Burner with oxygen shortage sensor

An oxygen shortage sensor is placed in a space defined above a burner unit exposed to the atmosphere. When an oxygen shortage condition is detected by the oxygen shortage sensor, an alarm is raised from an alarm unit or combustion of the burner unit is stopped by a combustion stopper. In such an apparatus, in order to secure a stable oxygen shortage detection by the oxygen shortage sensor, the oxygen shortage sensor is located in a space above the burner unit and in a casing having an opening formed on the side of the burner unit.

FIELD OF THE INVENTION 
The present invention relates to a burner in which an oxygen shortage 
sensor provided in the upper space of a burner unit exposed to the 
atmosphere is adapted to detect the lack of oxygen so that when the 
shortage of oxygen occurs, an alarm is issued from alarm means or the 
combustion of the burner unit is stopped by combustion stopper means. 
BACKGROUND OF THE INVENTION 
The perspective view of an ordinary oil stove is shown in FIG. 1 as an 
example of conventional burners. A reflector 2 is contained in a housing 
1, and a burner unit in the form of a combustion cylinder 3 is arranged at 
the central part of the curved surface of the reflector 2. The combustion 
cylinder 3 in turn contains a wick by which oil (kerosene) sucked up by 
capillarity is burned. As a result, the combustion cylinder 3 is red 
heated, and heat thus generated provides radiation heat or reflection heat 
in front of the stove by way of the reflector 2 thereby to effect the 
heating operation. A knob 4 is provided for vertically moving the wick. 
When the knob 4 is moved upward, a button 5 is depressed to ignite the 
wick, thereby starting combustion. When the other knob 25 is depressed 
downward, the knob 4 is disengaged and is restored to the original 
position. At the same time, the wick in the combustion cylinder 3 lowers 
to thereby extinguish the fire. 
The oil stove of this construction consumes oxygen in the working 
environment. If oxygen is in short supply, the oxygen concentration 
decreases slowly so that the lack of oxygen occurs in the combustion 
cylinder 3 while carbon monoxide increases in amount. 
In such a situation, the human body is adversely affected and sufficient 
ventilation of the room is necessary. The user thus consciously opens the 
window at predetermined time intervals to take in fresh air. If the user 
fails to take in fresh air, however, the oxygen concentration is reduced 
while carbon monoxide increases to cause the dangerous condition called 
"the lack or shortage of oxygen". 
In order to meet such a situation, an oil stove is required in which such a 
dangerous situation is detected and an alarm is issued by an illuminator 
24 used as alarming or warning means or in which the combustion is 
automatically stopped by combustion stopper means. Such an oil stove is 
required to include an oxygen shortage sensor for detecting the decrease 
of oxygen concentration or the increase of carbon monoxide. Various types 
of oxygen shortage sensors are conceivable. Among them, the most desirable 
one detects oxygen concentration or oxygen partial pressure or carbon 
monoxide. Such a sensor detects the shortage of oxygen directly but not 
indirectly and has the great advantage of high reliability. Nevertheless, 
the oxygen shortage sensor is incapable of performing the function thereof 
unless maintained at higher than a predetermined temperature on the one 
hand and undesirably operates in response to temperature changes on the 
other hand. The characteristics of an oxygen shortage sensor are shown in 
FIGS. 2(a) and 2(b). In the case where the oxygen shortage sensor is made 
of tin oxide or the like, for example, the resistance value thereof 
changes with oxygen concentration as shown in FIG. 2(a) if the ambient 
temperature is maintained constant, while the resistance value still 
continues to change with the change of temperature even when the oxygen 
concentration is kept substantially constant as shown in FIG. 2(b). When 
the oil stove is provided with the oxygen shortage sensor, therefore, the 
ambient temperature is required to be maintained substantially constant. 
Otherwise, an alarm may be falsely issued or combustion may be stopped 
even when oxygen is not in short supply. 
SUMMARY OF THE INVENTION 
The object of the present invention is to provide a burner in which oxygen 
shortage is detected in a stable manner. 
In order to achieve this object, according to the present invention, a 
casing or container is provided in a space above the burner unit and 
formed with an opening opposing the same and an oxygen shortage sensor is 
provided in the casing or container.

DETAILED DESCRIPTION OF THE INVENTION 
First, reference is made to FIG. 3. A reflector 2 is provided on the rear 
side of the upper portion of a box-shaped housing 1. A combustion cylinder 
3 used as an example of the burner unit is arranged at the central part of 
the reflector 2. By the rotational operation of the rotary knob 4, a 
cylindrical wick 6 is movable up and down in the combustion cylinder 3. By 
depressing an ignition knob 5 when the wick 6 moves up, a battery 7 
operatively interlocked therewith applies a voltage through a closed 
switch 8 to an ignition heater 9 on the one hand, while the ignition 
heater 9 is interlocked to move toward the wick 6. The wick 6 has already 
sucked up the oil (kerosene) by capillarity from a fuel tank 10, and 
therefore the oil can be fired by the ignition heater 9. The combustion 
cylinder 3 includes an inner flame cylinder 12 and an outer flame cylinder 
13. The air A for combustion is supplied into the inner and outer flame 
cylinders 12 and 13 by draft. 
The portable oil stove of this construction comprises a well-known oxygen 
shortage sensor 14 for detecting the oxygen concentration, partial 
pressure of oxygen or the concentration of carbon monoxide, which sensor 
is arranged in a casing provided in the upper space on the center line of 
the combustion cylinder 3. The lead wire 16 for the sensor 14 is led to a 
central circuit 17 through a route whose temperature is not raised so 
high. The control circuit 17 is supplied with a voltage through another 
lead wire 18 by the battery 7. 
When the wick 6 is moved up by turning the rotary knob 4, on the other 
hand, the cam 19 provided on the same axis as the rotary knob 4 actuates a 
microswitch 20 in response to the operation of the rotary knob 4. This 
microswitch 20 is for supplying the voltage of the battery 7 to the whole 
control circuit 17. 
The combustion cylinder 3 is adapted to burn gas supplied from the wick 6 
vertically moved by the operation of the rotary knob 4 thereby to 
discharge the exhaust gas B into the atmosphere upward. 
The casing 15 is mounted on the lower side of a roof plate 21 opposite to 
the combustion cylinder 3. 
In FIG. 4 showing a simple electrical circuit, an oxygen shortage sensor 14 
is connected with the battery 7 together with a resistor 37 thereby to 
obtain a detection output V across the resistor 37. When this detection 
output V is reduced below a predetermined value, the combustion stops or 
an alarm is issued. 
In this construction, the combustion in the combustion cylinder 3 causes 
the exhaust gas to move straight upward as shown by the arrow B in FIG. 3 
and surrounded the oxygen shortage sensor 14, so that the ambient 
temperature of the oxygen shortage sensor 14 is maintained substantially 
constant at 400 .degree.to 600.degree. C., thus indicating a resistance 
value corresponding to the oxygen concentration. 
In the process, the detection output V is provided across the resistor 37 
of FIG. 4, and when this detection output V exceeds a predetermined value, 
the combustion stops or an alarm is issued. 
According to the embodiment under consideration, the exhaust gas flows into 
the casing 15 by way of the lower opening thereof in such a manner as to 
surround the oxygen shortage sensor 14, and therefore the characteristic 
thereof is very stable as shown by A in FIG. 5, thus preventing any false 
actuation. 
If the oxygen shortage sensor 14 is arranged at such a position as 
designated by D in FIG. 3, by contrast, the oxygen shortage sensor 14 is 
brought into contact with the air C other than the exhaust gas and the 
temperature thereof is reduced, with the result that as shown by B in FIG. 
5, the detection output V is decreased while at the same time undergoing a 
great change, thus causing a false actuation. 
The general operation of the apparatus having the above-described 
construction will be explained. First, the rotary knob 4 is turned to move 
up the wick 6. (The wick moved up is shown in FIG. 3) The microswitch 20 
is closed by the cam 19 to supply a voltage to the control circuit 17, 
thus entering the state in which an oxygen shortage can be detected. Under 
this condition, the button 5 is depressed to bring the ignition heater 9 
near to the wick 6 on the one hand and the switch 8 is depressed to ignite 
the ignition heater 9 by supplying a voltage thereto from the battery 7 on 
the other hand. When the operator's hand is released from the switch 8 
after ignition, the button 5 is restored to the original position. By 
doing so, the oil (kerosene) gassified from the wick 6 normally burns by 
securing the combustion air between the inner flame cylinder 12 and the 
outer flame cylinder 13. The combustion heat is reflected on the reflector 
2 to transmit the reflection heat to the front side of the apparatus, 
while the heat transmitted upward reaches the casing 15 containing the 
oxygen shortage sensor 14 thereby to store the heat in the casing 15. At 
the same time, oxygen and carbon monoxide contained in the combustion 
flame are sent into the casing 15. The oxygen shortage sensor 14 operated 
normally at the temperatures from 400 .degree.to 600.degree. C. thus 
monitors the combustion state and applies an output signal thereof to the 
control circuit 17. 
Assume that the amount of oxygen in the air is reduced to about 18%. With 
increase in the carbon monoxide in the air, the resistance value of the 
oxygen shortage sensor 14 is reduced and the transistor 31 conducts 
through the comparator 22 in FIG. 7, so that a buzzer 24 used as an 
example of alarm means in FIG. 6 issues an alarm. The user then can 
prevent the oxygen shortage by opening the window or stopping the 
combustion. 
If the user fails to take note of the alarm and the oxygen concentration is 
futher reduced by 0.5 to 1.0%, then the transistor 26 is turned on through 
the comparator 30, so that the solenoid 27 is energized. A pendulum 28 
(FIGS. 3 and 6) which swings at the time of an earthquake or the like is 
actuated as if an earthquake has actually occurred, so that the thumb gear 
29 is disengaged thereby to restore all the parts to the original position 
(to the extinguished state with the wick 6 lowered). 
The manner in which the oxygen shortage sensor 14 is contained in the 
casing 15 is shown in detail in FIG. 8. The oxygen shortage sensor 14 is 
arranged substantially at the center of the casing 15. The casing 15 has a 
wall made of a metal material to secure as large a heat capacity as 
possible. 
The casing 15 of this construction is used in order that the combustion gas 
B of high temperature caused by the combustion flame may maintain a 
constant ambient temperature of the oxygen shortage sensor 14. If the 
casing of this type is lacking, the intrusion of external air C will cause 
a change of the ambient temperature of the oxygen shortage sensor 14, thus 
causing the false actuation of the sensor 14. Such an inconvenience is 
substantially prevented by the presence of the casing 15. Especially 
according to the present embodiment, the maximum size of the lower opening 
of the casing 15 is smaller than the maximum diameter of the combustion 
cylinder 3 so that the lower opening of the casing 15 is positioned in the 
rising flow of the combustion gas B, thereby making it difficult for the 
air C to intrude into the casing. 
The casing 15 is opened only at a part thereof opposed to the combustion 
cylinder 3 with all the other parts closed, and therefore the combustion 
gas that has made access as shown by the arrow B is turned for successive 
air replacements in the manner shown by the arrow B'. This casing 15 is 
required to be so constructed that the combustion gas is stored for a 
predetermined length of time and is replaced successively. Thus a through 
hole, if any, bored in the roof 21 does not pose any problem if it is of 
such a size as to allow the combustion gas B to be stored for the 
predetermined length of time. In the casing having no further opening 
other than the lower opening, the velocity of the combustion gas thus 
replaced depends on the size of the casing. 
Our experiments show that a rectangular casing (which may be replaced by a 
casing of any other shape such as oval, cylindrical casing with equal 
effect) with the opening area of 10 to 15 cm.sup.2 and the depth of 2 to 7 
cm will be preferably employed although depending on the size and 
sensitivity of the oxygen shortage sensor 14. This is also effective for 
preventing the intrusion of air C. Namely, the casing of this type may 
take various forms and no particular limitation of shape is required only 
if the above-mentioned conditions are satisfied. 
In FIG. 8, the oxygen shortage sensor 14 is protected by an insulator 14a 
which is mounted on the casing 15, a lead wire 14b being taken out through 
the insulator 14a. 
A catalyst may be used above the combustion cylinder 3 in order to purify 
the combustion exhaust gas. An embodiment including such a catalyst is 
shown in the sectional view of FIG. 9. An embodiment of a catalyst 60 and 
the casing 61 is shown in FIG. 10. A leg 62 is mounted under the roof 21 
of the housing 1. The casing 61 containing the catalyst 60 and the oxygen 
shortage sensor 14 is mounted on the leg 62. The catalyst 60 has numerous 
apertures 60a through which the exhaust gas B is passed. Before the 
catalyst 60, the exhaust gas passes around or through the surroundings of 
the oxygen shortage sensor 14 thereby to enable the detection of the 
concentration of oxygen and carbon monoxide. Numeral 63 designates a 
holder for the oxygen shortage sensor 14 and numeral 4a engaging holes for 
the leg 62. 
In this construction, the exhaust gas from the combustion cylinder 3 flows 
into the casing 61 from the lower opening as shown by the solid arrow B 
(the air flow shown by the arrow C) in FIG. 9, and after being purified by 
the catalyst 60, is discharged out of the housing 1 through the leg 62. 
In the process, the oxygen shortage sensor 14 detects the concentration of 
carbon monoxide in the exhaust gas, and when the concentration of the 
carbon monoxide increases with the decrease of oxygen in a room of 
insufficient ventilation, namely, when oxygen shortage progresses, the 
safety device mentioned above is actuated. 
Before the actuation of the safety device, the oxygen shortage sensor 14 
detects the concentration of carbon monoxide gas which has entered the 
casing 61 and stays therein, so that the detection signal is subjected to 
less fluctuations than when the concentration of carbon monoxide gas is 
directly detected with exhaust gas uprising from the lower portion. 
Further, because of the heat received from the catalyst 60, the temperature 
of the oxygen shortage sensor 14 fluctuates less with the result of very 
little fluctuation of the detection signal, thus preventing the safety 
device from being unreasonably actuated. 
Now, the casing 15 containing the oxygen shortage sensor 14 will be 
explained. As seen from FIG. 8, the oxygen shortage sensor 14 is arranged 
at substantially the center in the casing 15. The wall of the casing 14 is 
made of a metal material or the like to secure as large a heat capacity as 
possible. 
The casing 15 is used for the purpose of maintaining the oxygen shortage 
sensor 14 at a constant temperature by the exhaust gas (arrow B) as 
described above. In spite of the use of the casing 15, however, if air 
(arrow C) flows in from the periphery of the opening, the ambient 
temperature of the oxygen shortage sensor 14 may fluctuate thereby causing 
a false actuation. 
In FIG. 11 showing another embodiment, the oxygen shortage sensor 14 is 
provided above a baffle member 23 in the shape of a circular truncated 
cone which is attached to the opening portion on the combustion cylinder 
side of the casing 15. The diameter of the opening of the cone-shaped 
baffle member 23 decreases progressively from the combustion cylinder side 
opening toward the oxygen shortage sensor 14, and a metal wire netting 32 
is mounted on the upper opening of the baffle member 23, which netting is 
one example of a heat insulating porous member. As a result, the exhaust 
gas that comes up (arrow B) proceeds straight to the baffle member 23 and 
through the metal netting 32 to reach the oxygen shortage sensor 14. The 
external air (arrow C), on the other hand, can hardly get into the casing 
15 even though it proceeds against the baffle member 23. Thus the 
temperature of the oxygen shortage sensor 14 substantially remains 
unchanged but responds only to the exhaust gas. 
FIGS. 12(a) and 12(b) show that the oxygen shortage sensor 14 is provided 
above a W-shaped baffle member 23a which is mounted in a rectangular 
casing 15, and is easily mounted therein as the casing 15 is rectangular 
in form. Numerals 23b and 23c designate mounting lugs. 
FIGS. 13(a) and 13(b) show that the oxygen shortage sensor 14 is provided 
above the another baffle member 23d made of a spirally-formed band in the 
circular cylindrical casing 15. In view of the fact that the baffle member 
23d is easily fabricated and yet that it is arranged in parallel to the 
exhaust gas flow (arrow B), the exhaust gas can be brought into direct 
contact with the oxygen shortage sensor 14 on the one hand and external 
air C supplied from the peripheral edge area finds it hard to enter the 
casing 15 as it is blocked by the baffle member 23d on the other hand, 
thus preventing temperature change of the oxygen shortage sensor 14. 
FIGS. 14(a) and 14(b) show that the oxygen shortage sensor 14 is provided 
above the baffle member 23h made of three vertical boards 23g and a plate 
23f provided with apertures 23e, inserted in the rectangular casing 15. 
The oxygen shortage sensor 14 is protected by a porcelain type insulator 
33, which is in turn mounted on the casing 15. 
In this construction, even when the burner unit is open to external 
atmosphere and is easily cooled by wind or the like, an oxygen shortage 
can be accurately detected substantially without false actuation. 
A circuit configuration and operation of the control device will be 
explained. In FIG. 15, the positive terminal of the dry battery 7 is 
connected through the microswitch 20 to the point a, and the negative 
terminal thereof is connected to the point b. Across the points a and b 
are connected a series circuit of the ignition heater 9, point c and 
ignition switch 8; a power circuit for a timer IC 43, and a power circuit 
for a differential amplifier (hereinafter referred to as operational 
amplifier) 51. A current of about 3 mA flows into these circuits if the 
terminal voltage of the battery 7 is 3 V. An oscillation control resistor 
52 for the timer IC 43 is connected between terminals of the timer IC 43, 
which terminals are connected respectively through a capacitor 53 and a 
smoothing capacitor 54 to the point b. The output point e of the timer IC 
43 is connected to the non-inverting input terminal of the operational 
amplifier 51, and the point d is connected to the inverting input terminal 
of the amplifier. The output point f of the operational amplifier 51 is 
connected to the base of the transistor 47 through the resistors 45 and 
46, while the collector f' of the transistor 47 is connected through the 
resistor 55, point g, resistor 56, point g' and resistor 57 to the point 
b. The point f' is further connected through the resistor 58, point h and 
resistor 34 to the point b. The point h is connected to one terminal of 
the capacitor 36 and connected through the zener diode 50 to the base of 
the transistor 35. The emitter of the transistor 35 and the other terminal 
of the capacitor 36 are connected to the point b. The collector of the 
transistor 35 is connected to the point d. A series connection of the 
oxygen shortage sensor 14 and point i and resistor 37, power circuit for 
the operational amplifier 30, a limiting resistor 48 and LED 49 for 
indicating that the oxygen shortage sensor 14 is in operation are 
connected in parallel between the points f' and b. 
A second operational amplifier 60 is connected with the same power circuit 
by connecting the inverting (minus) and non-inverting (plus) terminals to 
the points g' and i respectively. The second operational amplifier 60 
produces an output at the point l. An alarm circuit 56 is connected 
between the points f' and b. The alarm circuit 56 contains a low-frequency 
oscillator circuit 57 which begins to operate when the output l of the 
operational amplifier 60 is raised to "high" level. The output terminal m 
of the low-frequency oscillator circuit 57 is connected through the 
resistor 58, point n, resistor 59 to the point b. The base and emitter of 
the transistor 31 are connected to the points n and b respectively. The 
collector of the transistor 31 is connected to a buzzer 24 as an example 
of the alarm means. 
A series circuit of a resistor 39, point k and resistor 40 is connected 
between the point j of the operational amplifier 30 and the point b, while 
a series circuit of a resistor 42 and diode 41 with the anode thereof 
connected to the point j is connected between the points j and i. The base 
of the transistor 26 is connected to the point k with the emitter 
connected to the point b and the collector connected to the point a 
through the solenoid 27. The solenoid 27 is connected with a diode 44 with 
the cathode thereof connected to the point a. 
In operation, the current of about 3 mA begins to flow when the microswitch 
20 is closed by the rotary knob 4. By closing the ignition switch 8, the 
ignition heater 9 is energized thereby to ignite the wick 6. At the same 
time, the point c becomes negative, and when the hand is released, it 
regains the potential of the point a. The point d connected to the reset 
terminal of the timer IC 43 is actuated at the same time, so that the 
timer is energized. Before the lapse of a predetermined time, the output 
point e is maintained "high" as compared with the point d, so that the 
output f of the operational amplifier 51 is maintained "high". Under this 
condition, the oxygen shortage sensor 14 is not yet actuated. When the set 
time of the timer (such as 10 minutes) passes, the signal level of the 
output point e is reduced to "low" state, the signal level of the output 
point f of the operational amplifier 51 is reduced to "low" state, 
transistor 47 is turned on, and the potential of the point f' becomes 
substantially equal to the potential of the point a. At this time point, 
the oxygen shortage sensor 14 begins to operate for oxygen shortage 
detection. On the other hand, electric current flows in the LED 49 through 
the resistor 48 so that the LED 49 is lit, thus indicating that the oxygen 
shortage detecting operation by the oxygen shortage sensor 14 is going on. 
Assume that the oxygen concentration is reduces. Then the resistance value 
of the oxygen shortage sensor 14 begins to decrease and the potential at 
the point i' slowly increases. When this potential exceeds that of the 
point i, the output point l of the operational amplifier 60 is switched to 
"high" from "low" state. With the change of the output of the operational 
amplifier 60 to "high" state, the low-frequency oscillator circuit 57 is 
activated and begins to oscillate, and the transistor 31 is turned on 
through the resistors 58 and 59, thus actuating the buzzer 24. 
With a further decrease of the oxygen concentration, the potential at the 
point i increases, and when it exceeds that of the point g, the output j 
of the operational amplifier 30 is raised to "high" state so that the 
transistor 26 and hence the solenoid 27 are actuated, and the rotary knob 
4 is disengaged, with the result that the wick 6 is lowered sharply to 
stop the combustion. 
In this way, when the oxygen shortage progresses to a certain degree, the 
buzzer 24 sounds, and when the lack of oxygen is further aggravated, the 
solenoid 27 is energized thereby to stop the combustion, thus providing 
dual safety functions. 
An intermittent operation of the oxygen shortage circuit will be next 
explained. Under normal conditions, when the point f' is raised to "high", 
the capacitor 36 is charged through the line including the resistor 58, 
point h, and resistor 34. When the point h increases in potential slowly 
and exceeds the level determined by the zener diode 50, the transistor 35 
is turned on. 
Since the collector of the transistor 35 is connected to the point d, the 
timer IC 43 is instantaneously reset on the one hand and the point e is 
raised to "high" to raise the point f to "high" state to turn off the 
transistor 47 on the other hand, thus extinguishing the LED 49. 
In this manner, the oxygen shortage sensor circuit for the oxygen shortage 
sensor 14 is disabled in operation for a predetermined length of time in 
initial stages of combustion, followed by the repetitive turning on and 
off of the oxygen shortage sensor circuit by the repetitive timer 
mechanism, so that the oxygen shortage is detected only during the short 
on-period of the oxygen shortage sensor circuit, and, the off period of 
the circuit is lengthened to prevent unreasonable consumption of the dry 
battery 7. Since an oxygen shortage, if any, does not occur in several 
minutes, the oxygen shortage detection cycles of several to several tens 
of minutes as shown in the above embodiment poses no practical unfavorable 
problem, and yet such a detection cycle can realize an extended length of 
service life. 
Further, by addition of the alarm circuit 56 including the low-frequency 
oscillator circuit 57, the buzzer 24 is operated intermittently, for 
example, it is turned on for 2 seconds and off for one second at the time 
of oxygen shortage, thus reducing the consumption of the battery 7 
considerably. 
It will be understood from the foregoing description that according to the 
present invention, a casing is provided in a space above the burner unit 
of the type opened to the outer atmosphere and provided with an opening 
faced toward the unit, and an oxygen shortage sensor is mounted in the 
casing in such a way that the heat of exhaust gas rising up from the 
burner unit stays within the casing, thus stabilizing ambient temperature 
of the oxygen shortage sensor. 
As a result, the oxygen shortage sensor performs the stable operation of 
oxygen shortage detection , so that at least selected one of the alarming 
and the stoppage of combustion can be implemented accurately with the 
detection of an oxygen shortage. A very high safety can be thus secured on 
the one hand and the alarming or stoppage of combustion is not 
inconveniently effected when the oxygen is not lacking on the other hand.