Ignition device
TECHNICAL FIELD 
     The present invention relates to an ignition device comprising an electric igniter, a lower housing and a sleeve which contains a main ignition charge and can be fitted in the said housing. The said sleeve is provided with a sealing part or a lower/end-part which faces the lower housing. The electric igniter comprises an insulating body (glass body), an electric pole device and at least one electrically connecting element located on an end surface of the insulating body and which connects the electric pole device and the electric igniter housing. The electric igniter also contacts different ignition charges which form part of the sealing function for the said main charge, via the said surface and the electrically connecting elements. 
     BACKGROUND ART 
     There already exists several designs of ignition devices. An ignition device is intended to be fitted in a particular type of ammunition unit e.g., artillery or anti-aircraft ammunition. The ignition device may comprise an electric ignition circuit and ignition charges which can be activated by the heat produced by one or more electric igniter filaments fitted in the ignition device and which are electrified when the electric circuit is initiated. The ignition charge(s) are so arranged that when they are activated the main ignition charge in the ignition device is ignited. 
     There are even electric igniters which include a glass body containing a centrally located electric pole device and an end surface where the electically connecting element has the form of metal layers applied onto the end surface by vapourization under vacuum. In such an electric igniter the heat releasing properties can be very accurately predetermined. 
     DISCLOSURE OF THE INVENTION 
     TECHNICAL PROBLEMS 
     There is a desire to be able to fit electric igniters of the said or similar types in various types of ignition devices. In this context there is a demand that the electric igniter should be contained inside the ignition device so that in addition to its ignition function it also insulates against moisture and seals against the pressure created in the gun (e.g., up to 500 Mpa). It is also important that a threaded, or bent, joint around the pyrotechnical charges can be eliminated thus preventing joints that loosen thereby causing accidental ignition of the ignition device. It must not be possible for the pyrotechnical charges to be displaced axially thus causing ignition by friction or the ignition charges to loose contact with the electrically connecting element. 
     SOLUTION 
     The object of this invention is to create a device which among other things solves those problems stated above. One of the main characteristics of this new device is that the said insulating body and ignition charges are located inside a ring-shaped device from the first end of which the said electric pole device protrudes, and that the ring-shaped device extends at least partially into a recess in the said lower housing. Another characteristic is that the said sealing part via a layer of filler in the ring-shaped device, presses the pyrotechnical charges against the said end surface and the electrically connecting element(s), and that the electric igniter is fixed to the ring-shaped device which in turn is fixed in the lower housing, e.g., via laser welding or some other method. 
     Further developments of the principle of this invention include, among other things, an extension of the ring-shaped device partially even into a recess in the sealing part of the said sleeve. The said sealing part also presses against the said layer of filler via for instance a bursting disc-type part. The sealing part is preferably made of aluminium or a similar metal and is relatively thin. 
     The ring-shaped device has metal-to-metal contact with the lower housing and/or the sealing part so that an electrical connection exists between the electric igniter, the ring-shaped device and the lower housing and/or the sealing part. The ignition device housing is connected electrically to a first potential. The electric igniter is initiated by transmitting a second potential to the electric pole device. The said potentials may be plus and minus potentials on a direct current source. 
     In a preferred embodiment of this invention the electric pole device extends via a recess in the lower housing so that it is accessible for application of the said second potential. One end of the electric pole device is centrally arranged in said insulating glass body and the other end is centered in said recess by means of a further insulating member. Further means have also been included for increasing the contact surface for said second potential. The electric pole device has the form of a rod which can be deformed when the second potential makes contact, so that in this way axially forces in the electric igniter are prevented. 
     ADVANTAGES 
     According to the proposed embodiment the igniting device is built into a very solid unit in which the ignition charges are given a distinct contact against the end surface of the electric igniter and the electrically connecting element on it. Axial movement of the ignition charges cannot take place thus preventing friction ignition and separation from the electrically connecting element. The entire unit can be carried out with relatively few parts thus contributing to simpler and safer manufacturing. Insulation and sealing functions are provided for and safety is ensured even in those cases where the ignition device is rammed more than once. 
     In addition, the contact resistance will be small in the electric circuits which will be established between the parts affected. The fixation between the electric igniter and the ring-shaped device on the one side, and the ring-shaped device and the lower housing on the other side, provides particular advantages as no heat is developed when the parts are joined to each other. 
     In the preferred embodiment having an increased contact surface for the second potential applied on the other end of the electric pole device preferably laser welding is used for connecting the contact disc with said electric pole device. The sleeve and lower housing may also be fixed to each other by means of laser welding if &#34;Loctite&#34; should prove to be insufficient. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     One embodiment of the present invention will now be described with reference to the accompanying drawings in which: 
     FIG. 1 is a longitudinal section of an ignition device according to the invention, and 
     FIG. 2 is an end view of the ignition device according to FIG. 1. 
     FIGS. 3, 4 and 5 are enlarged sectional views of portions of the ignition device of FIG. 1. 
    
    
     PREFERRED EMBODIMENT 
     This invention can for instance be used in an ignition device having a lower housing 1 and a sleeve 2. The lower housing is provided with a recess 3 having an internal thread 4 into which the sleeve 2 can be screwed. The lower housing is also provided with an external thread 6 via which the ignition device can be screwed into a projectile or other type of ammunition unit. The mantle of the sleeve 2 is provided with through outlet holes 7. The said sleeve also has a first end part or sealing part 8 and a second end part or sealing part 9. The sleeve contains the main ignition charge 10 which may be composed of black powder or some other pyrotechnical charge. The sealing part 9 has a first part 9a which covering the end surface 2a and also a part 9b which protrudes downwards inside the wall of the sleeve. The sealing part 9 is loose in relation to the wall of the sleeve 2. A shrunk-on tube is fitted on the outside of the sleeve so that it covers the exhaust outlets 7. The sealing part 9 is also provided with a central recess 9c the bottom of which functions as a bursting disc 9d. The sealing part 9 is made of aluminium and the bursting disc has a thickness of 0.5 mm approximately. On the opposite side and facing the recess 9c the sealing part is provided with a further recess 9e. 
     The lower housing 1 is also provided with a central recess 1a and an other recess 1b which connects with said central recess 1a but which has a considerably smaller cross-section than the latter. The latter recess opens out towards the end surface 1c of the lower housing. The opened-out part of the recess 1b is designated 1b&#39;. 
     A ring-shaped device 12 is fitted in the recesses 1a and 9e. The expression &#34;ring-shaped device&#34; should be seen in its widest sense and includes types of bushings, hollow cylinders, and similar. The said ring-shaped device extends partly into the recess 1a and partly into the recess 9e. This ring-shaped device also extends over a space 13 between the outer end surface of the sealing part 9 and the bottom surface of the lower housing 1 inside the recess 3. 
     The said ring-shaped device is fitted in the recesses 1a and 9e to ensure electrical contact between the ring-shaped device 12 and the lower housing 1 and between the ring-shaped device and the sealing part 9. The ring-shaped device is fixed in the lower housing by means of laser welding 14 which has the additional purpose of sealing the space between the ring-shaped device and the lower housing. The laser welding may be carried out by known methods and equipments and has the advantage that only a small amount of heat is developed during the actual welding. The ring-shaped device is so formed that it contains an electric igniter 15 and two pyrotechnical charges 16 and 17. In order to fill any possible space between the inner pyrotechnical charge 17 and the bursting disc 9d there is an inert layer of filler 18. 
     The said electric igniter may be of any known type e.g., the electric igniter described in the Swedish Pat. specification No. 431 681. The said electric igniter will not be described in more detail here, it should only be said that it comprises a glass body 19 and a centrally extending electric pole device 20 made of an electrically conductive material. The glass body 19 has an end surface 19a onto which, although not specifically shown, electrically connecting elements in the form of metal layers are applied by means of vapourization so that they extend between the electric pole device 20 and a part 21 which surrounds the glass body and is made of an electrically conductive material. The said electrically connecting elements thus form an electric circuit which is activated by an electric current being led through the electric pole device, the connecting elements and the said part 21. The electric igniter is completely located inside the ring-shaped device 12 which has an inner supporting surface 12a on which the inner edge of the part 21 is seated. The electric igniter is fixed to the ring-shaped device by means of a laser weld 22 at the other end surface (via the part 21) of the electric igniter, and consequently the said other end surface extends inside the inner edges of the ring-shaped device. 
     The electric pole device 20 extends into the recess 1b and out to the end surface 1c of the lower housing. Inside the opened-out part 1b&#39; of the recess 1b is located a centering device 23 made of an insulating material. The said material may be plastic. Outside the device 23 is located a washer 24 made of an electrically conducting material. The said washer is intended to form an extended contact surface for an impact device 25 via which a potential is transmitted to the electric pole device when the electric igniter is activated. The said washer 24 is fixed in the electric pole device by means of a laser weld 26. The outer edges of the said washer are sealed by means of an epoxy plastic seal 27. 
     The pyrotechnical ignition charges 16 and 17 can be of a type used in ignition devices. One or more ignition charges or layers may be used. The inert layer 18 may consist of antimony powder. 
     The said layer of filler 18 ensures that the charges 16 and 17 are always pressed against the end surface of the electric igniter. The layer of filler lies flush with the end surface 12b. 
     When manufacturing the ignition device according to this invention the electric igniter 15 is placed in the ring-shaped device 12 and then welded in position by means of laser weld 22. The ring-shaped device is then welded in the recess 1a by means of the laser weld 14. The layers 16, 17 and 18 are then laid in position whereupon the layer 18 is levelled out until it completely fills the space remaining between the outer charge 17 and the end surface 12b of the ring-shaped device. The sealing part 9 is then laid in position and tightened together with the sleeve 2 when fitting into the lower housing. If the sealing part 9 should turn (move) when fitting the sleeve 2 a possible friction ignition is prevented by the layer 18 of antimony powder. From the safety point of view this is a great advantage as the sealing part 9 can not cause friction ignition of the charges 16 and 17. The insulating centering device 23 is placed in the recess 1b&#39; and the conducting washer 24 is placed on top of the centering device and then welded in position by means of the laser weld 26. 
     The laser welds 14, 22 and 26 prevent moisture penetrating the ignition charges 16 and 17. The contact resistances between the various parts will be minimal. 
     When fitted in an actual ammunition unit the lower housing 1 is connected to a first potential on a utilized source of energy. When the ignition device is activated a second potential is transmitted to the impact device 25. An electric circuit is formed between the electric pole device 20, the electrically connecting elements, the part 21 via 22 on the electric igniter and further to the ring-shaped device 12 which like the lower housing 1 is made of electrically conductive material. The electric energy through the connecting elements causes heat to develop which in turn ignites the charges 16 and 17. The energy developed from the said charges causes the part 9d to be blown aside and the gases developed from the charges are able to ignite the main charge 10. When the charge 10 ignites hot gases are developed which flow out through the holes 7 and ignite the ammunitions&#39; propellant charge. 
     A &#34;Loctite&#34; seal can be formed between the sleeve 2 and the lower housing 1. If so required a laser weld 28 can be made between the said parts. FIG. 2 shows the recesses 29 for a key member in the rear surface 1c. The rod-shaped electric pole device 20 may be provided with wedge-shaped recesses which weaken the electric pole device 20 that it deforms when the device 25 is struck on impact. In such case the said weakenings are made in such a way that the electric igniter is prevented from moving axially when the device 25 impacts and at the same time retaining electrical contact. This invention is not limited to the above embodiment but can be varied within the scope of the following claims.