Electromagnetic impedance sensor and passenger protection system

An electromagnetic impedance sensor detects an object made of conducting material or soft magnetic material with contact-free. The sensor includes: a detection coil; and a detection circuit for supplying electricity to the coil and for measuring electromagnetic impedance change in the coil. The detection coil includes multiple coil portions provided by one wire. One coil portion has a side adjacent to a corresponding side of another coil portion. The side and the corresponding side extend along with a direction, and the side has a current flowing direction, which is the same as the corresponding side.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is based on Japanese Patent Applications No. 2007-15431 filed on Jan. 25, 2007, and No. 2007-308698 filed on Nov. 29, 2007, the disclosures of which are incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to an electromagnetic impedance sensor and a passenger protection system.

BACKGROUND OF THE INVENTION

An electromagnetic impedance sensor for detecting a detection object by using a coil, i.e., a search coil. Specifically, when the detection object is made of conductor or soft magnetic material, and the detection object approaches the search coil, an impedance of the search coil changes, so that the detection object is detected based on impedance change. This sensor is disclosed in, for example, JP-A-H09-175319.

The conventional sensor has a difficulty that detection sensitivity may disperse with reference to a position of the detection object in a detection space when the detection space is comparatively large in view of dimensions of the detection object. Here, the sensor can detect the object in the detection space.

This is because the detection sensitivity fluctuates with reference to a relationship between the position of the detection object in the space and the coil arrangement of the search coil. The search coil is arranged in the detection space to face the detection space in order to cover the detection space. Specifically, since magnetic flux at each portion of the detection space may disperse along with a direction in parallel to a coil surface of the coil, the detection sensitivity fluctuates.

Thus, it is required for the sensor to have high detection accuracy.

SUMMARY OF THE INVENTION

In view of the above-described problem, it is an object of the present disclosure to provide an electromagnetic impedance sensor. It is another object of the present disclosure to provide a passenger protection system.

According to a first aspect of the present disclosure, an electromagnetic impedance sensor detects an object with contact-free. The object is made of conducting material or soft magnetic material. The sensor includes: a detection coil having a coil surface, which faces a detection area in which the object is disposed; and a detection circuit for supplying alternating electricity to the detection coil and for detecting the object by measuring change of an electromagnetic impedance in the detection coil. The detection coil includes a plurality of coil portions, which are provided by one wire. Each coil portion is disposed on the coil surface to have a predetermined arrangement. The plurality of coil portions is sequentially arranged along with a first direction.

In the above system, the passenger protection element surely functions based on the signal from the electromagnetic impedance sensor, which has detection accuracy.

According to a second aspect of the present disclosure, a passenger protection system includes: the electromagnetic impedance sensor according to the first aspect of the present disclosure; a collision determination element for determining collision between the vehicle and an external body based on an output from the sensor; and a passenger protection element for protecting an passenger of a vehicle. The passenger protection element functions based on determination of the collision determination element.

In the above system, the passenger protection element surely functions based of the signal from the electromagnetic impedance sensor, which has detection accuracy.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

First Embodiment

An electromagnetic impedance sensor according to a first embodiment of the present disclosure is shown inFIGS. 1 and 2. The sensor is, for example, an eddy-current detection sensor for detecting a conductor.

FIG. 1shows a circuit of the sensor. The sensor includes a detection circuit2and a detection coil4. The detection circuit2energizes the detection coil to supply high frequency current having a high frequency in a range between a few kHz and a few MHz. Further, the detection circuit2detects supply current change in accordance with impedance change of the coil4. The coil surface, i.e., the coil opening surface of the coil4is arranged to face a detection space (not shown).

The supply current change is detected by measuring a voltage drop of a current detecting resistor. Alternatively, the inductance of the coil4and the capacitance of a capacitor connecting to the coil4may provide a self-oscillation circuit such as a Colpitts circuit, and the supply current change is detected by measuring frequency change of the self-oscillation circuit. A capacitor may be connected in parallel to or in series with the coil4so that the voltage change and/or the current change in the coil4increases. Further, a driving coil for forming alternating electromagnetic field may be arranged in the detection space in addition to the detection coil4. The detection coil4may detect an alternating voltage generated by electromagnetic induction of the alternating electromagnetic field.

The received alternating voltage is detected and smoothed to obtain the amplitude and/or the frequency of the alternating voltage so that change of the electromagnetic impedance of the detection coil4is detected. When the conductor approaches the detection coil4, the electromagnetic impedance is changed (e.g., reduced) by the eddy current loss. When the soft magnetic material approaches the detection coil4, the electromagnetic impedance is also changed (e.g., increased).

The detection circuit2for the electromagnetic impedance sensor may be a conventional circuit.

The detection coil4is shown inFIG. 2. The coil4includes a conductive wire1with an insulation coat for providing the coil4. The conductive wire1has a first end as a start terminal or start point30of the coil4and a second end as an end terminal or end point40.

The coil4includes longitudinal sides11,13,15,17,19,21,23,25and latitudinal sides12,14,16,18,20,22,24,26, which provide a figure eight. Specifically, each longitudinal side11,13,15,17,19,21,23,25extends along with a Y-direction, which is perpendicular to an arrangement direction of the figure eight. Each latitudinal sides12,14,16,18,20,22,24,26extends along with a X-direction, which is parallel to the arrangement direction of the figure eight. The longitudinal sides11,13,15,17,19,21,23,25and the latitudinal sides12,14,16,18,20,22,24,26are alternatively arranged, respectively. The end terminal40is disposed adjacent to the start terminal30. Here, the X-direction represents the arrangement direction and the latitudinal direction, and the Y-direction represents the longitudinal direction. InFIG. 2, i represents a current flowing direction at a certain time in a certain half-wave period.

Thus, the coil4provides first and second portions5,6, each of which has a two-turn coil. The first portion5includes the longitudinal sides11,19,13,21and the latitudinal sides12,20,18,26, and the second portion6includes the longitudinal sides15,23,17,25and the latitudinal sides16,24,14,22.

Since the first and second portions5,6are adjacent to each other, the longitudinal sides13,21,17,25are almost overlapped or adjacent to each other so that they13,21,17,25are arranged in parallel to each other. Accordingly, the longitudinal sides13,21,17,25also provide consecutive sides. In this embodiment, one conductive wire1provides the detection coil4having a rectangular shape with a length L and a width W. At the center of the rectangular shape, four sides13,17,21,25are arranged, and the four sides13,17,21,25are almost in parallel to each other, and have the same current flowing direction. Accordingly, sensitivity at the center portion of the detection coil4is prevented from being reduced, compared with a conventional art. Here, the center portion of the detection coil4is a center portion of an open surface of the coil4, and the sensitivity along with an axis of the coil4is prevented from being reduced. The axis of the coil4is perpendicular to the open surface of the coil4. Thus, the sensitivity of the sensor does not fluctuate so that the sensor has high detection accuracy.

In the conventional art, the sensitivity at the center portion of a detection coil is reduced, since the magnetic flux at the center portion is smaller than that at a periphery portion. Specifically, in a precise sense, the electromagnetic field generated by the detection coil4is provided by vectorial sum of the electromagnetic field generated by each side. Each side as a conductor generates the electromagnetic field around the side. The electromagnetic field near the conductor is stronger than that far from the conductor. A plane on which a detection object is disposed is spaced apart from the opening surface of the coil4by a distance between the plane and the opening surface along with the coil axis of the coil4. Thus, the electromagnetic field along with the coil axis, which is generated by each side, is not reduced, compared with the electromagnetic field along with the plane parallel to the opening surface. However, in the conventional art, as the diameter of the coil increases, the sensitivity at the center portion is much reduced. This difficulty is improved by the construction of the detection coil4shown inFIG. 2. Further, the figure eight coil4is easily formed, i.e., a winding step for forming the coil4is easy to perform.

Although the coil4shown inFIG. 2is a two-turn coil, the number of turns in the coil4may be different from two.

InFIG. 2, the consecutive side13,21and the other consecutive side17,25intersect each other by a predetermined angle. Thus, the electromagnetic field near the consecutive sides13,17,21,25, which is provided by current sum larger than current sum at other portions, is restricted.

Second Embodiment

FIG. 3shows another detection coil4according to a second embodiment of the present disclosure. The coil4further includes third to sixth portions7-10. The third portion7is adjacent to the second portion6in the X-direction. The fourth portion8is adjacent to the first portion5in the Y-direction. Here, the X-direction provides a first arrangement direction, and the Y-direction provides a second arrangement direction. The fifth portion9is adjacent to the second portion6in the Y-direction, and the sixth portion10is adjacent to the third portion7in the Y-direction. The fourth to sixth portions8-10are arranged line-symmetric to the first to third portions5-8. The coil4composed of the first to sixth portions5-10is formed from one wire1.

The coil4is formed such that the first to third portions5-7are arranged in the X-direction, and then, the fourth to sixth portions8-10are arranged in the X-direction, which are adjacent to the first to third portions5-7along with the Y-direction. Thus, the detection coil4having an almost rectangular shape with the length of L and the width of 2 W is formed. In six portions5-10of the coil4, two consecutive sides have the same current flowing direction, and are adjacent to each other. The sensitivity reduction at the center of the coil4is much restricted. Thus, the sensitivity of the sensor does not fluctuate so that the sensor has high detection accuracy.

Third Embodiment

FIG. 4shows the detection coil4according to a third embodiment of the present disclosure. The coil4is formed from one wire1. Specifically, wire arrangement, i.e., winding arrangement inFIG. 4is different from inFIG. 3. However, the coil4has similar arrangement of the portions5-10. Thus, sensitivity reduction at the center of the coil4is much restricted. Thus, the sensitivity of the sensor does not fluctuate so that the sensor has high detection accuracy.

Fourth Embodiment

FIG. 5shows the detection coil4according to a fourth embodiment of the present disclosure. The coil4is formed such that the first portion5is formed by winding the wire1with multiple turns to form a multiple-turn coil, and then, the second portion6is formed by winding the wire1with multiple turns, and so on. When one portion is ended, the wire1is bent at a right angle, and then, next portion is formed. Thus, two consecutive sides in two portions have the same current flowing direction, and are adjacent to each other. Thus, the sensitivity of the sensor does not fluctuate so that the sensor has high detection accuracy.

Fifth Embodiment

FIG. 6shows the detection coil4according to a fifth embodiment of the present disclosure. The coil4has multiple portions, each of which has triangle coil opening surface. The coil4is formed from one wire1, and two consecutive sides in two portions have the same current flowing direction. Thus, the sensitivity of the sensor does not fluctuate so that the sensor has high detection accuracy.

InFIG. 2, to reduce the magnetic field generated by the consecutive sides13,21,17,25, a distance between two consecutive sides may be increased. Specifically, the consecutive sides13,21,17,25may be arranged to broaden the distance therebetween in the X-direction. The distance between two consecutive sides is appropriately determined.

Although each portion5-10of the coil4has a square shape or a triangle shape, each portion may have another shape such as a trapezoid shape, a polygonal shape and a substantial circular shape. For example, when each portion has a substantial circular shape, adjacent two portions may be partially overlapped or partially intersect. Further, each portion may be completely adjacent to each other or overlapped each other.

Sixth Embodiment

An electromagnetic impedance sensor may be used for a lateral collision detector for a vehicle.FIG. 7shows an inside of a door100of a vehicle. The door100includes an outer plate101and an inner plate102. The outer plate101is disposed on an outside of the vehicle, and the inner plate102is disposed on an inside of the vehicle. The inner plate102faces the outer plate101, and is spaced apart from the outer plate101. The detection coil4is mounted on a side of the inner plate102, the side facing the outer plate101.

A pole laterally collides with the door100. Under a lateral collision condition defined in US FMVSS214, the pole has a cylindrical column with a diameter of ten inches (corresponding to 255 mm). The pole is crashed to the door100with a collision speed of 20 mph (corresponding to 32 km/hour). After ten milliseconds from the collision, rate of impedance change of the detection coil4is analyzed. Here, it is required for the sensor to detect the collision within 10 milliseconds in view of passenger protection.

When the pole collides with the collision speed of 20 mph, the outer plate101is deformed to be a shape shown as a dotted line inFIG. 7after ten milliseconds from the collision. Thus, the outer plate101is deformed to be a circular shape corresponding to the pole. A width W1of a concavity corresponding to the deformation of the outer plate101is 240 mm.

Here, the detection coil4has one of four types shown inFIGS. 8A to 8D. The first coil121shown inFIG. 8Ahas a rectangular shape with a longitudinal side of 1440 mm, which is parallel to a vehicle length direction, i.e., a vehicle horizontal direction. The first coil121has no partial coil. The second coil122shown inFIG. 8B, the longitudinal side of the second coil122is 1440 mm, and the coil122has two partial coils122a,122b. Thus, the second coil122corresponds to the coil shown inFIG. 2. The length of each partial coil122a,122bin the vehicle length direction is 720 mm. The third coil123shown inFIG. 8Chas the length of the longitudinal side of 1440 mm, and the coil123has four partial coils123a-123d. The length of each partial coil123a-123din the vehicle length direction is 360 mm. The fourth coil124shown inFIG. 8Dhas the length of the longitudinal side of 1440 mm, and the coil124has six partial coils124a-124f. The length of each partial coil124a-124fin the vehicle length direction is 240 mm.

Each coil121-124is tested under a condition that a collision position of the pole at the door100is shifted. Specifically, the center of the collision position is shifted from the center of the coil121-124to one end of the detection coil4.

The test results are shown inFIG. 9. VIIIA represents the result of the first coil121, VIIIB represents the result of the second coil122, VIIIC represents the result of the third coil123, and VIIID represents the result of the fourth coil124. Zero in the horizontal axis that shows a position from the collision center means that the center position of the pole is disposed at the center of the coil121-124, i.e., a curvature center of the deformed outer plate101is disposed at the center of the coil121-124. The vertical axis shows sensor detection sensitivity, i.e., rate of impedance change of the detection coil4. Minus means that the impedance is reduced. The rate of impedance change is calculated by dividing the impedance after collision by the impedance before collision.

As shown inFIG. 9, when the detection coil4is the first coil121which is a large one coil, the absolute value of the rate of impedance change is about 0.046 in a range between zero and 550 mm.

When the detection coil4is the second coil122, the absolute value of the rate of impedance change is maximized when the collision center is near the center of the detection coil122, so that the sensitivity of the coil122is high. However, as the collision center is displaced from the center of the detection coil122, the detection sensitivity is reduced.

When the detection coil4is the third coil123, the absolute value of the rate of impedance change is changed with a wave pattern. At a certain position, the absolute value of the rate of impedance change in the curve VIIIC is larger than that in the curve VIIIA corresponding to the first coil121. At another certain position, the absolute value of the rate of impedance change in the curve VIIIC is smaller than that in the curve VIIIA. Thus, the detection sensitivity is deviated, and there is some range in which the sensitivity is smaller than that of the first coil121.

When the detection coil4is the fourth coil124, the absolute value of the rate of impedance change is almost constant, i.e., 0.055. Specifically, the absolute value of the rate of impedance change is stabilized without depending on the position of the collision center is disposed. Further, the absolute value of the rate of impedance change in the curve VIIID is always higher than that in the curve VIIIA.

Thus, the width of the partial coil in the horizontal direction of the vehicle is set to be smaller than the width of deformation of the outer plate101caused by the collision of the pole, so that the detection sensitivity is increased. Further, the deviation of the sensitivity with regard to the collision position is reduced.

Thus, when the width of the partial coil in the horizontal direction of the vehicle is set to be smaller than 240 mm, the system can detect the collision of the pole within 10 milliseconds. Further, when the width of the partial coil in the horizontal direction of the vehicle is set to be smaller than 200 mm, the system can detect the collision of the pole within 6 milliseconds.

Seventh Embodiment

By using the above electromagnetic impedance sensor, a passenger protection system for a vehicle is formed.FIG. 10shows the passenger protection system.

The system includes an electromagnetic impedance sensor200, a collision determination device300and a passenger protection device400. The sensor200includes one of sensors shown inFIGS. 1-9. The collision determination device300determines collision between the vehicle and an object on the basis of the output from the sensor200. For example, when the sensor200is mounted on the door1, the collision determination device300determines whether the object collides with the door1. This determination is performed based on the impedance change. The protection device400is, for example, an air bag system. Based on the determination of the determination device300, the protection device400functions.

Here, the partial coil may be a circular coil shown inFIG. 11. The coil4includes a middle portion50, which is almost a middle point of the coil length. The coil4includes an outward coil51as a first coil and a homeward coil52as a second coil. The outward coil51is disposed from the start terminal30to the middle portion50, and the homeward coil52is disposed from the middle portion50to the end terminal40. Thus, a part of the outward coil51and a part of the homeward coil52provide a partial coil, and the other part of the outward coil51and the other part of the homeward coil52provide another partial coil. The outward coil51provides two halfway turns, which are connected to each other. The homeward coil52also provides two halfway turns, which are connected to each other.

The above disclosure has the following aspects.

According to an aspect of the present disclosure, an electromagnetic impedance sensor detects an object with contact-free. The object is made of conducting material or soft magnetic material. The sensor includes: a detection coil having a coil surface, which faces a detection area in which the object is disposed; and a detection circuit for supplying alternating electricity to the detection coil and for detecting the object by measuring change of an electromagnetic impedance in the detection coil. The detection coil includes a plurality of coil portions, which are provided by one wire. Each coil portion is disposed on the coil surface to have a predetermined arrangement. The plurality of coil portions is sequentially arranged along with a first direction.

In the above sensor, since the coil portions are coupled in series with each other, the detection coil commonly supplies the electricity and commonly measures the impedance change of the detection coil. Thus, the circuit construction is simplified.

Further, one wire provides multiple coil portions, so that fluctuation of magnetic flux density is reduced, and detection accuracy of the sensor is improved.

Alternatively, the plurality of coil portions may include one coil portion adjacent to another coil portion. The one coil portion has a side, which is adjacent to a corresponding side of the another coil portion. The side of the one coil portion extends along with a predetermined direction, and the corresponding side of the another coil portion extends along with the predetermined direction. The side of the one coil portion has a current flowing direction, which is the same as a current flowing direction of the corresponding side of the another coil portion. The current flowing direction of the one side of the one coil portion is parallel to the corresponding side of the another coil portion. Thus, the magnetic flux generated by the one side and the magnetic flux generated by the corresponding side reinforce each other. Thus, detection sensitivity at each portion of the detection area is prevented from fluctuating, so that the sensor has high detection accuracy.

Alternatively, the first direction is perpendicular to the second direction. Each coil portion includes a first side and a second side. The first side extends along with the first direction, and the second side extends along with the second direction. The plurality of coil portions is arranged along with the first direction. Further, the detection coil may further include an outward coil and a homeward coil. The outward coil provides a plurality of first halfway turns, which are sequentially connected to each other. The homeward coil provides a plurality of second halfway turns, which are sequentially connected to each other. One of the plurality of first halfway turns and a corresponding one of the plurality of second halfway turns provide one of the coil portions.

In the above cases, although the detection coil includes multiple coil portions arranged along with the first direction, a manufacturing process for the detection coil is simplified. Further, the number of connections of the detection coil is reduced. Thus, reliability of the sensor is improved.

Further, the detection coil may have a double-turn figure-eight shape, and the second side of the one coil portion intersects with the second side of the another coil portion. Further, the plurality of coil portions may include first to sixth coil portions. The first to third coil portions are arranged along with the first direction, and the fourth to sixth coil portions are arranged along with the first direction, and the first to third coil portions and the fourth to sixth coil portions are arranged along with the second direction. Each coil portion provides an at least two-turn coil. Furthermore, each coil portion may provide a multiple-turn coil. The one wire has a first end and a second end. The first end is adjacent to the second end. The one coil portion and the another coil portion are connected with the one wire in such a manner that the one wire is bent by a straight angle at a connection portion between the one coil portion and the another coil portion. Furthermore, each coil portion may have a square shape. The second coil portion is adjacent to the first coil portion along with the first direction so that the second side of the first coil portion is adjacent to the second side of the second coil portion. The second side of the first coil portion has a current flowing direction, which is the same as a current flowing direction of the second side of the second coil portion, the current flowing direction being parallel to the second direction. The fourth coil portion is adjacent to the first coil portion along with the second direction so that the first side of the first coil portion is adjacent to the first side of the fourth coil portion. The first side of the first coil portion has another current flowing direction, which is the same as a current flowing direction of the first side of the fourth coil portion, the another current flowing direction being parallel to the first direction.

Alternatively, the object may be an outer plate of a door of a vehicle. The detection coil is disposed on a side of an inner plate of the door, the side facing the outer plate. The inner plate is spaced apart from the outer plate. Each coil portion has a width in a horizontal direction of the vehicle. The width is equal to or smaller than 240 mm. In this case, the detection sensitivity is increased. Further, the deviation of the sensitivity with regard to the collision position is reduced.

According to a second aspect of the present disclosure, a passenger protection system includes: the electromagnetic impedance sensor according to the first aspect of the present disclosure; a collision determination element for determining collision between the vehicle and an external body based on an output from the sensor; and a passenger protection element for protecting an passenger of a vehicle. The passenger protection element functions based on determination of the collision determination element.

In the above system, the passenger protection element surely functions based of the signal from the electromagnetic impedance sensor, which has detection accuracy.