GB2270203A

GB2270203A - Acceleration sensor

Info

Publication number: GB2270203A
Application number: GB9316888A
Authority: GB
Inventors: Shigeru Shimozono; Ryo Satoh
Original assignee: Takata Corp
Current assignee: Takata Corp
Priority date: 1992-08-31
Filing date: 1993-08-13
Publication date: 1994-03-02
Also published as: JPH0682475A; DE4327933A1; GB9316888D0

Abstract

An acceleration sensor comprises a magnetized inertia member 14 movable longitudinally within a conductive cylinder 12, a conductive member 18 on the end surface of the inertia member 14 for contacting a pair of electrodes 40, 42 disposed at one end of the cylinder 12, and an attracting member 30 disposed near the other end of the cylinder 12 for magnetically attracting the inertia member 14. The magnetized inertia member 14 comprises a cylindrical metal case 18, a permanent magnet 16 inserted in the case 18, and a metal plate 20 on the end surface of the case 18. Only the front surface of the metal plate 20 consists of gold or gold alloy. <IMAGE>

Description

22704 203 ACCELERATION SENSOR

FIELD OF THE INVENTION

The present invention relates to an acceleration sensor and, more particularly, to an acceleration sensor adapted to detect a large change in the speed of a vehicle caused by a collision or the like.

BACKGROUND-OF THE INVENTION-

An acceleration sensor of this kind is described in U.S. Pat. No. 4,827,091. This known sensor comprises a cylinder made of a conductive material, a magnetized inertial member mounted in the cylinder so as to be movable longitudinally of the cylinder, a conductive member mounted at least on the end surface of the inertial member which is on the side of one longitudinal end of the cylinder, a pair of electrodes disposed at one longitudinal end of the cylinder, and an attracting member disposed near the other longitudinal end of the cylinder. When the conductive member of the magnetized inertial member makes contact with the electrodes, these electrodes are caused to conduct via the conductive member. The attracting member is made of such a magnetic material that the attracting member and the inertial member are magnetically attracted towards each other.

Acceleration sensors as the same are also described in Japanese Patent Application No.Hei 2-221996, No.2-221997, No.2-221998 and No.2-221999. (Called as Japanese Patent Laid-Opened No. Hei 4-104062, No.4-104063, No. 4-104064, No.4-104065 in sequence.) In this acceleration sensor, the magnetized inertial member and the attracting member attract each other. when no or almost no acceleration is applied to the sensor, the inertial member is at rest at the other end in the cylinder.

If a relatively large acceleration acts on this acceleration sensor, the magnetized inertial member moves against the attracting force of the attracting member. During the movement of the inertial member, an electrical current is induced in this cylinder, producing a magnetic force which biases the inertial member in the direction opposite to the direction of movement of the inertial member. Therefore, the magnetized inertial member is braked, sothat the speed of the movement is reduced.

When the acceleration is less than a predetermined magnitude, or threshold value, the magnetized inertial member comes to a stop before it reaches the front end of the cylinder. Then, the inertial member is pulled back by the attracting force of the attracting member.

When the acceleration is greater than the predetermined magnituder or the threshold value, e.g., the vehicle carrying this acceleration sensor collides with an object, the inertial member arrives at one end of the cylinder. At this time, the conductive layer on the front end surface of the inertial member makes contact with both electrodes to electrically connect them with each other. If a voltage has been previously applied between the electrodes, an electrical current flows when a short circuit occurs between them. This electrical current permits detection of collision of the vehicle.

As shown in Fig. 10, the conventional magnetized inertial member 1 consists of a magnet assembly comprising a permanent magnet (magnet core) 2 enclosed in a case 3 made of copper.

The front surface and all of the outer surface of the case 3 are goldplated through nickel-plated substrate layer. A packing 4 is made of a synthetic resin. This case 3 permits the magnetized inertial member 1 to smoothly slide on the inner surface of the cylinder. If the vehicle collides with an object, the inertial member 1 receives an acceleration. At this time, the case 3 allows the inertial member 1 to move into contact with the electrodes, thus causing them to conduct, i.e., they are short-circuited.

The conventional magnetized inertial member 1 shown in Fig.10, the goldplated layer is easy to wear - out when the magnetized inertial member 1 slides inside of the cylinder. When the gold plating is peeled of f, the friction resistance between the magnetized inertial member and the cylinder becomes greater. And since the gold Plating is done all over the surface of case 3, much gold is used making the cost high.

SUMMARY OF THE INVENTION

In accordance with a first aspect of the invention, there is provided an acceleration sensor comprising: a cylinder made of a conductive material; a magnetized inertial member mounted in the cylinder so as to be movable longitudinally of the cylinder; a conductive member mounted at least on the end surf ace of the inertial member which is on the side of one longitudinal end of the cylinder; a pair of electrodes which are disposed at this one longitudinal end of the cylinder and which, when the conductive member of the inertial member makes contact with the electrodes, are caused to conduct via the conductive member; and an attracting member disposed near the other longitudinal end of the cylinder and made of a magnetic material, the attracting member and the inertial member being magnetically attracted toward each other. The magnetized inertial member comprises, a cylindrical metal case, a permanent magnet inserted in the case, a metal plate which combined to the end surf ace of the electrodes 1 side of the case. Only the front surface of the metal plate consists of gold or gold alloy.

An acceleration sensor of a second aspect has a gold plating layer or a cladding layer of gold (or a gold-alloy) on only the front surface.

An acceleration sensor of a third aspect has the metal plate which is combined to the case by welding or caulking.

In this acceleration sensor according to the present invention, the outer surface of the case of the magnetized inertial member does not have a gold plating layer, so that the friction resistance between the magnetized inertial member and the cylinder does not fluctuate, even when the outer surface of the magnetized inertial member slides on the inner surface of the cylinder. Also, since less quantity of gold is used than prior art, the cost of the magnetized inertial member may be reduced.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 is a cross-sectional view of an acceleration sensor according to the invention; Fig. 2 is an enlarged cross-sectional view of the end of the magnetized inertial member; Fig. 3 is a cross-sectional view showing combining method of case and metal plate; Fig. 4 is a cross-sectional view showing combining method of case and metal plate; Fig-5 is a perspective view showing combining method of case and rear lid; Fig.6 is a front view of rear lid; Fig.7 is a cross-section view taken along VII-M line in Fig-6; Fig.8 is a perspective view of ratchet portion of rear lid; Fig.9 is a cross-section view showing combining method of case and rear lid; and Fig.10 is a cross-section view of conventional magnetized inertial member.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to the drawings, preferred embodiments will be explained.

Fig.1 is a cross-section view along longitudinal direction of a cylinder of an acceleration sensor according to the preferred embodiment of the present invention, and Fig.2 is an enlarged cross-section view of the front end of the magnetized inertial member 16.

Referring to Fig. 1, this sensor has a cylindrical bobbin 10 made of a nonmagnetic material such as a synthetic resin. A cylinder 12 made of a copper alloy is held inside the bobbin 10. A magnetized inertial member 14 is mounted in the cylinder 12. The magnetized inertial member 14 has a column shaped permanent magnet 16, a metal case 18 in which the magnet 16 and packing 17 made of synthetic resin are inserted and metal plate 20 combined to leading edge of the case 18 by spot welding.

The metal plate 20 consists of mother piece 20A cladded by gold 20B. Namely the metal plate 20 is prepared by facing a gold alloy plate on a mother material plate and rolling both of them into combination. The metal plate 20 is combined to the front end of the case 18 by spot welding. The case 18 is formed into a container-like shape by drawing. After inserting the permanent magnet 16 and the packing 17 into the case 18, the rear end of the case 18 is forced to bend inside so that the permanent magnet 16 and packing 17 are fixed.

The mother material 20A is made of an anticorrosive metal other than gold. A copper alloy such as phosphor bronze or stainless steel are given as examples as such a metal.

A gold silver alloy which contains 2 to 20 percent, especially around 10 percent of silver is suitable for the gold alloy. It is also suitable to put an intermediate layer of a silver alloy between the mother material 20A and the gold alloy layer 20B. A silverpalladium alloy which contains 40 to 70 percent, especially around 60 percent of palladium is suitable for the silver alloy.

Thickness of each of the gold alloy layer, and the intermediate layer is preferably 1 to 20 " m, more preferably about 2 to 6u m, respectively. The thickness of the mother material 20A is preferably 50 to 500jum, more preferably about 100 to 300 jum.

The case 18 preferably consists of German silver. (The German silver is nickel-copper-zinc alloy and consists of 5 to 33 weight percent of nickel, 50 to 70 weight percent of copper and 13-35 weight percent of zinc.) The bobbin 10 has an insert portion 22 at its one end. This insert portion 22 enters the cylinder 12. An opening 24 is formed at the front end of the insert portion 22. A pair of flanges 26 and 28 protrude laterally from the front end of the insert portion 22 of the bobbin 10. An annular attracting member or return washer 30 which is made of a magnetic material such as iron is held between the flanges 26 and 28.

The bobbin 10 has another flange 32. A coil 34 is wound between the flanges 28 and 32. A further flange 36 is formed at the other end of the bobbin 10. A contact holder 38 is mounted to this flange 36.

This contact holder 38 is made of a synthetic resin. A pair of electrodes 40 and 42 are buried in the holder 38. An opening 44 is formed in the center of the holder 38. The front ends of the electrodes 40 and 42 protrude into the opening 44. The electrodes 40 and 42 have arc-shaped front end portions. Parts of the arc-shaped front end portions are substantially flush with the front end surface of the cylinder 12.

Lead wires (not shown) are connected with the rear ends of the electrodes 40 and 42 to permit application of a voltage between them.

The operation of the acceleration sensor constructed as described thus far is now described. when no external force is applied, the magnetized inertial member 14 and the return washer 30 attract each other. Under this condition, the rear end of the inertial member 14 is in the illustrated rearmost position where it bears against the front end surface of the insert portion 22. If an external force acts in the direction indicated by the arrow A, then the inertial member - 14 moves in the direction indicated by the arrow A against the attracting force of the return washer 30. This movement induces an electrical current in the cylinder 12 made of a copper alloy, thus producing a magnetic field. This magnetic field applies a magnetic force to the inertial member 14 in the direction opposite to the direction of movement. As a result, the inertial member 14 is b.raked.

Where the external force applied to the acceleration sensor is small, the magnetized inertial member 14 comes to a stop an its way to one end of the cylinder 12. The inertial member 14 will soon be returned to its rearmost position shown in Fig. 1 by the attracting force acting between the return washer 30 and the inertial member 14.

If a large external force is applied in the direction indicated by the arrow A when the vehicle collides, then the inertial member 14 is advanced up to the front end of the cylinder 12 and comes into contact with the electrodes 40 and 42. At this time, the.plating laye.r 20 on the inertial member 14 which is made of a conductive material creates a shortcircuit between the electrodes 40 and 42, thus producing an electrical current between them. This permits detection of an acceleration change greater than the intended threshold value. Consequently, the collision of the vehicle is detected.

The aforementioned coil 34 is used to check the operation of the acceleration sensor. In particular, when the coil 34 is electrically energized, it produces a magnetic field which biases the inertial member 14 in the direction indicated by the arrow A. The inertial member 14 then advances up to the front end of the cylinder 12, shortcircuiting the electrodes 40 and 42. In this way, the coil 34 is energized to urge the inertial member 14 to move. Thus, it is possible to make a check to see if the inertial member 14 can move back and forth without trouble and if the electrodes 40 and 42 can be short-circuited.

In the above embodiment, the gold alloy layer 20B is formed on the surface of mother material 20A -by cladding. However, the gold alloy layer 20B may be formed on the surface of mother material 20A by plating.

In the above embodiment, metal plate 20 is combined to the case 18 by welding. However, the metal plate 13 may be combined to the case 18A as shown in Fig.4 by inserting a projection 13a of metal plate 13 into an opening 1.8a formed at the case 18A and by caulking or deforming the projection 13a shown in Fig. 3.

In the embodiments of Fig.1 and Fig.2, the permanent magnet 16 and packing 17 are fixed inside of the case 18 by bending rear end of case 18 to the inside. However, instead of the bending, a rear lid 52 can be mounted on a case 50 as shown in Figs. 5 to g.

A plurality (e. g. 3) of L-shaped ratchets 54 are mounted on a peripheral end of the lid 52, and a flexible piece 56 is cut and raised from the ratchet 54.A recess 58 to which the ratchet 54 fits is formed on the rear end of case 50.

1 0 When the lid 52 is inserted into the rear end of the case 50 so as to engage the ratchet 54 to therecess 58, the flexible piece 56 pushes the internal surface of the case 50 so that the lid 52 is fixed to the case 50 as shown in Fig.g.

A step 60 provided with the lid 52 enhances rigidity of the lid 52 so that the lid 52 is tough to be deformed.

As described above, an acceleration sensor according to the present invention has a stable coeffcient of friction between the magnetized inertial member and the cylinder in a long term, since gold or gold alloy is formed only on the leading end of the magnetized inertial member inserted in the cylinder. Thus the detection accuracy of the acceleration sensor is stabilized.

Also, less gold is used in quantity than the prior art, cost of the acceleration sensor is reduced.

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Claims

WHAT IS CLAIMED IS:

1. An acceleration sensor comprising:

cylinder made of a conductive material; magnetized inertial member mounted in the cylinder so as to be movable longitudinally of the cylinder; a conductive member mounted at least an the end surface of the inertial member which is on the side of one longitudinal end of-the cylinder; a pair of electrodes which are.disposed at said one longitudinal end of the cylinder and which.. when the conductive member of the inertial member makes contact with the electrodes, are caused to conduct via the conductive member; and an attracting.member disposed near the other longitudinal end of the cylinder and made of a magnetic material, the attracting member and the inertial member being magnetically attracted toward each other; said magnetized inertial member comprising a cylindrical metal case, a permanent magnet inserted in the case, and a metal plate which combined to the end surface of the electrodes' side of the case, only the front surface of the metal plate comprising of gold or gold alloy.

2 2. An acceleration sensor of claim 1, wherein said metal plate has a gold plating layer only on the front surface thereof.

3. An acceleration sensor of claim 1, wherein said metal plate comprises a mother material and a cladding layer of gold or gold alloy only on the front surface of the mother material.

4. An acceleration sensor of claim 1, wherein said metal plate is combined to said case by welding.

5. An acceleration sensor of claim 1, wherein said metal plate is combined to said case by caulking.

6. An acceleration sensor of claim 3, wherein said mother material ccffnprises one of copper alloy and stainless steel.

7. An acceleration sensor of claim 6, wherein said gold-alloy comprised 2 to 20 percent of silver.

8. An acceleration sensor of claim 7, said metal plate further comprises a silver alloy layer containing 40 to 70 percent of palladium between said gold alloy layer and said mother material.

9. An acceleration sensor of claim 6, wherein said gold alloy layer has the thickness of 1 to 20M m, and the thickness of said mother material is 50 to 500m m.

10. An acceleration sensor substantially as hereinbefore described with reference to the accompanying description and Figures 1 and 2; or Figures 3 and 4; or Figures 5 to 9 of the drawings.

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