SHOCK SENSOR

Abstract: A shock sensor (300) comprises: a lead switch (310) fixed in the sensor case, and having a lead contact which changes from a first state to a second state by a magnetic force; a magnet (315) fixed apart from the lead switch by a given distance in the sensor case; a shielding member (317) having a sufficient area to shield the lead contact from the magnet force when the member is in the steady-state position; and resilient members (323) holding the shielding member in the steady-state position between the lead contact and the magnet when the sensor is in the steady state so as to hold the lead contact in the first state, and moving the member to a position so as to cause the lead contact to reach the second state when the sensor receives a shock.

Description: Technical Field The present invention relates to a shock sensor and, more particularly, to a shock sensor suited for use in a safety air bag system for automobiles. Background Art Safety air bag systems for use in automobiles which respectively employ a shock sensor for sensing a shock which will be applied to a vehicle upon collision with the other vehicle or an object are intended to protect a driver from such a shock by starting an actuator for the safety air bag system with an output signal from the sensor which has sensed the collision shock, and inflating the air bag. FIGS. 1 and 2 respectively show an example of this type of conventional shock sensor. FIG. 1 shows a shock sensor which utilizes a magnetic repulsion force of magnets. This example of the conventional shock sensor is adapted to employ a main casing 141 having tunnel type chambers 142 and 143, which are provided parallel to each other, to house a reed switch 144 in one tunnel type chamber 142 and a pair of rod type magnets 145 and 146 in the other tunnel type chamber 143 so that the same magnetic poles (S pole in this example) of these magnets are arranged to oppose each other; for example, one rod type magnet 145 is slidably provided and the other rod type magnet 146 is fixed. This shock sensor is arranged so that the slidable rod type magnet 145 is positioned in a direction opposing to the direction of the shock to be detected. In this shock sensor, a pair of magnets 145 and 146 are kept at a position shown in FIG. 1, that is, a position away from the contact part 144a of the reed switch 144 by their magnetic repulsion force in a normal state where no shock is applied. When the shock sensor receives a shock in a direction where the shock sensor expects the shock in this normal state, the rod type magnet 145 slidably provided moves against the magnetic repulsion force produced between the rod type magnet 145 and the fixed rod type magnet 146 to approach the contact part 144a of the reed switch 144 and actuates the reed switch 144 by applying magnetism to this contact part 144a and the shock sensor detects the shock. FIG. 2 shows a shock sensor which utilizes spring resilience. This example of the conventional shock sensor is provided with a main casing 251 having tunnel type chambers 252 and 253 which are arranged parallel to each other, the tunnel type chamber 252 being adapted to incorporate a reed switch 254 and the tunnel type chamber 253 being adapted to incorporate a rod type magnet 255 to be slidable, and thereby the rod type magnet 255 is energized by the spring 256 to move away from the contact part 254a of the reed switch 254. In this shock sensor, the magnet 255 is kept at a position shown in FIG. 2, that is, a position away from the contact part 254a of the reed switch 254 by the resilience of the spring 256 in the normal state where no shock is applied. When a shock is applied to the shock sensor in this normal state in the lengthwise direction of the reed switch 254 where the resilience of the spring 256 is reduced, the magnet 255 moves against the resilience of the spring 256 to approach the contact part 254a of the reed switch 254 whereby the reed switch 254 is actuated by applying the magnetism to the contact part 254a and thus the shock sensor detects a shock. Any example of conventional shock sensors with the configuration as described above is provided with the magnets which are arranged to be slidable in the lengthwise direction of the reed switch and therefore, there has been a problem that the reed switch operates only with a shock applied to one side of the lengthwise direction of the reed switch and does not operate with a shock applied to the opposite side. US-5,010,216 discloses a switch which comprises a shield member disposed between a magnet and a reed switch and which is rotably mounted at an axis. If a shock is applied, the shield member rotates away from its regular position at which it is fixed by the magnet, thereby enabling the magnet to close the contact of the reed switch. This switch also functions if the direction of the shock is the same direction into which the shield member is to rotate. An object of the present invention made in view of the above problem is to provide a shock sensor capable of detecting a shock in a number of directions. Another object of the present invention is to provide a shock sensor capable of allowing to conduct operation tests more easily. Disclosure of the Invention A shock sensor according to the present invention is disclosed in claim 1. Claims 2 to 5 disclose particular embodiments of the invention. Brief Description of the Drawings FIGS. 1 and 2 are respectively a cross-sectional side view of a conventional shock sensor; FIG. 3 is a side view of a shock sensor 300, a first embodiment of the present invention; FIG. 4 is a partial cross-sectional approximate illustration as viewed along line A-A' of the shock sensor 300 of FIG. 3; FIG. 5 is a partial cross-sectional approximate illustration as viewed along line C-C' of the shock sensor 300 of FIG. 3; FIG. 6 is a partial cross-sectional approximate illustration as viewed along line B-B' of the shock sensor 300 of FIG. 4; FIG. 7 is an illustration of the procedure for testing the shock sensor 300; FIG. 8 is a partial cross-sectional approximate illustration of the shock sensor 800, a second embodiment of the present invention; FIGS. 9 and 10 are respectively an illustration of the principle of sensing operation of the shock sensor 800; FIG. 11 is a side view of the interior of the main casing of a third embodiment of the present invention; FIG. 12 is a cross-sectional side view of the main casing. Best Mode for Carrying Out the Invention Based on the accompanying drawings, preferred embodiments of the present invention are described in detail below. FIG. 3 is a side view of a shock sensor 300, a first embodiment of the present invention; FIG. 4 is a partial cross-sectional approximate illustration as viewed along line A-A' of the shock sensor 300 of FIG. 3; FIG. 5 is a partial cross-sectional approximate illustration as viewed along line C-C' of the shock sensor 300 of FIG. 3; FIG. 6 is a partial cross-sectional approximate illustration as viewed along line B-B' of the shock sensor 300 of FIG. 4. The shock sensor 300 has a rectangular main casing 301 made of relatively thick vinyl chloride sheet. A reed switch 310 is fixed on a vinyl chloride base 303 at the center of an inside bottom 301a of the main casing 301. The reed switch 310 is formed with a pair of reeds 313a and 313b which are hermetically sealed in a glass tube 311 together with an inert gas and has a pair of reeds 313a and 313b whose contact parts 313c are overlapped with a specified clearance. The contact parts 313c close when an external magnetic field is applied thereto. On the other hand, at the center of an internal upper surface 301b of the main casing 301, a rod type magnet 315 is fixed to the main casing 301 to be parallel with the reed switch 310 with a specified clearance between the rod type magnet 315 and the contact part 313c of the reed switch 310. The rod type magnet 315 is magnetized, for example, in a lengthwise direction of the reed switch 310. An electromagnetic shield plate 317 of, for example, a rectangular shape, made of electromagnetic mild steel or the like, is arranged in a clearance between the reed switch 310 and the rod type magnet 315. The electromagnetic shield plate 317 whose four corners are respectively connected to projections 321a, 321b, 321c, and 321d which are fixed inside the main casing 301 through springs 323a, 323b, 323c, and 323d is supported by the main casing 301. In a normal state, the electromagnetic shield plate 317 is kept by the springs 323a, 323b, 323c, and 323d at a position at which its central part faces the contact part 313c. The shape and size of the electromagnetic shield plate 317 are determined taking into account the working value of the reed switch 310, the magnitude of magnetic force of the rod type magnet 315, and the spring constants of the springs 323a, 323b, 323c, and 323d. A vinyl chloride partition 335 of 1 to 2 mm in thickness is fixed through connecting members 337 between the electromagnetic shield plate 317 and the rod type magnet 315 inside the main casing 301. The vinyl chloride partition 335 is intended to prevent the electromagnetic shield plate 317 from being magnetically attracted by the rod type magnet 315 due to external vibration. A test opening 345 is formed at the center of each side of the main casing 301. The test opening 345 is described later. The operation of the shock sensor 300 of the above configuration is described below. In the normal state in which no shock is applied to the shock sensor, the springs 323a, 323b, 323c, and 323d hold the electromagnetic shield plate 317 at a position where its central part faces the contact part 313c of the reed switch 310, and the magnetism from the rod type magnet 315 is shut off by the electromagnetic shield plate 317. Therefore, since no magnetic effect acts on the contact part 313c of the reed switch 310, this contact part is kept open. When the shock sensor detects a shock in this normal state, the electromagnetic shield plate 317 moves against the resilience of the springs in the direction opposite to the direction of the shock. This movement of the electromagnetic shield plate 317 causes a magnetic force of the rod type magnet 315 to act on the contact part 313c of the reed switch 310, so that this contact part is consequently closed to turn on the reed switch 310. Turning on of the reed switch 310 actuates shock detecting means (not shown) which is connected to the reeds 313a and 313b of the reed switch 310 to detect the shock. Referring to FIG. 7, the procedure for testing the shock sensor 300 is described below. The test of the shock sensor 300 is conducted with a testing jig 350. This testing jig is composed of a U-shaped abutment (T-shaped portion with fins) 350a which comes in contact with the electromagnetic shield plate 317 and a shank 350b. The testing jig 350 is inserted into the main casing 301 through the test opening 345 of the shock sensor 300. The U-shaped abutment 350a pushes the electromagnetic shield plate 317 to move it from the normal position. The movement of the electromagnetic shield plate 317 enables to test the shock sensor 300 without applying a shock thereto. The shock sensor 300 of the above configuration is capable of sensing a shock in all directions ranging from 0° to 360° which are parallel with the electromagnetic shield plate 317. In other words, if the position of the electromagnetic shield plate 317, opposing to the contact part 313c of the reed switch 310, coincides with the extending directions of the springs 323a, 323b, 323c, and 323d when the electromagnetic shield plate 317 is supported at a regular position by the springs, the shock sensor 300 can detect a shock in all directions ranging from 0° to 360°, which are parallel with the electromagnetic shield plate 317, around the position of the electromagnetic shield plate 317, opposing to the contact part 313c. If three springs are installed with a 120° angle interval therebetween instead of the springs 323a, 323b, 323c, and 323d, the same effect can be obtained. The sensitivity of the shock sensor 300 depends on the resultant resilience of a plurality of springs out of four springs 323a, 323b, 323c, and 323d and differs with the direction of a shock. In addition, the resilience (spring constants) of springs 323a, 323b, 323c, and 323d can be changed to adjust the sensitivities of the shock sensor 300 to shocks in different directions. In the first embodiment described above, the partition 335 is used. However, a non-magnetic member can be formed on the magnet 315 side of the electromagnetic shield plate 317 in place of the partition to prevent attraction between the electromagnetic shield plate 317 and the magnet 315. FIG. 8 is a cross-sectional side view showing a second embodiment of the present invention. In FIG. 8, a ring type magnet 818 is provided around a contact part 812a of a reed switch 812 housed in a main casing 811 and is fixed on its internal surface. An electromagnetic shield tube 819 made of electromagnetic mild steel or the like is provided in a clearance between the contact part 812a of the reed switch 812 and the ring type magnet 818 to be movable in a lengthwise direction of the reed switch 812, and is held by springs 820a and 820b at both its ends to face the central part of the electromagnetic shield tube 819 with the contact part 812a. Referring to FIGS. 9 and 10, the operation of a shock sensor 800 is described below. When no shock is applied to the shock sensor 800 as shown in FIG. 9, the reed switch 812 is not magnetized because the effect of magnetism from the ring type magnet 818 is shut off by the electromagnetic shield tube 819 as indicated by electric lines of force 825 in the figure, and therefore, the reed switch 812 remains open. When a shock is applied to the shock sensor 800 in the arrowhead direction 830 shown in FIG. 10, a magnetism from the magnet 818 acts on the reed switch 812 as indicated by the electric lines of force 825 because the shielding effect is partly lost on account of the movement (in the right direction in FIG. 10) of the electromagnetic shield tube 819, caused by the influence of the shock. As a result, part of the terminal of the reed switch 812 is magnetized under the influence of magnetism, and therefore, the contact part 812a is also magnetized and the contact is closed. As described above, the shock sensor using the ring type magnet 818 can sense a shock only in a lengthwise direction of the reed switch 812 as the conventional shock sensors because the movement of the electromagnetic shield tube 819 is limited to the lengthwise direction of the reed switch 812. However, a problem of damage of the magnets due to collision can be solved because the ring type magnet 818 is fixed. In the above-described embodiments, springs are used as resilient members but these members are not limited to springs and can be, for example, rubber-type resilient members. In brief, any member is acceptable which can hold the electromagnetic shield plate 315 or the electromagnetic shield tube 819 at a position where the central part of the electromagnetic shield plate 315 or the electromagnetic shield tube 819 faces the contact part of the reed switch and which can elastically support the electromagnetic shield plate 315 or the electromagnetic shield tube 819 so that the electromagnetic shield plate or the electromagnetic shield tube can move when a shock is applied. FIG. 11 is a side view of the interior of the main casing showing a third embodiment of the present invention. FIG. 12 is a cross-sectional side view of the main casing. In FIG. 11, a main casing 1111 incorporates a reed switch 1112 comprising a pair of reeds 1113a and 1113b which are hermetically sealed in a glass tube 1114 together with an inert gas so that the contact parts 1112a at the ends of the reeds 1113a and 1113b overlap each other with a specified clearance provided between the two contacts. The contact part 1112a closes when an external magnetic field is applied thereto. A magnet 1115 which is arranged above and in parallel with the reed switch 1112 with a specified clearance provided between the magnet 1115 and the reed switch 1112 and is fixed to the upper surface of the main casing 1111. The magnet 1115 is magnetized, for example, in a lengthwise direction of the reed switch 1112. On the other hand, an electromagnetic shield tube (electromagnetic shield member) 1116 which magnetically isolates the reed switch 1112 from the magnet 1115 is arranged around the reed switch 1112 and is held against the main casing 1111 by springs 1117a and 1117b at both its ends so that the central part of the electromagnetic shield tube 1116 faces the contact part 1112a of the reed switch 1112. The electromagnetic shield tube 1116 is formed with the same material such as, for example, carbon steel as for the springs 1117a and 1117b so that the electromagnetic shield tube 1116 is integral with the springs 1117a and 1117b. In other words, as known from FIG. 11, a wire is wound at a fixed pitch around both end portions of the assembly unit which serves as the springs 1117a and 1117b and in high density around the central portion of the assembly unit which forms the electromagnetic shield tube 1116, thus forming the integrated construction. The length of the electromagnetic shield tube 1116 is determined in consideration of the working value of the reed switch 1112, the magnitude of magnetism of the magnet 1115, and the spring constants of springs 1117a and 1117b. The operation of the shock sensor with the above configuration is described below. In a normal state where no shock is applied to the shock sensor, the electromagnetic shield tube 1116 is kept by the springs 1117a and 1117b at a position where the central part of the electromagnetic shield tube 116 is opposed to the contact part of the reed switch 1112, and this contact part 1112a of the reed switch 1112 is kept open because the magnetism from the magnet 1115 is shut off by the electromagnetic shield tube 1116 and therefore, the magnetism does not act on the contact part 1112a. When a shock in a lengthwise direction of the reed switch 1112 is applied to the shock sensor in the normal state, a force in the direction opposite to the direction of the shock energy acts on the electromagnetic shield tube 1116 due to the reaction of the shock. The reaction force causes the electromagnetic shield tube 1116 to move against the resilience of the spring 1117a (or the spring 1117b) in a lengthwise direction of the reed switch 1112. The magnetism from the magnet 1115 acts on the contact part 1112a of the reed switch 1112 owing to the movement of the electromagnetic shield tube 1116, so that the contact part 1112a is closed to make the reed switch 1112 conductive. The conductive reed switch 1112 allows the shock to be detected. When the shock is released, the electromagnetic shield tube 1116 is returned to its original position in the normal state by the resilience of the spring 1117b (or the spring 1117a) to magnetically isolate the reed switch 1112 from the magnet 1115. As a result, magnetism is prevented from acting on the contact part 1112a of the reed switch 1112, and thus this contact part opens. The shock sensor according to the third embodiment of the present invention is adapted so that the electromagnetic shield tube 1116 which is lighter in weight than the magnet 1115 is moved to detect a shock. Therefore, in order to detect a shock in a lengthwise direction of the reed switch 1112, the shock sensor can be installed by appropriately setting the spring constants of the springs 1117a and 1117b so that the lengthwise direction of the reed switch 1112 is vertically set. Such being the case, the installing direction of the shock sensor is not limited. The shock sensor according to the third embodiment of the present invention can be made of a reduced number of component parts by forming the electromagnetic shield member and springs as an integral assembly with the same material (electromagnetic mild steel) and consequently the assembly process can be more easy. Moreover, the shock sensor can be checked for proper operation by externally applying electrical signals to it without applying a shock if the electromagnetic shield tube and springs are formed with a material such as carbon steel, which provides a magnetism shielding effect and is electrically conductive, so that electrical signals can be entered into the shock sensor. Industrial Applicability As described in detail above, the present invention enables to provide a shock sensor which can sense shocks to be applied in a number of directions. In addition, in accordance with the present invention, a shock sensor which can be more easily checked for proper operation can be provided.

Claims: A shock sensor (300) comprising: a reed switch (310) which is fixed inside a main casing (301) and has a reed contact part (313c) which is switchable from a first state to a second state under the influence of magnetism; a magnet (315) which is fixed inside said main casing with a specified distance from said reed switch; a shield member (317) which has an area as large as sufficient to prevent magnetism from said magnet from affecting said reed contact part when said shield member (317) is arranged at a regular position; characterized in that said shock sensor (300) further comprises: a plurality of resilient members (323a, 323b, 323c, 323d) which are connected between the end of said shield member (317) and the main casing (301) and which support said shield member (317) between said reed contact part (313c) and said magnet (315), keeping said reed switch contact part (313c) to the first state in a regular state and enabling moving of said shield member (317) to a position which makes said reed contact part (313c) change over to said second state when a shock is applied to said shock sensor. A shock sensor according to Claim 1, wherein said reed switch (310) comprises two reeds (313a, 313b) which have said reed contacts composing said reed contact part (313c) and extend in specified directions, and said plurality of resilient members extend in said specified directions. A shock sensor according to Claim 1, wherein said shield member (317) is a flat plate of a rectangular shape and has a portion which closely approaches said reed contact when kept in a normal state and said plurality of resilient members are composed of three or more members and extend from said portion which closely approaches said reed contact. A shock sensor according to Claim 1, wherein said main casing (301) has an opening (345) for operation tests which is used to move said shield member (317). A shock sensor according to Claim 1, wherein said shield member (317) and said resilient members are respectively composed of a single spring, said spring being arranged around said reed switch.

Inventors: HAMAZAKI ISAMU, KOBAYASHI TATSUO, MAKIKI KAYOKO, MATSUEDA HISAHARU, NAKAMURA KIYOTAKA, WATANABE KAZUYA, HAMAZAKI, ISAMU, KOBAYASHI, TATSUO, MAKIKI, KAYOKO, MATSUEDA, HISAHARU, NAKAMURA, KIYOTAKA, WATANABE, KAZUYA, HAMAZAKI, ISAMU, OKI ELECTRIC INDUSTRY CO. LTD., KOBAYASHI, TATSUO, OKI ELECTRIC INDUSTRY CO, LTD., MAKIKI, KAYOKO, OKI ELECTRIC INDUSTRY CO. LTD., MATSUEDA, HISAHARU, OKI ELECTRIC INDUSTRY CO. LTD., NAKAMURA, KIYOTAKA, OKI ELECTRIC INDUSTRY CO. LTD., WATANABE, KAZUYA, OKI ELECTRIC INDUSTRY CO. LTD.
Applicants: OKI ELECTRIC IND CO LTD, OKI ELECTRIC INDUSTRY COMPANY, LIMITED
Application year: 1993
Main classification: H01H35
IPC codes: H01H35, H01H36, G01P21, G01P15