JPH0534368A - Magnetic fluid type acceleration sensor - Google Patents

Abstract

PURPOSE:To obtain an acceleration sensor which can detect acceleration accurately without the lowering of detection accuracy as caused by excessive acceleration even when it is added. CONSTITUTION:Four-stepped pins 60 are fixed on a main housing 10 at an equal angle interval and tips thereof are extended in such a manner as to be allowed to abut a part between magnetic poles of a permanent magnet 50. Even when excessive accelration is applied, the tip of the stepped pin 60 abuts the permanent magnet 50 to regulate a moving limit thereof so that a magnetic fluid 34 is stirred up so intensely as to cause a density distribution of magnetic fine particles thereby preventing the lowering of detection accuracy of acceleration. In addition, as the tip part of the stepped pin 60 is tapered, there is no blocking of the flow of the magnetic fluid 34 thereby achieving a detection with better acceleration without disturbing a relationship between the acceleration and the moving value of the permanent magnet 50.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic fluid type acceleration sensor, and more particularly to improvement of its detection accuracy.

[0002]

2. Description of the Related Art As a magnetic fluid type acceleration sensor, for example, there is one disclosed in Japanese Patent Application Laid-Open No. 2-90061. This acceleration sensor includes a housing 200 made of a non-magnetic material as shown in FIG. Housing 20
A space 202 is formed in the center of 0, and a magnetic fluid 204 is enclosed in the space 202. In the magnetic fluid 204, a permanent magnet 20 having a disc shape and having two pairs of magnetic poles is formed.
6 is suspended. Further, notches 20 extending toward the space 202 are provided at four locations on the outer peripheral surface of the housing 200.
8 are formed, and in each notch 208, the permanent magnet 2 is formed.
A Hall element 210 is provided near each magnetic pole 06. The Hall element 210 outputs a higher voltage as the distance to each magnetic pole becomes shorter, and each is connected to an acceleration calculation device (not shown) via a differential amplifier.

A large number of magnetic fine particles are dispersed in the magnetic fluid 204, and these magnetic fine particles are uniformly dispersed in the absence of a magnetic field gradient, but gradually increase toward a larger magnetic field if a magnetic field gradient is applied. It has the property of moving and becoming a density distribution according to the magnetic field gradient and becoming stable. Further, the pressure of the magnetic fluid increases as the density of the magnetic fine particles increases.

Arc-shaped isomagnetic lines are generated around the N and S poles of the permanent magnet 206, and the density of the magnetic fine particles is also equal on the isomagnetic lines. A concave portion 212 having an inner side surface that curves along substantially the same magnetic line is formed on the circumferential surface of the housing 200, and magnetic fine particles densely packed around each magnetic pole are accommodated in the concave portion 212. There is.
Therefore, if the permanent magnet 206 is eccentric with respect to the housing 200, the radial gap between the permanent magnet 206 and the housing 200 becomes non-uniform, and the pressure acting on the inner peripheral surface of the housing 200 increases in the portion where the gap is small. The reaction force of this pressure returns the permanent magnet 206 to the center of the housing 200. When the permanent magnet 206 rotates by a small angle, a pressure imbalance occurs in the recess 212, and this imbalance returns the permanent magnet 206 to the original phase. Since the magnetic fluid 204 has the same function as the elastic body, the magnetic fluid will be treated as an elastic body hereinafter.

In the above acceleration sensor, when acceleration is applied to the housing 200 fixed to the vehicle body, the permanent magnet 206 is moved by the inertial force in the direction opposite to the acceleration direction, and the inertial force and the elastic force of the magnetic fluid 204 are combined. Stop at the equilibrium point. Thus, the displacement of the permanent magnet 206 in the space 202 changes the output voltage of each Hall element 210. For example, if the permanent magnet 206 moves to the right as shown by the chain double-dashed line in FIG. 10, the output voltage of the Hall element 210 on the right side increases as the S pole approaches, while the output of the Hall element 210 on the left side increases. The voltage decreases with the separation of the south pole. Then, the output voltage of each of these Hall elements 210 is input to the respective differential amplifiers so that both Hall elements 210
The difference between the output voltages of the two is detected. Further, the difference in output voltage between the other pair of Hall elements 210 positioned in the vertical direction is detected in the same manner, and the difference in output voltage is input to the acceleration calculation device to calculate the magnitude and direction of acceleration. To be done.

[0006]

However, in the acceleration sensor described above, as the acceleration increases, the moving distance and moving speed of the permanent magnet 206 in the space 202 increase, and the magnetic fluid 204 is vigorously agitated. Therefore, there is a problem that the stable state of the magnetic fine particles is broken and the magnetic fine particles diffuse, and the elastic force characteristics of the magnetic fluid 204 change. That is, in the stable state of the magnetic fine particles, the elastic force of the magnetic fluid 204 was highest near the magnetic poles and lowest near the sidewalls of the space 202.
The elastic force of is averaged out. As a result, the elastic force in the vicinity of the side wall of the space 202 of the magnetic fluid 204 becomes higher than that in the stable state, and the relative movement amount of the permanent magnet 206 when a small acceleration is applied to the housing 200 decreases, and the acceleration There is a problem that the detection accuracy is lowered.

In view of this problem, an object of the present invention is to obtain an acceleration sensor which can always accurately detect the acceleration without destroying the stable state of the magnetic fine particles even when a large acceleration is applied. It is a thing.

[0008]

The gist of the present invention is to have a housing made of a non-magnetic material, a magnetic fluid enclosed in the housing, and a plurality of magnetic poles, which are suspended in the magnetic fluid. A permanent magnet, magnetic detection means provided in the vicinity of each magnetic pole of the permanent magnet for detecting displacement of the permanent magnet in the housing, and acceleration of the housing is calculated based on an output signal from the magnetic detection means. In a magnetic fluid type acceleration sensor including acceleration calculation means, a housing made of a non-magnetic material is provided with a plurality of movement limit defining projections that abut on a side surface of a permanent magnet and define a travel limit thereof, and the movement limit defining projections are provided. Is less than 1/3 of the thickness of the permanent magnet. The movement limit defining projection is preferably provided at a position deviated from the vicinity of the magnetic pole of the permanent magnet, but may be provided near the magnetic pole or may be provided along the entire circumference of the permanent magnet along its outer circumference.

[0009]

In the acceleration sensor configured as described above, when a large acceleration is applied to the housing,
The permanent magnet comes into contact with the movement limit regulation protrusion and does not move any further. The movement limit defining protrusion does not hinder the movement of the permanent magnet within the detection required range, but its size and position are determined so as to prevent the permanent magnet from moving beyond the detection required range.

Further, since the thickness of the movement limit defining protrusion is set to be ⅓ or less of the thickness of the permanent magnet, the adverse effect due to the formation of the movement limit defining protrusion can be suppressed. For example,
When the movement limit defining protrusion is provided at a position facing the magnetic pole, the gap between the permanent magnet and the housing is locally narrowed by the movement limit defining protrusion, and the elastic coefficient of the magnetic fluid is locally increased. However, the relationship between the acceleration applied to the housing and the amount of movement of the permanent magnet is disturbed, which may reduce the accuracy of acceleration measurement. Further, when the movement limit defining projection is provided at a position facing the portion between the magnetic poles, the elastic coefficient of the magnetic fluid is hardly affected but the flow of the magnetic fluid is hindered. When one magnetic pole approaches the housing, the space between the magnetic pole and the housing becomes narrower, so it is necessary for the magnetic fluid to flow out of the space. When the movement limit defining protrusion is provided, this may prevent the magnetic fluid from flowing out, which may deteriorate the responsiveness. In order to reduce these adverse effects, the thickness of the movement limit defining protrusion may be reduced, and in the present invention, the thickness is set to 1/3 or less.

[0011]

In the acceleration sensor according to the present invention,
Even if an excessive acceleration exceeding the required detection range is applied, the permanent magnet is prevented from moving more than necessary, which prevents the magnetic fluid from being vigorously stirred and destroys the density distribution of the magnetic particles. The elastic force of the fluid is always kept in a proper state. Therefore, the permanent magnet always moves accurately by an amount corresponding to the acceleration, and the accuracy of detecting the acceleration is improved.

Moreover, conventionally, all the accelerations applied to the acceleration sensor including the excessive acceleration are detected, and only the value within the detection necessary range is taken out by the structure of the electronic circuit. In the acceleration sensor according to the present invention, since the movement limit of the permanent magnet can be defined in advance so that only the acceleration in the required range is detected, it is necessary to limit the acceleration detection range by the configuration of the electronic circuit. Absent. Therefore, the circuit configuration of the acceleration calculation means is simplified, and the device cost is reduced.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described in detail below with reference to the drawings. 1 and 2, reference numeral 10 denotes a main housing made of aluminum. The main housing 10 has a bottomed cylindrical shape with a stepped fitting hole 16 formed in the center thereof. On the side wall of the small-diameter hole of the fitting hole 16, two sets of arc-shaped recesses 18, 20, 22, 24 facing each other are provided.
While the sub-housing 2 is formed in the large-diameter hole.
6 is fitted, and the opening of the fitting hole 16 is closed. The sub-housing 26 is made of aluminum similarly to the main housing 10, and is integrally fixed to the main housing 10 by a plurality of screws 30 made of a non-magnetic material at a flange portion outward in the radial direction. Thereby, the space 32 having the recesses 18 to 24 is formed in the main housing 10.

A magnetic fluid 34 is enclosed in the space 32. The magnetic fluid 34 is, for example, magnetic fine particles 36 (see FIG. 3) such as manganese zinc ferrite dispersed in isoparaffin. As shown in FIG. 2, a cylindrical protrusion 40 extending at a right angle is formed in the central portion of the sub-housing 26. The upper opening of the axial hole 42 of the protrusion 40 communicates with the atmosphere, while the lower opening penetrates the sub housing 26 and communicates with the space 32. Space 32 from top opening
The magnetic fluid 34 is injected into the inside, and the upper opening is closed by the rubber plug 44, and then the cap 46 is tightened on the upper end portion of the protrusion 40, whereby the magnetic fluid 34 is stored in the space 32.
Enclosed inside. The O-ring 48 seals the gap between the main housing 10 and the sub-housing 26 to prevent the magnetic fluid 34 from leaking from the space 32.

A permanent magnet 50 is suspended in the magnetic fluid 34. The permanent magnet 50 has a disc shape, and its length in the thickness direction is slightly shorter than the height of the space 32. The permanent magnet 50 has two pairs of magnetic poles, and the magnetic poles are suspended so as to face the recesses 18 to 24 of the space 32.

3 and 4 schematically show a large number of magnetic fine particles 36 dispersed in the magnetic fluid 34. The magnetic fine particles 36 are normally dispersed uniformly as shown in FIG. 4, but when a magnetic field gradient is applied by the magnetic poles, the magnetic fine particles 36 shown in FIG.
As shown in (3), it has a characteristic that it is attracted to the periphery of a magnetic pole having a large magnetic field and becomes stable. Since arc-shaped isomagnetic lines centering on the magnetic poles are formed around each magnetic pole, the isopycnic lines of the magnetic fine particles 36 are also arc-shaped centering on the magnetic poles.
The recesses 18 to 24 are formed along this isopycnic line, and the magnetic fine particles 36 are concentrated in the vicinity of the magnetic poles, and the density of the magnetic fine particles 36 is higher near the magnetic poles of the permanent magnet 50 in the space 32. The density becomes lower near the side wall of the. Since the pressure of the magnetic fluid 34 increases as the density of the magnetic fine particles 36 increases, the pressure of the magnetic fluid 34 increases as shown by the solid line in the graph of FIG.
Of the concave portions 18 to 24, which are higher in the vicinity of the magnetic pole and are separated from the magnetic pole.
It becomes lower toward the inner surface of. The isobars of the magnetic fluid 34 are formed along the inner side surfaces of the recesses 18 to 24, and the permanent magnet 50 is held in the center of the space 32 as if by an elastic body, and is in a state where rotation is prevented.

In the main housing 10, four stepped female screw holes 58 penetrating in the radial direction are formed at equal angular intervals, and stepped pins 60 are formed in each of these female screw holes 58.
Is fastened at the male screw portion formed at the base end thereof and is integrally fixed to the main housing 10.
The tip of each stepped pin 60 has a diameter smaller than ⅕ of the thickness of the permanent magnet 50, and extends into the space 32 between the four adjacent recesses 18 to 24. In the present embodiment, 1.
If an acceleration greater than 5 G is applied, one of the four stepped pins 60 abuts the outer peripheral surface of the permanent magnet 50 to define the movement limit of the permanent magnet 50, as shown by the chain double-dashed line in FIG. , The position and length of the stepped pin 60 are set. An O-ring 64 is provided on a part of the outer peripheral surface of the stepped pin 60 to prevent the magnetic fluid 34 from leaking from the female screw hole 58.

In this embodiment, the stepped pin 60 constitutes a movement limit defining projection.

As is apparent from FIG. 2, a protrusion 66 is formed on the lower end surface of the main housing 10, and a print plate 70 is attached to the protrusion 66 by a screw 68 made of a nonmagnetic material. The print plate 70 is made of glass epoxy, and a processing circuit 72 shown by a broken line is formed on the lower surface thereof. The processing circuit 72 is provided with a plurality of terminals, some of which are connected to a power source and ground (not shown). In addition, the processing circuit 72
Includes a plurality of differential amplifiers.

Further, on the outer peripheral surface of the main housing 10, four notches 74 extending toward the space 32 are formed at equal angular intervals. These four cutouts 74 are formed at positions corresponding to the recesses 18 to 24, respectively. Inside the cutouts 74, the holes are formed facing the recesses 18 to 24, that is, close to the magnetic poles of the permanent magnet 50. Element 8
0, 82, 84 and 86 are adhesively fixed. As shown in FIG. 2, the terminals of the Hall elements 80 to 86 are soldered to the print plate 70.
0 to 86 output the same voltage when the permanent magnet 50 is stationary and in a fixed position as shown in FIG. 1, but each magnetic pole approaches or separates due to the movement of the permanent magnet 50 in the space 32. By doing so, the output voltage is increased or decreased. The output voltages of the Hall elements 80 to 86 are input to the differential amplifier of the processing circuit 72 via the print plate 70, and the processing circuit 72 outputs signals corresponding to the moving direction and the moving amount of the permanent magnet 50.

In the present embodiment, the Hall elements 80-8
6, the print plate 70 and the processing circuit 72 constitute magnetic detection means for detecting the displacement of the permanent magnet 50.

The main housing 10 and the sub housing 26 are covered with an iron shield cover 90 and a shield plate 92. The shield cover 90 is fixed to the main housing 10, and the flanges formed at four positions on the opening periphery of the shield cover 90 and the shield plate 92 are fixed by the screws 94, so that the opening of the shield cover 90 is closed. Has been done. Further, a through hole 96 is formed in a part of the side wall of the shield cover 90, and a grommet 98 made of rubber is attached. The lead wire bundles 100 and 102 of the processing circuit 72 are led out to the outside through the grommet 98. There is.

The lead wire bundles 100 and 102 are connected to an arithmetic processing unit 104 provided outside the shield cover 90. The arithmetic processing unit 104 calculates the magnitude and direction of the acceleration acting on the permanent magnet 50 from the signal output from the processing circuit 72.

In the present embodiment, the arithmetic processing unit 104
Constitutes the calculation means.

The acceleration sensor constructed as described above is used by being fixed to the vehicle body. When the vehicle body is accelerated, acceleration is applied to the main housing 10, and the permanent magnet 50 is moved in the space 32 in the direction opposite to the acceleration by the inertial force. When the inertial force and the elastic force of the magnetic fluid 34 (apparent elastic force generated based on the pressure distribution) are in equilibrium, they stop. The moving amount and moving direction of the permanent magnet 50 at this time are converted into the magnitude and direction of the acceleration.

For example, if the permanent magnet 50 moves rightward in the right-left direction (referred to as the X direction) as indicated by the chain double-dashed line in FIG.
And the one S pole of the permanent magnet 50 approach each other, and the Hall element 8
The output voltage of 6 increases. Further, since the other S pole of the permanent magnet 50 moves away from the Hall element 82 close to the recess 20, the output voltage of the Hall element 82 decreases. The output voltages of the Hall elements 82 and 86 are input to the differential amplifier of the processing circuit 72, and the difference between the output voltages of the Hall elements 82 and 86, that is, the differential output voltage V substantially proportional to the movement amount of the permanent magnet 50 in the X direction. _X is required. In this case, since there is no difference in the output voltage between the Hall element 80 facing the recess 18 and the Hall element 84 facing the recess 22, the vertical differential output voltage V _Y in the Y direction is zero. Also,
When the permanent magnet 50 moves in both the X and Y directions, differential output voltages V _X and V _Y in both directions are output,
These differential output voltages V _X and V _Y are calculated by the arithmetic processing unit 104.
By inputting into, the magnitude of acceleration and the direction of acceleration are calculated in the arithmetic processing unit 104.

When the acceleration applied to the vehicle body is larger than 1.5 G, the permanent magnet 50 abuts on any of the four stepped pins 60, and the movement limit thereof is defined. In this way, the movement limit of the permanent magnet 50 is not defined, and the housing 1
When it is allowed to remarkably approach the inner peripheral surface of 0 or come into contact with the inner peripheral surface of 0, the flow velocity of the magnetic fluid 34 is increased and the magnetic fluid 34 is vigorously stirred and the magnetic fine particles 36
The density distribution of is approaching a uniform state. As a result, the pressure distribution of the magnetic fluid 34 changes as shown by the broken line in FIG. 5, and it becomes difficult for the permanent magnet 50 to move in a region where the acceleration is small, and the accuracy of acceleration detection is reduced. This inconvenience is prevented.

Further, in the conventional acceleration sensor, the movement limit of the permanent magnet is not specified, and the acceleration is calculated for all output voltages output from the Hall element. Therefore, the detection result of the acceleration becomes a straight line as shown in the graph of FIG. 6, and the processing circuit is configured so that only the value in the detection necessary range is extracted from the detection result. On the other hand, in the present embodiment, since the movement limit of the permanent magnet is defined in advance so that only the required range is detected, it is not necessary to limit the required detection range of acceleration by a complicated circuit configuration. That is, in the present embodiment, the required detection range of acceleration is set to −1.5 G to 1.5 G, and the stepped pin 60 prevents the permanent magnet 50 from moving beyond that range. As shown in FIG. 7, the acceleration can be detected only in the range of ± 1.5 G.

In the above embodiment, since the movement limit defining projections are the four stepped pins 60 that can come into contact with the portions between the magnetic poles of the permanent magnet 50, the permanent magnet 50 has a stepped pin 60. It is unavoidable that the movable range varies depending on the direction. Therefore, it is desirable to provide as many stepped pins 60 as possible, and as an ultimate mode thereof, as shown in FIGS. 8 and 9, a ring-shaped disc capable of contacting the entire circumference of the permanent magnet may be provided. It is possible. 8 and 9, the same members as those in the above embodiment are designated by the same reference numerals, and detailed description thereof will be omitted.

In this embodiment, the main housing 1
The fitting hole 152 of 50 is a stepped hole, and the sub housing 1
An annular fitting protrusion 156 formed in the lower portion of the fitting hole 54 is adapted to fit into a medium-diameter hole portion of the fitting hole 152, and the fitting protrusion 156 and the shoulder surface of the fitting hole 152 are connected to each other. A ring-shaped disc 158 is sandwiched between the two. Main housing 1
50 side wall of fitting hole 152 and sub housing 154
On the side wall of the fitting protrusion 156, four recesses are formed in the same phase, and four recesses 162 to 168 are formed in the space 160 formed by fitting the two. The inner peripheral surface 174 of the disk 158 is the space 160.
Has a diameter slightly smaller than the circle inscribed in the non-recessed portion. The disk 158 abuts the permanent magnet 50 on the inner peripheral surface 174 thereof to define the movement limit of the permanent magnet 50. The circumference of the disk 158 functions as a movement limit defining protrusion, and the thickness of the disk 158 is the same as that of the permanent magnet 5.
It is smaller than 1/10 of the thickness of 0, and the magnetic fluid 3
4 does not impede the flow of fluid and the influence of the pressure of the magnetic fluid 34 acting on the inner peripheral surface of the disk 158 is negligibly small.

Although the two embodiments of the present invention have been described above, the number and shape of the movement limit defining projections can be changed as appropriate. Further, the shape of the permanent magnet and the shape of the space in which it is enclosed may be other shapes. For example, in an acceleration sensor in which a permanent magnet is movable only in the X direction or the Y direction and only one direction of acceleration is detected, the permanent magnet and the space can be rectangular, and the movement in one direction is limited. The effect of the present invention can be obtained by defining by the defining protrusion.

Besides, the present invention can be implemented in various modified and improved modes based on the knowledge of those skilled in the art.

[Brief description of drawings]

FIG. 1 is a plan sectional view (a sectional view taken along line I-I of FIG. 2) showing an acceleration sensor according to an embodiment of the present invention.

FIG. 2 is a front sectional view of the acceleration sensor.

FIG. 3 is an explanatory view conceptually showing a dense state of magnetic fine particles of a magnetic fluid.

FIG. 4 is an explanatory view conceptually showing a dispersed state of magnetic fine particles of a magnetic fluid.

FIG. 5 is a graph showing a pressure distribution in a magnetic fluid in the acceleration sensor.

FIG. 6 is a graph showing an example of a detection range of acceleration by a conventional acceleration sensor.

FIG. 7 is a graph showing an example of a detection range of acceleration by the acceleration sensor of this embodiment.

FIG. 8 is a plan sectional view (a sectional view taken along the line VIII-VIII in FIG. 9) showing an acceleration sensor according to another embodiment of the present invention.

FIG. 9 is a front sectional view of the acceleration sensor.

FIG. 10 is a plan sectional view showing an example of a conventional acceleration sensor.

[Explanation of symbols]

 10 Main Housing 34 Magnetic Fluid 50 Permanent Magnet 60 Stepped Pin 70 Print Plate 72 Processing Circuit 80 Hall Element 82 Hall Element 84 Hall Element 86 Hall Element 104 Processing Unit 150 Main Housing 158 Disc

Claims (1)

Claim: What is claimed is: 1. A housing made of a non-magnetic material, a magnetic fluid enclosed in the housing, a permanent magnet having a plurality of magnetic poles and suspended in the magnetic fluid, Magnetic detection means provided near each magnetic pole of the permanent magnet for detecting displacement of the permanent magnet in the housing, and acceleration calculation means for calculating acceleration of the housing based on an output signal from the magnetic detection means. In the magnetic fluid type acceleration sensor including, in the housing made of a non-magnetic material, the movement limit defining projections that abut the side surface of the permanent magnet and define the travel limit are provided at a plurality of positions, and the thickness of the travel limiting specification projections. Is 1/3 or less of the thickness of the permanent magnet.