U.S. patent number 3,758,262 [Application Number 05/271,671] was granted by the patent office on 1973-09-11 for portable gas lighter with magnetically operated lid.
This patent grant is currently assigned to Dunhill Lighters Limited. Invention is credited to Anthony Roberts Harris.
United States Patent |
3,758,262 |
Harris |
September 11, 1973 |
PORTABLE GAS LIGHTER WITH MAGNETICALLY OPERATED LID
Abstract
The lid of a smoker's lighter is retained normally closed by
means of a magnet. The lid is spring biassed towards an open
position and the magnet acts directly against the lid which is of a
ferromagnetic material. A slide switch is provided to move the
magnet away from the lid so as to cause the lid to open. The slide
switch also makes an electrical contact which actuates an electric
ignition system.
Inventors: |
Harris; Anthony Roberts
(Hanworth, EN) |
Assignee: |
Dunhill Lighters Limited
(London, EN)
|
Family
ID: |
23036568 |
Appl.
No.: |
05/271,671 |
Filed: |
July 14, 1972 |
Current U.S.
Class: |
431/130;
292/251.5; 361/256; 431/255; 200/404; 335/205; 431/132 |
Current CPC
Class: |
F23Q
2/40 (20130101); F23Q 2/285 (20130101); Y10T
292/11 (20150401) |
Current International
Class: |
F23Q
2/40 (20060101); F23Q 2/28 (20060101); F23Q
2/00 (20060101); F23g 003/01 () |
Field of
Search: |
;317/81,92,93,96
;200/67F,61.62 ;335/285,186,205 ;219/441,442 ;292/251.5
;431/130,132,255,264,466 ;248/26A |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Mayewsky; Volodymyr Y.
Claims
I claim:
1. A smoker's lighter comprising:
an outer casing of such small dimensions that the lighter can be
used as a pocket lighter,
a lid having at least a part of ferromagnetic material, said lid
forming an openable part of said casing and being connected thereto
by hinge means,
spring means arranged to urge said lid to an open position,
a fuel tank mounted in the casing,
a gas control valve connected to said fuel tank to control the flow
of gas therefrom and arranged to open when the lighter is
operated,
a burner assembly mounted in the casing so as to be covered by said
lid in its closed position and connected to receive gas from the
gas control valve,
a magnet assembly movably mounted in the casing and arranged to act
directly on said lid in its closed position to retain said lid
closed against the force exerted by the spring means,
cell holder means mounted in the casing and adapted to receive at
least one electric cell,
a spark ignition circuit electrically connected to said cell holder
means,
switch means connected in said spark ignition circuit to control
the operation thereof,
spark ignition electrode means connected to the output of said
spark ignition circuit and mounted in the casing so as to
co-operate with the burner assembly to ignite gas issuing
therefrom, and
actuating means having an exterior part adapted for manual
operation, said actuating means being coupled to said magnet
assembly and said switch means, and being operative upon manual
operation of said exterior part to move said magnet assembly away
from said lid so as to decrease the force of magnetic attraction
thereon to allow the lid to open under the force exerted by said
spring means, and to actuate said switch means.
2. A lighter as claimed in claim 1, wherein the casing is generally
rectangular, the lid forms a part of the top face of the casing,
and said exterior part of said actuating means is located in a side
face of said casing.
3. A lighter as claimed in claim 1, wherein said burner assembly
includes an elongate burner tube, said magnet assembly includes a
generally "U"-shaped magnet having a pole-piece on each side of
said burner tube, and said magnet assembly is mounted on resilient
mounting means biassing said magnet assembly towards said lid in
its closed position.
4. A smoker's lighter comprising:
an outer casing provided with an openable lid, the lid having at
least a part of ferromagnetic material,
spring means arranged to urge said lid to an open position,
a fuel tank mounted in the casing,
a burner ssembly including a gas control valve, said assembly being
mounted in the casing so as to be covered by said lid in its closed
position and being connected to the fuel tank,
a sensor rod forming part of the burner assembly, said rod being
biassed against the lid in its closed position and adapted to open
said gas control valve when said lid is opened and to close said
valve when said lid is closed,
a magnet assembly movably mounted in said casing, arranged to
retain said lid closed by the force of magnetic attraction,
cell holder means mounted in the casing and adapted to receive and
make electrical connection to at least one electric cell,
a circuit for generating a high voltage electric spark connected to
said cell holder means,
mechanically operable contact means connected in said circuit to
actuate said circuit on closure of the contact means,
spark electrode menns connected to the output of said circuit and
mounted in the casing so as to co-operate with said burner assembly
to ignite gas issuing therefrom, and
actuating means having a part on the outside of said casing adapted
for manual operation, said actuating means being coupled to said
magnet assembly and said switch means, and being effective when
said manual operation is performed to move said magnet assembly to
decrease the magnetic attraction on the lid to allow said lid to
open under the influence of said spring means, and to close said
contact means, thereby effecting automatic opening and lighting of
the lighter.
5. A lighter as claimed in claim 4, wherein said burner assembly
includes flame adjustment means comprising:
wick means located in the path of gas through the burner
assembly,
a compression member arranged to compress said wick means to
increase its resistance to gas flow, and
a manually operable flame control coupled to said compression
member to adjust the degree of compression of said wick means.
Description
This invention relates to lighters of the type having an internal
fuel reservoir and primarily intended for lighting such items as
cigars, cigarettes and pipes. Such a lighter will be termed herein
a "smoker's lighter."
It is usual to provide a lid on a smoker's lighter to cover the
burner when the lighter is not in use.
According to the prsent invention means to retain the lid of a
smoker's lighter normally closed comprises a magnet. Preferably,
the magnet acts directly against a spring biassed lid of
ferromagnetic material.
The invention can be embodied in either a pocket lighter or a table
lighter.
By way of example only, a preferred embodiment of the invention
will now be described with reference to the accompanying drawings,
in which:
FIG. 1 shows an isometric view of a pocket smoker's lighter
embodying the invention,
FIG. 2 is a part sectional view illustrating the internal
arrangement of parts of the lighter with certain parts omitted for
clarity,
FIG. 3 shows an isometric view of potted electronic circuitry
employed in the lighter and cells used for powering the
lighter,
FIGS. 4a, b and c show the arrangement of components in the potted
electronic circuitry,
FIG. 5 is a diagrammatic isometric view of a lid catch for the
lighter,
FIG. 6 is an "exploded" view of some of the component parts of the
lid catch,
FIG. 7 corresponds generally to FIG. 2 but shows different details
of construction,
FIGS. 8 and 9 show to an enlarged scale details of construction of
a base plate used in the lighter, FIG. 8 being a sectional view and
FIG. 9 a plan view,
FIG. 10 illustrates the fuel tank and burner assembly of the
lighter,
FIG. 11 shows a side elevation of the fuel tank,
FIG. 12 shows a view from beneath of the fuel tank,
FIG. 13 shows a plan view of the fuel tank,
FIG. 14 shows an "exploded" isometric view of the top of the fuel
tank and part of a switch mechanism,
FIG. 15 shows an "exploded" isometric view of flame regulation
components,
FIG. 16 shows a partly sectional view of flame regulation
components,
FIG. 17 shows an insulator used in the lighter and
FIG. 18 shows the electronic circuit of the lighter.
It should be noted that the FIGURES are not all to the same scale
and that in the interests of clarity parts may be omitted or
simplified.
Referring to FIG. 1, the butane gas smoker's lighter there shown
comprises a hollow rectangular casing 1 having a sprung lid 2 and
base plate 3, a slide switch 4, a flame adjustment wheel 5, a
burner assembly 6 (only a part of which can be seen in FIG. 1) and
an ignition electrode 7. When the lighter is not in use the sprung
lid 2 is retained closed by a magnet 8. As will be appreciated the
external parts of the lighter are desirably given a high quality
ornamental finish to appeal to the eye. In particular the casing 1
and base plate 3 can be made of, or plated with, a precious metal.
The lid 2 is required to be in part at least of a ferromagnetic
material so as to be attracted by the magnet 8 but can of course be
plated with a precious metal.
Assuming the lid 2 to be closed, the lighter is operated by
depressing the slide switch 4 towards the base of the lighter
whereupon the lid 2 flies open, an electrical contact is made
within the lighter and a valve in the burner assembly 6 opens to
allow gas to exit for ignition. The slide switch is maintained in a
depressed condition and after a very short period of time (scarcely
perceptible to the user) a spark is generated at the ignition
electrode 7 and the gas ignites. The flow of gas is pre-set to some
convenient level by means of the flow adjustment wheel 5. Pipe
smokers will generally use a higher flow rate setting than
cigarette smokers. After use of the lighter the sprung lid 2 is
manually closed and the magnet 8 retains the lid closed until the
next occasion on which the slide switch 4 is operated. Closure of
the lid 2 stops the flow of gas through the burner assembly 6.
Now that a general description of the lighter has been given its
component parts will be described in detail. For this purpose the
description can be dealt with under several separate headings, viz.
general internal layout; lid catch; fuel tank; base-plate; gas
control mechanism; electronic circuitry and mechanical aspects of
the electronic circuitry.
GENERAL INTERNAL LAYOUT
FIG. 2 show most of the major internal component parts of the
lighter although certain parts are omitted for clarity of
illustration. Most of the internal space is taken up by a gas tank
9 and electronic circuitry 10 potted in an epoxy resin or other
suitable material. The electronic circuitry 10 is connected to a
switch contact wire 11 and to a transformer 12 (T2 in the circuit
diagram). The electronics circuitry 10 is potted so as to be in the
shape of a rectangular box with a "step" therein as can be seen in
FIG. 3. The "step" is used to accommodate two electric cells 13
which are held in a plastics material tray (not shown) including
means for making connection to the cells. The cells are connected
in series and the positive pole of the series connected cells is
connected to the casing 1.
The arrangement of parts within the potted circuitry 10 is shown in
FIGS. 4a, b and c. FIG. 4a shows the component layout with a
direction of view corresponding to that of FIG. 2. FIG. 4b and 4c
show views at right angles to the direction of view of FIG. 4a,
FIG. 4b being a side view and FIG. 4c an end view. The component
reference numbers are the same as those used in the circuit diagram
FIG. 18. The layout shown in FIGS. 4a, b and c is thus considered
to be self-explanatory.
LID CATCH
FIG. 5 shows a diagrammatic view of the lid catch. A compression
spring 14 shown in broken outline is provided to urge the lid 2
open, the lid being provided with a hinge (not shown) at 15. As may
best be seen in FIG. 6, the magnet 8 is generally "U" shaped with a
north pole piece 16 and a south pole piece 17 and has a base
portion 18 which is received in a rectangular yoke 19. Screws 20
and 21 are provided to bear upon and so retain the magnet 8 in the
yoke 19. The slide switch 4 is attached to the yoke 19 by means of
a push-fit location lug 22 received in a hole 23 in the yoke
19.
FIG. 7 shows the mechanical arrangements for biassing the slide
switch 4 in its UP position (it should be noted that the magnet 8
is omitted from FIG. 7). A helical compression spring 24 disposd
coaxially about a tube 39 forming part of the burner assembly 6
acts at its lower end against a washer 25 positioned directly
beneath the yoke 19. The yoke 19 is shaped at 26 so as to conform
to the shape of the tube 39 against which it lies so that the yoke
can slide vertically. It will be seen that the casing 1 is recessed
at 27 to provide a sliding surface for the slide switch 4. When the
slide switch 4 is in its UP position and the lid 2 is closed the
poles of the magnet 8 are in contact with the under surface of the
lid. The lid 2 which (as previously explained) is at least in part
of ferromagnetic material is retained closed against the action of
the spring 14 by the force of magnetic attraction. When the slide
switch 4 is depressed the poles of the magnet 8 are moved away from
the lid and the force of the spring 14 becomes more powerful than
the magnetic attraction and the lid springs open to assume a
vertical position. The return of the lid 2 to its closed position
is achieved manually.
FUEL TANK
Details of the fuel tank 9 are shown in FIGS. 10 to 14. The fuel
tank is moulded from a plastics material such as that known as
"DELRIN" (registered Trade Mark). The burner assembly 6 and filler
valve 40 are moulded during manufacture of the tank into the
positions shown. Burner tubes and filler valves are components
quite familiar to those skilled in the art of making smoker's
lighters and hence a detailed description is not necessary here.
The burner assembly 6 is preferably of the type described in
British Pat. No. 822,374 or No. 828,813 and the filler valve can,
for example, be of the type described in British Patent
Specification No. 784,357 or No. 966,967.
The fuel tank 9 includes a hole 41 for reception of switch
components as will be further described later. Typically the wall
thickness of the tank will be 0.04 inches.
BASE-PLATE
Details of the base-plate 3 and the means by which it is retained
in position are shown in FIGS. 8 and 9. Referring to FIG. 8, the
lower end of the casing 1 is provided with recessed portions 28 and
29. The base-plate 3 is provided with a projection 30 for entry
into the recessed portion 30 and a retractible projection 31 for
entry into the recessed portion 29. The base plate 3 has a groove
32 formed therein which acts as a mounting for the retractible
projection 31. The retractible projection 31 consists of a short
length of springy wire of slightly smaller diameter than the width
of the groove 32. The shape of the wire could generally be
described as a flattened ".OMEGA.". One end, 33, of the wire is
secured in the groove 32 by stamping the upper wall of the groove
at point to bend the upper wall towards the lower wall to trap the
wire in position. A threaded screw hole 34 is provided in the
base-plate 3 to receive a retaining screw 35 (shown in broken
outline). When the screw 35 is removed from its hole the natural
springiness of the wire causes its end 36 (shown in broken outline)
to move into a position a little to the right (as shown) of the
position normally occupied by the central axis of the screw 35 so
that the projection 31 is retracted to allow the base-plate 3 to be
removed from the casing 1 for cell replacement and refuelling. When
(with the base-plate 3 in position) the screw 36 is inserted the
point of the screw (which is suitably shaped) displaces the end 36
of the wire so that the projection 31 is thrust outwards into the
recessed portion 29 so retaining the base-plate 3 in the casing
1.
It will be understood that other types of base-plate can be used.
For example, a base-plate which requires to be slid sideways
against spring pressure to disengage a projection from a recess can
be used. Alternatively a "snap-in" type base-plate can be used. If
desired a hole and dust cap, corresponding in position to the
filler valve, can be provided in the base-plate so that the lighter
can be refuelled without removing the base-plate.
GAS CONTROL MECHANISM
Gas control mechanisms for smokers' lighters are well known to
those skilled in the art and therefore a lengthy description is not
necessary here. As previously stated, the burner assembly 6 is
preferably of the type described in British Patent No. 822,374 or
No. 828,813. FIG. 10 shows a view of the fuel tank 9, flame
adjustment wheel 5 and burner assembly 6 with other components
omitted. The burner assembly 6 comprises a central spring mounted
rod 42 fitted coaxially within the tube 39. The rod 42 is able to
move longitudinally against the action of the spring (not shown)
which urges the rod 42 upwards (as seen in the drawing). The rod 42
is connected to a valve (not shown) which allows gas from the fuel
tank to exit through the tube 39 when the rod is in its "UP"
position. The top end of the rod is arranged to act against the lid
2 of the lighter. When the lid 2 is closed the rod 42 is depressed
against the action of the spring and the valve (not shown) is
closed. When the lid is open the rod 42 moves upwards, the valve
opens and gas flows out of the fuel tank 9. Closure of the lid once
more depresses the rod against its spring and shuts off the gas. By
this means, opening and closure of the lid 2 of the lighter is made
to provide a simple but effective on/off control over the flow of
gas.
The component parts of the lighter used for flame regulation are
shown in FIGS. 15 and 16 (FIG. 16 being to a larger scale than FIG.
15) with other parts omitted. Flame regulation in smokers' lighters
is within the knowledge of those skilled in the art so that a
simple description here will suffice.
The flame adjustment wheel 5 is of a resilient plastics material
and has a knurled front 43 for operation by the user and a hole 44
with projections 45 arranged to push onto and mate with a splined
shaft 46 on an screw member 47. Gas from the fuel tank 9 exists to
the tube 39 by way of a slot 48 in a housing 49, thence through a
wick 50 and a central passage 51 in a compression member 52, and
thence by way of the gas on/off valve (not shown) to the tube 39.
The wick 50 lies between the compression member 52 and a seating
comprising a rubber pad 53 and a lower compression member 54. The
screw member 47 has an external thread 55 arranged to mate with a
corresponding thread in the part (not shown) in which it is fitted.
Thus operation of the flame adjustment wheel 5 causes axial
movement of the screw member 47 so that the wick 50 is compressed
to a greater or lesser degree according to the sense of movement of
the flame adjustment wheel 5. As will readily be understood, the
wick 50 in a highly compressed condition will resist the passage of
gas therethrough to a greater extent than when the wick is less
compressed and control over the rate of flow of gas is thus
achieved.
ELECTRONIC CIRCUITRY
Referring to FIG. 18, a battery E is connected to supply the
ignition system of the lighter which comprises an ignition switch
SW1; an inverter constituted by transistors VT1 and VT2, and a
transformer T.sub.1 ; an inverter control circuit constituted by
transistors VT3 and VT4; resistors R.sub.1, R.sub.2, R.sub.3 and
capacitors C.sub.2 and C.sub.3 ; a full-wave bridge rectifier
constituted by diodes D.sub.1, D.sub.2, D.sub.3 and D.sub.4 ; a
triggering circuit constituted by triggering diode D.sub.6 and
resistors R.sub.4 and R.sub.6 ; and a discharge circuit constituted
by a capacitor C.sub.1, a step-up transformer T.sub.2, a thyristor
D.sub.5, and ignition electrodes IE. As will be explained in more
detail later, operation of the switch SW1 causes the production of
an electric spark at the ignition electrodes IE to ignite the fuel
of the lighter. Examples of suitable types and values of components
for the circuit are set out in the table below.
Component Type or Value E Two mercury cells each type MP625H VT1,
VT2, VT3 each 2N3794 VT4 2N4291 R .sub.1 180 .OMEGA. .+-. 5% 0.1W R
.sub.2 10k .OMEGA. .+-. 5% 0.1W R .sub.3 68k .OMEGA. .+-. 5% 0.1W R
.sub.4, R.sub.5 each 1k .OMEGA. .+-. 5% 0.1W C .sub.1 33 .mu. F 40V
electrolytic C .sub.2, C.sub.3 each 0.1 .mu. F 30V D .sub.1,
D.sub.2, D.sub.3, D.seach IN 4148 D .sub.5 TIC 45 D .sub.6 D 32 T
.sub.1 first primary P.sub.1 16 turns centre-tapped seconnd primary
P.sub.2 16 turns centre-tapped secondary S.sub.2 200 turns on an 8
mm diameter toroidal ferritecove T .sub.2 primary 12 turns
secondary 2500 turns SW1 normally open single pole switch
Transformer T.sub.2 is preferably of the type described in British
Patent Application No. 5981/72 entitled "Formers for Inductive
Devices and Devices and Apparatus Employing Same."
The inverter is designed to have a high efficiency so that the time
taken to charge the capacitor C.sub.1 can be kept low. In this
respect, silicon transistors selected for low collector-emitter
saturation voltage at the operating currents involved are employed
in conjunction with a toroidal ferrite transformer. The bridge
rectifier diodes are high frequency types also chosen to maintain
high efficiency. In this respect a full-wave rectifier arrangement
is preferred to a half wave arrangement.
The collectors of transistors VT1 and VT2 are connected to
respective ends of the primary winding P.sub.1 of transformer
T.sub.1 and their emitters are connected in common to the negative
pole of battery E. The bases of transistors VT1 and VT2 are
connected to respective ends of the primary winding P.sub.2 of
transformer T.sub.1. As will be explained in more detail later,
transistors VT3 and VT4 are connected to control the base current
to transistors VT1 and VT2 and so control operation of the
inverter. The inverter functions in a known manner as a
multivibrator square-wave oscillator with transformer coupling to
provide the necessary feedback.
The secondary winding of transformer T.sub.1 has one end connected
to the cathode of diode D.sub.1 and the anode of diode D.sub.4 and
its other end connected to the cathode of diode D.sub.2 and the
anode of diode D.sub.3. The anodes of diodes D.sub.1 and D.sub.2
are connected in common to the negative pole of the battery E. The
cathode of diodes D.sub.3 and D.sub.4 are connected in common to
one end of trigger diode D.sub.6 whose other end is connected to
one end of resistor R.sub.4 whose other end is connected through
resistor R.sub.5 to the negative pole of the battery E. Thyristor
D.sub.5 has its anode connected to the cathodes of diodes D.sub.3
and D.sub.4 and its cathode connected to the negative pole of the
battery E. The trigger electrode of thyristor D.sub.5 is connected
to the junction of resistors R.sub.4 and R.sub.5. The full-wave
rectified output of transformer T.sub.1 thus appears across
thyristor D.sub.5.
Components VT3, VT4, R.sub.1, R.sub.2, R.sub.3, C.sub.2 and C.sub.3
constitute the inverter control circuit. The emitter of transistor
VT3 is connected to the centre-tap of primary-winding P.sub.2 of
transformer I.sub.1 and its collector is connected to the base of
transistor VT4. The collector of transistor VT4 is connected in
common to the base of transistor VT3, one end of capacitor C.sub.2,
one end of capacitor C.sub.3 and one end of resistor R.sub.3. The
emitter of transistor VT4 is connected to one end of resistor
R.sub.1 the other end of which is connected to the end of capacitor
C.sub.2 remote from the base of transistor VT3. The end of resistor
R.sub.3 remote from the base of transistor VT3 is connected to the
negative pole of the battery E. Resistor R.sub.2 is connected from
the junction of resistor R.sub.1 and capacitor C.sub.2 to the
negative pole of battery E. The common ends of resistors R.sub.1
and R.sub.2 and capacitor C.sub.2 are connected to the centre-tap
of primary winding P.sub.1 of transformer T.sub.1 and to the pole
of switch SW1 remote from the battery E. The end of capacitor
C.sub.3 remote from transistor VT3 is connected to the positive
output (cathodes D.sub.3 and D.sub.4) of the bridge circuit
constituted by diodes D.sub.1, D.sub.2, D.sub.3, D.sub.4.
The positive pole of electrolytic capacitor C.sub.1 is connected to
the cathodes of diodes D.sub.3 and D.sub.4 and its negative pole is
connected to one end of the primary winding of transformer T.sub.2.
The other end of the primary winding is connected to the negative
pole of the battery E. One end of the secondary winding of
transformer T.sub.2 is connected to the negative pole of the
battery E. The other end of the secondary winding of transformer
T.sub.2 is connected to the ignition electrode 7. The other
ignition electrode is constituted by the rod 42 which is connected
to the positive pole of the battery E. The positive pole of battery
E is connected to the casing 1.
On closure of the switch SW1 the positive pole of the battery E is
connected to the top end (as shown) of capacitor C.sub.2 and a
positive going waveform consequently appears at the base of
transistor VT3. The emitter of transistor VT3 is connected to the
negative pole of the battery E by way of the centre-tap of the
primary winding P.sub.2 so that the said positive going waveform
tends to turn transistor VT3 ON. As a result collector current for
transistor VT3 is drawn from the base of transistor VT4 which tends
to turn VT4 ON. Collector current from transistor VT4 feeds the
base of transistor VT3 which in turn draws more current from the
base of transistor VT4. Thus, transistors VT3 and VT4 form a
complementary pair switch and closure of switch SW1 results in both
of transistors VT3 and VT4 turning ON.
Transistor VT3 feeds base current to transistors VT1 and VT2 of the
inverter which oscillates and continues oscillating so long as the
switch SW1 is closed to supply collector current and so long as
transistor VT3 supplies base current to the transistors of the
inverter.
When the inverter is functioning a square-wave output appears at
the secondary winding S.sub.1 of transformer T.sub.1 of
approximately 70V peak to peak amplitude at a frequency of
approximately 40kHz. The output of the circuit will, of course, be
somewhat less if the battery has deteriorated through age or use.
The inverter and rectifier change the battery voltage from a level
of a few volts to a level considerably greater.
The full-wave rectified output of the secondary winding S.sub.1
charged capacitor C.sub.1 through the primary winding of
transformer T.sub.2. Trigger diode D.sub.6 remains non-conducting
until its breakdown voltage is reached and so long as the voltage
across trigger diode D.sub.6 is less than the breakdown voltage the
voltage drop across resistors R.sub.4 and R.sub.5 is effectively
zero. A point is soon reached as capacitor C.sub.1 charges when the
voltage across trigger diode D.sub.6 is equal to its breakdown
voltage, whereupon the diode D.sub.6 conducts and a signal appears
at the junction of resistors R.sub.4 and R.sub.5 which triggers the
thyristor D.sub.5 into a state of conduction. Capacitor C.sub.1 now
rapidly discharges through the primary winding of transformer
T.sub.2 and thyristor D.sub.5 (which, of course, remains conducting
until the current through it becomes equal to zero) and as a result
a very high voltage (about 7kV) is induced in the secondary winding
of transformer T.sub.2. The high secondary voltage causes a
fuel-igniting spark to occur between the ignition electrodes
IE.
The energy required to ignite the butane gas of the lighter is
approximately 2mJ and in the present circuit at least 15mJ would be
stored in capacitor C.sub.1. While the energy available in the
spark depends upon the efficiency of the transformer T.sub.2 this
value of stored energy in capacitor C.sub.1 more than compensates
for expected losses in transformer T.sub.2.
The use of trigger diode D.sub.6 and thyristor D.sub.5 allows a
high charging rate of capacitor C.sub.1 to be employed since the
open circuit output voltage of the inverter and rectifier can be
made significantly greater than the maximum working voltage of the
capacitor C.sub.1. This fact is advantageous because the size of
capacitors of a given value increases with their rated working
voltage.
The discharge of capacitor C.sub.1 also results in a negative going
spike being applied through capacitor C.sub.3 to the base of
transistor VT3. This negative going spike causes both transistors
VT3 and VT4 of the inverter control circuit to turn OFF. As a
result the flow of base current to the transistors of the inverter
ceases and the inverter stops oscillating. The negative going spike
will charge capacitor C.sub.2 in such a manner as to maintain the
transistors VT3 and VT4 OFF. This charge decays through the
resistances associated with capacitor C.sub.2 but the transistors
VT3 and VT4 remain OFF until a positive going waveform is again
applied at the base of transistor VT3 by a further actuation of the
switch SW1.
It will be appreciated that to obtain the spark discharge the user
must continue to operate the switch SW1 for the multivibrator to
function sufficiently long for the voltage on capacitor C.sub.1 to
be built up. Once capacitor C.sub.1 has discharged it will be
observed that the inverter is turned off. Thus, for a single
actuation of the switch the inverter runs for a sufficient time to
produce the spark, after which it remains off irrespective of
whether or not the user keeps the switch depressed.
The switch action does not need to be mechanically timed --
providing the contact is made the inverter will run only for the
time necessary to charge the capacitor with sufficient energy to
create one ignition spark. This means that no energy is wasted
after the capacitor is fully charged (a fixed time charging system
would have to allow sufficient time for a partially used battery to
charge the capacitor, which would thus be more than necessary for a
fresh battery). The time (normally scarcely perceptible to the
user) required for the capacitor to charge and a spark to be
produced will increase as the battery ages and can serve as a
useful indication of the necessity to renew the battery.
Nevertheless, the ignition system should continue to operate even
with fairly extended charging times.
MECHANICAL ASPECTS OF THE ELECTRONIC CIRCUITRY
The mechanical details of the switch SW1 are illustrated in FIG. 2
and 14. A helical compression spring (not shown) is located in the
hole 41 (FIG. 14,) so as to act against the switch contact wire 11
(FIG. 2). A contact pin 56 is inserted in the end of the hole 41
remote from the contact wire 11 and is biased by the spring into
contact with the internal face of the slide switch 4. The slide
switch 4 is made of an insulating material with a fluted front face
and an area 58 of conducting material on its inside face. The
conducting area 58 is connected to the positive pole of the battery
through the casing 1 (the area 58 slides against the casing 1).
When the slide switch 4 is in its UP position the contact pin
touches the insulated part of the slide switch 4, but when the
switch 4 is depressed the pin 56 comes into contact with the area
58 and connection is made through the spring in hole 41 to contact
wire 11 which in turn is connected to the electronic
components.
The high voltage parts of the circuit need careful insulation to
ensure that unwanted discharges do not occur. The shaping of the
insulation about the ignition electrode 7 can be seen in the
Figures. A shield 57 (FIGS. 1 and 17) of a ceramic or other heat
resistant insulating material is placed about ignition electrode 7
to help avoid such unwanted discharges. The burner assembly 6 is
connected to the positive pole of the battery E through the yoke 19
(which is of metal) and the casing 1.
It will be appreciated that the described embodiment has many
advantages over prior art lighters. The provision of the inverter
and rectifier to change the level of voltage supplied by the
battery to a higher level enables a smaller capacitor to be
employed for the storage of a given amount of energy than if the
capacitor has been charged by the battery alone. This provides an
advantageous economy in the space required within the lighter for
the electrical components (the height of the lighter shown in FIG.
1 can be as little as 7 cms). Further, low voltage cells are
employed which are relatively cheap and easily obtainable. The use
of the inverter also provides a rapid means for charging the
capacitor which is desirable in respect of repeated operation of
the lighter and further no load is imposed on the cells during a
period of non-use. The use of the trigger diode is particularly
advantageous in respect of the speed of charging the capacitor and
the use of the thyristor ensures a rapid discharge of the capacitor
without any problems of the "contact bounce" type (a thyristor,
once triggered, remains conducting until the voltage across it
drops to zero).
Other forms and modifications are possible within the scope of the
invention. For example, the invention can be embodied in a table
lighter. In a table lighter a more squat arrangement of components
would generally be desirable. The thyristor can if desired be
replaced by a mechanical switch contact and the trigger diode can
be omitted, but the use of the components shown to provide
automatic ignition is preferred. Transistors of the opposite
conductivity types to those shown can be employed and other
inverter arrangements are possible. For example, an oscillator
employing a single transistor could be used. The inverter could
employ a piezo-electric solid-state transformer. It is also
contemplated that a voltage multiplier of the diode voltage-doubler
type could be used. At least some of the electrical components of
the lighter could be made in integrated circuit form. One or more
rechargeable cells could be used to power the lighter. It is not
essential for the electronic components to be potted as
described.
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