US3428041A - Heating control system with time delay relay - Google Patents

Description

Feb. 18, 1969 HEATING J. R. WILLSON 3,428,041 CONTROL SYSTEM WITH TIME DELAY RELAY Filed June 6, 1967 Sheet of 2 32 IN VEN TOR.

JAMES R.W|LLSON BY A TTOR/VEYS Feb. 18, 1969 J. R. WILLSON 3,428,041 HEATING CONTROL SYSTEM WITH TIME DELAY RELAY Filed June 6, 1967 Sheet .2 of 2 INVENTOR. JAMES R. W] LLSON BY United States Patent 8 Claims ABSTRACT OF THE DISCLOSURE A forced air heating control system including a time delay rel'ay having a bimetal strip and a mechanical latching member which cooperate to open and close circuits to a heater fan and an electric igniter.

Background of the invention The invention relates to a heating control system and mor particularly to time delay control relays and relay circuits "for forced air heating systems.

In order to maintain an adequate heat level in an area from a remote heater installation, it has been found that the electrical circuit for the circulating fan of a forced air heating system can be suitably opened or closed by a time delay relay operable in response to the on-otf temperature control of the area being heated. Many of these heater installations such as roof top units, also generally require electric ignition systems tor dependable operation. In these systems it is desirable to have an automatic ignition device with flameproving means which may be operable in response to the same on-off temperature control that initiates the starting and stopping of the fan.

Summary of the invention The invention is generally characterized in that a time delay relay which is in the electrical circuit for the circulating fan of a forced air heating system is also in electrical circuit with the furnace igniter and a flame sensing element, A single time delay relay including a bimetallic strip and a mechanical latching member cooperate to connect a fan and an igniter in electrical circuit when a room thermostat calls for heat but provides temporary protection to spurious electrical or flame interruptions and lock-up protection to the system if the furnace 'fails to ignite.

Some important advantages of this invention are that it provides lock-up to a safe position when hazardous conditions are present while permitting continuous electrical ignition and tan starting when momentary electrical or flame interruptions occur. The use of a single time delay relay in the heating control circuit insures automatic furnace, tan and electric igniting start and stop operations in response to a thermostatic control switch while at the same time providing maximum safety lfeatures.

It is, therefore, an object of the present invention to provide a novel heating control circuit for automatically starting a fanand allowing electric ignition of the furnace in response to the operation of a remote control switch, and in addition, to provide a novel time delay relay for controlling the switching of electrical control circuits in a forced air heating installation.

Brief description 0 the drawings FIG. 1 is a circuit diagram of an embodiment of the invention illustrating the heating control system in an off position;

FIG. 2 is a circuit diagram of the embodiment of FIG. 1 illustrating the system in an on position;

FIG. 3 is a circuit diagram similar to FIG. 1 with ice additional components and illustrating the system in a lock-up position; and

FIG.4 is a circuit diagram of another embodiment of the invention.

Description of the preferred embodiments As is illustrated in FIG. 1, a forced tem includes a main burner 10 flow of fuel under the control valve 12 and being ignited by an electric igniter 14; an electric circulating fan '16 forces air heated by burner 10 to a space that is to be temperature controlled. A flame responsive assembly, indicated generally at 18, includes a thermal bulb 20 disposed to sense the flame at the burner 10, a capillary tube 22 and a contractable and expansible bellows or power element 24; the bulb 20, capillary tube 22 and power element 24 constitutes a closed system filled with a thermally responsive fluid, such as mercury, whereby the presence of a flame at the burner 10 effects an expansion of the power element 24 for a purpose to be described hereinafter.

An electric circuit for controlling the heating system is supplied over power leads L and L from any suitable power source, which are connected by conductors 26 and 28, respectively, to the primary winding 30 of a transformer 32. Assuming a 110 volt source at leads L and L the transformer 32 is stepped down to 24 volts at its secondary winding 34 that has conductors 36 and 38. A conventional space thermostat 40, suitably located in the space being temperature controlled, and a convention-al high limit switch 42, suitably located in the plenum chamber of the furnace embodying the burner 10, are serially connected in the conductor 38 which extends at a common junction 44, while the conductor 36 extends to a common junction 46. A conductor extends from the common junction 44 to the terminal T connected to a thermal switch TS that is operated between open and closed positions by the power element 24.

A time delay relay, indicated generally at 48, includes a generally U-sh-aped frame 50, one end of which pivotally carries an E-shaped lifter 52 and a latch bar 54 on a common pivotal axis. The latch 54 is transversely disposed to the center leg of the litter 52 and a coil spring 56 is mounted in compression between the top of the latch 54 and the top leg of the lifter 52. A lever arm 58 is 'pivotally mounted adjacent the opposite end of frame so that its free end extends into the space defined by the E shaped lifter. An operating rod 60 engages the undersurtace of the lever arm 58 and is secured to spaced actuating blades 62 and 64 having free ends integrated at 66 which is biased by a coil spring 68 mounted in compression between the actuating blade end 66 and the bottom wall of frame 50.

An overcenter U-shaped spring 70 is mounted between a cutout edge of actuating blade 62 and an edge of an actuated blade 72 which is formed as a tongue in the cutout portion of the actuating blade 62 and which is electrically connected to a conductor 71 extending to the common junction 44. The specific details of the snap acting switch elements may take any suitable form, such as illustrated in US. Patents No. 2,237,705 and No. 2,458,518. The actuated blade 72 is made of a current conducting material and carries a contact 74 for movement into and out of engagement with a fixed contact 76 mounted on a fixed blade 77 also of current conducting material. The other actuating blade 64 is similar to blade 62 and includes the similar elements of overcenter spring 80, actuated blade 82 but having a double faced contact 84 thereon for cooperation in one position with a fixed contact 86 on an upper fixed blade 87 and in an opposite position with a fixed contact 88 on a lower fixed blade 90. A bimetal element 91 has one end secured to air heating sysbeing supplied with a of 'a solenoid operated the top of frame 50 on the end above the pivot mount for lever arm 58 and extends superimposed thereover with a transversely bent end portion disposed for engaging the free end of the lever arm 58.

An electric heating coil 92 is wound around the bimetal 91 and has one end connected to a conductor 93 which is connected to the common junction 46 and includes a series connection with the solenoid coil 120 of the valve 12. The other end of heating coil 92 is connected to a common junction 94 having one conductor 95 connected to the fixed blade 77 and another conductor 96 connected to a common junction 97. A conductor 98 from the common junction 46 to the common junction 97 includes the coil of a relay R which has a pair of normally open switches RS1 and RS2. The relay switch RS1 is serially connected in a conductor 99 extending from the common junction 97 to the terminal T connected to the thermal switch TS. The relay switch RS2 is serially connected in a conductor 88 extending from the fixed blade 87 to the igniter 14 and the other conductor 3 for the igniter 14 is directly connected to the lead line L The circulating fan 16 has a pair of terminal posts, one of which is connected by a conductor 4 to the conductor 3 and the other of which is connected by a conductor to the lower fixed blade 90.

In the following description of a sequence of operation, it is to be understood that the heating system components including elements 10, 14, 16, 18, 20, 22 and 24 are also part of FIGS. 2, 3 and 4, but have not been shown thereon for the sake of brevity. FIG. 1 represents the various positions of the control components when the space thermostat 40 is open, i.e., contacts 76 and 86 are closed by switch arm blade contacts 74 and 84, respectively; contact 89 is open so the circulating fan is deenergized; and, the relay switches RS1 and RS2 are open to the igniter 14 cannot be energized.

When space thermostat 40 calls for heat, it is closed as shown in FIG. 2 and completes a circuit traced as follows: from the secondary winding 34 of the transformer 32 through the conductor 38, the closed spaced thermostat 40, the normally closed limit switch 42, common junction 44, conductors 71, blade 72, contacts 74 and 76, blade 77 and conductor 95 to common junction 94; thence through a series connected network comprising the heater coil 92, conductor 93, control valve coil 120, common junction 46 and conductor 36 to the other side of the transformer secondary 34, with the coil of relay R being in a parallel circuit between the common junctions 94 and 46 by means of conductor 96. Accordingly, the control valve 12 is opened so there is a flow of fuel to the burner 10, which is ignited by the igniter 14 which is energized by a circuit traced from power line L through blade 82, contacts 84 and 86, fixed blade 87, conductor 88 and closed relay switch RS2, the igniter 14 and conductor 3 to the power line L At the same time, the energized heater coil 92 in the time delay relay 48 effects heating of the bimetal 91 which is caused to bend upwardly and eventually pivot the lifter 52 clockwise as viewed in FIG. 2. The bottom leg of lever 52 also commences the upward movement of the lever arm 58 whereby the operating rod 60 and the attached actuating blades 62 and 64 are aided in their upward movement by the coil spring 68; during such movement blades 62 and 64 cause rotation of their respective overcenter springs 70 and 80 until they pass dead center positions, after which the movable switch blades 72 and 82 are moved with a snap action to their posi tions shown in FIG. 2 wherein contacts 76 and 86 are open and contacts 84 and 89 are closed. Closure of contacts 84 and 89 completes a circuit for the circulating fan traced from power line L through movable blade 82, closed contacts 84 and 89, fixed blade 90, conductor 5, terminals on the circulating fan 16, conductor 4 and conductor 3 to the power line 5. Thus, a short time after the burner is ignited, the circulating fan 16 is energized to force the warm air through the heating system.

The opening of the contact 86 opens the circuit for the igniter 14 which is deenergized. However, the burner 10 continues to operate so that the flame sensor bulb 20 is heated and the resulting expansion of the power element 24 closes the thermal switch TS. The contact 76 is opened simultaneously with the opening of contact 86, however, the heating coil 92 remains energized by another circut including the thermal switch TS. The bimetal 91 and heating coil 92 have a predetermined time delay characteristic which is greater than the time it takes for the closure of the thermal switch TS by the flame sensor assembly 18-24; thus, the thermal switch TS closes before the bimetal 91 effects opening of control 76. With normal operating conditions, the system will function automaticallywith the burner 10 being cycled thermostatically in response to operation of the space thermostat 40.

When undesirable interruptions occur after ignition, the operation of the time delay relay provides the control system with several protective features. Such interruptions which might be likely to occur are those due to a power failure, a rapid opening of the thermostat contacts or by an opening of the flame sensor contacts after a flame failure. An interruption of this nature will cause relay R to return to its normal position, gas valve 12 to immediately close and time delay relay 48 to return to its normal position.

When this happens recycling occurs in the same way as when controlled by the space thermostat 40.

If ignition does not occur, however, the flame switch TS will not close before the time delay relay 48 pulls in. Relay R is then released through the opening of switch 76 and the heater coil 92 is deenergized. With flame switch TS opened, bimetal 91 does not continue to bend far enough to clear the latch 54 and is brought into the lock-up position shown in FIG. 3.

In this position, even though bimetal 91 cools, switches 62 and 64 cannot transfer their contacts back to their normal position because of the latch 54. Gas valve 12, therefore, cannot open and the igniter 14 is prevented from being energized. To be released from the lock-up position, the bimetal 91 must either be heated sufficiently to clear the latch 54 or a manual release in the form of a push button 153 acts on the lifting member 52 may be provided.

An electrical reset for so heating the bimetal 91 is shown in FIG. 3 wherein an electrical switch 143, and 147 is connected through a conductor 14 and a resistor 139 to the conductor 38 and thus remove the time delay relay 48 out of lock-up. A third relay switch RS35 is also shown in FIG. 3 which connects a lamp 104 and its conductor 102 to the conductor 3 in order to indicate lock-up conditions.

FIG. 4 shows a modified heating control system which may be employed with a thermistor type of flame sensor. With this embodiment the electrical load of the gas valve 12 and heater coil 92 are carried by relay switch RS3 to minimize the load on the thermistor 221. Relay R operates switch RS3 and switches RS1 and RS2 in the thermistor path and conductor 88, respectively. The system operation is similar in all other respects to that described in the embodiment of FIGS. 1 and 2.

In the event that the time delay relay 48 fails in the embodiments described, interruption of the main burner gas at the end of the delay period is provided by wiring the gas valve 12 in series with the time delay heater 92. With this provision, any failure of the time delay relay heater, disconnected wires, or bimetal failure will result in a fail safe or lock-up position.

Inasmuch as many changes could be made in the above constructions and many more widely different embodiments of the present invention could be \made without departing from the scope thereof, it is intended that all matter contained in the foregoing description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

1. In a heating control system, the combination including a fan motor for circulating air heated by a burner, an electric igniter for said burner, a thermostatic switch movable between on and off positions, and an electrical input circuit comprising:

a bimetal heating element,

a first time delay switch,

a second time delay switch,

'a heating network for said bimetal heating element including said first time delay switch connected to said input circuit in response to said thermostatic switch being in its on position,

means including said second time delay switch connecting the igniter to the input circuit in response to said thermostatic switch being in its on position, and

means responsive to said bimetal element after a predetermined time delay ior disconnecting said first time delay switch from the heating network and for switching the input circuit from the igniter to the fan motor with said second time delay switch.

2. The combination of claim 1 wherein said time delay switches have -a normal position and an active position, means in said heating network for returning said time delay switches to their normal positions in response to spurious electrical or flame interruption signals, and means in said responsive means for preventing said switches from returning to their normal positions in response to a lock-up signal.

3. The apparatus of claim 1 wherein said heating network comprises a heating coil wound around said bimetal electrically connected between the thermostatic switch and said first time delay switch, a flame sensing circuit connected between the thermostat and said coil, said flame circuit closing an electrical current path to said coil in response to a flame signal, and said bimetal moving said responsive means to a recycle position in response to heating signals from both said time delay circuit and said flame sensing circuit.

4. The apparatus of claim 3 wherein said responsive means establishes a lock-up condition in response to heating signals only from said time delay circuit.

5. The apparatus of claim 3 wherein said responsive means includes a latching member for holding said first and second time delay switches in a lock-up position in response to a lock-up signal.

6. In a heating control system having a fan motor for circulating air heated by a burner and an electric igniter for said burner, the combination including a thermostatic control switch,

an electrical current input circuit,

flame sensing means,

a third delay relay circuit comprising a relay heating switch and an electric igniter switch each having a normal position and an active position,

a bimetal strip,

an electrical heating element in the vicinity of said bimetal strip,

means act uable by said bimetal strip for moving said switches from their normal positions to their active positions after a predetermined time delay,

said heating switch in the normal position connecting the heating element in a first heating circuit with the thermostatic switch and said input circuit,

said ignition switch in the normal position connecting the igniter to said input circuit and in said active position connecting the fan motor to the input circuit,

relay means connected to said thermostatic switch for connecting a second heating circuit to said heating element, and

said first and second heating circuits during normal operation supplying suflicient heat to bend the bimetal for a period of time greater than said predetermined time for moving said actuable means to a recycle position.

7. The system of claim 6 further comprising means for returning said time delay switches to their normal positions for system recycling in response to spurious electrical or flame interruption signals.

8. The system of claim 6 further comprising means for locking said switches in their active positions in response to lock-up protection signals, and means for preventing system recycling in response to said lock-up signals.

References Cited UNITED STATES PATENTS 2,160,592 5/1939 King 236-11 2,375,900 5/1945 De Lancey.

JAMES W. WESTHAVER, Primary Examiner.

US. Cl. X.R. 236-11

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