US2348951A

US2348951A - Control mechanism

Info

Publication number: US2348951A
Application number: US406591A
Authority: US
Inventors: George D Bower
Original assignee: AUTOMATIC CONTROL CORP
Current assignee: AUTOMATIC CONTROL Corp
Priority date: 1941-08-13
Filing date: 1941-08-13
Publication date: 1944-05-16
Anticipated expiration: 1961-05-16

Description

' M y 16 1944. G. D. BOWER 2,348,951

CONTROL MECHANISM Filed Aug. 13, 194 1 2 Sheets-Sheet 1 EYWJQW 29M 47- rap/4W6.

Patented May 16, 1944 UNlTED STATES PATENT OFFICE 2,348,951 CONTROL MECHANISM George D. Bower, University City, Mo, asslgnor to Automatic Control Corporation, St. Louis, Mo-., a corporation of Delaware Application August 13, 1941, Serial No. 406,591

8 Claims.

The present invention relates to a control mechanism particularly adapted for use with burners. 1

The case is related to copending application, Serial No. 366,512, filed November 22, 1940 by this inventor.

The invention in most complete form includes a burner-operating or fuel supply device here represented as a burner motor, an ignition device, a control motor with suitable cam-operated switches designed to operate in desired order, a safety or stack switch, also called combustion switch, a space thermostat, and relays controlled thereby. The arrangement is such that the burner motor will be operated for a given starting period, during which ignition may take place, thereafter for a running period, if ignition has occurred and combustion continued, the running period being determined by the space thermostat, and finally a scavenging period. It also provides a lock-out if ignition does not become properly effective during the starting period.

In general, the mechanism employed to illustrate the invention of this application is the same as that shown in the copending application 366,512. However, there is added hereto in particular, a means to prevent continued operation of the burner if the control motor fails.

The major object of this invention is to provide a control having a timing mechanism giving sequential operations, and wherein, if the timing mechanism fails to provide such sequential operations, the mechanism will prevent continued operatic-11 of the fuel supply device. Particularly, the burner motor will be stopped within a safe period of time even though the control motor fail to function properly. An especial object of this invention is to cause stoppage of the fuel supply device in the event the control motor is blocked duringthe starting period.

In the operation of this-control the room thermostat eflects closure of an instituting circuit dependent upon a cool stack switch, and by means of which instituting circuit the control motor is put in operation. Thereafter, a holding circuit is established for the control motor, dependent upon a power failure relay, but designed to hold the. control motor operation for the duration of predetermined starting period. Following this, continued operation of the control for an intermediate period isdependent upon the previous establishment of combustion within the burner or furnace. If combustion has occurred and continued, the control motor will remain in operation throughout the intermediate period until a running period is established, whereupon the control motor will stop, but the burner motor Will continue dependent upon the continuation of demand by the room thermostat, the existence of combustion, and the continuation of power. When the room thermostat is satisfied, the control motor is again caused to operate for a scavengingperiod after which the control is returned to its starting position ready for recycling.

In combination with the above, the present invention provides a control for preventing continued operation of the fuel. supply device, and indeed the entire control in the preferred form, if the control motor fails during the starting period, since the burner motor may be held in circuit regardless of the condition of the room thermostat andregardless of whether combustion has actually occurred or not during closure of the holding circuit. Failure of thecontrol motor during the starting period ismore dangerous than failure during the running. period, since the combustion has occurred during the latter, so that the burner may operate on the limit," which provides a safety control. But Where combustion has not occurred, as may be during the starting period, especially in combination with a failure of ignition, the furnace could become flooded with a combustible orperhaps explosive mixture and would be in. a dangerous condition. And the present control incorporates the above feature with means to prevent continued operation of the fuel supply means upon failureof combustion during the running period, and means to prevent operation of the fuel supply means during the scavenging period.

It has been found desirable to effect this con: trol throughthe means of a timed switch associated with the igniter, this timer being independent of the control motor itself. However, this is merely one means of accomplishing the desired results.

While the invention will be described in a con: trol with a control motor and a circuit with which. it has particular value, it will be manifest that it can apply to other such circuits and other timingmeans than a control motor.

The objects of the invention are to provide the sequential control with the safety features set out hereinbefore.

In the drawings:

Fig. 1 represents a wiring diagram of a control with one type of control-motor-failure safety mechanism;

Fig. 2 is a wiring diagram of another type of such mechanism;

operations are basically the same. It will be understood, however, that the features are not limited by this illustration. For instance, reference is made to the warp switch type of control with which many of the present mechanisms, such as the safety for timing means blocking, may be used.

The several cams which will be designated herein as I0, I I, and I2, respectively, are mounted on a shaft I3 driven by the control motor CM, similar to the mechanism in application 366,512.

The cam II), which will be designated as the front cam, has a low portion I5 followed by a middle portion I6 and a high portion IT. This cam operates three switches I8, I9 and 20. It has a cam follower 2| that engages the cam edge. When the follower- 2| is on the edge I5, the switch I8 is closed and the switches I9 and are open. When the follower reaches the intermediate ed e I6, it opens the switch I8. Then when it subsequently rises to the high edge II, it closes switches I9 and 20 substantially simultaneously, as the two switches are closed to operate almost together by a spacer connector 22. When the follower reaches the end of the edge I1 and drops again to the edge I5, it will open switches 20 and I9 at one time and will at the same time reclose the switch I8.

A development of the edge shaping of this cam is shown at F at the lower part of Fig. 3.

The middle cam I I has a low edge 24, a first middle edge 25, an upper edge 26, and a second middle edge 21. This cam operates switches 29 and 3|]. As the cam' rotates counterclockwise with the follower 28 on the upper edge 26, the

switches

29 and 39 will both be closed. The spacer 3| causes the switch 29, after closure, to close the switch 30. When the follower drops to the edge 21, the switch 30 will open but the switch 29 will remain closed. Then when the follower drops to the lower edge 24, the switch 29 will open and both switches will remain open until the follower reaches the end of the low edge 24 and rises onto the middle edge which recloses the switch 29. Thereafter when the follower again rises to the high edge 26, the switch will also close. The development of the edge of cam I! is shown at M at the lower part of Fig. 3.

The rear cam I2 has a low edge followed by a middle edge 36 and that, in turn, is followed by a high edge 31. The cam has a follower 38 that operates the switches 39 and 49.

With the cam follower 38 on the low edge 35, the switch 39 will be closed and the switch 40 open. A spacer member M connects the follower with one of the switch blades on the switch 40. As the cam rotates counterclockwise, the follower will rise to the middle edge 36, which will open the switch 39 but will not close the switch 40. When the follower 38 finally reaches the high edge 31, it will close the switch 40. Then, when it falls to the low edge 35, it will open the switch 40 and simultaneously close the switch 39.

The disposition of the several switches in circuit with the various mechanisms is shown in the wiring diagram, Fig. 1. Two

power lines

50 and 5| are provided for connection to a power source. A limit switch L is put in one power line. A transformer 52 has a primary 53 and a secondary 54I. One end of the primary 53 is connected to the power line 5|. The op osite end of the primary is connected to one end of one contact of the stack safety switch, such as described in the copending application referred to, which is closed when the stack switch is cold. The other lead from this cold stack switch is connected to the one terminal of the switch 49, the other terminal of which is connected to the other power line 50.

The secondary 54I of the transformer is connected in series with a relay coil 56 and with a room thermostat 5! that closes when the temperature in the space to be controlled reaches a certain minimum value. Preferably the room thermostat has an anticipating heater 62 in series therewith, for purposes to be described. The term "room thermostat will be used in a generic sense to indicate any such space thermostat or similar control.

The relay 56 operates two

switches

58 and 59. The switch 58 releases against the terminal 60 when the relay coil is deenergized and closes with the terminal 6I when the coil is energized. The closure of the switch 58 with the contact may sometimes hereafter be designated as the switch 69, and in like manner the similar closure with the contact 9| may be designated as the switch 6 I.

The switch 58 is connected into the power line 50. The contact 6| connects with the timed switch 39 which, in turn, connects to one side of the control motor CM, the other side of which is connected with the power line 5I. Between the switch 39 and the control motor is mounted one terminal of the switch I9, the other terminal of which is connected to one side of the relay switch 59 closed when the relay is energized; and the other side of the switch 59 is connected with the primary 53 between it and the safety switch 54. This relay switch 59 may be omitted if desired. I

A shunt circuit around the switch 6| is pro vided by connecting the switch 20 into the power line 50 ahead of the switch 6| with its other terminal connected to the switch 30 and to the line from the switch BI.

The aforementioned line from the switches 29 and GI also leads into one part 55 of the stack or combustion switch which is adapted to close only when the stack switch is hot. The other side of the stack switch 55 leads to the burner motor BM itself, and also leads to the switch29, the other terminal of which is connected to the igniter device and to a timed heater 63 which is in parallel with the ignition device, when both are a connected to the power line 5I. This timed heator operates to heat and ultimately to operate the relay switch 64 in the main power line 50, as will be described. The relay 64 may be of bimetal, and is of the type known in the art requiring a manual reclosinc.

An additional line is interposed from a point between the stack switch 55 and the parallel circuits leading through the igniter to the burner motor, to a point between the switches I9 and 59. This circuit includes the switch 39.

A scavenging circuit leads from the switch to to the switch I8, the other terminal of which is connected to the circuit from the switch 39 eading toward the control motor.

In: the modification of zrwhich, as will be shown, provides constant ignition, the switch29 isshifted from the stem circuit feeding both the relay heater 63 and the igniter to the branch circuit alone'to the heater 63. While the description given herein refers to a burner-motor. it is obvious that the invention is valuable in connection with other types of full-supply device. A solenoid valve may be mentioned for illustration. As previously noted, other timing means than a control motor may be used, and thermostats of different types may be used, both as space thermostat and combustion switches. The description is merely related'to one of the most desirable examples of controls with which the present inventions may be used.

OPERATION Normal cycling At thestart, as shown in Fig. 3, the cam switches 4|], 3!] and 29 are closed. Likewise, the heat relay switch 54 is normally closed. The switch 58 is closed against the terminal 60, and the switch 59 is open because the relay 56 is not energized. The room thermostat 51 is open.

The stack switch 54 is closed because the stack switch is cold. The stack switch 55 is, for the same reason, open.

At this starting position, which is shown in Fig. 1, none of the circuits is closed save that through the primary 53, which is inefiective because the secondary 54I is not. in a closed circuit.

When the thermostat 5'|.closes, it will close the secondary circuit and energize the coil 56 which, in turn, will close the switches BI and 59 to set up the instituting circuit. The control motor will be energized from the line 5|] through the switch 64, the switch BI. the switch 30, the control motor and the line 5|.

After the lapse of about two and one-half seconds, the switches and Hi close. The closure of the switch 2|] shunts the switch BI and holds the control motor in circuit independently of the condition of the relay 56, insuring operation of thecontrol through a starting cycle even if the thermostat reopens. Closure of the switch I9 establishes an additional circuit through the primary 53, putting the primary in parallel with the control motor through the switches 20 or BI, and 30. This additional circuit to the relay is dependent upon energization of the coil '56. The primary then becomes independent of the circuit through the

switches

40 and 54.

After the lapse of five seconds, the switch 4!! opens and the switch 39 closes. Openingof the switch 40 opens the instituting circuit and leaves energization of the primary 53 under control of the switch 59 which, in turn, is dependent upon continuation of power and upon the room ther mostat. Closing'of switch 39 with the switch I9 closed establishes a circuit to the burner-motor which comes from either the switch 20 or the switch 6|, the switch 30, theswitch I9, the switch 39, the burner motor to the line 5|. The burner motor thus starts to deliver a fuel mixture to the furnace (of course the burner motor is here merely illustrative of fuel supply devices).

At this time, the switch 29 is closed. Thereupon the igniter begins to function simultaneously with the burner motor to provide ignition for the mixture delivered to the furnace. Likewise, at this time power is supplied to the heater 63 which begins to heat up and which is designed to reach a critical .heat content after the lapse of a'predetermined number of seconds.

Thestarting cycle has thus been fully established and continues to its end with no change in the cam switches. However, upon the establishment of ignition or flame, the stack switch unit is effective almost instantly, as described in the copending application, with the result that the switch 54 opens and the switch 55 closes.

Opening of the switch 54 has no effect, because the switch 40 is already open to break the instituting circuit. Closing of the switch 55, however, establishes anew circuit to the-burner motor from-a point ahead of the switch 30. through the switch 55. This new circuit is also established to the igniter and the heater 63, as is evident, and it likewise provides a circuit that may pass upwardly through the switch 39 to hold the primary 53 and for other functions as will appear. This circuit is dependent upon combustion.

After the lapse of sixty seconds, the starting phaseof the starting cycle terminates with the opening of the switch 30. Thereafter, the burner motor is dependent upon the circuit through the switch 55 which is in turn dependent upon combustion such as to maintain the switch 55 closed. Likewise, the primary 53 is dependent upon the same switch-55, because all circuits from the line 50 tothe line 5| are open except that through the switch 55. This circuit to the primary goes from the switch 55 through the switch 39' to the relay switch 59. Also with the switch I9 still closed, the control motor is held in operation from the switch 39 through the switch I9.

The foregoing circuits establish the intermediate phase during which continued operation of the mechanism is dependent upon successful combustion with consequent closure of the. safety switch 55.

After the lapse of seventy seconds, the starting cycle ends and the running cycle may be established. At this time, the switches 20, I9 and 29. open and the switch I8 closes.

Opening of the switch 20 breaks the starting cycle holding circuit shunting the switch 58. Continuation of the circuits previously established is thus again made dependent upon closure of the switch. 6| which, in turn, is dependent upon an unsatisfied and hence closed room thermostat and upon continuation of power. As is further evident, these circuits are further de-- pendent upon continuation of combustion.

Opening of the switch I9 breaks the circuit to the control motor which. therefore, stops.

Opening the switch 29 stops the igniter from operating. and also deenergizes the heater 53. This heater is designed so that it will not generate enoughheat to open the switch 64 within the lapse of time between its first being energized to the establishment of the running period. As here shown, this interval is sixty-five seconds. The heater may be designed to be effective within a minute and one-half, to employ an illustration.

The running period depends upon continued energization ofthe primary 53 for the coil 56, whichv latter requires the thermostat 51, the switches 6| and 59, the switch 55, and the switch 39 to remain closed. It will be observed that the switch 35 is held closed through the running period.

Upon satisfaction of the room thermostat, it opens nd the coil 55 is'deenergized. This forthwith opens switches 5| and 59 and closes the switch 56). Opening the switch 59 deenergizes the primary and prevents re-energizing of the primary until the instituting circuit is once again established through the

switches

40 and 54. Opening of the switch 6| likewise breaks the circuit to the burner motor and further breaks the holding circuit to the primary.

Closing of the switch 60 establishes a scavenging circuit which operates through the switch 18 to the control motor and puts the control motor directly across the line.

Thereupon the control motor again begins to operate. At this time, there is no parasitic circuit through the switch 55 should the same remain closed after the scavenging circuit is established, theswitch 35 being open.

The scavenging cycle will continue without changing the operation until the starting position is again reached. However, during this time, after the lapse of seventy-five seconds (the time of the running period being omitted), the switch 39 will open. After the lapse of two hundred twenty-five seconds, the switch 29 will reclose. After the lapse of two hundred and thirty seconds. the switch 30 willreclose. will be noted that the switch 29 is closed when the switch 30 recloses, so that if the combustion switch 55 has stuck closed, the igniter will operate as soon as the oil restarts when switch 30 recloses,- setting up a parasitic circuit through the switch 55. After the lapse of two hundred thirty five seconds, the switch 40 will reclose.

After the lapse of two hundred and forty seconds, the switch l8 reopens which breaks the circuit to the control motor and that motor stops. The mechanism is then in starting position ready to recycle.

Abnormal operations so that the cam switches do not operate in their proper sequence, the burner may continue to operate for an indefinite period. If ignition has occurred, this could cause the furnace to run on the limit switch, but if combustion has also failed, the fuel supply means would continue to discharge fuel into the furnace to produce a dangerous condition. I

The heater 63 is designed so that it will open the relay switch 64 after a given timeinterval, as heretofore described. With this added safety feature, the burner motor cannot flood the furnace under the described condition, because, after the la se of something over a minute, the heater 63 will open the entire control by opening the switch 64. When the switch 64 opens, the relay G is deenergized, the switch 59 opens and the switch 58 opens. The switch 60 will be closed, but at this time the switch i8 is open. Thus, the mechanism will stop operation entirely.

The switch 64 is one which, when it opens, cannot reclose without manual reclosing. When it is found to be open the trouble can be sought and remedied, and the switch manually reclosed. If the blocking of the control motor, occurs during the intermediate period, after the switch has opened, the stack switch 55 will open and break the circuits.

Afailure of the control motor to start at th termination of the running period will produce no dangerous effect in this control, because when the room thermostat opens the relay switch 59 opens and the relay switch Bil closes, regardless of the control motor. In this condition, the primary 53 is deenergized so that reclosing of the room thermostat cannot restart the control. The switch I8, having closed at the beginning of the running period, will have put the control motor in circuit, but the burner motor circuit is completely open. The control will then remain dormant as far as its cycle is concerned until the control motor is repaired.

If power fails during the first part of the starting cycle after the instituting circuit is open. and then power is reestablished, a circuit to the control motor will exist through the switches. 20 and 30. Likewise, a circuit to the burner motor will be established through those switches together with switches I9 and 39, and acircuit will be established to the igniter through the four main switches, plus the switch 29. If ignition occurs during this part of the starting cycle, as it normally will, the stack switch 55 will close providing a holding circuit as in the normal cycle, for both the control motor and the burner motor during the intermediate period when the switch is open. However, at the end of the intermediate cycle, and at the beginning of the normal running cycle, the switch 2! will open, which will break the aforementioned circuit through the switch 55 because of the fact that the switch 5! is open. But the switch l8 closes at the time the switch 20 opens, with the result that the scavengin period will be established for the control motor and the mechanism will be returned to starting position. If power fails during the intermediate period between sixty and seventy seconds and is then restored, if the failure has been long enough to break the flame and open the switch 55, the mechanism will lock in that position because all of the circuits from the line are open. This lock-out will occur if ignition does not exist during the intermediate period, under all circumstances. If, however, the failure is so brief that the stack switch is unaffected, the control will proceed to the end of the intermediate period and will pass into the scavenging period as before.

' If power fails during the running period, the effect is the same as if the room thermostat had opened and the control will operate through the scavenging period and return tothe starting position ready for a new cycle.

If ignition does not occur by the beginning of the intermediate period and does not exist throughout the period, the stack switch will either remain open or reopen. This isthe lOCk-s out condition because it=brings all circuits to the burner motor, the igniter, the control motor and the primary, through the switch 55 in this interval. Thiswill require manual reset of the cam switches, which are provided with the mechanism described in this applicants copending case, Serial No, 366,512, filed November 22, 1940.

If combustion fails during the running period, the switch 55 will open, andthis will have the same effect as opening of the room thermostat. The mechanism will cycle through the scavenging period and return to its starting position supplied without ignition.

wherefrom it will institute a new cycle if the .room thermostat remains closed.

If the combustion or safety switch 55 sticks in its cold position, the eifect will be the same as if ignition had not occurred and lock-out will take place upon the opening of the switch 353.

If the safety switch fails in its hot position, the mechanism will operate without change until the switch 39 recloses, because the room thermostat will in due course operate the

switches

53 and 59. As heretofore described, the igniter is in operation at this time, so .that fuel is not However, no new cycle can be instituted because the switch iii will not close to establish the instituting circuit. The mechanism, under these circumstances, will lock in its starting position.

If the relay fails in the open position shown, the mechanism cannot start because starting depends upon closing the switch If the relay fails with the switches 5i and 59 closed, at the end of a running period, for instance, the mechanism will run on the limit switch L until that switch opens. When that switch does open once, the switch 55 may open upon cooling .of the stack switch, as described in the aforementioned copending application. This will cause a lock-out because the burner motor cannot start in this position of the control to re-heat the stack switch.

If the relays fail closed and the stack switch fails closed at the same time, at the end of a running period, the mechanism will run on the limit switch. If combustion stops upon opening of the limit switch, it will be reestablished upon reclosure of the limit switch in the continuous ignition type of control of Fig. 2. If the relay fails closed and ignition fails to occur during the intermediate period, the look-out will, nevertheless, occur because after the switchiil opens the entire circuit is dependent upon a closed stack switch 55, which in turn is dependent upon combustion. If the relay fails closed and the control motor blocks during the starting period, the heater 63 will open the switch '64, requiring manual reclosure of "the latter switch. If the relay fails closed and the control motor blocks at the end of a running period, the effect will be the same as if the control motor had not blocked, because the scavenging circuit cannot be closed. The device will operate on the limit switch until that "switch opens once, whereupon the switch 55 will open and the control will lock.

If the stack switch sticks in cold position, the effect will be the same as failure of ignition so that it makes no difference if ignition fails in combination therewith or not. If, during the starting period ignition has occurred but then fails, and the stack switch fails hot, the burner motor will be held in circuit until the anticipating heater 62 opens the 'room thermostat, where the relay will be-opened. This will occur at the end of the predetermined interval for the anticipating heater, ordinarily from '7 to 15 minutes. Upon opening of the relay, the scavenging period will start, and uponits completion, the control will stop and not restart.

If the stack switch fails hot and the control motor blocks, during the starting period, the heater 63 will open the switch 64, which requires manual reset. If the stack switch fails hot after the running period, and the control motor fails to operate, the mechanism will merely look at the beginning of the scavenging period because the relay will have opened the switch 6|, cutting ofi the burner motor.

If combustion fails and the control motor blocks during the starting period, the heater '53 will operate the switch 64. as above described.

If the relay fails hot, and the stack switch fails hot after momentary ignition, during the starting period, and the control motor blocks, the switch 64 will be opened to prevent furnace from being flooded. -If the relay fails hot and the ignition fails and the control motor blocks, the stack switch 55 will be opened, andlockout will occur. The switch 64 forms a double safety here,

as upon failure of allfour during the starting period, the switch 56 will open. If ignition fails during the running period and the relay sticks in hot position, the stackswitch will, nevertheless, open and break the circuits. Hence, if the control motor blocks at the same time no dangerous condition will arise. Upon operation of the manual reset which advances the cams into the scavenging period, the scavenging operation will not occur because of the fact that the switch 60 is open and the control motor is blocked. However, the burner motor will not operate.

Upon failure of the stack switch in hot position, coupled with failure of ignition after temporary ignition during the starting period, accompanied by blocking of the control motor, the heater 63 will operate the switch 64 and open the control circuits. Upon failure of the stack switch in hot position after the running period accompanied by failure of the control motor, the control will block with the burner motor inoperative, because of the opening of the switch 6i.

Upon any of the above failures, which causes continued operation of the burner motor, if the connection is made as in Fig. 2, ignition may occur so that the mechanism will run on the limit switch, at least untilthe limit switch opens once.

Of course, if ignition fails the results will be the same as those in Fig. 1.

If the room thermostat fails in hot position, the control will run on the limit switch. Once the limit switch opens andthe stack switch cools, the relay will open and the control scavenge out to recycle. If the thermostat fails in hot position and the stack switch fails in hot position, the device will operate on the limit until the limit switch opens releasing the relay and causing the scavenging operation without subsequent re cycling. If the thermostat fails in hot position and the relay fails in hot position, the device will operate on the limit until that opens, which will stop the burner motor. This will be followed by opening of the stack switch 55. Thereupon the mechanism will lock in that position, be,cause the burner motor cannot operate "to :reclose the stack switch.

What is claimed is:

1. In a mechanism of the kind describeda fuel supply means, a timing device forcontrolling the operation of the fuel supply means, anexternal control adapted to respond to conditions influenced by the fuel supply means to initiateoperation of the timing device, said timing device :including means to maintain the fuel supply means in operation regardless of the condition of the external control, for a predetermined period of time, and means independent of the existence or lack of combustion to prevent unlimited operation of the fuel supply means upon failure of the timing device to move beyond the conditions of said predetermined period.

2. In a mechanism of the kind described, a fuel supply means, timing mechanism having means to provide a starting period for the. fuel supply means during which ignition may occur, and having means to provide a lock-out of the fuel supply means if ignition does not occur during said starting period, and means to render the fuel supply means inoperative by preventing continued operationthereof if the timing means fails in the starting period and does not reach the lock-out. v

3. In a mechanism of the kind described, a

fuel supply means,combustion-responsive means, timing mechanism having-means toprovide a starting period for the fuel supply means, and

having means dependent upon actuation of the combustion-responsive means upon existence of combustion to provide. a running period for the fuel supply means, deenergizing means operable to prevent continued operation of the. fuel supply means upon failure ofthe timing mecharunni period.

t 4, In a mechanism of the kind described, a fuel supply means, a timing mechanism having means to provide a starting period for the fuel supply means, of predetermined length during which ignition may occur, having means to provide a running period after the starting period, and having means to stop the fuel supply means if combustion does not occur during the starting period, delayed-action means having a period for operation longerthan the length of the starting period, adapted to render the fuel supply means inoperative if the timing device fails by excessive protraction of the starting period, and means to render thedelayed-action means inoperative at the end of the starting period.

5. In a control, a fuel supply means adapted to supply fuel to be ignited, a timing device including a rotating motor'and a plurality of switches sequentially closed by rotation of the motor, means to' start rotation of the motor, means in cluding one of said switches closed after start of the motor, tomaintain the motor in operation'for a predetermined amount of rotation of the motor comprising a starting period during which ignition may occur, means to maintain the fuel supply meansin operation during said starting period, said means being released by the timing motor at the end of said period, means dependent upon existence of combustion at the end of the starting period to continue operation of the fuel supply means, and means independent of the existence or lack of combustion to prevent continued operation of the fuel supply means upon blocking of the motor during the starting position. 6. In a mechanism of the kind described, a fuel supply means, a timing device for controlling the operation of the fuel supply means, an external control adapted to respond to conditions influenced by the fuel supply means to imtiate operation of the timing device, said timing device including means to maintain the fuel supply means in operation regardless of the condition of the external control, for a predetermined period of time, and means independent of the existence or lack of combustion to prevent unlimited operation of the fuel supply means upon failure of the timing devic to move beyond the conditions of said predetermined period, said last named means including a heater adapted to be energized when the means to maintain the fuel supply device in operation is actuated, and a heat-responsive switch operated by the heater and controlling the fuel supply means, said heater being of insufiicient capacity to operate said switch within the normal limit of said predetermined period.

'7. In a mechanism of the kind described, a fuel supply means, a timing device for controlling the operation of the fuel supply means, an external control adapted to respond to conditions influenced by the fuel supply means to initiate operation of the timing device, said timing device including means to maintain the fuel supply means in operation regardless of the condition of the external control, for a predetermined period of time, and means independent of the existence or lack of combustion to prevent unlimited operation of the fuel supply means upon failure of the timing device to move beyond the conditions of said predetermined period, said last named means including a heater adapted to be energized when the means to maintain the fuel supply device in operation is actuated, and a heat-responsive switch operated by the heater and controlling the fuel supply means, said heater being of insuflicient capacity to operate said switch within the normal limit of said predetermined period, said switch likewise being disposed to control the timing device, to effect deenergization thereof upon operation of the switch by the heater.

8. In a mechanism of the kind described, a fuel supply means, a timing device for controlling the operation of the fuel supply means, an external control adapted to respond to conditions influenced by the fuel supply means to initiate operation of the timing device, said timing device including means to maintain the fuel supply means in operation regardless of the condition of the external control, for a predetermined period of time, and means independent of the existence or lack of combustion to prevent unlimited operation of the fuel'supply means upon failure of the timing device to move beyond the conditions of said predetermined period, said last named means including a heater, a switch operated by the timing means during the predetermined time to energize the heater, said timing means opening said switch at the end of said time, and a heat-responsive switch operated by the heater and controlling, the fuel supply means, said heater being of insufiicient capacity to operate said switch within the normal limit of said predetermined period.

GEORGE D. BOWER.