Battery initiator system

In a reserve battery initiator a unitary moulded ampoule (10) containing an electrolyte comprises two portions conjoined by a mechanically weak section (11). The ampoule (10) may be ruptured by a striker (3) which is released when the initiator is subjected to sufficient an accelerative force to overcome a detent mechanism. The ampoule may also contain an insert (12) to transmit to the weak section the force imparted by the striker. The insert (12) may additionally have a cutting effect on the weak section (11). Conveniently the insert is in the form of a frustrum with a narrow end contiguous with the inner face of the ampoule at the location where the striker (3) impacts and a wide end contiguous with the inner face of the weak section (11).

The present invention relates to a reserve battery initiation device which 
is designed to be triggered by acceleration of a reserve battery unit 
incorporating the device. 
Reserve batteries are batteries which can be brought into operation as 
desired, usually by introduction of an electrolyte into the battery and 
which, until the time when such operation commences should remain highly 
stable and not suffer from deterioration. Reserve batteries commonly 
comprise a cell stack in which adjacent cells are separated by solid 
plates coated for example on one side with a layer of lead and on the 
other with a layer of lead dioxide. The plates are commonly of steel. To 
initiate operation of the battery an electrolyte is introduced into the 
cell stack and the electrolyte is usually one which produces soluble 
reaction products at the electrodes, eg perchloric or fluoroboric acid. 
This helps to prevent bridging of the plates in a cell which might occur 
if the reaction products were deposited as solid matter. 
Some batteries intended for applications in which they are rapidly rotated 
while in use are formed with flat parallel bi-polar plates disposed in 
planes perpendicular to the axis of rotation. In one such known 
arrangement the plates are annular and the stack thus forms a cylinder 
with a coaxial cylindrical space therethrough in which space it is 
convenient to place the source of the electrolyte. Thus when the 
electrolyte is released it will be thrown outwards by the spinning motion 
of the whole unit and provision of apertures in the radially inner walls 
of each of the cells allows the electrolyte to enter the cells and to 
initiate operation of the battery. 
The electrolyte is generally held in an ampoule which may be formed of 
plastics material or of a thin metal. Various systems have been devised to 
rupture the ampoule to initiate battery operation but all of these suffer 
from disadvantages for a variety of reasons. In particular when the 
ampoule is made of a thin material there is a danger of it being broken 
accidentally through rough handling of the battery/initiator unit, and to 
make the ampoule of metal (which must be one which will be almost 
completely resitant to chemical attack by the electrolyte) is relatively 
expensive in any event. For these reasons ampoules of inert plastics 
material, especially polyethylene, have been very widely used to contain 
the electrolyte for reserve batteries. These have generally been provided 
with a portion of wall which is considerably weaker than other portions of 
the ampoule wall so that the wall fractures preferentially thereat. Such 
weak sections have in the past been provided by machining away a portion 
of the ampoule wall to produce a mechanically weak section formed by a 
V-notch at which fracture is caused to occur by striking the ampoule 
against an anvil or by the effect of gas pressure generated by a 
rapidly-burning charge, ignited by a moving element housed in the 
initiator. 
In these arrangements the movement required to break the ampoule or to 
cause it to be broken may be initiated by some independant action or may 
occur automatically as the result of an acceleration of the system, in 
which case the inertia of a part of the system which is free to move 
relative to the system as a whole is used to produce the desired relative 
movement. In this latter case the movement may be caused to commence only 
when a pre-determined rate of acceleration is exceeded over a 
predetermined period, suitable detent means being employed to prevent 
movement taking place until this has occurred. 
This reduces the danger of an unwanted release of the electrolyte from the 
ampoule occurring as for example might otherwise happen if the 
battery/initiator unit were merely allowed to fall freely on to a surface 
which would cause it to experience a high deceleration but of almost 
instantaneous duration. 
Ampoules with machined weak sections have proved to be not entirely 
satisfactory in operation. In particular it is very difficult to achieve 
consistent machining of the weak sections since the extent of machining is 
dependent on such variables as the nature of the plastics material, the 
skills and conscientiousness of the operative and the condition of the 
machining tools. Because of these factors the thinness of the ampoule 
walls at the weak section is in practice quite variable and as a result 
the performance of the ampoules under striking impact is not consistent. 
This means that for a batch of ampoules which are arranged to be struck 
with the same force and the weak sections of which have nominally the same 
strength, some will not in fact rupture due to under-machining of the weak 
section, while with others of the batch the maximum height from which they 
may be dropped without rupture may be less than that expected based upon 
the nominal (design) thickness of the weak section. 
A further disadvantage of machined weak sections is that machining cuts 
through one of the skins of the ampoule moulding and thus removes one of 
the barriers to migration of the electrolyte thorugh the wall of the 
ampoule, the skins being more resistant to migration than the material 
betweeen them. Reserve battery systems are often by their very nature 
required to be kept awaiting use for long periods of time, eg many years 
in the case of a warning system energiser, and this reduced resistance to 
migration of the electrolyte can mean a loss of activity of the battery 
after long storage. 
According to the present invention a reserve battery initiator comprises an 
ampoule for containing an electrolyte solution, said ampoule having two 
portions, conjoined by a mechanically weak section, one portion being 
moveable relative to the other upon rupture of the weak section to release 
the electrolyte solution from the ampoule, a striker mounted to impact 
with the said ampoule so as to rupture the ampoule at its mechanically 
weak section; and an insert being contiguous with the weak section which 
extends in a closed path and with the area of impact of the striker, said 
insert being arranged to transmit a force imparted by the striker from the 
said area of impact directly to the immediate region of the weak section 
to fracture said weak section at each point along said closed path. 
Conveniently the two portions of the ampoule and the seak section are 
integrally moulded. 
In one advantageous embodiment of the initiator of this invention the 
initiator includes detent means which restrain the striker and ampoule 
from coming together until the initiator is subjected to a predetermined 
acceleration for a predetermined period. In the latter event it can 
conveniently be arranged that, on release of the detent means either the 
ampoule or the striker will become freely movable relative to the other 
and, if the predetermined acceleration is sustained, the inertia of the 
released component causes the striker and ampoule to strike together with 
a sufficient force to cause rupture at the weak section. 
It will be appreciated that the factors which govern the breaking strength 
of the ampoule are the acceleration to which it is to be subjected, the 
duration of this acceleration, and the masses of the respectively moveable 
parts of the initiator. It is desired to set the breaking strength at such 
a level that rupture will occur reliably at the design acceleration and 
duration with given masses but will not occur at accelerations and/or 
duration which are not greatly different from the design values. This is 
in order to allow as wide a safety margin as possible and particularly to 
guard against the possibility of inadvertant actuation of the device 
through its being dropped. 
Typically, when the initiator is required to be actuated on being subject 
to an acceleration of 1600 g operative for a pierod of 11/2-2 milliseconds 
a strker of weight 7 g travelling a distance of 0.4 inch will cause 
rupture of an ampoule made of polyethylene with a weak section of 
thickness 6 thousandths of an inch with high reliability. It has been 
found that thicknesses of up to 13 thousandths of an inch may be broken 
under such circumstances but not very reliably. Although it is desirable 
to have the weak section of the ampoule reasonably thick in order to 
reduce or if possible eliminate electrolyte migration losses through the 
walls of the ampoule to achieve this in general would require more massive 
strikers and ancillary parts and as weight in the intended applications is 
usually at a premium, it is generally undesirable to make these parts too 
heavy. 
To ease this situation therefore it is useful to ensure that the 
accelerative force of the striker is imparted with the maximum efficiency 
to the ampoule weak section. This is achieved by incorporating within the 
ampoule a member designed to transfer the blow of the striker against one 
wall of the ampoule to the region of the weak section of the ampoule. It 
should be pointed out here that it will be more convenient to arrange that 
the striker strikes the ampoule at a location which is remote from the 
weak section so that it will not enter the area at which rupture has 
occurred and thus restrict or prevent the escape of the electrolyte. This 
sort of arrangement also makes possible rupture at the sides of the 
ampoule so that electrolyte can escape freely ifthe unit is spinning about 
the axis along which the accelerative force is operative. It is therefore 
particularly convenient to have the force transfer member in the form of a 
frustrum with the narrow end situated against the inner face of the 
ampoule with which the striker collides and the wide end situated against 
the inner face of the thin section of the ampoule. Even greater 
effectiveness is achieved by having slits extending up the frustrum from 
the wide end thereof, which allow the edges to splay outwardly when the 
ampoule and hence frustrum is struck by the striker. It is found that 
these edges will effectively cut into the walls of the ampoule at the thin 
section and in this way thin sections of up to double the thickness which 
would be ruptured under otherwise identical conditions can be broken. 
The force transferring insert is conveniently made of an inert plastics 
material, as is the ampoule, eg the insert of ABS and the ampoule of 
polyethylene. Both the ampoule and the insert, may be moulded in any 
conventional manner for plastics moulded articles, methods for doing this 
being generally well known in the art. Alternatively these parts may be 
made from other materials eg metals, but the materials should be inert in 
the presence of the electrolyte solution over long periods of time (maybe 
up to 15 years). Also of course manufacturing ampoules with thin sections 
of metal would be more difficult than moulding equivalent articles from 
plastics materials and for these reasons and for reasons of expense it is 
much preferred to mould the ampoules from plastics materials. 
The striker will generally be made of a metal such as stainless steel or a 
heavy alloy. In this way the sapce taken up by the part will be minimized, 
this often being an important consideration also with devices of this 
nature.

In FIG. 1 there are shown an annularly-disposed reserve battery comprising 
a cell stack 1 and as shown generally at 2, a battery initiator. These 
parts together comprise a reserve battery/initiator unit. The initiator 2 
comprises a cylindrical striker 3 of stainless steel which is slideable 
within a tubular striker guide 4, also of stainless steel, upon release of 
steel retaining balls 5 forming part of a detent mechanism. The retaining 
balls 5 are accommodated in a groove 6 formed around the circumference of 
the striker 3 and are held there in the normal, "rest", position of the 
device by detent means comprising an annular sleeve 7 which is slideable 
along the outer face of the guide 4. Normally the sleeve 7 is restrained 
against movement by the detent spring 8 which bears against an annular 
flange 9 around the upper edge of the sleeve. Situated within the annular 
battery or cell-stack 1 is an ampoule 10 of moulded polyethylene and 
having moulded therein an annular weak section as shown at 11. The ampoule 
contains electrolyte and a rigid plastics insert 12 of frustroconical form 
designed to transmit a downward force acting on the top of the ampoule (in 
the sense of FIG. 1) into a downward force acting on the base of the 
ampoule. A plurality of slots extend longitudinally from the wide end of 
the insert 12. 
The reserve battery 1 is arranged within a housing 13 and the various parts 
of the initiator device can be brought together before the whole system is 
sealed by closing with an initiator housing 14 which fits tightly to the 
battery housing 13. 
The operation of the embodiment shown is as follows. If the 
battery/initiator unit is accelerated upwardly (in the sense of FIG. 1) at 
a sufficient rate and for a sufficient time, the inertia of the sleeve 7 
will cause it to move downwardly relative to the remainder of the unit to 
release the balls 5 from the groove 6. The downward motion of the sleeve 7 
is opposed by the spring 8, and the rate and period of acceleration 
necessary to release the balls 5 is thus determined by the spring 
characteristics and the mass and dimensions of the components. 
On release of the balls 5, the striker is free to move within the sleeve 7 
and upon sustained upward acceleration of the unit as a whole, will be 
caused as a result of its inertia to strike the ampoule 10. The force of 
this impact is transmitted to the base of the ampoule around its 
circumference by the insert 12. The weak section 11 of the ampoule is so 
designed having regard to the mass of the striker and the distance through 
which it must travel to strike the ampoule, that when the whole unit 
continues to be accelerated upwardly at the predetermined rate necessary 
to release the balls 5, the impact of the striker is sufficient to 
reliably cause fracture of the weak section. In a modification of the 
device the insert 12 has slits extending in from its large diameter edge 
(ie upwardly from the lower edge in FIG. 1) so that when the striker hits 
the ampoule the insert is caused to splay outwardly and this edge cuts 
into the ampoule thin section to either shear through it or at least to 
raise the stresses induced therein and thus to ease its fracture. With all 
other factors being kept the same this means that the thickness of the 
ampoule weak section can be increased whilst still obtaining reliable 
fracture thereof. 
On fracture of the ampoule 10 the electrolyte is released to flow into the 
cell-stack 1 and the battery thus becomes operational. In the case of the 
embodiment of the invention illustrated it is intended that a spinning 
motion will be applied to the whole unit so that the electrolyte is then 
thrown outwardly into the annularly disposed battery and is held therein 
by centrifugal force. 
To prevent damage to the cell stack and battery body the striker 3 is 
arrested before it enters the ampoule/cell stack space by an annular lip 
15 formed around the bottom of the inner face of the striker guide 4. 
It will be appreciated that in the operation of the initiator, electrolyte 
solution contained within the ampoule is released only when the whole unit 
is subjected to a predetermined rate and duration of upward acceleration. 
Because the weak section of the ampoule is moulded this acceleration can 
be predetermined with far greater accuracy than heretofore. This leads to 
greater certainty that the unit can be activated when required, together 
with a reduced risk of accidental activation.