Igniter assembly actuated by parachute deployment, and flare containing the same

RELATED APPLICATIONS

Priority is claimed of provisional application No. 60/145,129 filed in the U.S. Patent & Trademark Office on Jul. 22, 1999, the complete disclosure of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a novel igniter assembly for igniting combustible compositions in a highly reliable manner, and in particular to an igniter assembly which includes a combustible illuminant composition and as actuated by deployment of an associated parachute. This invention also relates to devices comprising the novel igniter assembly, such devices including, by way of example, illuminating flares.

2. Description of the Related Art

Among the various environments in which illuminating flares are used, perhaps the most common environment for the use of flares involves the illumination of military battle grounds. In such applications, the flares are launched above ground or water areas suspected to contain enemy personnel and vehicles. Essentially, the illumination provided by the flare facilitates visual detection of the enemy personnel and vehicles, thereby providing more precise identification of target locations at which to aim arsenal. The illuminating effect provided by the flare is typically enhanced by equipping the flare with a parachute, which both increases the flight and time of descent for the illuminating flare and, upon deployment thereof, provides a requisite force for actuating an igniter housed in the flare.

The use of flares to ascertain the precise location of enemy targets can provide obvious military advantages. However, the availability and widespread use of military flares has negated this advantage somewhat, since there is an increased likelihood of opposing military forces also possessing flares. Thus, in order to gain a military advantage from the flares, it is paramount that the flares operate in a highly reliable and dependable manner, since flare failure can provide the opposing military force additional time to launch their own flares and arsenal.

An example of an illuminating flare that is reliable by conventional standards, e.g., about 87% of the time, is shown in

FIGS. 5-7

herein. It is believed that one of the largest contributors, if not the largest contributor, to failed firing of this illuminating flare is the misfiring of the flare igniter. The flare, which is generally designated by reference numeral

200

in

FIG. 5

, comprises an aluminum casing

202

partitioned into two compartments. The forward compartment is the larger of the two compartments, and contains a solid illuminant fuel

204

designed to enhance nighttime vision and an igniter assembly

206

for initiating burning of the illuminant fuel

204

. In the illustration, the aft compartment is the smaller of the two compartments, and contains a parachute

208

and a timing device (unnumbered). The timing device, inserted at an aft end of the casing

202

, detaches from the flare casing

202

at a predetermined time to create a passageway through which the parachute

208

can deploy. Upon deployment through the passageway, the parachute

208

slows the rate of descent of the flare

200

, thereby extending the time during which the burning illuminant fuel

204

is maintained at an elevated position. In this manner, the illuminating effect provided by the burning illuminant fuel

204

is enhanced.

A conventional igniter is disclosed in U.S. Pat. No. 4,155,306 and illustrated in

FIGS. 6 and 7

herein. Referring to

FIG. 6

, the igniter

206

includes a housing

212

formed of a molded piece of LEXAN (polycarbonate) or light-weight metal. The housing

212

has longitudinally extending internal walls

213

and ridge

213

a

, which are receivable into an aluminum cap (not shown). The internal walls

213

and the ridge

213

a

define upper and lower hollow compartments

215

, and a diametrically extending raceway

214

interposed between the upper and lower compartments

215

. The raceway is defined in part by the ridge

213

a

of the internal wall

213

. The ridge

213

a

has a depth less than that of the remainder of the internal walls

213

. For convenience, the ridge

213

a

is shaded. The function of the ridge

213

a

is explained in further detail below.

A sliding cartridge (also referred to herein as a slider)

216

is disposed in the raceway

214

and is slidable along the raceway

214

. The slider

216

comprises a spring-loaded striker arm

218

, a torsion spring (located at position

220

), and a pistol primer (containing small amount of explosive)

222

. The striker arm

218

is depicted in a loaded or cocked position in FIG.

6

. The torsion spring

220

urges the striker arm

218

to pivot about pin

224

and towards the position shown in

FIG. 7

, in which the striker arm

218

rests against the primer

222

. A cam surface

225

of the housing

212

obstructs the striker arm

218

from moving towards the primer

222

and, in combination with the urging force of the spring

220

, prior to actuation maintains the slider

216

in the position depicted in FIG.

6

.

Located below the raceway

214

is a pellet cavity

226

containing an ignitable composition, such as boron potassium nitrate (BKNO

3

) pellets. The pellet cavity

226

is in communication with the solid illuminant fuel

204

through an orifice (not shown).

The slider

216

is operatively connected to the parachute

208

via cable or lanyard

230

, which extends along a cable raceway (not shown) formed in the aluminum casing

202

. The cable

230

contains a first swage ball

232

accommodated within recess

234

for securing the cable

230

to the slider

216

. The recess

234

is in communication with a slot

236

, which is sufficiently wide to permit passage of the cable

230

, but to obstruct passage of the first swage ball

232

. At the end of the cable

230

is a second swage ball (not shown, but positioned behind the first swage ball

232

in FIG.

6

). The cable

230

extends between the first swage ball

232

and the second swage ball along an axial direction, that is, perpendicular to the portion of the cable

230

passing through the slot

236

(i.e., into the sheet on which

FIGS. 6 and 7

are shown). The second swage ball is encapsulated into the internal wall

213

. The encapsulation of the second swage ball in the internal wall

213

serves as a safety mechanism to protect against unintentional firing by preventing tension in the cable

230

from prematurely moving the slider

216

along the raceway

214

.

In operation, the igniter assembly

206

is actuated by the force generated upon parachute

208

deployment. Upon actuation of the parachute

208

, the deploying parachute pulls the cable

230

towards the aft end of the flare

200

. When properly operated, the force imparted on the cable

230

by the deploying parachute

208

is sufficient to dislodge the second swage ball from the housing

212

and move the slider

216

in tandem with striker arm

218

and the primer

222

across the raceway

214

with sufficient force to overcome the frictional resistance between the cocked striker arm

218

and the cam surface

225

, as well as the frictional resistance between the slider

216

and the raceway

214

, thus passing the striker arm

218

under the cam surface

225

.

After the slider

216

has moved a sufficient distance for the striker arm

218

to clear the cam surface

225

, the urging force of the torsion spring

220

pivots the striker arm

218

about pin

224

and towards the primer

222

, which is now located over the cavity

226

containing pellets. Impact of striker arm

218

against the primer

222

detonates the primer

222

. The heat and flames generated by the detonation of the primer

222

pass through an orifice and ignite the BKNO

3

pellets in cavity

226

, which in turn ignites a wafer, which in turn ignites the solid illuminant fuel

204

. Because the ridge

213

a

of the internal wall

213

extends in depth only a portion of the way across the depth of the raceway

214

, a clearance is defined (between the ridge

213

a

and the opposing cap surface) through which the striker arm

218

can pass as the striker arm

218

pivots towards the primer

222

.

Although effective by conventional standards, flares possessing the igniter assembly

206

function correctly only approximately 87% of the time. In the majority of the cases in which failure occurred, the slider mechanism

216

was found to have traveled only part of the way down the raceway, with the cable found either broken or intact. The reasons for these failures are believed to be as follows: The deployment of the parachute

208

imparts an instantaneous shock force to the cable

230

, causing the second swage ball to dislodge from the slider wall in which the second swage ball is encapsulated. However, the remaining force imparted to the cable

230

by parachute deployment is not always sufficient to overcome additional frictional forces at the slider/raceway interface and the interface between the cocked striker arm

218

and the cam surface

225

. These frictional forces can prevent the slider

216

from moving sufficient distance to clear the cam surface

225

and reaching and striking the primer

222

. One reason for the high frictional force at the slider/raceway interface is that the cable does not pull at the center of the slider

216

. Another reason is that the ridge

213

a

defining the top of the raceway

214

does not extend along the full depth of the slider

216

(in order to provide a clearance for passage of striker arm

218

as the striker arm

218

pivots from the cocked state to the firing state). The presence of this clearance is believed to allow the slider

216

to rotate somewhat about its longitudinal axis in the raceway

214

during sliding movement, thus increasing frictional forces.

SUMMARY OF THE INVENTION

It is, therefore, an object of this invention to overcome the above-discussed problems by the provision of an igniter assembly which reduces sticking of the slider in the raceway.

It is another object of this invention to provide an igniter assembly that has built-in safety features to significantly reduce the risk of the flare being accidentally fired due to impact. These safety features include, for example, the placement of the pellet cavity out of alignment with respect to the primer and striker arm prior to firing, and in one particularly advantageous embodiment, a static force minimum of preferably 50 lbs, more preferably 90 lbs, to cause ignition.

In accordance with a preferred embodiment of this invention, the striker arm and the primer are stationary relative to the igniter housing, in contrast to the known assembly shown in

FIGS. 6 and 7

. The pellet-containing chamber, which is stationary in the known assembly shown in

FIGS. 6 and 7

, is in accordance with the present invention incorporated into the slider so that the pellet chamber is not aligned with the striker arm in the cocked position. In the preferred embodiment, another feature for preventing the unintentional firing and ignition of the illumination composition involves providing the slider with a motion restricting bridge.

At least one of the following design features is desirably incorporated into the novel igniter assembly to accomplish the above and other objects, although the scope of the invention is not hereby limited. First, the igniter housing has raceway-defining walls having a depth (along the longitudinal direction of the flare) substantially equal to the depth of the slider, so that the slider does not contact any ridges during movement along the raceway. Second, greater symmetry is utilized in the slider to keep pulling forces in balance. Third, the distance of slider travel along the raceway is shortened. Fourth, the slider is made of a material that is more compatible with the igniter housing on a coefficient of friction basis. Fifth, the encapsulated swage ball is replaced by a less complex safety mechanism, such as a motion restricting bridge.

This invention is also directed to devices containing the novel igniter assembly. A representative non-limiting device intended to be covered by this invention is an illuminating flare.

This invention is also directed to a method of illuminating a field with an illuminating flare comprising the novel igniter assembly described herein.

Other objects, aspects and advantages of the invention will be apparent to those skilled in the art upon reading the specification and appended claims which, when read in conjunction with the accompanying drawings, explain the principles of this invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings serve to elucidate the principles of this invention by illustration. In such drawings:

FIG. 1

is a plan, partially phantomed view of an igniter assembly (without an enclosure cap) in accordance with one embodiment of this invention, depicting a slider and striker arm of the igniter assembly in a loaded state;

FIG. 2

is a plan, partially phantomed view of the igniter assembly of

FIG. 1

, but depicting the slider and striker arm in a firing state;

FIG. 3

is an isolated, perspective view of the slider of the igniter assembly of

FIGS. 1 and 2

;

FIG. 4

is an exploded perspective view of the igniter assembly of

FIGS. 1-3

;

FIG. 5

is a partially sectioned view of a known flare;

FIG. 6

is a plan, partially phantomed view of a known igniter assembly, depicting a slider and striker arm of the igniter assembly in a loaded state;

FIG. 7

is a plan, partially phantomed view of the known igniter assembly of

FIG. 6

, but depicting the slider and striker arm in a firing state;

FIG. 8

is a top plan view of a cartridge depicting the striker arm in a fired position; and

FIG. 9

is a side sectional view of the cartridge of FIG.

8

.

DETAILED DESCRIPTION OF THE INVENTION

An example of a basic design of the illuminating flare with which the igniter of this invention is compatible is shown in FIG.

5

. In the interest of brevity, and because the design of known illuminating flares is within the purview of the skilled artisan, the following discussion will be limited to the novel igniter assembly of this invention.

Referring to

FIG. 1

, the igniter

106

includes a housing

112

formed of a molded piece of LEXAN (polycarbonate). The housing

112

has longitudinally extending internal walls

113

, which are receivable into an aluminum cap

150

(

FIG. 4

) of the casing so that peripheral portion

112

a

of the housing

112

abuts the periphery of the aluminum cap

150

. Groove

112

b

assists in aligning the housing

112

and the aluminum cap

150

with the flare body. The internal walls

113

define a top hollow compartment

115

a

, a bottom hollow compartment

115

b

, and a diametrically extending slider raceway

114

. Although the compartments

115

a

and

115

b

are optional, their presence is preferred in order to lower material costs and provide a venting feature discussed in greater detail below. A sliding mechanism (also referred to herein as a slider)

116

is disposed in the raceway

114

and is slidable along at least a portion of the raceway

114

. In a preferred embodiment, the slider

116

is capable of sliding about 0.5 inches (about 1.27 cm) along the raceway

114

. Each of the internal walls

113

defining the raceway

114

has a depth (perpendicular to the plane of

FIG. 1

) set substantially equal to the depth of the sliding mechanism

116

.

The slider

116

is movable between a loaded state depicted in

FIG. 1 and a

firing state depicted in FIG.

2

. Referring to

FIG. 1

, the slider

116

has a central pocket

116

a

constructed and arranged to receive a stationary cartridge

117

. (Although not shown in the figures, the cartridge

117

can further be provided with a pin hole and pin for retaining the striker arm

118

in the cocked position during assembly.) The slider

116

comprises a motion restricting bridge

128

positioned at an open end of the central pocket

116

a

. A stationary cutter

140

of the cartridge

117

is positioned in the central pocket

116

a

and contacts the motion restricting bridge

128

. Although not shown, the region of the motion restricting bridge

128

contacted by the stationary cutter

140

may contain a notch to facilitate fracture of the bridge

128

. When in the loaded state depicted in

FIG. 1

, contact between the motion restricting bridge

128

and the stationary cutter

140

obstructs the slider

116

from sliding towards the firing position depicted in

FIG. 2

, unless a sufficient force is applied to the slider

116

to break the bridge

128

along cutter

140

. The slider

116

also has incorporated therein a pellet cavity

126

and striker pin clearance slot (also referred to herein as the striker arm clearance slot)

119

, the purpose of which will be explained in greater detail below. An aluminum strip (not shown) lines a portion of the pellet cavity

126

through which the explosion from the primer

122

penetrates during actuation. The aluminum strip serves to protect the pellets from accidental ignition in the event that the primer material undergoes undesired ignition by means other than the striker arm. The pellet cavity

126

is movable into communication with a wafer (not shown), which is in communication with solid illuminant fuel. The pellet cavity

126

contains an ignitable composition, such as boron potassium nitrate (BKNO

3

) pellets. Preferably, the pellet cavity

126

is capable of receiving at least eleven BKNO

3

pellets. (The pellets are preferably loaded into the cavity

126

after the igniter assembly has been assembled. Since the pellet cavity

126

moves, an oblong hole is provided in the base of the housing to allow pellet loading through the housing, as well as communication between the pellet cavity

126

and the wafer over the entire path of movement of the pellet cavity

126

.) The size of the slider

116

is determined by taking into account the diameter of the boron pellet cavity and the clearance slot

119

needed for passage of the spring-loaded striker arm

118

.

As shown in

FIGS. 8 and 9

, the cartridge

117

is generally of a known construction and comprises the spring-loaded striker arm

118

, a torsion spring

120

, and a pistol primer

122

. The cartridge

117

can be either formed separately from the housing

112

or injection molded into the housing

112

during formation of the housing

112

so that the cartridge

117

and housing

112

are integral. The striker arm

118

, the torsion spring

120

, and the pistol primer

122

are then assembled in the cartridge

117

. In the loaded state illustrate in

FIG. 1

, the torsion spring

120

urges the striker arm

118

to pivot about pin

124

towards the position shown in

FIG. 2

in which the striker arm

118

is seated against the primer

122

. However, when the slider

116

is in the loaded state, a cocking wall portion

124

of the slider

116

obstructs the striker arm

118

from moving from its cocked position towards the primer

122

.

The slider

116

is operatively connected to the parachute via cable (or lanyard)

130

, which extends along an axial channel (not shown) contained in the flare body. The cable

130

is attached to the slider

116

via a swage ball

132

, which is accommodated within recess

134

of the slider

116

for securing the cable

130

to the slider

116

. The recess

134

is in communication with a slot

136

, which is sufficiently wide to permit passage of the cable

130

, but sufficiently narrow to obstruct passage of the swage ball

132

therethrough. Preferably, the cable

130

is aligned with the longitudinal axis (center) of the slider

116

. Instead of using a roller pin to redirect the cable

130

near the end of the flare, a LEXAN molded surface having a relatively large radius can be used to redirect the cable

130

towards the longitudinal axis of the slider

116

. Enlarging of the turn radius reduces the likelihood of cable

130

breakage.

In operation, the igniter

106

is actuated by the force generated upon parachute deployment. Upon actuation of the parachute, the cable

130

is pulled with the deploying parachute. When properly operated, the force imparted on the cable

130

by the deploying parachute is sufficient to cause the cable

130

to pull the slider

116

from its loaded state to its firing state while simultaneously breaking motion restricting bridge

128

along the stationary cutter

140

. After the bridge

128

has been broken, the bridge segments (designated by reference numerals

128

a

and

128

b

in

FIG. 2

) flare over the cutter

140

and keep the slider

116

from moving backwards (i.e., towards its loaded state position). The cutter

140

is preferably designed with a small radius on the tip rather than a sharp edge, so that over time the edge of the cutter

140

will not wear throught the bridge

128

due to normal vibrations experienced during transportation of the flare.

Movement of the slider

116

into the firing state depicted in

FIG. 2

moves the striker arm

118

out of contact with cocking wall portion

124

and aligns the striker arm

118

with striker pin clearance slot

119

. As shown in

FIG. 3

, the cocking wall portion

124

can contain a guide slot

124

a

for receiving the striker pin (unnumbered) at the distal end of the striker arm

118

. Provision of this guide slot

124

a

prevents the tip of the striker pin from becoming embedded in the wall portion

124

, thus further enhancing the reliability of the igniter. The striker arm

118

is hence permitted to move through the striker pin clearance slot

119

(due to the urging force imparted by the torsion spring

120

) until the striker arm

118

strikes against the primer

122

.

Movement of the slider

116

into the firing state depicted in

FIG. 2

also moves the cavity

126

to align the cavity

126

with primer

122

. Thus, detonation of the primer

122

starts an ignition sequence by which the BKNO

3

pellets, the wafer, and the illuminant composition are sequentially ignited.

The bridge

128

provides a variable safety feature for controlling the force required to move the slider

116

. The stress on the bridge

128

is equal to force over area. By increasing the height of the bridge

128

, more stress is required to break the bridge

128

. In one embodiment, the bridge

128

height was set at about 0.0305 cm (0.12 inch) to 0.356 cm (0.14 inch) to prevent backward movement of the slider

116

and provide a minimum pull force requirement of at least 50 lbs force, more preferably 90 lbs force to move the slider

116

into the firing state shown in FIG.

2

.

As mentioned above, the bridge

128

can be provided with a notch for facilitate fracture of the bridge

128

with cutter

140

.

Another optional safety feature is the provision of one or more holes (not shown) through the walls

113

defining the raceway

114

so that, if by some mishap the primer

122

were to unintentionally ignite before the slider

116

is moved to its firing state, the gases generated by ignition of the primer

122

can be vented to one or both of the outside compartments

115

a

and

115

b

to prevent ignition of the BKNO

3

pellets.

In identifying suitable materials for making the igniter assembly, the following criteria were taken into consideration: (a) form the igniter housing and slider from a material having a friction coefficient at least as low as LEXAN sliding against LEXAN; (b) permit inspection of igniter assembly by making housing from a transparent material; (c) provide good mating properties with aluminum case by choosing material having low coefficient of thermal expansion; and (d) select materials having high impact strength to avoid shattering, high tensile strengths to avoid breakage at cable slot, and high glass transition and distortion temperatures. Preferably, polycarbonate is selected as the material of choice for the igniter housing and polycarbonate with 7% TEFLON is selected as the material of choice for the slider.

Representative infrared illuminating compositions that may be used with this invention are disclosed in U.S. Pat. Nos. 3,411,963, 5,056,435, 5,587,522, 5,912,430, and 6,123,789, the disclosures of which are incorporated herein by reference.

Parachute deployment systems and conventional flare assemblies modifiable for use with the igniter of this invention are disclosed in U.S. Pat. Nos. 5,386,781 and 5,347,931, the disclosures of which are incorporated herein by reference.

The foregoing detailed description of the invention has been provided for the purpose of explaining the principles of the invention and its practical application, thereby enabling others skilled in the art to understand the invention for various embodiments and with various modifications as are suited to the particular use contemplated. The foregoing detailed description is not intended to be exhaustive or to limit the invention to the precise embodiments disclosed. Modifications and equivalents will be apparent to practitioners skilled in this art and are encompassed within the spirit and scope of the appended claims.