a load sensor that has excellent noise resistance, temperature characteristics, and the like and can detect a wide range of loads with high accuracy, for example, so that it can be used for vehicles. is there.

[0004]

In order to achieve the above object, the present invention provides a load sensor for receiving a load and outputting a detection signal corresponding to the load, the first elastic member having a first elastic coefficient. A member, a first displacement member that is displaced in a predetermined direction while deforming the first elastic member under the load, and when the deformation of the first elastic member reaches a predetermined value, An elastic deformation inhibiting member for inhibiting further deformation of the first elastic member in response to the displacement of the first displacement member, and a second elastic member having a second elastic coefficient larger than the first elastic coefficient And when the deformation of the first elastic member is equal to or less than the predetermined value, the displacement of the first displacement member is received via the first elastic member, and the deformation of the first elastic member is the predetermined value. Is reached, the displacement of the first displacement member is changed by the elastic deformation. A second displacement member that is displaced in the predetermined direction while deforming the second elastic member by receiving the force via the prohibition member; and a detection signal that detects displacement of the first and second displacement members. And a load sensor provided with a detection unit for outputting the load sensor.

[0005]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a load sensor according to the present invention. The housing 1 made of a two-chamber structure has
An opening 1a is provided at an end, and a movable plate 2 (first displacement member) is provided in the opening 1a. The opening 1 is also provided between the first chamber 1b and the second chamber 1c inside the housing 1.
The movable plate 3 is provided in the opening 1d.
(A second displacement member) is provided. Movable plate 3
Has a cylindrical portion 3a (elastic deformation inhibiting member) projecting into the first chamber 1b. The cylindrical portion 3a functions as a stopper for a coil spring 9 described later.

A magnet 4 is provided on the inner surface of the movable plate 2.
A first magnetic source is mounted, and a pair of magnetic pole pieces 5a and 5b made of a magnetic material are provided on both sides of the magnet 4 to form a part of a magnetic circuit of the magnet 4. A displacement detecting element 6 is provided in a gap formed at the tip of the pole pieces 5a and 5b, and is attached to the movable plate 3 via a support piece 7 and a base 8. A coil spring 9 as a first elastic member having a distal end surface in contact with the inner surface of the movable plate 2 is provided in the cylindrical portion 3 a of the movable plate 3.
(Having a spring constant K _A ), and the movable plate 2
Are biased in a direction away from the movable plate 3.

Similarly, a magnet 10 (second magnetic source) is mounted on the inner surface of the movable plate 3, and a pair of magnetic pole pieces 11 a and 11 b made of a magnetic material stand on both sides of the magnet 10. Has been established. Pole pieces 11a, 1
1b, a displacement detecting element 1
2 are provided. The displacement detecting element 12 includes a support piece 13
And is attached to the case surface of the electronic circuit 14 via. The electronic circuit 14 applies a predetermined voltage to the displacement detecting elements 6 and 12, and processes an output signal thereof. Further, the movable plate 3 is provided in the second chamber 1c of the housing 1.
A coil spring 15 (second elastic member) for urging the coil in the direction of the first chamber 1b is provided. The coil spring 15 has a spring constant K _B.

As the displacement detecting elements 6 and 12, an MR element (magnetic thin film magnetoresistive element) belonging to a magnetic sensor is used. In this MR element, a resistance element is formed using a magnetic metal evaporated thin film of Ni-Fe or the like. When a parallel magnetic field is applied to the resistance element, an internal current is generated when the direction of the current and the direction of the magnetic field are parallel. It has the characteristic that the resistance is maximized and orthogonally minimized. Also, even if both directions are the same, M
The resistance value changes according to the strength (magnetic flux density) of the magnetic field passing through the R element. In the present invention, a sensor is configured using the change in the magnetic flux density. Further, the MR element has characteristics of good heat resistance, a small temperature coefficient, operation in a weak magnetic field, and high sensitivity. Therefore, MR
The element is most suitable for sensors used for vehicles.

In the load sensor shown in FIG. 1, when a load F is applied to the movable plate 2, the movable plate 2 moves toward the movable plate 3 in accordance with the magnitude of the load F. At this time, the pole pieces 5a and 5b move together with the movable plate 2,
The magnetic flux density of the magnet 4 exerted on the displacement detecting element 6 changes. At this time, the magnetic circuit is changed from magnet 4 to pole piece 5
a → displacement detecting element 6 → pole piece 5b → magnet 4, the area of the displacement detecting element 6 interposed in the magnetic field changes due to the movement of the movable plate 2, and the displacement is detected in accordance with the applied magnetic flux density. The output voltage (detection voltage) of the element 6 changes.

The movable plate 3 starts moving when the load F applied to the movable plate 2 exceeds the urging force of the coil spring 9. Therefore, the movable plate 3 does not move unless the movable plate 2 moves. The magnetic pole pieces 11a and 11b move with the movement of the movable plate 3, and the magnetic flux density of the magnet 10 exerted on the displacement detecting element 12 changes, thereby forming a magnetic circuit in the same manner as the displacement detecting element 6.
The output voltage (detection voltage) changes according to the change in the magnetic flux density given to the displacement detection element 12. When a strong load F is applied to the movable plate 2 such that the movable plate 2 comes into contact with the distal end surface of the cylindrical portion 3a, the movable plate 2 and the movable plate 3 thereafter move integrally, but the displacement is detected only by the displacement detection element 12. , And the detection value of the displacement detection element 6 becomes a constant value.

As described above, in the load sensor according to the present invention, the applied load F is replaced with a change in stroke by the elastic members of the coil springs 9 and 15, and the change in stroke is detected by the displacement detection elements 6 and 12. are doing. Then, a load sensor is formed by two sensor portions in which elastic members having different spring constants K are arranged in a two-stage configuration so that a relatively small load F to a large load F can be detected. With this configuration, when the sensor is used as a sensor for detecting the initial load of a FR-based 4WD vehicle, the detection can be performed with high accuracy.

FIG. 2 shows the change of each part of the load sensor according to the load F in FIG. In FIG. 2, components that are not necessary for description are omitted for easy understanding of the displacement state. (A) when the load F (external force) is small, (b) when the load F is medium, and (c) when the load F is large. When the load F is small, since the force applied to the movable plate 2 is small, the movable plate 2 does not move due to the reaction force F _{A0 of the} coil spring 9. Therefore, no output signal is generated in any of the displacement detection elements 6 and 12. At this time, the cylindrical part 3
The distance between the tip surface and the inner surface of the movable plate 2 of a (stopper) is L _0.

Next, when a moderate load F is applied, the movable plate 2 moves by a distance L to the movable plate 3 as shown in FIG. At this time, since the load F exceeding the biasing force of the coil spring 9, a coil spring 9 is compressed, further since the compression coil spring 15, the movable plate 3 is also moved by the distance L _B while receiving a reaction force F _B. The distance of the movable plate 2 and the cylindrical portion 3a, shrinks from L ₀ of (a) of FIG. 2 to L _A. The moving distance L of the movable plate 2 is represented by the following equation. Then, FIG.
In the state of (1), the electronic circuit 14 includes the displacement detection elements 6 and 1
2, two detection signals are input. _{L = (L 0 -L A)} + L B

Next, as shown in FIG. 2C, when a large load F is applied to the movable plate 2, each moving distance of the movable plate 2 and the movable plate 3 is changed to the state shown in FIG. From, it becomes even larger. At this time, the movable plate 2
Is in contact with the distal end surface of the cylindrical portion 3a,
The reaction force of the coil spring 9 becomes maximum ( _FAMAX ). For a load F greater than this, the movable plate 2 and the movable plate 3 move integrally, and only the detection amount from the displacement detection element 12 changes.

FIG. 3 shows the relationship between the applied load F and the displacement L of each movable plate. The thick solid line in the figure indicates load characteristics, and the functional ranges of the coil springs 9 (spring A) and 15 (spring B) are indicated by spring constants (K _A , K _B ). FIG.
If the load F shown in (a) is equal to or less than the reaction force F _A0 , the displacement of the movable plate 2 is L = 0. When a load F exceeding the reaction force F _A0 is applied to the movable plate 2, the movable plate 2 moves a distance L. At this time, the coil spring 9 (spring A) forms a reaction force by the spring constant K _A , and continues to the point L ₁ in FIG. L ₁ is represented by the following equation. _{L 1 = (F B0 -F A0} ) / K A

Next, as shown in FIG. 2B, when a load F (> F _B0 ) at which the movable plate 2 and the movable plate 3 can move is applied to the movable plate 2, the movable plates 2 and 3 are moved. Move together. At this time, the spring constant is
(Spring A) and 15 (Spring B) are combined and given by the following equation. The change of the spring constant in this operation state is until the movable plate 2 comes into contact with the cylindrical portion 3a. Spring constant _{= K A · K B / (} K A + K B)

Next, as shown in FIG. 2C, when the movable plate 2 comes into contact with the cylindrical portion 3a, the compression of the coil spring 9 is fixed, and thereafter, only the coil spring 15 responds to the load F. Change. Therefore, the spring constant K of the coil spring 15
Only _B becomes functional. As shown in (c) of FIG. 2, the distance L ₂ in a state where only the coil spring 15 (spring constant K _B) to function, represented by the following formula. L ₂ = L ₀ + L _B0

FIG. 4 shows the configuration of the electronic circuit 14. The electronic circuit 14 includes a determination circuit 16 to which the output voltages of the displacement detection elements 6 and 12 are input, and a correction circuit 17 that performs a predetermined correction on the output signal of the determination circuit 16. The discriminating circuit 16 discriminates a function of converting the resistance change of the displacement detecting elements 6 and 12 into a voltage value, a function of detecting a set amount of the coil spring 15 to calculate a correction amount, and a characteristic switching point. Has functions. The correction circuit 17 receives the data from the discrimination circuit 16 (the coil spring 15).
The output characteristic (load-output voltage) is corrected based on the correction of the set and the characteristic switching point).

FIG. 5 shows how the determination circuit 16 determines the characteristic switching point. The region where only the coil spring 9 (spring A) is functioning, the region where the coil springs 9 (spring A) and 15 (spring B) are functioning, and the region where only the coil spring 15 (spring B) is functioning Each has a different spring constant characteristic. Therefore, the switching point (characteristic change point) is determined.

The discriminating circuit 16 also detects the amount of set of the coil spring 15. The coil spring 15 is configured to function when the load is high. For this reason, in a vehicle that has been used for many years, it is necessary to prevent the detection accuracy from lowering even if the coil spring 15 is set. Therefore, the amount of set of the second-stage coil spring 15 is detected using the first-stage coil spring 9 having no or small set.

FIG. 6 shows the correction processing of the correction circuit 17. In this correction processing, the load-sensor output (voltage) characteristic is corrected to be a straight line based on the characteristic switching point and the set amount determined as shown in FIG. Characteristics are obtained.

FIG. 7 shows a load-displacement characteristic when the set of the coil spring is not corrected. This characteristic is for the sensor portion including the coil spring 15 and the displacement detecting element 12, and the solid line shows the load characteristic at the initial stage, and shows a linear characteristic because there is no sag. A broken line indicates a load characteristic in which sag has occurred due to aging, and this gives variation in detection accuracy. The load / displacement characteristic due to the sag becomes a characteristic that is translated in parallel except for both ends.

FIG. 8 shows a load-displacement characteristic in which the set of the coil spring is corrected. In the figure, a spring A is a coil spring 9 for low load, and since this stress is small, the set is settled to a level that does not affect the accuracy. Therefore, the set of the coil spring 9 (spring A) can be ignored.
The spring B is a coil spring 15 for a high load, and there is a great possibility that settling that lowers the detection accuracy will occur.

[0024] During the early spring B when given an arbitrary load F _C to the spring B displacement of (absence of sag) and L _B,
This is detected in advance and stored in the determination circuit 16. On the other hand, the displacement of the spring A when given an arbitrary load F _C in the spring A and L _A. Next, an arbitrary load F _C is applied to the spring B having a set, and the displacement L _B ′ of the spring B at that time is detected. Based on this detection result, the amount of change [Delta] L of the displacement based on the sag can be determined by ΔL = L _B '-L _B.

The change amount ΔL described above, the switching points in FIG. 5, and the outputs of the displacement detecting elements 6 and 12 are provided from the determination circuit 16 to the correction circuit 17. Correction circuit 17
Performs a predetermined operation based on these inputs, and
Outputs linear characteristics of load and sensor output.

FIG. 9 shows a load sensor according to the present invention mounted on a vehicle (4).
An example in which the present invention is applied to transfer of a WD vehicle is shown. The transfer is used to transmit power from the engine to the rear wheels and selectively to the front wheels to switch between 4WD drive and 2WD drive. The transfer includes a transfer case 20, a shaft 21 that transmits engine output and serves as a drive shaft for rear wheels,
Clutch 2 provided between the clutch and the sprocket 22d
2. A pressure plate 23 for pressing the multi-plate clutch 22, a lever 24 supported on a pivot bearing 25 of the transfer case 20 for transmitting a thrust force to the pressure plate 23, and one end of the lever 24 is engaged with the other end of the lever 24. A link 26, a pressing member 27 which is engaged with the other end of the link 26 and is movable in the direction of arrow X, a load sensor 28 disposed adjacent to the pressing member 27, a cylinder portion 29 for accommodating the load sensor 28, a rod A thrust force generator 31 for transmitting a thrust force to a movable plate 2 (not shown) of a load sensor 28 via a drive shaft 30, a front wheel drive shaft 32, and a torque for transmitting the rotational force of the multi-plate clutch 22 to the front wheel drive shaft 32. The chain 33 is provided.

The multi-plate clutch 22 includes inner clutch plates 22 attached at regular intervals in the axial direction of the shaft 21.
a, a clutch casing 22b loosely fitted to the shaft 21 so as to cover the inner clutch plate 22a, and an outer clutch plate 22c fixed to the inner peripheral surface of the clutch casing 22b so as to be alternately positioned on the inner clutch plate 22a. It has. One end of the multi-plate clutch 22 is connected to a sprocket 22 d that meshes with the chain 33. The front wheel drive shaft 32 includes a chain 33
The sprocket 32a meshes with the sprocket 32a.

A motor 34 is provided for driving the thrust force generator 31, and its rotation is controlled by reduction gears 35, 3.
The power is transmitted to the thrust force generator 31 via the first and second thrusters 37. A control unit 38 is provided for controlling the motor 34. When the driver performs a button operation (or lever operation) for switching between 2WD and 4WD,
The rotation speed control and the on / off control of the motor 34 are executed in accordance with an instruction issued according to the operation.

Next, the operation of the transfer having the above configuration will be described. When used as 2WD, the driving force of the engine is transmitted to the rear wheels via the shaft 21, but since the multi-plate clutch 22 is not functioning, the outer clutch plate 22c does not rotate, and Shaft 3
No driving force is transmitted to 2. When the driver performs an operation to switch to 4WD, the instruction is input to the control unit 38,
The control unit 38 rotates the motor 34. Reduction gear 35,
The rotational force of the motor 34 decelerated by 36 and 37 is transmitted to the thrust force generator 31. The thrust force generator 31 converts the rotational force into a thrust force, and transmits the thrust force to the load sensor 28 via the rod 30. The load sensor 28 detects the applied thrust force and sends the detected value to the control unit 38 as detection data.

The thrust force generated by the thrust force generator 31 is sequentially transmitted to the pressing member 27 and the link 26 via the load sensor 28, and the other end of the lever 24 is pushed leftward in the drawing. As a result, the pressure plate 23 has the inner clutch plate 22a and the outer clutch plate 22c.
And the clutch casing 22b is
And rotate together. The rotation of the clutch casing 22b is transmitted to the chain 33 via the sprocket 22d, and the front wheel drive shaft 32 rotates. at this point,
The front wheel drive shaft 32 rotates together with the shaft 21,
The state becomes the 4WD state. It should be noted that the degree of coupling between the inner clutch plate 22a and the outer clutch plate 22c of the multi-plate clutch 22 changes in accordance with the thrust force generated by the thrust force generator 31, and the state of transmission of the rotational force to the front wheels can be changed. The control unit 38 compares the detected value of the load sensor 28 with the set value set in the control unit 38 in order to keep the coupling state of the multi-plate clutch 22 at the control value, so that the deviation becomes zero. The number of rotations of the motor 34 is controlled.

In a direct drive type 4WD vehicle,
The thrust axial pressure of the rear wheel shaft 21 is detected by the load sensor 28 and is used for controlling the distribution of the driving force of 4WD. In order to perform the optimal distribution control using the load sensor 28, it is required that a relatively small load can be detected, the load is not affected by temperature and noise, and the load is small and the cost is low. This need is met by using the load sensor of the present invention shown in FIG. In other words, a high-precision control is possible by using a two-stage sensor unit including two elastic members and two movable plates and using an MR element that satisfies the conditions of noise resistance and temperature characteristics. Become.

In the above embodiment, the MR element is used as the displacement detecting element. However, the present invention is not limited to this. If the displacement detecting element has the same characteristics and compactness, The type does not matter.

Further, each of the movable plate 2 and the coil spring 9, and each of the movable plate 3 and the coil spring 15 may be fixed or may be in a state of simply being in contact with each other.

Further, the magnets 4 and 10 may be electromagnets. Further, the positional relationship between the magnet and the pole piece and the displacement detecting element may be changed.

In the above embodiment, the electronic circuit 14
Is provided in the housing 1, but it is also possible to provide a structure that is installed at a place away from the housing 1 and connected to the displacement detection element by a lead wire (or a cable).

[0036]

As is apparent from the above description, according to the load sensor of the present invention, a two-stage configuration in which a sensor mechanism composed of a movable member and an elastic member is arranged in series, and two sensor mechanisms are provided in accordance with an applied load. It is operated continuously to detect the amount of displacement (movement) of each movable member, so that the requirements of noise resistance and temperature characteristics can be satisfied, and it can be applied to vehicles to increase the load in a wide range. It can be detected with accuracy.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a load sensor according to the present invention.

FIG. 2 is an explanatory diagram showing a change of each part according to a load F of a load sensor of the present invention.

FIG. 3 is a characteristic diagram showing a relationship between an applied load F and a displacement L of each movable plate.

FIG. 4 is a block diagram illustrating a detailed configuration of the electronic circuit of FIG. 1;

FIG. 5 is an explanatory diagram showing the determination of a characteristic switching point of the determination circuit of FIG. 4;

FIG. 6 is an explanatory diagram illustrating a correction process of the correction circuit in FIG. 4;

FIG. 7 is a characteristic diagram showing a load-displacement characteristic in the case where there is no sag correction of a coil spring.

FIG. 8 is a characteristic diagram showing load-displacement characteristics of the coil spring in which sag has been corrected.

FIG. 9 shows a vehicle (4) to which the load sensor according to the present invention is applied.
It is sectional drawing which shows the transfer of a WD vehicle).

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Housing 2 Movable plate 3 Movable plate 4 Magnet 5a, 5b, 11a, 11b Magnetic pole piece 6, 12 Displacement detection element 7 Supporting piece 8 Base part 9, 15 Coil spring 10 Magnet 14 Electronic circuit 16 Discrimination circuit 17 Correction circuit

Continued on the front page (72) Inventor Yasuhiro Niikura 2418 Washizu, Kosai-shi, Shizuoka Prefecture Within Fuji Univance Co., Ltd. (72) Inventor Nobuyoshi Morita 192-265, Wago-cho, Hamamatsu-shi, Shizuoka Prefecture

Claims (6)

[Claims] 1. A load sensor that receives a load and outputs a detection signal corresponding to the load, wherein the first elastic member has a first elastic coefficient, and the first elastic member receives the load and deforms the first elastic member. A first displacement member that is displaced in a predetermined direction while the first elastic member is deformed in response to a displacement of the first displacement member when the deformation of the first elastic member reaches a predetermined value. An elastic deformation inhibiting member for inhibiting further deformation, a second elastic member having a second elastic coefficient larger than the first elastic coefficient, and a deformation of the first elastic member is equal to or less than the predetermined value. When,
The displacement of the first displacement member is received via the first elastic member, and when the deformation of the first elastic member reaches the predetermined value, the displacement of the first displacement member is converted to the elastic deformation. A second displacement member that is displaced in the predetermined direction while deforming the second elastic member by receiving through the prohibition member; and detecting the displacement of the first and second displacement members and detecting the detection signal. A load sensor, comprising: a detection unit that outputs a signal. 2. The first and second elastic members include a first elastic member.
And a second coil spring, wherein the first displacement member is a first plate provided at one end of the first coil spring, and wherein the second displacement member is a first coil. A second plate provided at the other end of the spring and one end of the second coil spring, wherein the elastic deformation inhibiting member is positioned in parallel with the first coil spring, and the first coil spring 2. A plate or a tubular member having one end which contacts the first plate when deformed, and which is fixed to the second plate.
The load sensor as described. 3. The detecting means comprises: first and second magnetic sources provided on the first and second plates;
First and second pole pieces provided on the first and second plates to form a magnetic circuit in combination with the first and second magnetic sources, and the first and second pole pieces The first and second displacement detecting elements for detecting displacement of the first and second displacement detecting elements, and an arithmetic circuit for outputting a detection signal based on a change in an output voltage of the first and second displacement detecting elements. Load sensor. 4. The arithmetic circuit calculates a low load value based on a change in output voltage of the first displacement detection element, and applies a high load value based on a change in output voltage of the second displacement detection element. 3. The load sensor according to claim 2, wherein the load sensor calculates. 5. The load sensor according to claim 3, wherein said arithmetic circuit has a correction circuit for correcting a set of said second coil spring. 6. The load sensor according to claim 1, wherein the first plate is displaced by receiving a thrust force applied to a pressing plate of a multi-plate clutch of a transfer for a four-wheel drive vehicle as the load.