US2828692A - Electrical igniter - Google Patents

Description

April 1, 1958 R. o. WEBSTER ELECTRICAL IGNITER Filed June 18, 1956 [Mm/ra AGENT United States Patent ELECTRICAL IGNITER Robert 0. Webster, Falls Church, Va., assignor to Atlantic Research Corporation, Alexandria, Va., a corporation of Virginia Application June 18, 1956, Serial No. 591,934

11 Claims. (Cl. 102-702) This invention relates to new and improved electrical igniters for use in initiating the burning of a combustible charge such as the solid or liquid propellant of a rocket, torpedo, jet assist take-ofi unit, catapult, gas generator unit and the like. More specifically, it relates to electrical igniters equipped with novel safety features to prevent premature or accidental ignition of the propellent charge.

The igniter charge in the igniter unit is subject to accidental combustion due to such factors as inadvertent or stray electrical discharge, mechanical shock or selfignition. When the igniter is in position in the device which it is to actuate, accidental ignition of the igniter charge initiates premature burning of the propellent in the rocket or the like with frequently disastrous results.

The object of this invention is to provide electrical igniters which are equipped with safeguards against premature electrical ignition of the igniter charge.

Another object is to provide electrical igniters which, in the event of accidental ignition of the igniter charge due, for example, to mechanical shock or self-ignition, possess safety means permitting discharge of the burning igniter charge particles and high temperature gases in a direction away from the chamber containing the propellent charge so that they do not contact and thereby prematurely ignite the propellent.

Other objects and advantages of my invention will become obvious from the following detailed description and the drawings.

In the drawings:

Figure 1 is a plan view of the igniter, parts being broken away.

Figure 2 is a side elevational view of the igniter.

Figure 3 is a section taken along lines 33 of Figure 1.

Figure 4 is a cross-section taken along lines 4-4 of Figure 3, showing the parts in safe position.

Figure 5 is a cross-sectional view similar to Figure 4 showing the parts in armed position.

Figure 6 is a diagrammatic view showing the wiring system in safe position.

Broadly speaking, my invention comprises an igniter characterized by one or more safety features which maintain the igniter in unarmed or safe position until the igniter is ready for firing at which point the igniter is armed in such manner that the firing circuit is no longer interrupted or ignition of the propellent prevented.

One of the safety features of my invention comprises a slidable low-resistance electrical conductor or shunt which, in safety position, contacts the terminals or other electrical contacts between which an electrical squib is interposed and thereby shunts stray or accidentally applied current from the squib. To arm the igniter preparatory to firing, the shunt is shifted away from its bypass position across the electrical squib contacts so that the electric current can pass directly through muib and actuate the desired ignition sequence.

An additional safety factor comprises a switch which can be attached to the igniter body and is connected in 2,828,692 Patented Apr. 1, 1958 series circuit with the squib. In the safety position, the switch is kept open, thereby interrupting the electrical firing circuit. Thus accidental actuation of the electrical squib is prevented both by the interrupted firing circuit and the shunt by-pass. The switch is maintained in the open or safety position by means movable with the shunt which, while in by-pass engagement across the electrical squib contacts, depresses the switch plunger. Removal of the shunt from the electrical squib contacts to ready the igniter for firing simultaneously removes the shunt from depression contact with the switch plunger, thereby permitting the switch terminals to come into contact and close the igniter electrical firing circuit.

The shunt alone or in combination with the aforedescribed switch prevents accidental electrical actuation of the igniter squib. However, there is some danger of explosion of the igniter charge because of mechanical shock or self-ignition. Should this occur when the igniter is in position in the combustion chamber of the rocket or other device, the propellent charge is ignited with resultant premature firing. To prevent such accidental firing, I have devised a safety blow-off feature whereby accidental ignition of the igniter charge results in expulsion of the burning particles and high temperature combustion gases in a direction away from the propellent charge so that the latter is not ignited. This mechanical blow-off feature comprises an outer wall or closure plate on the igniter which, in safety position, is disengageably secured so that it can be ejected by the burning igniter charge, thereby providing a safe vent for the combustion products. In the armed position, this plate is locked to the igniter receptacle and the combustion products of the igniter charge are forced to vent into the propellent chamber. The aforedescribed electrical shunt, when placed in the armed or firing position, serves also to secure the closure plate to the igniter receptacle by actuation of a locking mechanism.

The accompanying drawings illustrate the various safety features of my invention.

The igniter body 1 comprises a receptacle or cup 2 adapted to be inserted into and fastened to the chamber wall of the rocket or other device containing the propellent charge to be ignited. The fastening means can be peripheral, external threads 3 on the igniter cup, as shown, which cooperate with threads in the igniter-receiving mouth of the combustion chamber or it can be any other desired and suitable joining means. The igniter cup contains a suitable igniter or explosive charge such as black powder 4.

The bottom or base 5 of the igniter cup comprises, at least in part, a non-combustible element which ruptures under pressure. The desired rupturability can be attained in any desired manner as, for example, by forming the bottom of or incorporating into it, a sheet of metal or plastic sufficiently thin and frangible to cause the sheet to break when a determined level of igniter charge combustion gas "pressure is reached. Another method of ensuring rupturability is by making the bottom of varying thickness as shown and providing lines of weakness as, for example, in the form of radiating lines 6 along which the base opens out under pressure. Figure 3 shows schematically in dotted lines the effect of rupture of a base weakened in such a manner as to burst open into pieshaped segments. The number and arrangement of the lines of weakness can be varied as desired in order to control the direction of discharge of ignition products from the igniter into combustion chambers of dilferent designs.

The mouth of the igniter cup is sealed by insertion of closure plate 8 which is secured to the cup by disengageable means such as the several attachment clips 9.

The clips are fixed to flange 10 which extends laterally from the rim of the cup and engage flange 11 of the closure plate. The attachment clips should be strong enough to hold the closure plate to the igniter cup against ordinary handling forces but sufliciently weak to give and allow the closure plate to be expelled under explosive force from the igniter charge when the plate is not in fixed engagement as will subsequently be described. The rupturable base of the igniter cup should be engineered to certainly withstand higher pressures than the attachment clips so that the latter can yield before the cup bot tom can rupture.

The igniter cup is provided with an annular groove 12 which is contiguously aligned with a similarly shaped groove 13 in the closure plate. The split C-shaped retaining or locking ring 14, in the normal or safe position, is inherently contracted so as to be within the closure plate groove 13 as shown in Figures 3 and 4. When in this position, the locking ring does not engage the igniter cup and, therefore, does not interfere with movement of the closure plate relative to the igniter cup. Should the igniter charge accidentally explode, the pressure of the combustion gases overcomes the resistance of the disengageable holding means or attachment clips and ejects the closure plate rearwardly. The hot combustion products of the burning igniter charge vent rearwardly away from the propellent charge, leaving the bottom intact, and thus prevent discharge of the burning igniter charge into the combustion chamber and firing of the rocket or other device.

To fixedly engage the closure plate with the igniter cup, the locking ring is expanded into the annular igniter cup groove so that it overlaps grooves 12 and 13 by means of a slidable member or arming rod 15 provided with cammed surfaces 16, which engage the free ends of the locking ring, as shown in Figure 5. The closure plate is now locked into place and in this armed position, firing of the igniter will cause rupture of the base and release of the burning igniter charge into the combustion chamber, resulting in initiation of combustion in the rocket or other device being actuated. To prevent combustion gas leakage, a seal can be provided between the closure plate and igniter cup, such as the O-ring seal 17 shown in Figure 3.

The arming rod, which lies flush against the recessed exterior surface of the closure plate, extends radially through a lateral slot 18 in the flanged rim of the igniter cup and a registering slot 19 in the closure plate and thus acts as an additional member holding the plate to the cup. To provide for expulsion of the closure plate in the event of accidental ignition while in the safety position, the arming rod can be made of narrow cross-section in the dimension perpendicular to the plate as shown and it can be provided with a line of weakness 39 coincident with the plane of the interface of the closure plate and igniter cup so that it will yield and break outward under pressure.

The igniter is actuated by means of an electrical squib 20 or, if desired, a plurality of such squibs, which can be inserted, as shown in Figure 3, in the black powder charge. The squib is attached to electrical contacts such as the terminal binding posts 21 and 22 which extend through and project exteriorly of the closure plate and are insulated therefrom. The arming rod 15, which is a lowresistance electrical conductor, is provided With groove 23 and slot 24 so that it can be brought into disengageable contact with electrical squib contacts 21 and 22 as shown in Figures 1, 3 and 4. In this safety position the arming rod serves as an electrical shunt by diverting electric current from the squib, thereby preventing accidental electrical actuation of the squib by stray electric current or accidental closing of the electrical firing circuit. In this position, also, the arming rod is not in expansion engagement with the locking ring and does not effectuate .4 locking engagement of the closure plate with the igniter cup.

To arm the igniter, namely to place it in electrical firing readiness, the slidable arming rod or shunt is moved out of by-pass relation with both electrical squib contacts as shown in Figure 5 and the full current can then pass through and actuate the squib. Simultaneously the arming rod expands the retaining ring into locking engagement with the igniter cup and closure plate. 1

The electrical squib contacts can be connected directly to the source of firing current. However, as an additional safety feature, a switch 28 can be interposed in the igniter firing circuit by connecting it in series with the squib as, for example, by attachment to one of the electrical squib contact leads 25, and to wire 29 which leads to connector 27 which in turn connects the igniter to the source of current (not shown). Said switch as shown comprises a fixed arm 36 and a movable arm 37, carrying the respective terminals 33 and 32, the arm 37 being intermediately pivoted to provide an oscillatory movement to said arm. The end of the arm 37 opposite the terminal 32; is connected by a pin and slot connection to a reciprocating plunger 31 projected by a spring 38 to rock the arm 37 in such direction as to close the switch. The spring-biased movement of the plunger is limited by a tab 30 carried by the arming rod 15 which moves into the path of projection of the plunger as the arming rod is placed in safety position, thus holding the switch open and providing a gap in the firing circuit serially related to the shunt aiforded by the arming rod, as shown in Figures 1, 3 and 4. Thus accidental triggering of the electrical firing switch has no effect on the igniter.

When the igniter is armed, namely placed in firing readiness by sliding the arming rod or shunt out of by-pass contact with the squib terminals, the arming rod tab is simultaneously removed from engagement with the switch plunger so that the plunger is released, as shown in Figure 5, permitting the switch terminals 32 and 33 to come into contact and to close the igniter electrical firing circuit. Current sent into the igniter circuit can now actuate the squib and thereby fire the igniter charge.

The exterior portion of the electrical igniter circuit, including the switch, can be combined as a unit in a protective housing 34 and attached to the back or closure plate of the igniter. The igniter cup and closure plate can be made of any suitable material such as plastic or metal.

The movement of the arming rod from safe to armed position can be accomplished by any suitable means such as by a handle 35, which can be manually operated or by means not shown, for example, lanyard, lever, gear, screw and crank, hydraulic piston, electrical solenoid or the like.

Figure 6 is a schematic diagram of the igniter electrical firing circuit in safety position showing the arming rod shunt in by-pass contact with the squib terminals and in engagement with the switch plunger, thereby keeping the switch terminals open and interrupting the circuit.

It will be understood that although the illustrative example described above and in the drawings shows all of the safety features of my invention, such combination does not necessarily delineate the scope of the invention. The shunt can be employed alone or in combination with the switch with a conventional igniter which is not equipped with a mechanical closure plate expulsion means. The shunt by-pass can also be employed in combination with my novel closure plate blow-off safety feature with the arming rod serving the dual function of low-resistance electrical conductor and locking ring expansion means with or Without the switch.

I claim:

1. An igniter adapted to be inserted into the opening in the wall of a chamber containing a combustible charge, said igniter comprising a receptacle for an igniter charge, an electrical squib for igniting said igniter charge, a pair of electrical contacts bridged by said squib, a movable electrical shunt disengageably bridging said contacts whereby electric current is diverted from said squib, a switch in series circuit with said squib and an electrical source, said switch including a movable arm normally in closed switch position, said shunt including an element operatively related to said movable arm to open said switch when said shunt is in bridge position, whereby the igniter electrical firing circuit is interrupted.

2. An igniter comprising a cup containing an igniter charge adapted to be inserted into the opening in the wall of a chamber containing a combustible charge, said cup having its mouth facing outwardly with respect to said chamber and having an inner wall rupturable under pressure exerted by combustion products of the igniter charge, a plate adapted to be inserted into the mouth of the cup forming a closure therefor, means for disengageably securing the plate to the cup, said securing means being yieldable to pressure exerted by combustion products of the igniter charge whereby the closure plate can be ejected outwardly, said securing means being yieldable to release said ejectable closure plate at pressures lower than that required to burst said rupturable wall, said cup and said closure plate being provided with oppositely positioned contiguous annular grooves, a split locking ring normally contained within the groove of the closure plate, slidable means for expanding said locking ring into overlapping relationship between said contiguous grooves whereby said closure plate and said cup are fixedly engaged, an electrical squib for igniting the igniter charge, and a pair of electrical contacts bridged by said squib, said slidable means for expanding the locking ring functioning as an electrical shunt disengageably bridging said contacts when the slidable means is out of expansion engagement with the locking ring, whereby electric current is diverted from said squib, said slidable means, when disengaged from by-pass contact with said electrical squib contacts moving into expansion engagement with the locking ring, thereby placing said igniter in firing readiness.

3. An igniter comprising a cup containing an igniter charge adapted to be inserted into the opening in the wall of a chamber containing a combustible charge, said cup having its mouth facing outwardly with respect to said chamber and having an inner wall rupturable under pressure exerted by combustion products of the igniter charge, a plate adapted to be inserted into the mouth of the cup forming a closure therefor, means for disengageably securing the plate to the cup, said securing means being yieldable to pressure exerted by combustion products of the igniter charge whereby the closure plate can be ejected outwardly, said securing means being yieldable to release said ejectable closure plate at pressures lower than that required to burst said rupturable wall, said cup and said closure plate being provided with oppositely positioned contiguous annular grooves, a split locking ring normally contained within the groove of the closure plate, slidable means for expanding said locking ring into overlapping relationship between said contiguous grooves whereby said closure plate and said cup are fixedly engaged, an electrical squib for igniting the igniter charge, a pair of electrical contacts bridged by said squib, said slidable means for expanding the locking ring functioning as an electrical shunt disengageably bridging said contacts when the slidable means is out of expansion engagement with the locking ring, whereby electric current is diverted from said squib, and a switch in series circuit with said squib, said switch including a movable arm normally in closed switch position, said slidable means including an element operatively related to said movable arm to open said switch when said slidable means is in bridging shunt position, whereby the igniter electrical firing circuit is interrupted, said slidable means, when contacts and from said switch moving into expansion engagement with locking ring, thereby placing said igniter in firing readiness.

4. The igniter of claim 2 in which the slidable means has a portion provided with cam faces positioned to expand the locking ring.

5. The igniter of a claim 3 in which the slidable means has a portion provided with cam faces positioned to expand the locking ring.

6. An igniter adapted to be inserted into the opening in the wall of a combustion chamber containing a combustible charge, said igniter comprising a receptacle for an igniter charge, said receptacle having two walls constructed to release under pressure from the igniter charge combustion products, one of said walls releasing at lower pressure than the other, the wall that releases at higher pressure being adjacent the combustible charge when said igniter is positioned in said combustion chamber, movable locking means, operative at will, for locking against release that wall which responds to lower pressure, an electrical squib for igniting the igniter charge, and a pair of electrical contacts bridged by said squib, said movable locking means functioning as an electrical shunt disengageably bridging said contacts when the movable means is out of locking position holding the wall responsive to lower pressure against release, whereby electric current is diverted from said squib, said movable means, when disengaged from by-pass contact with said electrical squib contacts, moving into locking position preventing release of the wall responsive to lower pressure, thereby placing said igniter in firing readiness.

7. An igniter adapted to be inserted into the opening in the wall of a combustion chamber containing a combustible charge, said igniter comprising a receptacle for an igniter charge, said receptacle having two walls constructed to release under pressure from the igniter charge combustion products, one of said walls releasing at lower pressure than the other, the wall that releases at higher pressure being adjacent the combustible charge when said igniter is positioned in said combustion chamber, movable locking means, operative at will, for locking against release that wall which responds to lower pressure, an electrical squib for igniting the igniter charge, a pair of electrical contacts bridged by said squib, said movable locking means functioning as an electrical shunt disengageably bridging said contacts when the movable means is out of locking position holding the wall responsive to lower pressure against release, whereby electric current is diverted from said squib, and a switch in series circuit with said squib, said switch including a movable arm normally in closed switch position, said movable means for locking against release that wall which responds to lower pressure including an element operatively related to said movable arm to open said switch when the movable locking means is in bridging shunt position, whereby the igniter electrical firing circuit is interrupted, said movable locking means, when disengaged from by-pass contact with said electrical squib contacts and from said switch, moving into locking position preventing release of the wall responsive to lower pressure, thereby placing said igniter in firing readiness.

8. An igniter adapted to be inserted into the opening in the wall of a combustion chamber containing a combustible charge, said igniter comprising a receptacle for an igniter charge and having a rupturable wall and an ejectable wall both subject to igniter charge combustion product pressure within the receptacle, the rupturable wall being adjacent the combustible charge when said igniter is positioned in said combustion chamber, means for securing said ejectable wall to said receptacle, said securing means being yieldable to release said ejectable wall at pressures lower than that required to burst said rupturable wall, movable locking means for locking said ejectable wall against release at pressures higher than that required to burst said rupturable wall, an electrical squib for igniting the igniter charge, and a pair of electrical contacts bridged by said squib, said movable locking means functioning as an electrical shunt disengageably bridging said contacts when the movable locking means is out of locking position holding the ejectable wall against release, whereby electric current is diverted from said squib, said movable locking means, when disengaged from by-pass contact with said electrical squib contacts, moving into locking position preventing release of the ejectable wall, thereby placing said igniter in firing readiness.

9. An igniter adapted to be inserted into the opening in the wall of a combustion chamber containing a combustible charge, said igniter comprising a receptacle for an igniter charge and having a rupturable wall and an ejectable wall both subject to igniter charge combustion product pressure Within the receptacle, the rupturable wall being adjacent the combustible charge when said igniter is positioned in said combustion chamber, means for securing said ejectable wall to said receptacle, said securing means being yieldable to release said ejectable wall at pressures lower than that required to burst said rupturable wall, movable locking means for locking said ejectable wall against release at pressures higher than that required to burst said rupturable wall, an electrical squib for igniting the igniter charge, a pair of electrical contacts bridged by said squib, said movable locking means functioning as an electrical shunt disengageably bridging said contacts when the movable locking means is out of locking position holding the ejectable wall against release, whereby electric current is diverted from said squib, and a switch in series circuit with said squib, said switch including a movable arm normally in closed switch position, said movable means for locking the ejectable wall against release including an element operatively related to said movable arm to open said switch when the movable locking means is in bridging shunt position, whereby the igniter electrical firing circuit is interrupted, said movable locking means, when disengaged from by-pass contact with said electrical squib contacts and from said switch, moving into locking position preventing release of the ejectable wall, thereby placing said igniter in firing readiness.

10. An igniter adapted to be inserted in the opening in the wall of a chamber containing a combustible charge, said igniter comprising a receptacle for enclosing an igniter charge, an electrical squib within said receptacle for igniting said igniter charge, a pair of electrical contacts carried by said receptacle, in circuit with said squib, a switch in series circuit with said squib, movable means carried by said receptacle engageable with said contacts for establishing a shunt across said contacts whereby current can be diverted from said squib, said shunt establishing means being operatively related to said switch for closing the latter responsive to shunt establishing movement of said means.

11. An igniter adapted to be inserted in the opening in the wall of a combustion chamber containing a combustible charge, said igniter comprising a receptacle for enclosing an igniter charge, including two walls constructed to release responsive to pressure of the igniter charge combustion products, one of said walls releasing at lower pressure than the other, the wall that releases at higher pressure being between the igniter charge and said combustion chamber when said igniter is in inserted position, locking means, unitary with said receptacle for locking against release that wall which responds to lower pressure, an electrical squib within said receptacle for igniting said igniter charge, a pair of electrical contacts carried by said receptacle, in circuit with said squib, a switch in series circuit with said squib, movable means carried by said receptacle engageable with said contacts for establishing a shunt across said contacts whereby current can be diverted from said squib, said shunt establishing means being operatively related to said switch and to said locking means, to open said switch and release said locking means responsive to shunt establishing movement of said shunt establishing means.

References Cited in the file of this patent UNITED STATES PATENTS 2,682,223 Lewis June 29, 1954 2,775,201 Conway Dec, 25, 1956 FOREIGN PATENTS 20,467 Great Britain of 1902 KARL H. AXLINE v U. 8. DEPARTMENT OF COMMERCE PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 2,828,692 Robert O. Webster It is hereby certified that error appears .in the printed specification of the above numbered patent requiring correction and that the said Lettere Patent should read as corrected below.

Column 8, line 11, for "closing" read opening Signed and sealed this 17th day of June 1958.

(SEAL) Attest:

, ROBERT c. WATSON Attesting Officer April 1,, 1958 r Conmissioner of Patents U. S. DEPARTMENT OF COMMERCE PATENT OFFICE CERTIFICATE OF CORRECTION Patent No} 2,828,692 Robert 0. Webster April 1,1958

It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 8, line 11, for "closing" read opening Signed and sealed this 17th day of June 1958.

(SEAL) Attest:

KARL .7

H AXLINE ROBERT C. WATSON Attesting Officer Comnissioner of Patents.

U. S. DEPARTMENT OF COMMERCE PATENT OFFICE CERTIFICATE OF CORRECTION Patent Noa 2,828,692 Robert O. Webster April 1, i958 It is hereby certified that error appears .in the printed specification of the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 8, line 11, for "closing" read opening Signed and sealed this 17th day of June 1958.

(SEAL) Attest:

KARL H. AXLINE ROBERT C. WATSON Attesting Officer Comissioner of Patents.

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