US2263225A - Fuel burner control system - Google Patents

Description

Nov. 18, 1941. v H T, SPA ROW 2,263,225

FUEL BURNER CONTROL SYSTEM Filed Jan. 28, 1939 6 I ,fin'omtor b3 Huberi T. Sparrow Patented Nov. 18, 1941 UNITED STATES PATENT OFFICE.

FUEL BURNER coN'raor. SYSTEM 7 Hubert '1. Sparrow, Minneapolis, Minn., asalgnor to Minneapolis-Honeywell Regulator Company, Minneapolis, Minn., a corporation of Delaware Application January as, 1939, Serial No. 253,321

22 Claims.

- stat, and a certain length of time to open the switch after the heater has been deenergized. Therefore if a power failure should occur stopping the burner motor, and then the power should return before the bimetallic timer had had sufficient time to open the burner motor switch, the burner motor would be immediately reenergized without the interposition of a time period sufficient to clear the furnace of combustible gases. Although such a system would probably operate satisfactorily, still a system which provides for a scavenger period each time the burner motor is shut down is preferred.

It is therefore an object of the present invention to provide a system of the above type having a means for providing a scavenger period whenever the burner is shut down.

A further object is to provide a system of this type in which the burner motor switch is opened independently of the timer whenever the heater for the timer is deenergized for any reason whatever and to prevent reclosing o! the switch until the timer has cooled off sufficiently to return to its cold position.

A further object is to provide a magnetic interlock between a thermal timer and a switch operated thereby, the interlock being so designed that the switch will move to one of its positions independently of the timer whenever the heater for the timer is deenergized.

A still further object of the invention is to provide a system in which a timer, under the control of a room thermostat or other control instrument, operates a switching means which, in the cold position of the timer, closes the ignition circuit and holds the burner motor circuit and which, as the timer heats up, first closes the burner motor circuit and later opens the ignition circuit, means,being provided also for returning the switching means to its original position independently of the timer whenever the burner motor is deenergized and for preventing its movement from this position until the timer 55 has returned to its original position.

35 Mounted at one end on a bracket These and other objects will readily become apparent as the following specification is read in the light of the accompanying drawing, in which Figure 1 is a diagrammatic illustration one 5 form of my invention employing intermittent lgnition, and

Figure 2 is adiagrammatic illustration of a slightly modified form having a constant ignition. The present application is drawn to the same basic system that has been disclosed in the applications of John M. Wilson Serial Nos. 253,337 and 253,338 and filed on Jan. 28, 1939, and the application of William J. McGoldrick Serial No.

253,309 filed Jan. 28, 1939.

Referring to Figure 1 of the drawing, a space thermostat is generally indicated at H and comprises a bimetallic element 12 which is fixed at one end and at its free end carries a switch arm III which, on a decrease in temperature,

'20 is adapted to engage a stationary contact H.

Although a thermostat of the bimetallic type has been disclosed, it will be understood that any other type of control instrumentality may be used, such as a bellows thermostat or a pressure responsive device. V

Indicated generally at i5 is a safety switch which is composed of a pair of resilient contact blades I8 and I! which are mounted at one end on the brackets l8 and I9, respectively. The

blade l5 carries at its free end a contact 20 and the blade ll carries at its free end a contact 2|, these contacts being held in engagement under certain conditions which will be later described.

24 is a thermal timer 25 in the form or a bimetallic element. ,At its free end the bimetallic element carries an insulating tip 26 and in the cold position of the timer 25 such as shown in Figure l,

the tip 26 engages underneath the spring blade I! and holds the contacts 20 and 2| in engagement. Closely associated with the timer 25 is a heating element 21 which is adapted to heat the bimetallic timer 25 and cause it to flex toward the left, as seen in Figure 1. The upper end of the timer carries a contact 28 which in the cold position of the timer engages stationary contact 29. The upper end of the timer also carries contact 30 which under certain conditions cooperates with the contact 31 which is mounted on resilient blade 32 connected to the bracket 33.

A combustion switch is indicated generally at 35 and is composed of a switch arm 36 which cooperates with a. stationary contact 31. This combustion switch is of the type in which a temperature responsive element responds to the temperature of combustion, either in the furnace or in the stack, and operates the switch arm 36 by means of a slip friction connection so that the switch arm moves in response to changes in temperature rather than any definite temperature. In this particular switch, the switch arm 36' engages the stationary contact 31 on an increase in temperature andopens the circuit on a decrease in temperature.

Pivoted about a common pivot 48 is a pair of members 4| and 42. These members may be composed of some suitable magnetic material such as soft iron, It will be seen that the weight of the-member 4| is all to the right of the pivot member will rotate in a clockwise direction until it engages the stop 43. Wrapped around one leg of the member 4| is a coil 44 which when energized produces a magnetic pull causing the member 4| to attract the member 42 thereby preventing their separation. The member 42 is connected to the thermal timer 25 by means of the link 45. Pivoted at 46 is an arm 41 which carries at its lower end a mercury switch 48. The switch 48 carries at one end a pair of electrodes 49 and 58 and inserted into the other end of the switch and extending longitudinally of the switch for the major portion thereof is a second pair of electrodes 5! and 52. The arm 41 is connected to member 4| by means of the link 53 and with the member 4| engaging the stop 43, it will be seen that the switch 48 is tipped to a position where themercury 54 closes the circuit between the electrodes 49 and 58 and opensthe circuit between electrodes 5| and 52.

, Insulatingly carried by the upper leg of the. member 4| is a switch contact 55 mounted on supplied by means of the supply lines 62 and 63.

Operation As shown in Figure 1, the space thermostat II is satisfied and has been satisfied for alength of time sufficient to permit the thermal timer 25 to return to its cold position, at which time it moves the contact 28 into engagement with the stationary contact 29, The member 42 has been moved into, engagement with the member 4| whose position is determined by the stop 43, and

r 48 as seen in Figure 1 so that if unconfined this 2,2ecf225 On a decrease in temperature in the space due to the fact that the burner is shutdown, the bimetallic element |2 will move the switch arm l3 into engagement with the stationary contact l4 and this action will set up the following circuit energizing the heater 21: supply line 62, conductor 65, bracket |8, switch blade l6, contacts 28 and 2|, switch blade l1, bracket l9, conductors 66 and 61, bimetallic element l2, switch arm l3, contact I4, conductors 68, 69, and 18, heater 21, conductor 1|, coil 44, conductors 12 and 13, switch blade 58, contacts 51 and 55, switch blade 56, and conductors 14 and 15 back to the other supply line 63. The ignition device is simultaneously energized through part of the above circuit from supply line 62, conductor 65, safety.

switch I5 as traced above, conductors 66 and 61, space thermostat conductors 68 and 11,

electrodes 49 and 58, conductor 18, ignition de-' vice 6|, conductors 19 and 13, switch blade 58, contacts 51 and 55, switch blade 56, and conductors 14 and 15 back to the other supply'line 63.

Thus when the space thermostat calls for heat, the heater 21 and the ignition device 6| are simultaneously energized so that a spark is supplied for-igniting the fuel and the timing movement of the thermal timer 25 is initiated. It will be noted also that as the heater 21 is energized, the coil 44 which cooperates with the magnetic member 4| is also energized so that the two links and 53 will be magnetically locked together by the members 4| and'42 rendering the thermal timer 25 operative to actuate the, switch 48. As the thermal timer 25 starts to heat, it will flex toward the left as indicated in Figure 1 and will pull the switch arm 41in a clockwise direction through the links 45 and 53 and the magnetic interlock 4| and 42. As the switch 48 r is swung to the left, the mercury 54 will first bridge the electrodes 5| and 52 which will energize the burner motor 68 through the follow,- ing circuit: supply line 62, conductor 65, safety switch l5, conductors 66 and 88, electrodes 52 and 7 5|, conductor 8|, burner motor 68, and conducthis movement has brought the contacts 55 and 51 into engagement with each other. The switch 48 is in a position where the electrodes 49 and 58 are bridged by the mercury and the circuit between the electrodes 5| and 52 is opened. The combustion switch having last responded to a decrease in temperature is in open position and the safety switch is in its normally closed position. The circuit to the heater 21 and the ignition device 6| is opened at the space thermostat and the circuit to the burner motor is opened at the electrodes 5| and 52 so that the system is completely deenergi'zed and no power is being drawn from the supply lines 62 and 63;

tors 82 and 15 back to the other supply line 63. The energization of the burner motor 68 while the ignition device is energized will normally produce combustion within the furnace and as a result of this combustion the combustion responsive switch arm 36 will engage the contact 31. As the thermal timer 25 continues to move to the left, the switch 48 will be tipped to a point where the mercury 54 will break the circuit between electrodes 49 and 58, thereby deenergizing the ignition device. 6|. Continued flexing of the thermal timer 25 will eventually bring the contact 38 into engagement with the contact 26 and 'if combustion has been established and the switch 36, 31 closed the following shunt circuit will be set up around the heater 21: from one side of the heater 21, conductor 18, conductor 85, switch arm 36, contact 31, conductor 86, bracket 33. switch blade 32, contact 3|, contact 38, bimetallic element 25, and bracket 24 back to the other side of the' heater 21. This shunt circuit 'will deenergize the heater 21 causing the thermal timer to cool and flex toward the right until it breaks the shunt circuitat the contacts 38 and heater 21 is reenergized heating the timer, and causing it to reclose the contacts 38 and 3|. The thermal timer 25 will continue to make and break the contacts 38 and 3| in this manner as long as the system remains in-this condition, and with As soon as this shunt circuit is broken, the

the thermal timer oscillating back and forth in this small range the coil 44 remains energized and the switch 43 remains in a position where the circuit between the electrodes 49 and 50 is broken and the circuit between the electrodes 50 and 52 is closed. This is the normal running condition of the system and at this time the burner motor will remain energized and the ignition device will remain deenergized.

As a result, the temperature in the space will begin to rise and when it has risen above the control point the bimetallic element I2 will move the switch arm l3 out of engagement with the stationary contact l4. This permanently breaks the circuit through the heater 21 and also through the coil 44 and as soon as this circuit is broken there is no more magnetic attraction between the members 4| and 42 and the member will therefore be moved by gravity in a clockwise direction until it engages the stop 43, at which time it will have moved the switch 48 back to the position shown in Figure 1, when the burner motor circuit will be broken at the electrodes 5| and 52 and the mercury 54 will bridge the electrodes 43 and 50. This will not immediately reenergize the ignition device, however, because the circuit will be open at the switch arm I3 and contact I4. Immediately after the thermostat l2 has broken the circuit, the thermal timer will still be hot and will be holding the member 42 toward the left as seen in Figure i so that the dropping out of the member 42 causes a separation of the contacts 55 and 51. It is now impossible to reclose the starting circuit even though the switch arm I3 should be moved into engagement with the contact |4 because this starting circuit must pass through the contacts 55 and 51. This is true of the circuit. for the heater 21 and it is also true of the ignition device 6 I. The switch contacts 55 and 51 therefore prevent the burner motor 60 from being restarted after it has once been shut down until a predetermined time has elapsed, this time being the time necessary for the thermal timer 25 to cool sufliciently to return the member 42 tov the position shown in Figure 1, at which time the contacts 55 and 51 are in engagement.

The above description of operation covers the normal starting and shut-down of the control system. Let it be assumed now that the space thermostat calls for heat and the starting circuits as set forth above have been established'and the thermal timer 25 has flexed toward the left to close the burner motor circuit and subsequently open the ignition circuit. If for some reason, combustion does not take place, the switch arm 36 will not engage contact 31 so that when the contacts and 3| are brought into .engagement, the shunt circuit around the heater 21 will not be set up. The heater will therefore remain energized and the timer will continue to flex toward the left pressing back the contact blade 32, and eventually the tip 23 will pass from beneath the contact blade l1 permitting it to flex downwardly due to its bias. This will separate the contacts 23 and 2| which will shut off the electrical power to the entire system. The'contact blade l1 engages the tip 2| in such a'manner at this time that the switch will be locked in open position and in order to v re-estahlish the supply of power to the system, the safety switch I! must be manually reset. In order to accomplish this purpose, a manual reset member generally indicated at 33 has been-provided.- This reset membercomprises a long legll and a short leg 32 7 and a stem 33 which is provided with a reset button 94 and which is slidable in the stationary support 95. In order to reset the switch, the button 94 is pressed vertically upwardly which raises the legs 9| and 32 and the leg 9| raises the switch blade I6 out of the path of movement of the switch blade I1 and then the switch blade |1.is moved back to its latched position where it engages the upper side of the tip 25. It will be noted at this time that the switch contacts 20 and 2| still remain in open position, and if the thermal timer 25 has cooled sufficiently for the tip 26 to again move beneath the blade I1 then as the button 34 is released the blade I1 will be held in its raised position and the bias of the blade IE will return the contact 20 into engagement with the contact 2|. If the space thermostat is still calling for heat, the system will make another attempt at a normal start.

If the system is running normally and if flame failure occurs, the combustion responsive thermostat will move the switch arm 36 away from the contact 31 and the heater 21 will remain energized causing the thermal timer to continue to flex to the left until it trips the safety switch |5 to open position and locks itself out as described above.

If the switch arm 36 should become fused on the contact 31 so that these contacts will not separate when the system is shut down, it will be impossible to start the burner motor. The reason for this is that when the space thermostat closes the starting circuit at l3, I4, the heater 21 will be shunted by a circuit passing through the combustion switch 35, the conductor 85, bracket 33, switch blade 32, conductor 96, stationary contact 29, contact 28, bimetallic element 25, and bracket 24. This prevents the energization of the heater 21 and hence the thermal timer 25 will not be heated and will not close the circuit to the burner motor through the switch 48.

One of the main objects of the present invention is to provide a system which would move the burner motor switch to closed position immediately upon the failure of the power and which would prevent the reclosing of the switch until after a predetermined time interval had elapsed. The present system accomplishes this result due to the magnetic members 4| and 42 and the coil 44.. Under normal operating conditions, the coil 44 is energized to lock the magnetic link between the links 45 and 53, but if the power should fail, even though the failure is only a momentary one, the coil 44 will be deenergized permitting the member 4| to drop back against the stop 43 and open the burner motor circuit at the switch 53. Even though the power is now immediately returned, the switch 48 will remain in the same position because the circuit to the coil 44 cannot be reclosed until the thermal timer 25 cools sufflciently to move the member 42 back to the position shown in Figure 1, at which time the contact 51 will be brought into engagement with the contact 55.

This system therefore provides for a minimum time interval during which the burner motor must remain deenergized after it has once been deenergized for any reason whatever. The time interval in each case is determined by the time necessary for the thermal timer to return to its cold position from its hot position.

Figure 2 discloses a slight modification of the invention disclosed in Figure 1. The space thermostat ll, safety switch I, combustion switch 35, as well as the burner motor 60 and ignition device 6|, remain the same and will not again be described in detail. The magnetic members 4| and 42 are again pivoted on a common pivot 40 and again they carry the switch blades 56 and 58 with their associated contacts 55 and 51, In this case a coil IN is wound around the member 4| and when this coil is energized, it acts as a primary winding of a transformer of which the high current winding I02 acts as the secondary. The thermal timer in this case is composed of a bimetal I03 which is of a type that is relatively highly resistant to the fiow of electric current so that as current passes through the bimetal, heat is generated sufficient to cause the bimetal to flex toward the left in the manner produced by the heater 21 on the bimetal 25 in Figure 1.

I As the space thermostat calls for heat, a circuit is closed from the supply line 62, conductor I04, safety switch I5, conductors I05 and I06, bimetallic element I2, switch arm I3, stationary contact I4, conductors I01, I08, and I09, switch blade 58, contacts 51 and 55, switch blade 56, conductors H and III, coil NH, and conductors H2, H3, and 4 back to the other supply line 63. This circuit energizes the coil |0| which induces a low voltage in the high current secondary winding I02. The high current is caused to flow in the following circuit: from one end of the coil I02 through conductor 5 to the upper end of the bimetallic element I03 through the bimetallic element, bracket 24, conductor I09, switch-blade 58, contacts 51 and 55, switch blade 56,and conductor ||0 back to the other side of the coil I02. The flow of current through the bimetallic element I03 causes it to heat due to its resistance properties and flex towards the left. As the energization of the coil |0| also produces a magnetic effect which tends to hold the members 4| and 42 together, the bimetallic element I02 will pull the link 53 and switch I20 with it as it flexes to the left. It will be noted ,that the switch I20 carries only two electrodes |2| and I22 which in the cold position of the bimetallic element |03 are open circuited, but as the element I03 flexes toward the left the switch I20 is tipped in a direction to cause the mercury I23 to bridge these electrodes. This closes a circuit from the supply line 62 through the conductor I04, safety switch l5, conductor I05, conductor I25, electrode |2|, mercury I23, electrode 122, conductors I26 and I21, burner motor 60, and

- conductors I28, H3, and 4 back to the supply line 63. The ignition device 6| is connected in parallel across the burner motor 60 by means of conductors I29 and I30 so that in this modification the ignition device is energized at all times with the burner motor. The closure of the burner motor and ignition circuits normally establishes combustion and as a result the combustion switch will move to closed position. As the bimetallic element continues to flex toward the left it will eventually bring the contact 30 into engagement with the contact 3| and at this time a shunt circuit will be set up around the bimetallic element I03 from the coil I02 so that no current will be flowing through the element and it will therefore begin to cool and flex toward the right. This circuit may be traced as follows: from one end of the coil I02' through conductor 5, contacts 30 and 3|, contact blade 32, conductor 86, stationary contact 31, switch arm 36, conductor 85, conductors I08 and I09, switch blade 58, contacts 51 and 55, contact blade 56, and conductor 0 back to the other side of the coil I02. As the switch contacts 30 and 3| are opened due to the cooling of the bimetallic element I03 the shunt circuit is broken and the bimetallic element will again begin to heat causing it to flex to the left and reclose the contacts 30 and 3|. This again closes the shunt circuit and bimetallic element I03 will continue to oscillate back and forth making and breaking the contacts 30 and 3| in the same manner as in the modification disclosed in Figure 1. At this time, of course, the switch I20 will be held in the position where it maintains the burner motor and ignition circuit closed When the space thermostat is satisfied, it moves the switch arm I3 out of contact with contact I4, which breaks the circuit to the coil |0| thereby releasing the member 4| for rotation in a clockwise direction by means of gravity to open the switch I20. Deenergization of the coil |0| also deenergizes th coil I02 and the timer I03 therefore starts to cool and as the member 4| separated the contacts 55 and 51 as it dropped out, the starting circuit cannot be reestablished until the timer I03 has returned to its cold position in which it moves contacts 55 and 51 into engagement again,

The system in Figure 2 will act in the same manner as the system in Figure 1 on failure to obtain ignition, failure of combustion after the system is in running condition and power failure. In each case after the burner motor is shut down, there is a minimum period during which it cannot be restarted and this period is determined by the time required for the timer I03 to move from its hot or normal running position to its cold position when it recloses the contacts '55 and 51. The system of Figure 2 is also provided with the conductor 96 and the contacts 29 and 28 prevent the system from being started in the event that the combustion switch contacts 36 and 31 have been stuck in their closed position. This result 'is obtained because the bimetallic element I03 is shunted by the following circuit: from one side of the coil I02, conductor 5, contacts 28 and 29, conductor 96, spring blade 32, conductor 86, stationary contact 31, switch arm 36, conductors 85, I08, and I09, switch blade 58, contacts 51 and 55, switch blade 56, and conductor I I0 back to the other side of the coil I02.

It will be appreciated that the system of Figure 2 can be made into an intermittent ignition system in the same manner as the system of Figure 1. The systems are otherwise functional equivalents, the only difference between them 1 being in the manner in which the timer is heated.

Various changes and modifications may occur to those who are skilled in the art and it is therefore to be understood that I am to be limited only by the scope of the appended claims and not by the embodiments disclosed.

I claim as my invention:

1. A fuel supply control system comprising in combination, fuel supplying means, a timer, 8. switch in control of said fuel supplying means,

- means connecting said timer and said switch whereby said switch is normally actuated by said timer, a condition responsive device for energizing said timer to cause it to move from a first position in which said switch is open to a second position in which said switch is closed, means responding to power failure for moving said switch to open position at any time independently of said timer, and means preventing the reclosing of said switch until after said timer has returned to said, first position.

2. A fuel supply control system comprising in combination, fuel supplying means, a timer, a switch in control of said means, means connecting said timer and said switch whereby said switch is normally actuated by said timer, a main switch, a condition responsive device for closing said main switch and energizing said timer to cause it to move from a first position in which said control switch is open to a second position in which said control switch is closed, means for returning said control switch to open position independently of said timer whenever said main switch is opened, and means preventing the reclosing of said control switch until said timer has returned to said first position.

3. A fuel supply control system comprising in combination, fuel supplying means, a timer, a switch in control of said means, means connecting said timer and said switch whereby said 'switch is normally actuated by said timer, electrical means for energizing said timer, 'a circuit for said energizing means, a condition responsive device for closing said circuit to energize said timer thereby causing it to move from a deenergized position in which said switch is open to a second position in which said switch is closed, means responsive at any time to power failure or the opening of said circuit by said condition responsive device for opening said switch independently of said timer, and means preventing the reclosing of said switch until after said timer has returned to said deenergized position.

4. A fuel supply control system comprising-in combination, fuel supplying means, a timer movable from an initial position when energized and returning to said initial position when deenergized, a switch in control of said means, means for connectingsaid timer and said switch whereby the latter is operated by the former, a condition responsive device for energizing said timer,

members against relative movement whereby said switch may be operated by said timer, an energizing means for said timer, a circuit for said energizing means, a condition responsive device for closing said circuit to cause said timer to move from a deenergized position in which said switch is open to a second position in which said switch is closed, power failure causing deenergization of said electrical holding means whereby said first member moves said switch to open position, and means preventing reenergization of said electrical holding means until said timer moves back to said deenergized position.

7. A fuel supply control system comprising in combination, fuel supplying means, a switch in control of said means, a timer, 9, connection between said timer and said switch comprising first and second members mounted for relative movement, said first member being connected to said returning to said initial position when deenercondition has been satisfied for breaking said connection and moving said switch to open position.

e. A fuel supply control system comprising in combination, fuel supplying means, a switch in control of said means, a timer, a connection between said timer and said switch comprising first and second members mounted for relative movement, said first member being connected to said switch and biased in a direction to open said switch, said second member being connected to said timer, electrical means for holding said switch and biased in a direction to open said switch, said second member being connected to said timer, electrical means which when energized holds said members against relative movement whereby said switch may be actuated by said timer, an operating means for said timer, energization of said operating means causing said timer to move from an initial position and deenergization of said operating means causing said timer to return to its initial position, and a condition responsive device for energizing said operating means and said electrical holding means 1 for moving said timer from its initial position in which said switch is open to a second position in which said switch is closed, said condition responsive device deenergizing said operating means and said holding means upon being satisfied whereupon said first member immediately moves said switch to open position independently of said timer, 7

V 8. A fuel supply control system comprising in combination, fuel supplying means, a switch in control of said means, a timer, a connection between said timer and said switch comprising first and second members mounted for relative movement, said first member being connected to said switch and biased in a direction to opens said switch, said second member being connected to said timer, electrical means which when energized holds said members against relative movement whereby said switch may be actuated by said timer, an operating means for said timer, 8. condition responsive device for energizing said operating means and said electrical holding means for moving said timer from a first position in which said switch is open to a second position in which said switch is closed, said-condition responsive device deenergizing said operating means and said holding means upon being satisfied whereupon said first member immediately moves said switch to open position independently of said timer, and means to prevent the reenergizatlon of said operating means and said holding means until said timer returns to said firstpo sition.

9. A fuel supply control system comprising in combination, fuel supplying means, a switch in control of said means, a timer, a connection between said timer 'and said switch comprising first and second members of magnetic material mounted for relative movement, said first mem her being connected to said switch and biased in a, direction to open said switch, said second mem-- her being connected to said timer, electrical means for magnetizing one of said members whereby it attracts the other member and pre- I an initial position and deenergization of said operating means causing said timer to return to said initial position, and a condition responsive device for simultaneously energizing said electrical means and said operating means for moving said timer from a first position in which said motor switch is open to a second position in which said switch is closed, deenergization of said electrical means by said condition responsive device or by power failure causing said first member to immediately move said switch to open position.

10. A fuel supply control system comprising in combination, a fuel supplying means, a switch in control of said means, a timer, a connection between said timer and said switch comprising first and second members of magnetic material mounted for relative movement, said first member being connected to said switch and biased in a direction to open said switch, said second member being connected to said timer, a first coil around one of said members for magnetizing it whereby it will attract the other member and prevent relative movement between them, means for energizing said timer including a second coil electromagnetically associated with said first coil, a circuit for said first coil, a condition responsive device for closing said last named circuit whereby said timer is caused to move from a first position in which said switch is open to a second position in which said switch is closed, said condition responsive device also acting to open said circuit and deenergize said coil whereupon said first member immediately opens said switch.

11. A fuel supply control system comprising in combination, fuel supplying means, a switch in control of said means, a timer, 8, connection first and second members of magnetic material mounted for relative movement, said first member being connected to said switch and biased in a direction to open said switch, said second member being connected to said timer, a first coil around one of said members for magnetizing it whereby it will attract the other member and prevent relative movement between them, said timer comprising a thermal element of a material resisting the flow of electric current, asecond coil electromagnetically associated with said first between said'timer and said switch comprising coil, a circuit including said thermal element and said second coil, and a condition responsive element for energizing said first coil which induces a current flow in said second coil causing said thermal element to heat and move from a first position in which said switch is open to a second position in which said switch is closed, deenergization of said first coil by said condition responsive device or by power failure causing said first member to move said switch to open position independently of said thermal element.

12. A fuel supply control system comprising in combination, fuel supplying means, a switch in control of said means, a timer, a connection between said timer and said switch comprising first and second members of magnetic material mounted for relative movement, said first member being connected to said switch and biased in a direction to open said switch, said second member being connected to said timer, a first coil around one of said members for magnetizing it whereby it will attract the other member and prevent relative movement between them, means for energizing said timer including a second coil electromagnetically associated with said first coil, a circuit for said first coil, a condition responsive device for closing said last named circuit whereby said timer is caused to move from a first position in which said switch is open to a second positon in which said switch is closed, said condition responsive device also acting to open said circuit and deenergize said coil whereupon said first member immediately opens said switch and a switch in series with said first coil, said last mentioned switch comprising a, first contact carriedby one of said members and a second contact carried by the other of said members, said contacts being closed only when said members are in juxtaposition whereby said first coil cannot be reenergized unless said thermal element is in said first position.

13. A fuel supply control system comprising in combination, fuel supplying means, a circuit therefor, an ignition device, a circuit therefor, switch means in said circuits, a timer, a connection between the timer and the switch means whereby the latter is operated by the former, means for energizing said timer, a circuit for said energizing means, a condition responsive device for closing said circuit to cause said timer to move from a first position, in which said switch means closes said ignition circuit and opens said fuel supplying means circuit, to a second position, said movement causing said switch means to first close said fuel supplying means circuit and later open said ignition circuit, means responsive at all times to power failure for immediately returning said switch means to its first position, and means preventing reenergization of said energizing means until said timer has returned to its first position.

14. A fuel supply control system comprising in combination, fuel supplying means, a circuit therefor, an ignition device, a circuit therefor,

switch means in said circuits, a timer, a connection between the timer and the switch means whereby the latter is operated by the former,

means for energizing said timer, a circuit for said energizing means, a condition responsive device for closing said circuit to cause said timer to move from a first position, in which said switch means closes said ignition circuit and opens said fuel supplying mearrs circuit, to a second position, said movement causing said switch means to first close said fuel supplying means circuit and later open said ignition circuit, means responsive at all times to power failure or an opening of said circuit for said energizing means by said condition responsive device for immediately returning said switch means to its first position, and means preventing reenergization of said energizing means until said timer has returned to its first position.

1 15. A fuel supply control system comprising in combination, fuel supplying means, a circuit therefor, an ignition device, a circuit therefor,

switch means for controlling said fuel supplying means and ignition circuits, a, normally closed second switch in control of both circuits, a timer, a connection between said timer and said switch means whereby the latter is actuated by the former, an energizing means for said timer in series with said second switch, said timer having a deenergized position in which said switch means opens said fuel supplying means circuit and closes said ignition circuit, said timer having a second position in which it opens said second switch, a condition responsive device for closing the circuit to said energizing means to cause said. timer to move from said deenergized position toward said second position during which time said switch means first closes said fuel supplying means circuit and later opens said ignition circuit, means responsive to combustion for normally preventing said timer from moving into said second position but permitting such action if combustion does not take place, means responsive to the deenergization of the circuit to said energizing means for moving said switch means to its first position independently of said timer, and means preventing the reenergization of the circuit to said energizing means until said timer has returned to its first position.

16. In a device of the character described, in combination, a thermal timer, a control device having a plurality of control positions, means connecting the timer and control device, a heater for said thermal timer, a condition responsive device for energizing said heater to cause said thermal timer to move said control device from a first control position to another control position, and means responsive to the deenergization of said heater for moving said control device back to said first control position independently of said timer.

17. In a device of the character described, in combination, a thermal timer, a control device having a plurality of control positions, connections between said timer and said control device including an electromagnetic holding device, a

timer on deenergization of said circuit, and means preventing reclosing of said circuit until said thermal timer has returnedto its cold position.

18. A fuel supply control system comprising in combination, a fuel supply control means, a timer, connections between said control means and timer, means for energizing said timer to cause it to move from a first position in which said fuel supply control means is inoperative to a second position in which said fuel supply control means is operative, said timer returning to its first position upon deenergization. and means for rendering said fuel supply control means inoperative again independently of said timer whenever said timer is deenergized.

19. A fuel supply control system comprising in combination, fuel supplying means, a switch in control thereof, a timer, connections between said switch and timer, said timer, when energized, moving from a first position in which said switch is open, to a second position in which said switch is closed, and when deenergized returning to said first position, a main switch, a condition responsive device for closing said main switch and energizing said timer, and means for returning said control switch to open position regardless of the position of said timer.

20. A fuel supply control system comprising in combination, fuel supplying means, a timer, a switch in control of said means, means connecting said timer and said switch whereby said switch is normally actuated by said timer, electrical means for energizing said timer to move from a first position in which switch is open, to a second position in which said switch is closed, said timer returning to said first position upon deenergization, a circuit for said electrical energizing means, a condition responsive device for closing said circuit to energize said timer, and means responsive to power failure or the opening of said circuit by said condition responsive device for opening said switch regardless of the position of said timer.

21. A fuel supply control system comprising in combination, fuel supplying means, a timer having a deenergized position. means for energizing said timer, a switch in control of said fuel supplying means, connections by means of which said timer, when energized, closes said control switch, and means for opening said control switch independently of said timer substantially immediatelywhenever said timer is deenergized.

22. A fuel supply control system comprising in combination, fuel supplying means, a timer having a deenergized position, means for energizing said timer, a switch in control of said fuel supplying means, connections by means of which said timer, when energized, closes said control switch, means for opening said control switch independently of said timer substantially immediately whenever said timer is deenergized, and means preventing the reenergization of said timer until after'it has returned to its deenergized position.

HUBERT 'I'. SPARROW.

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