US2624812A

US2624812A - Timing device

Info

Publication number: US2624812A
Application number: US262A
Authority: US
Inventors: Burton E Shaw; Giuffrida Philip
Original assignee: Comb Control Corp
Current assignee: Combustion Control Corp
Priority date: 1948-01-02
Filing date: 1948-01-02
Publication date: 1953-01-06
Anticipated expiration: 1970-01-06

Description

Jan. 6, 1953 a. E. SHAW ETAL 2,624,812

TIMING DEVICE Filed Jan. 2, 1948 3 Sheets-Sheet l I lnve nIur's BURTON E, SHAW g PHILLIP GUIFFRIDA Jan. 6, 195 3 8. E. SHAW ETAL 2,624,812

TIMING nsvxcs Filed Jan. 2, 1948 3 Sheets-Sheet 2 lnvB nInPs BURTON E. SHAW PHILLIP GUIFFRIDA Patented Jan. 6, 1,953

UNITED STATES PATENT OFFICE 2,624,812 TIMING DEVICE Burton E. Shaw, East Boxford, and Philip Giuffrida, Lawrence, Mass, assignors to Combustion Control Corporation, Cambridge, Mass, a corporation of Massachusetts ApplicationJanua-ry 2, 1948, Serial No. 262

Claims. 1

This invention relates to furnace controls and particularly to a timing or program switch suitable for controlling the starting operations of furnaces of the full-automatic, fluid fuel-burning type.

The types of fuel burners now in common use fall into three generally recognized classiflcae tions, manual, semi-automatic, and full-automatic. The manual type of burner is 'both ignited and shut down by an operator. The semi-automatic type is manually ignited, but has an electrically controlled fuel supply system which is shut down by a thermostat or similar control when sufficient heat has been produced. The full-automatic type has an electrically controlled ignition system in addition to the fuel supply system, and heating periods are initiated-and terminated by a thermostat,pressu-re switch, cr -similar control, without any-attention from an operator under normal conditions. On full-automatic burners ignition is ordinarily accomplished by passing a high-voltage spark between electrodes in the vicinity of the fuel-admitting orifice. Burners of the large capacity, industrial type may in addition, employ a pilot burner to ignite the main burner. To insure safe and proper operation, the ignition, pilot, and main burner must be put into operation in a certain sequence and at accurately timed intervals. Theoptimum delay periods between starting operations depend on the capacity and construction of the burner and the type of fuel used. For example, on a typical oil burner ignited by a gas pilot, the electric ignition, pilot valve and burner motor are energized simultaneously. After an interval, generally referred to as the fuel valve delay or ignition period, during which the pilot flame becomes established, the main fuel valve is opened. The pilot is left burningthereafter for an additional period, known as post-ignition, to insure proper ignition of the main flame. The optimum fuel valve delay period for different makes and capacities of burners may vary from'5 to v3.0 seconds. The post-ignition period-is ordinarily between 30 and 80 seconds in duration.

To insure safe operation of the pilot ignited type of burner, it is necessary to prevent opening of the main fuel valve if the pilot is not burning, and for this reason, a flame failure detection device responsive to the pilotflame should be, in

control of themain fuel valve circuit, upon termination of the fuel valve delay period. ,On an oil burner ignited onlybyspark electrodes, however, itis necessary, to hold themainfuel valve open for-a shorttlme to permit ignition. For

2 this purpose, monitoring of the flame by the fl m failure control must be delayed for a time after opening of the fuel valve. This interval is known as the priming period and runs concurrently with, but usually is shorter than, the post-ignition period.

From the foregoing discussion, it is apparent that a timing control designed for universal use in the many existing types of furnace installations must be readily adjustable to suit individual requirements. Nevertheless, to insure safe and efflcient operation, once the proper delay periods for a particular burner have been determined, the settings of the control device must be accurately maintained, regardless of line voltagefluctuations and other disturbing factor-s normally encountered.

It is accordingly the chief object of this invention to provide a timing control of thistype which is considerably more accurate and stable in its operation than controls heretofore used for the purpose. In particular, this control is designed to eliminate 'errors due to line voltage fluctuations. It is well known that large fluctuations in line voltagearecommon in industrial installations because of the-high current demands of machinery and other electrically powered industrial equipment. The performance of the warp switch type of timer, for e xample', may be unsatisfactory insome installations because thetimed periods are dependent on the heating effect of current through a resistance coil, and therefore on the line voltage. Errors may also occur in such switches due to change in characteristics of the bimetallic leaves.

Another object is to provide a control in which the delay periods may be accurately and continuously adjusted in the field by the average factory maintenance vman using only a common screw driver. This provision represents a considerable a dvance over the controls now in common use in which the durations ofthe various periods are eithe not adjustable at all, or adjustable only in one or two steps.

Other objects are to produce a control of this type which'rnaintains its accuracy indefinitely, which is small and compact, but will withstand severe usage, Which may be operated manually for observation and testing, a'nd whichis relatively cheap to manufacture and simple to install. i

The invention comprises generally a small synchronous motor which rotates a number ofcams mounted on its shaft. The cams operate spring leaves which are designed'to open and close con- 3 tacts in control circuits of the burner. Several of the cams may be shifted to provide adjustment of the delay periods, and a suitably calibrated dial is mounted on the face of the device. The cam assembly may be rotated by a hand knob. The motor and hand knob are connected to the cam assembly through one-way clutches to prevent turning of the cams in the wrong directions with possible resultant damage to the motor and cam contacts. The contacts are of high current capacity and are all readily accessible for cleaning. The switch here described is primarily designed for operation with a control circuit similar to that shown in the copend-ing application of E. Craig Thomson, Serial No. 788,836, filed November 29, 1947.

In the drawings:

Fig. 1 is a front view of the device;

Fig. 2 is a side view;

Fig; 3 is a cross-section, partly broken off, taken along lines 33 of Fig. 2; v

Fig. 4 is an exploded view of the motor shaft and cams disassembled;

Fig. 5 is a cross-section taken along lines 55 of Fig. 2;

Fig. 6 is a view similar to Fig. 1 with the dial, hand knob, rear contacts, and some of the mounting parts omitted;

Fig. 7 is a diagram of a typical electrical circuit employing the device;

Fig. 8 is a graph showing the various timed periods in relation to the position of the timer motor; and

Fig. 9 is a view, partly broken away, along lines 99 of Fig. 6.

Referring first to Figs. 1, 5, and 6, master cam I ordinarily machined or molded from an insulating plastic, is pressed or molded onto a metal bushing II which rides on shouldered shaft I2. The shaft I2 is secured by set screw I to the shaft I3 of synchronous motor I4. The master cam is hollow so as to fit over housing I6 of motor I4, for the purpose of reducing shaft overhang to a minimum. A second plastic cam I1 is molded onto bushing 22 which rides over bushing II. Cams l8, I9, and also made of insulating material, and dial 2| slide over bushing 22. Bushing II terminates in a toothed face 25 which is engaged byserrated disk 25. The disk is slotted in the center and fits over fiatted end 23 of shaft I2 where it is yieldingly held in place by coil spring 26 secured by washer 21 and cotter pins 28. The motor normally turns clockwise, as observed from the face of the dial, and drives the cam through engagement of the serrations of disk 25 with the teeth of face 2 3. If the motor should be incorrectly connected and revolve in the opposite direction disk 25 slides over face 24 and the cam assembly is disengaged from the motor. Damage to the motor and cam contacts under such a condition is thus prevented.

Bushing 22 is grooved near its outer end to receive S-shaped leaf spring 29, as shown in Fig. 6. When knob 36 is in place, set screws 3| project into groove 32 and engage the ends of spring 29. It is apparent that with this arrangement cam IT can be driven by the knob only in the clockwise direction when screws 3| engage the free ends of the spring 29. This one Way clutch arrangement protects the device against damage in case the knob is turned in the Wrong direc tion.

The motor and its associated field coil I36 and core I29 are secured to back plate I26 by screws I28. A base block I23, also screwed to plate I26 4 provides support for the contact leaf s rin 4 95, 9e, 91, a1, 9|, as, and so which are sp ced f r m each other by insulating spacers I22 and assembled onto the base block by means of screws I26 and I26. Further toward the rear, leaf springs til, 38, 39, and 36 (Figs. 2 and 3) are similarly spaced apart by insulating spacers E32 and fastirlled to has: block I23 by screws 13!. Any suita e suppor ing frame ma i plate 126 and block I23. y be used place of The synchronous motor in the example of the device here shown is so geared down that shaft I2 makes one revolution in 120 seconds, coming to rest, when the burner is in normal operation at the point where steps 36 on cam face 35 (Figs 3 and 6) has just cleared the end of leaf spring 36. this position contacts 37 and ii are open In Fig. 6, it may be seen that the end of spring leaf 88 is approaching step 86 of cam surface 93 and contacts are closed. On a few degrees turn of the motor spring leaf 68 drops oif steps 86 opening contact .5. Simultaneously spring leaf 81, which is connected to leaf 88 by insulatmg spacer 89 (Figs. 6 and 9 springs in, closing contacts 44. As the motor continues to rotate leaf 96 drops off the step 86 of cam surface 96 closing contacts 46. Simultaneously leaf 9 WhlCh s connected to leaf 96 by insulating spacer 99, spr ngs in to close contacts t2 (Fig. 6). At this point, the end of leaf 36 has started up rise 34 on cam surface 35. Contacts 6'! close next and, when the top of rise 34 is reached leaf 33 is forced back to close contacts 6|. As the end of leaf 36 moves down the other side of ri e 34 contacts 4| open again. 7 k I When step II I of cam 22 reache leaf 90, which is connected to leaf 9? tgirfifiafi mg spacer 92, contacts 65 close and contacts 44 open. The position of cam 28 with respect to cam I 0 is adjustable within the limits I2! and IE5 of slot I64 cf cam I9 in a manner and for a purpose to be described later. In the position shown in Fig. 6, the opening of contacts 44 and closing of contacts 45 occur substantially simultaneously with the closing of contacts 6i.

As seen in Fig. 2, leaf 9? rides over cams I8 l9 and 20. When step In of cam 2e reachesthe end of leaf 9?, this leaf and leaf which is connected to it through insulating spacer 98 drop infigenngt 1contacts 42.

er ur er rotation of the motor, iGI, which rides over the surface of Ca if 2123 I63 (Figs. 2 and 6) drops off step II2 of cam II, opening contacts 46. At this stage contacts and 37 are closed, and contacts ii 46 open. The motor continues to rotaze t li assembly until a revolution is completed and leaf 36 drops off step 33, opening contacts 3'1. Spring leaf 39 acts as a stop for leaf 36 and insu e a sharp break of contacts 3?. l S ig. 7 shows an example of a co 1 control system which is described ir i r n f'e t si l 1n copending application, SerialNo. 788 836 filed November 29, 1947, by E. Craig Thomson. In Fig 7 the cams are schematically indicated but con tact points corresponding to the contacts of Figs 1, 2, 3 and 6 are correspondingly numbered combustion chamber, generally indicated as I 2 has mounted therein a main burner I33 p1 0 (111011132. main flame 69 and a. pilot burner I34 producing pilot flame I0. Fuel to the main flam 1S supphed through blower 68 and fuel line I? controlled in a well-known manner by a solenoid valve 'I6. Fuel to the pilot is supplied through fuel line I3 controlled by solenoid valve 74. The

5. pilot is ignited by spark electrodes 12 which are excited by ignition transformer 15. A name fail-' ure detection device, here illustrated as responsive either to a photocell 62 or to a name electrode 1|, energizes relay 60, closing contact 63 and opening contact 64, when eitherthe pilot or the main flame is burning. On cooling, con tact first 41, then contact 49, engages contact 50 and with rising temperature, the operation is reversed. The device for initiating heating cycles is here represented as a conventional three wire thermostat 48 having

contacts

41, 49 and 56. The system also includes a power relay 65 controlling normally open contacts'and an aux iliary relay 54, controlling normally open con-- tacts 55 and 51, and normally closed contact 56. The closing of

contacts

50 and 49 establishes a circuit from secondary 5| through 50, 41, 56 to timer motor M, and. the motor starts to revolve. As previously described contact 45 o ens soon after the start of the timing cycle.- This contact is in the circuit'of the main fuel valve. Since the circuit is at this time broken at 61, the opening of 45 has no effect, but this arrangement permits location of step 86 on cam to serve the double purpose of opening contact 45 and at a later point in the

cycle closing contacts

42 and 46. Contact 44 closes at the same time that contact 45 opens. After 42 and 46 are closed contact 37 closes, shunting out 56 so as to establish a holding circuit for motor l4. Contact 4| then closes. Up to this time none of the operating circuits of the burner have-been energized and the burner has remained shut down. The delay between the starting of timer motor and the closing of contact 4| is known as the scavenging period and insures the dissipation of unburned gases in the combustion chamber before the ignition is turned on. I The closing of contact 4| initiates. the starting cycle by completing the energizing circuits of relay 54, through 58, 4|, 41-, and 56 to secondary and of relay 65, through 64, 42, 44, 58, 4|, 41, and 59 to secondary 5|. Relay 54 closes holding contact 55, which shunts contact 4| and thermostat holding contact 51, which shunts 49 to 41, so as to hold relay 54 energized until 41 separates from 56, and opens contact 55. Relay65 closes its holding contact 66 and main contact 61, which completes the circuits to the burner motor 68, pilot valve '14, and ignition transformer 15. Under normal conditions the burner motor starts to run and the pilot ignites. Soon afterward the flame failure safeguard 6|, in response to the detection of flame by electrode H, energizes relay cc closing contact 63, which shunts

contact

42 and 44. Since contact 63 is in the circuit of the main fuel valve 16, it is apparent that the pilot name must be established in order for the main fuel valve to be opened. Contact 4| opens again after a few seconds, but relays 54 and 65 are now held in through contact 55. After a certain delay, which may be varied by the-setting of cams i9 and. 26-, contact 45 closes. Under normal conditions, with contact 63 closed, the closing of contact 45 completes the circuit to main fuel valve 16. The main valve then opens and the main flame ignites shortly thereafter. Contact 44 opens simultaneously with the closing of 45. As the circuit is here shown, the energizing circuit relay 65 is then dependent on contact 63, that is, the flame failure device is in control of the system and if the flame should be extinguished, relay 60 would become deenergized opening contact 63 and causing main relay 65 to drop out and shut down the burner. On certain types or burners, for example, those consuming oil or pulverized coal, it may be desirable to allow for a certain delay known as the priming period between the opening of the main fuel valve and monitoring of the flame. In this case, a jumper is connected across

terminals

58 and 59, and contact 63 is then shunted by contact 42 for a certain period after the opening of 44. This period is adjusted by the settin of cam 20 in a manner to be described later. At the end of the priming period, contact 42 opens. Later in the cycle con tact 46 opens, shutting off the pilot and ignition. The interval between the closing of 4| and open ing of 46, is designatedthe ignition period" and varies in length according to the setting of em IT. The burner is then in normal running con= dition, with only the main flame burning. The timer motor continues to revolve until leaf 35 drops off step 33 breaking contact 31 and leaving the cam assembly in the starting position with all the timer contacts open except contacts 45, which hold in the main fuel valve circuit.

The relationship of the various periods in the starting cycle can be best understood by reference to Fig. 8. Line 13 indicates the starting position. Line 13 indicates the closing of contact 4|, which ends the scavenging period. The fuel valve delay or ignition period which begins with the closing of 4| (line 19) may vary from zero seconds (line 19) to line 82, representing in this example approximately 30 seconds. The priming period starts with the end of the fuel valve delay, somewhere between

lines

19 and 82, and may vary from zero to a line approximately 90 from the starting point, representing approximately thirty seconds. In the switch here shown by way of example, the zero priming period is achieved by omitting the juniper across

terminals

58 and 59 as previously described. The opening of contact 42, which determines the priming period may be adjusted to give between 15 and 30 seconds delay. The post ignition period starts from the end of the fuel valve delay period, between

lines

19 and 82, and may be adjusted from zero to seconds for zero fuel valve delay, and from zero to 55 seconds for the maximum fuel valve delay of 30 seconds.

The priming period setting is intended to be made by the manufacturer of the control or one especially familiar with the operation of the control system. The device is accordingly purposely designed so that removal of the dial is required.

Referring to Figs. 4 and 6, cam 20 is secured to cam l9 by screw H6 which runs through slot |09 into tapped hole E8 and cam l9 and the head of which rests in groove I68 in cam 20. If the screw is loosened, cam 20' may be rotated with respect to cam l9 within the limits of groove I08. The setting shown in Fig. 6 allows leaf 91 to drop off steps Ill and 3, which coincide opening contact 42 and thereby terminating the priming period, fifteen seconds after leaf drops off step H3 closing fuel valve contacts 45. If cam 2|! is rotated counterclockwise, step is moved so as to lag behind steps 3. Leaf 91 which extends over both cams is thus held out longer, during the revolution of the cam assembly, delayin the opening of contact 42, while leaf 96 which extends only over cam l9, continues to drop out at the same point in the cycle. The priming period, according to the arrangement here shown, may be extended up to thirty seconds.

The fuel valve delay and post ignition periods are intended to be set at the furnace installation by e, maintenance man of ordinary skill. Referring toFigs. 4 and 5, dial 2! is provided with a fuel valve scale I31, and a post ignition scale I38. A pointer I35 rides in slot I36 next to the fuel valve scale. This pointer and the dial are secured by screw I I which extends through slots I09, I04, and H9 in cams 20, I9, and 22 and hole 8I in cam I8, and engages threaded hole I20 in cam I0. The dial is fixed to cam I9 by pin II! which extends through slot I09 in cam 20 into hole I39 in the dial. When screw H0 is loosened, the dial and earns I9 and 20 may be rotated independently of cam I0 so that step I I3 may be positioned to give a delay in the doing of contacts 45 up to 30 seconds after the closing of M by rise 34 of cam face 35 engaging leaf 35. The scale I 31 iscalibrated so that the position of pointer I35 indicates the length of this delay period. Since a zero fuel valve delay is ordinarily not desirable, pointer I35 is so designed as to limit the minimum setting in slot I 36 to about seconds. For special conditions, however, the pointer may be removed, so as to extend the adjustment range to zero.

The fuel valve adjustment is made with the cam assembly in the starting position. With the dial and fuel valve pointer held in place, cam I! may be rotated by the knob 30. Cam I! controls leaf NH, and the position of step I I2 determines the delay in closing contacts 46 which shut off the ignition system of the burner. Pointer I2! is held in slot I43 by tab I49 and secured in place by screw I II which enters fiat I92 of bushing 22.

Since scale I38 moves with scale I37, the position of pointers I21, indicates the period between the closing of fuel valve contacts 45 and the opening of ignition contacts 46. Scale I38 therefore directly indicates the post ignition period. After the settings are made, screw III] is tightened so that the whole cam assembly moves together.

From the foregoing description, it will be clear that the switch herein disclosed is designed to regulate the starting operations of a furnace system with a high degree of accuracy and reliability, The timing operation is entirely independent of line voltage fluctuations and wear or fatigue of the switch parts, being dependent only on line frequency which is considerably more stable than line voltage. The effect of frequency variations is further made negligible by the gearing down of the timer motor. The construction of the cams and spring leaves insures positive contact action and permits the use of heavy duty contacts wherever desired. The range and simplicity of adjustments makes the device adaptable for use in a wide variety of burner installations.

It will be further noted that the arrangement of several of the contacts so as to operate in pairs, and the cooperating arrangement of the cam surfaces permits all the necessary timing operations to be accomplishedwith a minimum of working parts.

Since certain changes may be made in the above-described article and different embodiments of the invention could be made without departing from the scope thereof, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted asillustrative only and not in a limiting sense.

What is claimed is:

1. A program switch comprising: a synchronous motor having a drive shaft fiatted toward its outer end, a master cam secured to a bushing which is mounted on said motor shaft, said bushing terminating in a toothed face; a slotted disk mounted on the flatted part of said shaft and having a serrated edge adapted to engage said toothed face; a retaining spring for holding said disk in yielding contact with said face; a second cam secured to a second bushing which is mounted freely on said first-named bushing; a groove near, and a slot across, the end of said second bushing; an S-shaped leaf spring lying in said groove and slot; a handle having inner projections for engaging the ends of said spring to drive said second cam; a pointer fixed to said second bushing; a dial freely mounted on said second bushing and carrying a scale over which said pointer rides; a circumferentially slotted cam fixed to said dial; a slot in said dial coinciding with the slot in said last-named cam; a second pointer riding in said dial slot and a second scale on said dial cooperating with said second pointer; a screw extending through said second pointer and the slots in said dial and last-named cam into a tapped hole in said master cam for the purpose of securing all of said cams together; and a plurality of spring leaf contacts adapted to be operated by said cams.

2. A program switch according to claim 1 wherein said contacts comprise several pairs of leaf springs, the first leaf of each pair acting as a cam follower and the second leaf being substantially rigidly spaced away from the first.

3. A program switch according to claim 2 having a second circumferentially slotted cam adjustably secured to the first-named slotted cam, one of said cam followers riding only on said first-named slotted cam and another of said cam followers riding on both said slotted cams.

4. A program switch according to claim 1 having a second circumferentially slotted cam adjustably secured to the first-named slotted cam. 5.A program switch according to claim 1 wherein said master cam is recessed to receive said motor.

BURTON E. SHAW. PHILIP GIUFFRIDA.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS