US2287784A - Control device - Google Patents

Description

June BGS 1942@ L. L.. CUNNINGHAM 2,287,784

CONTROL DEVICE Filed Feb. 2o, 1959 INVENTOR .Eems Ll-unningham 2% AZTORNEY.

Patented June 30, 1942 maar.

UNITED STATES PATENT OFFICE CONTROL DEVICE Application February 20, 1939, Serial No. 257,485

(Cl. G- 81) 23 Claims.

Thi's invention relates in general to control Qdevmes and more particularly to automatic control devices for use ,in air conditioning systems.

In air conditioning systems it is customary to provide some form of heating plant and some form of cooling plant to temper and condition the air being treated by the system. This invention relates to an improved automatic control device which will respond to the various physical conditions encountered in an air conditioning system such as pressure, vacuum, temperature, etc., for the purpose of automatically controlling the action of the heating plant, the cooling plant, or other associated devices.

It is an object of the invention to provide an improved control device for air conditioning systems which will function to regulate the system in a more reliable and satisfactory manner.

A further object is to produ-ce an improved control device which will perform accurately with adequate sensitivity and which may be economically built.

In control devices of the above character it is customary that the control point or value at which the device opens its control elements differs from the value at which the device closes the control elements. This is known as the oper- S ating differential and it is a primary object of this invention to provide an improved structure whereby this operating differential may be readily varied.

A further object is the provision of an improved adjustable lost motion connection between the operating mechanism and the control elements to provide an operating differential for the control device.

An additional object is to provide improved snap acting means for the control elements which maintains the elements in their open or closed position while the operating differential is being traversed by the lost motion connection.

Under certain conditions control devices of the above character are arranged to respond to pressure conditions produced by varying temperature changes, and it is customary to provide a sealed tube or bulb connected to the control device which contains a volatile uid responsive to temperature changes for actuating the control elements. It is accordingly a further obje-ct of this invention to provide an improved tube or bulb arrangement in which positive reliable operation of the control elements is assured at all times.

In accordance with the foregoing, it is also a further object to provide an improved bulb or tube containing a temperature responsive volatile fluid in which the vapor portion of the uid is trapped within the bulb and prevented from passing into the control operating mechanism.

An additional object is to provide simple and reliable means for Calibrating and adjusting the device. j

Other objects and advantages reside in certain novel features of construction, arrangement and combination of the parts which will be hereinafter more fully described and particularly pointed out in the appended claims.

Referring now particularly to the accompanying drawing which shows a preferred form of the invention:

Fig.`l shows a front elevation of the control device.

Fig. 2 is a side cross sectional View taken along the line 2 2 of Fig. 1 showing a vertical thermal element connected to the device.

Fig. 3 is a cross sectional view taken along the 4 line 3--3 of Fig. 1 showing the main adjusting means for the device.

Fig. 4 shows a fragmentary portion of the switching and adjusting mechanism.

Fig. 5 is a partial cross section of a horizontal thermal elementand associated well for the device.

Fig. 6 is a partial cross section of a remote bulb thermal element for the device.

Referring now particularly to Fig. 1, the control device shown comprises essentially a base member or casing 4 having a turned up ange around its edges and a threaded bushing 5 on the rear side for connecting an electrical conduit thereto. A pivot pin 6 is driven into and rigidly supported by a boss l formed on the base (See Fig. 3.) A freely movable operating arm or lever 8 is pivotally supported by a pair of formed ears 9 to the pivot pin 6. The freely movable level 8 has a projecting tail lil formed at one of its ends. The other of its ends is flared and fastened to one end of an insulating member Il by rivets I2. To the other end of the insulating member Il there is fastened a magnetic member I3 having an armature portion iii and a pair of ears i5. A pin i6 passes through the ears i5 and serves to pivotally support a rigid movable contact carrier Il. A flexible contact blade l is fastened at one of its ends to one end of the rigid contact carrier il by means of a movable contact i9 and a second movable contact 2l is secured to the free end of the iiexibie blade i8. The lever 8 and the insulating member il together With the magnetic member i3 comprise a freely movable arm for operating the switching mehcanlsm.

The stationary portion of the switching mechanism is supported on an insulating block 22 suitably fastened to the base 4 by means of a screw 23. A pair of terminal brackets 24 are secured to the insulating block 22 by screws 26 extending from the rear of the block. A pair of adjustable contact screws 28v are threaded into suitable bent ears formed from the terminal brackets`24, and are arranged in a position so as to engage the movable contacts 2l and I9 respectively. Terminal screws 33 for the attachment of connecting wires are threaded into the terminal brackets 24. Magnetic biasing means such as a magnet 35 is secured to the insulating block 22 by the screw 36 in a position to cooperate with the magnetic armature I4.

A biasing means such as a biasing coil spring 31 has one of its ends fastened to thevlever element t. IThe other of its ends is secured to a spring bracket 38 which in turn is fastened to the base li by rivets 39.

An actuating means such as as Bourdon tube assembly is provided for actuating the switching mechanism. This includes a supporting bracket 4i securely fastened to the base 4 by screws 42. An actuator or Bourdon tube 43 is fastened at one end to the supporting bracket 4I by any suitable means such as soldering. The other end of the tube 43 is closed with a plug 43a and suitably sealed. A thermal element for actuating the Bourdon tube 43 is provided such as that shown in Fig. 2. This consists of a thin walled L- shapecl tube 44, one end of which is fastened in a suitable manner to the supporting bracket 4l. The tube 44 is counter bored at its lower end to receive a sealing plug 45. The extending ends of the tube 44 are rolled over after the insertion of the plug 45 to securely hold it in place. The end is then tightly sealed by any suitable material such as solder. Before the thin walled tube 44 is closed, however, a pair of tubes are inserted in its interior for reasons which will be pointed out hereinafter. These tubes comprise a tubular member 46 concentric with and tting tightly into the interior of the thin Walled tube 44 and extending for a portion of the length oi the upper end of the tube, together with a smaller second tubular member 41 concentric with the first tube 46 and partially extending into it at the lower end with a tight t. This arrangement iorms a temperature sensitive bulb at the lower portion of the thermal element which is most remote from the supporting bracket 4i.

A volatile fluid fill suitable for the desired temdit) perature range of the instrument is provided for f the Bourdon tube and thermal element assembly. Normally'the fluid exists in a vapor state in a small portion of the cavity of the thermal element as shown at 48 and in a liquid state in the remaining free space in the thermal element and Bourdon tube assembly as shown at 48a. Since -the liquid vapor `line of the uid fill is normally situated somewhere in the bulb portion of the thermal element, this portion is the sensitive portion. The liquid portion of the uid fill passes from the thermal element to the Bourdon tube 43 proper and vice versa through a passage in the Bourdon tube supporting bracket 4i such as the opening 49 shown in Fig. 5. The pair of tubes 46--41 trap the vapor portion 48 of the fluid fill in the bulb portion of the thermal element to prevent the passage ofthe vapor from the sensitive poion of the thermal element to the Bouramarsi don tube proper. If the vapor were not trapped erratic operation of the Bourdon tube known as gulping would result.

The Bourdon tube is adjustably loaded in the following manner. Ari irregular shaped bell crank 50 is arranged to pivot about the pivot pin 6. The pivot pin 6 passes through a pair of elongated bearing openings 5I in each side of the bell crank 5U. A small ball bearing 52 is placed in each of the elongated openings 5I and serves to carry the applied bearing load of the bell crank 50 on the pivot pin 6. These balls 52 are restrained from transverse motion by a locking collar 53 on the pivot pin 6, the ears 9 on the lever arm 8 and the boss 1 on the base 4. A projecting portion 54 of the lbell crank 50 is arranged to receive one end of a biasing or loading spring 55 which passes through an opening therein. The other end of the spring 55 is threaded onto the external surface of a stud or collar 56 into which an adjusting screw 51 is threaded. The screw 51 passes through a collar 51a and an opening 58 in the base flange 4. The tension of the spring 55 maintains the head of the screw 51 against the collar 51a which engages the base flange 4.

The Bourdon tube 43 is operatively connected to the bell crank 56 by means of an adjustable link arrangement. A first member 59 of the link is pivotally connected at one end to the plug 43a of the Bourdon tube 43 by a screw 6I. A second member 62 of the link is pivotally connected at one end to a projection 63 on the bell crank 50 by a screw 64. The free ends of the first and second members 59 and 62 are arranged so as to be adjacent to and overlap one another. Two screws 65 passing through a two hole washer 66 and a slot 61 in the iirst member 59 and threaded into the second member 62 serve to adjustably hold the two members 59 and 62 in any adjusted position.

A lost motion connector is associated with the operating mechanism for imparting motion of the actuating member 43 to the freely movable lever arm 8 to initiate movement of the same. This includes connector bracket 68 which is se cured to the bell crank 56 by means of screws 69. A differential calibrating screw 1|, which may be considered a fixed element after calibration, is

threaded through the base of the connector. bracket 58 in a position to engage the lever arm 8 under certain conditions as will be more fully explained hereinafter. A cam shaft 12 is supported on either endby integral bearing projeotions 13 and 14 rotatably positioned in apertures in the bell crank 56 and the connector bracket 68, respectively.

The projection 13 is provided with a groove into which the forked end of a leaf spring 16 is fitted in order to retain the cam shaft 12 in its proper place and to frictionally restrain the free rotary movement of the same. The leaf spring 'i6 'is fastened to the bell crank by the screw 69. A differential adjusting means is provided for the lost motion connector and comprises a cam l? having a continuously variable radius of curvature provided with an integral manualadjusting projection 18. The cam 11 is suitably fastened to the cam shaft 12 as by staking .and is so arranged that when the cam projection 18 is manually rotated between a pair of stops 19 and Si the distance between the end of the calibrating screw 1| and the lower surface of the cam 11 is changed. A stop member 82 fastened to the base 4 by rivets 83 is provided with a forked end to limit the amount of movement of the lever 4arm 8 and therefore its associated mechanism.

An indicator bracket 84 is secured to the stud or collar-58 and is provided with a pointer 85 at its end which passes through an elongated slot in a scale plate 86 and serves to indicate the adjustment of the loading spring 55. Screws 81 passing through elongated slots in the scale plate 86 thread into a scale plate bracket 88 which in turn is fastened to the base flange by rivets 89, (see Fig. 2) so that the scale plate may be adjustably positioned.

Fig. 5 illustrates a modification of a form of thermal element that may be used with the device. As shown the thin walled tube 44 projects horizontally from the support bracket 4I.

elongated rod 9i having a narrow slot 92 extending from' one of its ends to the other is inserted into the thin walled tube 44 in such a position that the slot 92 will be at the bottom of the tube when the thermal element is mounted in its normal horizontal position. This rod 9i serves the same purpose in the horizontal element as the tubes 46-41 served in the vertical element (Fig. 2). The vapor portion 48 of the liquid iill is trapped along the top of the tube 44.

A well is provided for supporting any of the thermal elements shown in position in a boiler or hot Water tank for example. It comprises a thin walled member such as an extruded tube 93 which snugly engages the thin walled tube 44 and is securely fastened as by soldering to a threaded well plug 94 as shown. The well plug 94 is counterbored at one end to receive packing material 95 which is securely held in the place provided by a packing nut 96. The rod 9i (Fig. 5) and tube 46 (Fig. 2) serve to prevent the collapse of the thin walled tube 44-under the crushing action of the packing 95 and the packing nut 96 as well as trap the vapor in the bulb portion of the thermal element as explained.

Fig. 6 illustrates another modication of the vthermal element in the form of a remote bulb type. In this case a tubular sleeve 91 is pressed over a capillary tube 98 substantially as shown and the resulting assembly is pressed and sealed into the thin walled tube 44 as shown. The capillary tube 98 extends approximately one half way into the cavity or bulb at one end of the tube 44 and the proportions are so arranged that the vapor portion 48 of the liquid llla is above the entrance to the capillary tube 98 regardless of the position of the thermal element in order to prevent the passage of vapor from the thermal element into the Bourdon tube 43. The free end of the capillary tube 98 is sealed to the support bracket 4I. Any practical length of capillary tube 98 may be used. The tube 9i also serves to prevent collapse of the tube 44.

A cover 99 for the control device is illustrated in Fig. 2. A window IUI of suitable transparent material is provided for the scale plate 86. The window lili is secured to the cover 99 by rivets l02. Wing screws |83 passing through the cover 99 and threading into the base iiange i serve to hold the cover in its correct position.

The thermal element may be dispensed with ii' it is desired to operate the device directly by pressure. `In this case the support bracket 4I would be provided with a threaded nipple in order that it might be threaded directly into the pressure source.

Operation- Assume that the device is in control of a heating plant such as a hot water boiler and is set to control at a temperature or 160 F.

asmdicated by the pointer ss (rig. 1). Kiss that the differential cam 11 is set at A for minimum differential as shown in Fig. l oi the drawing so as to Just come into contact with the top side of the lever arm 8 when the differential Calibrating screw 'Il is just in contact with bottom side of the lever arm 8, and that the temperature of the boiler water is increasing from a. temperature of 140 F. The temperature of the bulb portion of the thermal element will be at 140 F. and the vapor pressure of the I'ill will have a certain definite value to which all por- .tions of the Bourdon tube assembly will be equally subjected. This pressure will stress the Bourdon tube and will tend to cause the sealed end 43a to deflect in an upward direction to cause the clockwise rotation of the bell crank 56 about its pivot pin 6.

However, the loading spring 55 exerts an opposing eifort on the bell crank and tends to cause counterclockwise rotation of the same. Since the temperature of the thermal element is below the control point. the effort exerted by the Bourdon tube 43 on the bell crank 50 will be less than the opposing effort exerted by the loading spring and the difference between these efforts or the unbalance force, will he taken up by the diierential cam 'i1 bearing on the lever arm 8. This unbalance force is transmitted along the lever arm 8 and ultimately appears at the contacts 28-29 or partially there and partially at the lever stop 82 depending upon whether or not the magnitude of the force is suiiicient to cause excessive deflection of the lever arm 8. The stop member t2 is provided to prevent deflection of the lever arm beyond its elastic limit.

Assume now that the temperature ofI the boiler water rises.' .As it does the temperature of the sensitive portion of the ll increases causing a corresponding increase in its vapor pressure. As a result the Bourdon tube exerts a greater ef fort in an upward direction. As this action proceeds a point is reached .when the effort ex'- erted on the bell crank 50 by the Bourdon tube 43 equals the opposing eiiort of the loading spring 55. At this point there is no longer any effort exerted on the lever arm 8 bythe diierential cam lll and the contact eiort is that due solely to the magnetic attraction of the magnetic armature i4 to the magnet 95. As the temperature rises still higher the eifort of the Bourdon tube 43 exerted on the bell crank 50exceeds the opposing effort of 'the loading spring 55. New the unbalance force between the two eiorts appears at the differential adjusting screw l i. This force in combination with the biasing spring 2l tends to rotate the lever element 9 in a clockwise direction in opposition to the eiort of the magnety 35. Finally a point is reached where the combined efforts or the Bourdon tube 43 and the biasing spring 3l! exceed the combined opposing efforts of the loading spring 55 .and the magnet 35 and movement of the freely movable lever arm is initiated. The lever arm then snaps in a 'clockwise direction under the effort or the biasing spring 3l? and the resultant effort ci the Bourdon tube 43 and the loading spring 55, opening the contacts i8 and i9 and interrupting theelectrical circuit passing therethrough. Motion of the Jfreely movable arm i3 in the clockwise direction is limited by the stop 82% with which the tail i8 engages.

The movable contacts iuti engage and engage with the pair of fixed contacts 2t with a positive snap action in each direction of movement. In the contact opening movement the lever arm 8 is actuated as has been pointed out and gradually moves the armature I4 in opposi tion to the force of the magnet 35 until a balance of force is reached between them. Shortly after the balance is reached the armature is moved rapidly away by the lever arm because the force of the arm together with its somewhat resilient tension is now stronger than the pull of the magnet, and the contacts are opened with snap action. However, due to the flexibility of the blade I8, the movable contacts I9-2I remain in engagement with the xed contacts for a short interval after the aforesaid balance of force has been passed.

In the closing movement of the contacts the lever arm 8 is actuated and gradually moves the armature I4 closer into the magnetic influence of the magnet 35. As the magnetic attraction becomes greater a position of the lever arm is finally reached where the magnet takes full control and snaps the armature toward it. The contacts close with snap action shortly before the armature completes its full travel because the flexible blade I8 carries the contacts I9-2I slightly ahead of the armature. With the contacts engaged the flexible blade I8 is slightly exed from its parallel position with the rigid contact arm I1 because the rear side of contact I8 is now engaged by the arm I1 and is tightly held thereto by the force of the magnet. The engagement of the contacts prevents the armature from actually engaging the magnet while the constant pull exerted by the magnet prevents the contacts from opening should the control be subjected to shocks or vibrations.

Assume now that interruption of the electrical circuit causes a change in conditions and the boiler temperature begins to drop. Correspondingly, the vapor pressure of the fill will decrease and the sealed end of Bourdon tube 43a will tend to deflect downward under the action of the loading spring 55. As this action progresses, the tail l of the freely movable arm 3 will move away from the top stop 82 by the cam 11 engaging the lever arm 8 and the armature lil will approach closer to the magnet 35. As the gap between the armature I4 and the magnet 35 decreases, the magnetic effort of the magnet increases. Finally, when the sensitive portion of the fill reaches a temperature of 160 F. minus the minimum temperature differential of the control, the magnetic effort exerted on the movable arm 8 will exceed the opposing resultant force of all other forces acting on the movable arm and it will snap in a counterclockwise direction to the contact closed position reestablishing the electrical circuit previously interrupted.

The above description concerns the operation of the device when the differential cam 11 is set for minimum differential. By rotating the cam 11 in a clockwise direction to another setting, (see Fig. 4) the operating differential 'of the device may be increased. Rotating the differential cam 11 to any of the positions B or C indicated on the bracket 88, increases the distance between the top of the Calibrating adjusting screw 1I and the bottom surface of the differential cam 11 so that the lever arm 8 is no longer restrained by the clamping action of the adjusting screw 1| and the cam 11, as in Fig. l, but is free to move a certain distance within the gap formed between the cam and adjusting screw without engaging either. Under these conditions a certain amount of lost motion is introduced between the actuating means and the actuated means, that is, between the bell crank assembly and the freely movable contact arm assembly. The amount of this lost motion determines the amount of operatin'g dierential above the minimum.

Assume again that the controlv is set at a temperature of 160 F. and that the temperature of the boiler water is increasing from F. Under these conditions the Bourdon tube 43, because of the increasing temperature of the thermal element, causes the bell crank 50 to tend to rotate in a clockwise direction. The adjusting screw 1I does not immediately engage the under side of the lever arm 8. rlhe freely movable arm 8 remains in contact closed position under the force of the magnet 35 against the biasing spring 31. The bell crank 50 continues to rotate until the lost motion gap is absorbed and screw 1I engages the lower surface of the lever arm 8. Ultimately when the temperature of the thermal element reaches F. suiiicient force will be applied to the lever arm 8 to initiate movement of the arm and open the Switch. The tail piece I0 engages` the top stop 82 leaving a gap between the lever arm 8 and the cam 11.

Under decreasing temperature conditions. a similar action ensues. The bell crank 50 rotates counterclockwise under the resultant effort of the Bourdon tube 43 and that of the loading spring 55 while the freely movable arm 8 remains in its open contact position under the force of the spring 31 against the magnet 35. The bell crank 50 continues to rotate until the lost motion gap between the upper surface of the lever arm 8 and the lower surface of the cam 11 is taken up and the cam 11 engages the lever arm 8. Force is then applied to the lever arm through the cam 11 which moves the arm toward the magnet. Ultimately, when the temperature of the thermal element reaches 160 F., minus the minimum differential, minus the differential due to the gap or lost motion, the contacts snap closed.

The force of the spring 31 serves in the ca pacity of insuring that the switch arm will remain stable in Contact opened position after being actuated to that position by the Bourdon tube operation and after the lost motion gap is taken up. The pull of the magnet 35 holds the switch arm in the opposite or contact closed position after being actuated thereto, through the lost motion gap.

It is to be understood that the differential of the device may be altered from the minimum to the maximum (A to C), by introducing increasingly larger amounts of gap between the cam 11 and the adjusting screw 1I. This adjustment amounts to introducing increasingly larger amounts of lost motion between the Bourdon tube 43 and its associated parts, which make up the actuating means, and the lever arm 8 which l make up the actuated means.

By turning the adjusting screw 51, the amount of loading or opposing force exerted by the loading sp' ng 55 on the Bourdon tube may be varied. onsequently the vapor pressure of the ll necessary to neutralize this opposing force at the control point is varied as well as is the temperature corresponding to the vapor pressure.

Several elements of the device are made adjustable in order to take care of normal manufacturing variation and to accurately calibrate the device. The contact screws 28 and 29 serve to adjust the maximum magnetic effort and the minimum operating differential as well as serve as contacts. The differential adjusting screw 1l serves to establish the desired relation of itself to the differential cam 11, and to the lever arm 8 as explained. The adjustable link 59-62-66 connecting the Bourdon tube 43 with the bell crank 58 serves as a means for correctly establishing the proper relation between the Bourdon tube 43 and the loading spring 55 in order that the indicator 85 fastened to one end of the loading spring 55 will indicate the approximate control point of the device on the indicator scale plate 86. The slots and screws 81 in the indicator scale plate 86 allow a small amount of motion of the plate relative to the indicator 85 and serve as a means for accurately cal-ibrating the scale plate 86 with the indicator so that it will indicate the exact control point. By screwing the stud 5B more or less into the spring 55 the active portion of this spring may be reduced or increased. This varies the distance that the spring will deflect for a given change in load thereon, or in other words varies the spring rate of the spring. This provision for factory adjustment of the spring rate permits the instrument to be calibrated at the factory so as to make the pointer 85 correctly indicate the control point of the instrument over the entire scale range after the scale plate 86 is correctly calibrated for one point.

As is well understood the switch arm 8 may be arranged so that it operates reversely from that described so as to close the contact when the Bourdon tube is actuated.

While a specific embodiment of the invention has been disclosed and described, it will be ap parent that many changes or modifications in the specic details of the elements can be made without departing from the spirit of the invention, and it is therefore desired that the invention be limited only by the scope of the appended claims.

What is claimed is:

l. In a control device, a base, a Bourdon tube mounted on said base, a freely movable switch operating arm having two positions, magnetic biasing means for holding said arm in one position, spring biasing means for holding said arm in its other position, a pivot pin for supporting said arm on said base, a lost motion member pivoted on said pin, a calibrating screw on said lost motion member arranged to engage one end of the arm, an adjustable cam also arranged to engage said arm, a second pivot pin for supporting said adjustable cam on said lost motion member, an adjustable connector between said Bourdon tube and said lost kmotion member whereby motion of said Bourdon tube in one direction will cause said Calibrating screw to engage one side of the arm and initiate movement of the arm to one of its positions and motion of said Bourdon tube in the other direction will cause said adjusting cam to engage the other side of the arm and initiate movement of the arm to the other of its positions, and an adjustable loading spring fastened to the lost motion member for loading the Bourdon tube a variable amount whereby the operating point of the Bourdon tube is changed.

2. In a control device, a supporting base, a switch arm pivoted between its ends to the base, switching means carried on one end of the switch arm, a bell crank pivoted to the base and having two extending arms, physical condition respon-E sive means connected to one of. the bell crank arms for rotating the bell crank in one direction,

a loading spring connected to the other of the bell crank arms for rotating the bell crank in the opposite direction, an adjustable cam pivoted to the bell crank, a Calibrating screw supported on the bell crank and arranged opposite the adjustable cam and providing a lost motion space be tween it and the cam, the other end of said switch arm extending into the lost motion space between the adjustable cam and the Calibrating screw, the adjustment of the cam varying the lost motion space between it and the calibrating screw in order to provide a variable amount of lost motion to the operation of the switch arm, the rotation of the bell crank by the physical condition responsive means being effective to engage the Calibrating screw with the switch arm to actuate the same after the lost motion has been taken up, and the rotation of the bell crank in the opposite direction by the loading spring being effective to engage the adjustable cam with. the switch arm to restore it after the lost motion has been taken up, and means for imparting snap action to the operation of? the switch arm.

3. In a control device, a base, a switch arm pivoted to the base, a lever also pivoted to the base, physical condition responsive means connected to the lever and adapted to rotate it in one direction, resilient means also connected to the lever and adapted to rotate it in another direction, an adjustable cam pivoted to the lever and arranged on one side of the switch arm, a Calibrating screw carried on the lever and ar ranged on the other side of the switch arm with a differential gap therebetween7 said adjustable cam adapted to vary the differential gap between it and the Calibrating screw, said physical condi tion responsive means eilective to rotate the lever and gradually close the differential gap until the Calibrating screw engages the switch arm and actuates the same, said resilient means effective to rotate the lever in opposition to the physical condition responsive means to gradually widen the differential gap until the adjusting cam en:x gages the switch arm and actuates the same, and means for controlling the movement of the switch arm with snap action, said last means holding said switch arm in the position in which it was last moved,

4. In a control device of the character de= scribed, a base, a movable switch arm pivoted to the base, switch means actuated by the moven ment of the switch arm, a bell crank lever piv oted to the base, a Bourdon tube mounted on the base, an adjustable link connecting the Bourdon tube with the bell crank whereby the operation of the Bourdon tube rotatesthe bell crank, a loading spring having one end adjustably secured to the base and the other-end connected to the bell crank for rotating the same back to normal position when the Bourdon tube is restored, an adjustable means on thefbell crank arranged on one side of the switch, arm, a second adjustable means arranged on the bell crank on the other side of the switch arm, the distance between both of said adjustable means constituting a lost mo tion gap between which the switch arm extends and is actuated, said adjustable means actuated by movement of the bell crank to operate the switch arm after traversing the lost motion gap, means for imparting snap action to the move@ ment of the switch arm, said snap action means holding said switch arm in the last position which it was actuated, and stop means entice base for limiting the operating movement ci' the switch arm.

5. In a control device, a freely movable switch arm arranged to be actuated to one of two positions, a resilient actuator for imparting force to said switch arm in one direction, a loading spring for imparting force to the switch arm in the other direction, a pair of movable contacts, means for pivotally supporting the movable contacts on the switch arm, an armature supported on the switch arm between the movable contacts, a. pair of fixed contacts arranged n cooperable relation with the movable contacts, a permanent magnet supported between the fixed contacts in a position to influence the armature when the switch arm is actuated whereby the movable contacts are actuated with snap action, said magnet serving as a biasing means to hold the switch arm in contact closed position, a tension spring for biasing the switch arm in contact opened position, both of said biasing means cooperating jointly with the actuator and loading spring to operate the switch arm at a minimum operating differential and an adjustable lost motion means arranged between the actuator, the loading spring and the switch arm for increasing the operating differential. Y

6. In a control device, a freely movable switch arm, actuating means for moving the switch arm in either of two directions, a pair of movable contacts and a pair of fixed contacts, means for pivotally supporting the movable contacts from the end of the switch arm in cooperable relation to the fixed contacts, an armature supported on the switch arm between the movable contacts, a permanent magnet supported between the fixed contacts in a position to influence the armature when the switch arm is actuated whereby the contacts are actuated with snap action, a lost motion connecting means arranged between the actuating means 'and the switch arm and adapted to engage the switch arm after traversing a lost motion gap, said lost motion means providing an operating differential for the control device, means for adjusting the extent of the lost motion gap to vary the operating differential, said magnet serving to hold the switch arm bi ased in contact closed position during the interval that the lost motion connecting means is traversing the lost motion gap in one direction of movement of the actuating means, and a ten(- sion spring for holding the switch arm biased in contact opened position during the movement of the actuating means in the opposite direction.

7. In a control device, a base, a bell crank pivoted to the base and having two lever arms, a temperature responsive means connected to one arm for actuating the bell crank in one direction, a loading spring having one end connected to the other arm for actuating the bell crank in the opposite direction, a switch arm pvoted on the base, adjustable means spaced apart on the bell crank and movable therewith to operate the switch arm, the gap between said adjustable means comprising a lost motionspace between which said switch arm extends and is operated, means on the base for holding the switch arm I biased in its operated position after the temperature responsive means or the loading spring has operated it thereto, an adjustable screw bearing on the base and threadedly engaging one end of the loading spring to vary the tension thereof whereby the temperature point at which the temperature responsive means actuates the switch arm is predetermined, an indicator carried by the adjustable end of the loading spring, an indicating plate on the base cooperating with the indicator, and means for Calibrating the position of theindicating plate on the base.

8. In a control device, a base, pressure responsive means on the base, switching mechanism acuated thereby, a temperature responsive fluid for actuating said pressure responsive means, supporting means for the uid comprising a thin vertically disposed tube secured at one end to the base and sealed at the other end, a second tube arranged tightly inside of the rst tube at the upper portion of the first tube, a third tube arranged to extend within the second tube for only a portion of the length of the second tube and disposed at the lower portion of the first tube and having a smaller diameter than the first tube to provide a space therebetween, said third tube being supported at its upper end from the lower end of the second tube and having its lower end spaced from the sealed end of the rst tube, said fluid lling the inside of all of said tubes except for a portion extending from the lower end of the second tube around the outside of the third tube and the inside of the first tube, said portion providing a vapor bulb space whereby pressure of the fluid is exerted through said tubes for actuating the pressure responsive means when the fluid vaporizes in the bulb space in response to temperature change, said tubes arranged to trap the vapor in the vapor bulb space.

9. In a control device, a base, pressure responsive means on the base, switching mechanism actuated thereby, a temperature responsive fluid for actuating the pressure responsive means, supporting means for the fluid comprising a thin horizontally disposed tube sealed at one end and secured at the other end to the base, a rod fltting tightly inside of and extending from the secured end of the tube for a distance toward the sealed end, said rod having a longitudinal slot formed throughout its length and extending along the bottom side thereof, said fluid filling the slot in the rod and the inside of the tube except for a portion below the top longitudinal surface of the tube between the sealed end of the tube and the end of the rod to provide a vapor bulb space whereby pressure of the fluid is exerted through the tube and slot to actuate the pressure responsive means when the fluid vaporizes in the bulb space in response to temperature changes, said tube and slot arranged to trap the vapor in the vapor bulb space.

l0. In a control device, a base, pressure responsive means, switching mechanism actuated thereby, a temperature responsive fluid for actuating the pressure responsive means, means for supporting the fluid comprising a horizontally disposed tube sealed at one end and having a flexible connection at the other end extending to the base, a second tube tightly fitting inside the first tube for a distance toward the sealed end, a third tube comprising an extension of said flexible connection tightly tting inside said second tube and extending from the connected end of the first-tube for a distance beyond the end of the second tubev but spaced from the sealed end of the first tube, said fluid filling said rst tube and the portion of the third tube projecting beyond the end of the second tube exceptv said tubes arranged to trap the fluid vapor in the vapor bulb space.

11. A control device of the class described, comprising a base, pressure responsive means mounted on the base, switching mechanism operated thereby, an elongated bulb associated with the pressure responsive means, means for mounting the bulb, said mounting means exerting a crushing force upon the bulb, a temperature responsive liquid in the pressure responsive means and bulb, said bulb having a'vapor space above the liquid level in the bulb, and restriction means within the bulb having an opening below the liquid level in the bulb whereby the vapor generated in the bulb is trapped in the bulb, and whereby the mounting means is prevented from crushing the bulb.

12. A control of the class described, comprising an actuating means, a switching means, a lost motion means for increasing the diierential of the switching means connecting said actuating means and said switching means together, said actuating means including a bell crank, a physical condition responsive means secured to one arm of the bell crank and a tension spring opposing the physical condition responsive means secured to the other arm of the bell crank, calibrating means for adjusting the spring rate of the tension spring, and adjusting means for adjusting the force of the tension spring.

13. A control device of the class described, comprising a switching means, an actuating means for operating the switching means, a lost motion means connecting said actuating means and said switching means together for varying the differential at which the switching means operates, said lost motion means including a cam member having a continuously variable radius of curvature over its working range for adjusting the amount of lost motion, and a screw disposed adjacent to the cam member for Calibrating the same, said cam member and said screw being secured to the actuating means.

14.`A control device of the class described, comprising a switching means, an actuating means for operating the switching means, a los't motion means connecting said actuating means and said switching means together for varying the differential at which the switching means operates, said lost motion means including a cam member having a continuously variable radius of curvature over its Working range for adjusting the amount of lost motion, a screw disposed adjacent to the cam for Calibrating the same, said cam member and said screw being secured to the actuating means, said switching means including two pairs of engaging contacts, one contact of each pair being pivotally supported in a manner to subject each contact to equal pressure when said contacts are engaged.

15. A control of the class described, comprising an actuating means, a switching means, a lost motion means connecting said actuating means and said switching means together for increasing the differential at which the switching means operates, said actuating means including a bell crank, a physical condition responsive means secured to one arm of the bell crank and a tension spring opposing the physical condition responsive means secured to the other arm of the bell crank, Calibrating means for adjusting the spring rate of the tension spring, and adjusting means for adjusting the force of the tension spring, said lost motion means including a cam member having a continuously variable radius of curvature over its working range for adjusting the amount of the` lost motion, said cam member being pivotally secured to said actuating means.

16. A control of the class described, comprising an actuating means, a switching means, a lost motion means connecting said actuating means and said switching means together for increasing the differential at which the switching means operates, said actuating means including a bell crank, a physical condition responsive means secured to one arm of the bell crank and a tension spring opposing the physical condition responsive means secured to the other arm vof the bell crank, Calibrating means for adjusting the spr'ing rate of the tension spring, and adjusting means for adjusting the force of the tension spring, said lost motion means including a cam member having a continuously variable radius of curvature over its working range for adjusting the amount of the lost motion, said cam member being pivotally secured to said actuating means, and said switching means including two pairs of engaging contacts disposed in series circuit arrangement, said switching means being arranged to subject each contact to equal pressure when said contacts are engaged,

17. A control of the class described, comprising an actuating means, a switching means, and a lost motion means connecting said actuating means and switching means together, said lost motion means including a cam member having a continuously variable radius of curvature over its Working range for adjusting the amount ol 10st motion, said actuating means including a thermal element, means for mounting the thermal element, said mounting means comprising means for exerting a crushing force upon the thermal element, and means within the thermal element for preventing the crushing of the same.

18.' In a device of the class described,A the combination of a lever having a pivot intermediate its ends whereby said lever has a rst portion between said pivot and one of its ends and a s-econd portion between said pivot and the other of its ends, said first and second portions of the lever extending in generally opposite directions, a two-position switching mechanism including a movable contact structure arranged for actuation by the rst portion of said lever, snap action means for causing movement of said movable Contact structure with snap action between its two positions, means for maintaining the end of said first portion of the lever in a rst position when the switching mechanism is in a first position and for maintaining the end of said-,rst portion of the lever in a second positionA when the switching mechanism is in a second position, a pressure responsive element having an end portion which assumes various positions correspond;A

ing to various values of pressure applied to said element, spring biasing means for said pressure responsive element, operating means actuated by movement of said end portion for rocking said lever about its pivot for thereby shifting said switching mechanism from one position to another, said operating means including a longitudinally adjustable connection between said end portion and said lever, said operating means also including a lost motion mechanism, said lost motion mechanism including a supporting member for supporting rst and second spaced and independently adjustable abutment m-embers adapted for engagement with the second portion of said lever, said second portion of the lever extending between said abutment members so that one ofl said abutment members determines the limit of lost motion in one direction and the other abutment member determines the limit of lost motion in the opposite direction, whereby adjustin'gof one of said abutment members relative to said supporting member varies only the value of pressure at which the switching mechanism is shifted in one direction and adjusting of the other abutment member relative to said supporting member varies only the value of pressure at which the switching mechanism is shifted in the opposite direction, and additional adjusting means for simultaneously varying the pressures at which the switching mechanism is actuated in each direction without varying the difference between said values, said additional adjusting means comprising an adjusting member arranged to bodily shift a portion of said spring biasing means,

19. vIn a device of the class described, the combination of a lever having a pivot intermediate its ends whereby said lever has a first portion between said pivot and one of its ends and a second portion between said pivot and the other of its ends, said first and second portions of the lever extending in generally -opposite directions, a two-position switching mechanism including a movable contact structure arranged for actuationV by the iirst portion of said lever, snap action means for causing movement of said movable contact structure with snap action between its two positions, means for maintaining the end of said first portion of the lever in a rst position when the switching mechanism is in a rst position and for maintaining the end of said first portion of the lever in a second position when the switching mechanism is in a second position, a pressure responsive element having an end portion which assumes various positions corresponding to various values of pressure applied to said element, spring biasing means for said pressure responsive element, operating means actuated by movement of said end portion for rocl ing said lever about its pivot for thereby shifting said switching mechanism from one position to another, said operating. means including a longitudinally adjustable connection between said end portion and said lever, said operating means also including a lost motion mechanism, said lost motion mechanism including a supporting member for supporting first and second spaced and independently adjustable abutment members adapted for engagement with the second portion of said lever, one of said abutment members comprising a flat ,cam rotatably mounted on said ing the difference between said values, said additional adjusting means comprising an adjust-.

v its ends whereby said lever has a first portion tation of said cam, said second portion of the lever extending between said abutment members so that one of said abutment members determines the vlimit of lost motion in onev direction and the other abutment member determines the limit of lost motion in the opposite direction,

tional adjusting means for simultaneously vary- I ing the pressures at which the switching mechanism is actuated in each direction without varybetween said pivot and one of its ends and a second portion between said pivot and the other of its ends, said first and second portions of the lever extending in generally opposite directions, a two-position switching mechanism including a movable contact structure arranged for actuation by the rst portion of said lever, snap action means for causing movement of said movable contact structure with snap action between its two positions, means for maintaining the end of said- -first portion of the lever in a first position when the switching mechanism is in a first position and for maintaining the end of said first portion of the lever in a second position when the switching mechanism is in a second position, a pressure responsive element having an end portion which assumes various positions corresponding to various values of pressure applied to said element, Spring biasing means for said pressure responsive element, operating means actuated by movement of said end portion for rocking said lever about its pivot for thereby shifting said switching mechanism from one position to another, said operating means including a lost motion mechanism, said lost motion mechanism including a supporting member for supporting first and second spaced and independently adjustable abutment members adapted for engagement with the second portion of said lever, one of said abutment members comprising a flat cam rotatably mounted on said supporting member so that its periphery limits relative movement between said lever and the supporting member, stop means for limiting rotation of said cam, said second portion of the lever extending between said abutment members so that one o1' said abutment members determines the limit of lost motion in ing mechanism is actuated in each direction without varyingthe difference between said values, said additional adjusting means comprising an adjusting member arranged to bodily shift a portion of said spring biasing means.

21. In a device of the class described, the combination of a lever having a pivot intermediate its ends whereby said lever has a first portion 'between said pivot and one of its ends and a second portion between said pivot and the other of its ends, said iirst and second portions of the lever extending in generally opposite directions, a switching mechanism comprising a pair of spaced stationary contacts, a pair of movable contacts for cooperating with said stationary contacts, a nexible spring member secured to and extending between said movable contacts, a rigid pivoted contact carrier attached to and carrying said flexible spring member and movable contacts,

said rigid contact carrier being actuated from one A position to another by the first portion of said lever, means including snap action means for causing movement of said contact carrier with a snap action when actuated by said lever and for rendering said contact carrier and the part of the lever actuating the same stable in their new positions, a pressure responsive element having an end portion which assumes various positions corresponding to various values of pressure applied to said element, spring biasing means for said pressure responsive element, operating means actuated by movement of said end portion for rocking said lever about its pivot for thereby shifting said switching mechanism from one position to another, said operating means including a longitudinally adjustable connection between said end portion and said lever, said operating means also including a lost motion mechanism, said lost motion mechanism including a supporting mem- .ber for supporting rst and second spaced and ndependently adjustable abutment members adapted for engagement with the second portion of said lever, one of said abutment members comprising a flat cam rotatably mounted on said supporting member so that its periphery limits relative movement between said lever and the supporting member, stop means for limiting rotation of said cam, said second portion of the lever extending between said abutment members so that one of said abutment members determines the limit of lost motion in one direction and the other abutment member determines the limit of\lost motion in the opposite direction, whereby adjusting of one of said abutment members relative to said supporting member varies only the value of pressure at which the switching mechanism is shifted in one direction and adjusting oi'. the other abutment member relative to said supporting member varies only the value of pressure at which the switching mechanism is shifted in the opposite direction, and additional adjusting means for simultaneously varying the pressures at which the switching mechanism is actuated in each direction without varying the diference'between said values, said additional adjusting means comprising an adjusting member arranged to bodily shift a portion of said spring biasing means.

22. A control device of the class described, comprising a switching means, an actuating means for operating the switching means, a lost motion means connecting said actuating means and said switching means together for varying the differential at which the switching means operates, said lost motion means including a cam member having a continuously variable radius of curvature over its working range for adjusting the amount of lost motion, said cam member being secured to the actuating means.

23. In a control instrument, the combination of, a first lever means having a pivot, a condition responsive device for rocking said first lever means about its pivot upon change in value of the condition to which the condition responsive device responds, a pair of spaced abutments carried by said first lever means, a second lever means having a pivot substantially in alignment with the pivot of the first lever means and extending between said spaced abutments whereby one of the abutments is adapted to engage one side of said second lever means and the other abutment is adapted to engage the other side of said lever means, and a control mechanism actuated by said second lever means.

LEWIS L. CUNNINGHAM.

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