US3057398A - Fuel burner control system - Google Patents

Description

United States This invention relates to control systems for fuel burners and more particularly to fuel burners control systems having provisions for automatically protecting against unsafe burner conditions. I

In many automatically controlled fuel burners, fuel delivery means, such as a valve or pump, controls delivery of fuel to the burner and electrical ignition device means is employed to ignite fuel delivered to the burner. The fuel delivery means and the ignition means are initially energized by a burner control switch, such as a thermal switch or a fluid pressure switch when heat is required. After ignition of the fuel occurs, a combustion switch, responsive to combustion of the fuel, deenergizes the ignition means while the fuel delivery means continues to function until deenergized by the burner control switch when the burner has satisfied the heat requirements. The combustion switch will then reclose and the burner control system will be in condition to permit the burner to restart when the 'burner control switch again calls for heat.

In the event that the fuel does not ignite within a certain time after its delivery to the burner begins, it is desirable to stop its flow to prevent the accumulation of a dangerous quantity of fuel. A great variety of control systems have been employed in the past to automatically stop the delivery of fuel to the burner in the event combustion of the fuel does not occur within a predetermined time. In one well-known form of control system, a timing motor and a series of cam-operated switches controlled by the timing motor are operated with a burner control switch and a combustion switch to control operation of the burner ignition and fuel supply devices. Such control systems usually have also included one or more electromagnetic relays and/or an electromagnetically operated clutch through which the cam-operated switches are driven by the timing motor. For the most part, these control systems have been complex and expensive.

The principal object of this invent-ion is to provide a simplified and low-cost, motor-operated burner control system requiring little operating power and using no relay or clutch, yet having provisions for automatically protecting against unsafe burner conditions.

Another object of the invention is to provide a burner control system of the timing motor type, wherein the control apparatus is simple and inexpensive in construction, yet is durable and dependable in operation.

In the preferred embodiment of my invention, 1 provide an electric timing device which cooperates with a combustion-responsive switch to control the operation of a fuel burner including a fuel delivery device and ignition means. The timing device comprises an alternating current, synchronous motor which drives through a speed reducer mechanism a timing shaft having cam means thereon for actuating timer switches at predetermined times after the motor is started. The. motor drives the timing shaft in one direction only away from an initial atent 3,057,398 Patented Oct. 9, 1962 position and a resetting spring is used to return the shaft to its initial position when the motor is deenergized. A first timer switch is connected in parallel with a first set of normally closed contacts of the combustion-responsive switch in an energizing circuit for the timer motor. A second timer switch is connected in an energizing circuit for the fuel delivery means and the ignition device. Both timer switches are open in the initial position of the timing shaft and when the circuits are energized through a burner control switch, energization of the timer motor is completed through the combustion-responsive switch. The two timer switches close shortly. after the motor is energized. The closed second timer switch completes the circuit to the fuel delivery means and the ignition mean-s, while the closed iirst timer switch serves to maintain the motor energized after the combustion-responsive switch contacts open upon occurrence of combustion. After further energization of the motor, the first timer switch will reopen and, if the combustion-responsive switch has opened, the motor will be deenergized and the resetting spring will return the shaft in the reverse direction. This will reclose the first timer switch and this cycle of opening and closing the first timer switch will be repeated until the burner control switch is opened. If combustion does not occur, the combustion-responsive switch contacts will remain closed and the motor will remain energized after opening of the first timer switch and continue movement of the timing shaft past a position where the second timer switch is opened and to a further position where it is held by stop means until the burner control switch is opened. If desired, the combustion-responsive switch may be provided with a second set of contacts to deenergize the ignition means after occurrence of combustion.

Other features and advantages of the invention will be apparent from consideration of the following description, taken in connection with the accompanying drawing, in which:

FIG. 1 is a diagrammatical view of a fuel burner control system embodying the invention; and

FIGS. 2 and 3 are diagrammatical views showing modifications of the control system.

Referring to FIG. 1, there is shown a control system for a fuel burner which is provided with an ignition device 10 for igniting fuel supplied to the burner. a fuel delivery device 11 for controlling the flow of fuel to the burner and a combustion switch means 12 which is responsive to the absence or presence of combustion in the burner. In a gas burner, ignition device 10 may be an electrical transformer for providing high voltage to a spark gap while the fuel delivery device 11 may be an electrically operated valve which when energized admits fuel to the burner. Combustion switch means 12 is of a conventional type and comprises two switches 13 and 14 operated by a thermally responsive element which is arranged to be subjected to the heat of the burner. Switches 1-3 and :14 are closed in the absence of combustion and will open in the presence of combustion. Eelectric power is supplied to the control system from power lines 15 and 16 through a burner control switch 17 which may he a thermostat that is located in the space being heated by the fuel burner.

The control system is further provided with a timing device which after initial closure of switch 17 provides for energization of the ignition device 10 and the fuel delivery device 11 and which further provides for shutting down the fuel burner if combustion is not established or fails during operation of the burner. The timing device includes a self-starting timing motor 18 that can remain constantly energized without being damaged when indefinitely stalled. Motor 18 is preferably a synchronous hysteresis motor as it is important that motor 18 always operate in the same direction when energized. Motor 18 is coupled by a speed reducer or gear reduction mechanism 19 to an operating member or timing shaft 20 for driving the shaft in a clockwise direction as indicated in the drawing until a stop-engaging arm 21 carried by shaft 20 engages the left-hand side of a fixed stop 22. The shaft 20 is biased in a counterclockwise direction to cause stop-engaging arm 21 to normally engage the right-hand side of stop 22 by means of a. resetting spring 23 which is attached at one end to the shaft 20 and at the other end to a stationary support 24. The gear reduction mechanism 19 is of a type that can be reversibly driven so that spring 23 is effective after the motor 18 is deenergized to return the shaft 20 in a counterclockwise direction to its initial or starting position at a slow speed determined by the inertia and friction of the gear reduction mechanism 19 and the armature of the motor 18.

The shaft 20 also carries a cam 25 whose cam surface includes a high edge 26, a low edge 27 and an intermediate edge 28 between edges 26 and 27. The cam 25 operates two timer switches 29 and 30 which are shown as comprising three resilient blades 31, 32 and 33 suitably insulated from each other. Blade 31 has a contact 34 adapted to engage a contact 35 on blade 32 to form switch 30. Blade 32 has a second contact 36 adapted to engage a contact 37 on blade 33 to form switch 29. Associated with blade 33 is a cam follower 38 adapted to engage the edges of the cam 25.

When the follower 38 is in engagement with low edge 27 of the cam 25, both switches are open. When the cam 25 is rotated in a clockwise direction by the motor, engagement of the high edge 26 by the follower 38 closes both switches 29 and 30. Further clockwise rotation of cam 25 causes switch 29 to open as the follower 38 reaches the intermediate edge 28. When the follower 38 rides upon the low edge 27 after still further clockwise rotation, switch 30 also will open.

The circuit connections for the control system of FIG. 1 are as follows: One side of the motor 18 is connected by line 39 to power line 16 and the other side of the motor 18 is connected to power line 15 through line 41, combustion switch 13, lines 42 and 43, and burner control switch 17. Timer switch 29 is connected in parallel with combustion switch 13 by lines 41 and 44 which connect blade 31 to one side of switch 13 and by lines 45 and 42 which connect blade 32 to the other side of switch 13. One side of the fuel delivery device 11 is connected to power line 16 and the other side is connected to the power line 15 through line 46 to blade 33 of timer switch 30, contacts 37 and 36, blade 32, lines 45 and 43, and burner control switch 17. The ignition device 10 is connected in parallel with the fuel delivery device 11 by a connection from one side to power line 16 and by a connection from the other side through line 47, combustion switch 14, and line 48. It will be apparent that combustion switch 14 serves merely to deenergize the ignition device 10 after combustion has occurred and could be omitted if continuous ignition were desired by conmeeting the ignition device 10 in direct parallel connection with the fuel delivery device 11.

Operation The operation of the control system of FIG. '1 is as follows: When the burner control switch 17 is closed in response to a requirement for heat, the motor 18 will be energized through a circuit including combustion switch 13. If, due to a malfunction of the combustion switch means 12, switch 13 is open or if the motor 18 is inoperative to drive cam 25, switches 29 and 30 remain open and the fuel delivery device 11 cannot be energized. Thus, operation of the fuel burner would not be attempted upon the occurrence of such malfunctions of the control system. Normally, however, the motor 18 would rotate cam 25 in a clockwise direction from its initial position shown in FIG. 1. After the motor 18 has rotated the cam 25 for a predetermined time interval such as one second, the high edge 26 is engaged by the follower 38 to close both switches 29 and 31 The closure of switch 29 establishes a circuit that shunts the combustion switch 13 while at the same time the closure of switch 30 completes a circuit energizing the ignition device 10 and the fuel delivery device 11.

If combustion of the fuel at the burner occurs in a normal manner, the combustion switches 13 and 14 will open in a short interval of time. Opening of switch 14 will deenergize the ignition device 10 but opening of switch 13 will not deenergize the motor 18 since switch 13 is now shunted by switch 29. The motor 18, therefore, continues to rotate and, after a period of time sufficiently long for combustion to occur under normal conditions, the cam follower 38 moves into engagement with the intermediate edge 28 to open switch 29. Since combustion switch 13 has also opened, opening of switch 29 now deenergizes the motor '18. The resetting spring 23 then rotates timing shaft 20 in a counterclockwise direction at a slow speed determined by the friction and inertia of the gear reduction system until the cam high edge 26 reengages cam follower 38 and switch 29 recloses. The motor 18 then turns the shaft 20 in a clockwise direction and the cycle of opening and closing switch 29 is repeated until power is removed as by opening of the burner control switch 17. During this cycling period the fuel delivery device :11 remains energized through switch 30.

Upon opening of switch 17 when the heat requirements have been fulfilled by the burner or in the event of an electrical power interruption, the entire circuit is deenergized. The resetting spring 23 rotates the shaft 20 in a counterclockwise direction until the stop-engaging arm 21 is brought up against the stop 22. When the combustion-responsive switches 13, 14 reclose, the control system will be in condition to again place the burner in operation in response to closing of the burner control switch 17.

If, for any reason, energization of the ignition device 10 and the fuel delivery device 11 does not result in combustion of the fuel, the combustion-responsive switch 13 remains closed, continuing energization of the motor 18. After a predetermined length of time, the cam low surface 27 comes into engagement with cam follower 38 to open switch 30, thereby deenergizing the ignition device 10 and the fuel delivery means 11. The motor 18 continues to rotate in a clockwise direction until it is stalled when the arm 21 is brought up against the left side of stop 22. The cam 25 will remain in this stalled position with both switches 29, 30 open until the circuit is deenergized. If a combustion failure occurs during operation of the burner, the combustion-responsive switches 13, 14 will reclose and maintain the motor 18 continuously energized, thereby causing switch 30 to interrupt the circuit to the fuel delivery device 11 after a predetermined period of time.

It will be apparent that the circuit of the control system is so arranged that the system will fail safely if the motor 18' is inoperative. Neither can the burner be placed in operation if the combustion-responsive switch means 12 fails since switch 13 must be closed to initiate operation of motor 18 and must open in a predetermined time interval after the burner is placed in operation to maintain energization of the fuel delivery device 11.

FIGURE 2 Madification In FIG. 2 is disclosed a slightly modifiedforrn of the system disclosed in FIG. 1. In this figure, parts corresponding to parts in FIG. 1 are given the corresponding reference numeral with the prefix 1. The system of FIG. 2 has the same ignition device 110, fuel delivery device 111, burner control switch 117, motor 118, gear reduction mechanism 119, shaft 120, stop-engaging arm 121 and resetting spring 123. The combustion-responsive switch means 112 is shown with a single contact arm, double break arrangement of switches 113, 114. The switches 129, 130 are operated by separate cams 125a and 12Sb to provide the same switching operations as switches 29, 30 in FIG. 1. Although the circuit connections are somewhat different, it is obvious that the sequence of operation of the circuit of FIG. 2 is identical to the operation of the circuit of FIG. 1.

FIGURE 3 Modification FIG. 3 shOWs a further modified form of the system disclosed in FIG. 1. Components of the modified system which have counterparts in the system of FIG. 2 are given the reference numeral of FIG. 2 with the prefix 2 substituted for the prefix 1. In the system of FIG. 3, the mechanical stop has been eliminated and instead, a third timer switch 260 is connected in series circuit relation with the motor 218 and the combustion-responsive switch 213 to provide electrical stop means for the motor. Switch 260 is shown as including a blade 261 carrying a contact 262 adapted to engage contact 263 on blade 231. Associated with blade 261 is cam follower 238a which engages the edges of cam 225a. A notch is formed in the intermediate edge 228a of cam 225a to provide a low edge 264. The edges of cam 225a are so arranged that as cam follower 238a enga es edges 226a, 228a and 264, respectively, switches 229, 260 are closed, switch 229 is open and switch 260 is closed, and switches 229, 260 are both open.

Operation FIGURE 3 The sequence of operation of the system of FIG. 3 is identical to the operation of the systems of FIGS. 1 and 2 in normal starting, running and shutdown of the burner. With the parts in their normal standby or initial positions shown in FIG. 3, closing of burner control switch 217 completes a circuit energizing motor 218. This circuit may be traced from line 215 through switch 217, lines 250, 252, motor 218, line 253, blade 261, contacts 262, 263, blade 231, line 254, and combustion-responsive switch 213 to line 216. After initial clockwise rotation of the motor shaft 221), cam 225b causes closing of switch 230 to energize the fuel delivery device 211 and the ignition device 211), while at the same time, cam 225a causes closing of switch 229 to establish a shunt circuit across combustion -tresponsive switch 213. When combustion is established at the burner, combustion- responsive switches 213, 214 open. This has no effect upon operation of the motor 218 which remains energized through a circuit including line 256 and switch 229. Rotation of shaft 220 continues in a clockwise direction until cam 225a causes switch 229 to open. The spring 223 then rotates the shaft 220 slowly in a counterclockwise direction until switch 229 recloses to energize motor 229 again. This cycle of opening and closing switch 229 continues with normal burner operation until the circuit is deenergized as by opening of switch 217. After a short time, spring 223 will return the cams 225a, 225b to their original positions. A short time thereafter the combustion-responsive switches will reclose and the system is ready for another operating cycle.

In the event of ignition failure, the combustion-responsive switch 213 remains closed, maintaining the motor 218 energized, and, after a predetermined time interval, cam 2251) causes switch 230 to open, thereby shutting down the burner. Upon further rotation of the motor shaft 220, cam 225a causes switch 260 to open. This deenergizes the motor 218 and the shaft 220 is returned in a counterclockwise direction by spring 223 until switch 260 recloses. The motor 218 again rotates the shaft in a clockwise direction and the cycle of opening and closing switch 260 is repeated until the circuit is deenergized. During this cycling, switch 230 remains open and the burner remains shut down. Upon a flame failure, the burner will be shut down in an identical manner after the combustion- responsive switches 213, 214 close.

While the invention has been illustrated and described in connection with preferred embodiments and has included certain details, it should be understood that the invention is not to be limited to the precise details herein illustrated and described since the same may be carried out in other ways falling within the scope of the invention as claimed.

What is claimed is:

1. In a control system for a fuel burner having a fuel delivery means which, when energized, causes the delivery of fuel to the burner; a combustion-responsive switch which is closed in the absence of burner combustion and is open in the presence of burner combustion, and a power circuit energized on demand for heat from the burner; the combination comprising a switch-operating member mounted for reciprocating movement between an initial position and a final position; an electric timing motor for driving said operating member in a predetermined direction from said initial position to said final position at a timed rate; means yieldably biasing said operating member to said initial position and effective to move said operating member in a direction opposite to said predetermined direction for returning said operating member to said initial position when said timing motor is deenergized; first and second timer switches controlled by movement of said operating member; said timer switches being open 'in the initial position of said operating memher and being closed when said operating member is moved from said initial position; said first timer switch being reopened upon movement of said operating member in said predetermined direction beyond a first predetermined position; said second timer switch being reopened at a second predetermined position upon a further movement of said operating member in said predetermined direction beyond said first predetermined position; said first and second positions being intermediate said initial and final positions; -a timing motor circuit including said combustion-responsive switch connecting said timing motor with said power circuit for initially energizing the timing motor and for maintaining the timing motor energized n the absence of combustion; and operating circuit including said first timer switch connected in parallel with said combustion-responsive switch for controlling energization of said timing motor after opening of said combustion-responsive switch; said operating circuit being alternately opened and closed by said first timer switch after opening of said combustion-responsive switch as said operating member is alternately driven to said first position by said timing motor and then returned from said first position by said biasing means; and a fuel delivery means circuit including said second timer switch connecting said fuel delivery means with said power circuit for energizing the fuel delivery means following initial operation of the timing motor and for de-energizing the fuel delivery means if said operating member is driven beyond said second position.

2. A control system according to claim 1 wherein said timing motor is an unidirectional alternating-current synchronous motor having a speed reducer connected to rotate said operating member at a uniform speed in said predetermined direction, said speed reducer being of a type that can be reversibly driven by said biasing means.

3. A control system according to claim 2 including a fixed stop and means associated with said operating member engaging said fixed stop to stall said timing motor when said operating member reaches said final position.

4. A control system according to claim 2 including a normally closed third timer switch in control of said tim- 7 8 ing motor and operated by said operating member; said second timer switches until said power circuit is deoperating member opening said third timer switch as it energized. moves to said final position to interrupt said timing motor circuit; said interruption of said timing motor circuit R fer nces Cited in the file of this patent causing said operating member to be moved from said 5 UNITED STATES PATENTS final osition b said biasin means; and said 0 eratin mernlger being alternately rsoved by said timiin mote? 2445 Mesh July 1948 and then by said biasing means to and then from said 2472398 Berger June 4 final position without reclosing either of said first and 2519889 Crawfopd 1950

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