US2882371A - Control apparatus - Google Patents

Description

April 195.9 (2. J. BISHOFBERGER 2,882,371

CONTROL APPARATUS Filed Feb. 5, 1958 2 Sheets-Sheet 1 INVENTOR. CARL J. BISHOFBERGER A 7' TOR/VEY April 1959 c. J. BISHOFBERGER 2,882,371

CONTROL APPARATUS 7 Filed Feb. 5, 1958 2 Sheets-Sheet 2 F INVENTOR.

CARL J. BISHOFBERGER ATTORNEY United States Patent CONTROL APPARATUS Carl J. Bishofberger, Minneapolis, Minn., assignor to Minneapolis-Honeywell Regulator Company, Minneapolis, Minn, a corporation of Delaware Application February 5, 1958, Serial No. 713,476

7 Claims. (Cl. 200-138) The present invention is directed to a heat sensitive control device and specifically to the novel slip-friction and heat sink arrangement incorporated therein. Further, the invention is directed to a heat sensitive control device incorporating a flat bimetal element wherein means are provided to minimize wiping, between the contact located on the bimetal element and a fixed contact, upon a flexing of the bimetal element.

In any device utilizing a bimetal for a heat sensitive device, one of the main problems encountered is in the provision of a sufl'iciently large bimetal element to provide the necessary output force but which bimetal element is small enough so that its cost is minimized. It is well recognized that in most heat sensitive devices the largest single cost factor is the bimetal element. By providing proper design and miniaturization of parts of the heat sensitive device, the size of the bimetal element of the heat sensitive device can be maintained at a minimum.

Further, the miniaturization referred to above is important especially when the heat sensitive device takes the form of a flame detector for use with and when located within an oil burner blast tube, in that the air for the burner must pass through the blast tube and any impediments placed in the air path interferes with the free flow of air, and hence interferes with the flame pattern. Thus, the smaller the flame detector, the more eflicient the oil burner blast tube and the flame pattern produced thereby.

In the heat sensitive device disclosed herein, a novel slip friction arrangement is shown, the elements of which are: easily formed, capable of being miniaturized, and devoid of close tolerances. Also, the unique design of the slip friction arrangement allows for a reduced size of the entire heat sensitive device, and consequently, the allowability of utilizing a relatively small piece of bimetal. The heat sensitive device is further characterized by the fact that while the bimetal is connected directly to the slip friction arrangement and hence to the support therefor, these portions do not provide an effective heat sink inasmuch as a reduced connection between the bimetal and the slip friction arrangement is utilized.

Further, since a flat bimetal element tends to bow or flex when exposed to a change in temperature, the provision of a contact on a flat, cantilever bimetal element, for cooperation with a fixed contact usually results in the relative moving of the contacts and a Wiping there- 'between. In certain applications, while a small amount of contact wiping is desirable to keep the contact surfaces clean, it is also desirable to keep the contact wiping to a minimum due to the arcing resulting between the contacts and the grinding of foreign matter between the contacts which results upon an excess of contact wiping. As disclosed herein, the bimetal element, and its associated contact, is located with respect to the slip friction arrangement and the remainder of the construction so that with the contacts engaging each other and upon flexing of the bimetal element, the supported end of the bi- 2,882,37l Patented Apr. 14, 1959 metal element moves toward the fixed contact to compensate for a movement of the contact located on the bimetal element in the opposite direction caused by the flexing, thereby reducing contact wiping.

It is therefore an object of this invention to provide a heat sensitive device which permits the utilization of a relatively small piece of bimetal.

Another object of this invention is to provide a slip friction arrangement wherein the elements are small and easily formed and which elements require no appreciable tolerances.

It is a further object of this invention to provide a heat sensitive device including a bimetal element and a support therefor wherein the support does not act effectively as a heat sink.

Still another object of this invention is to provide a heat sensitive device wherein the flat bimetal element thereof and the support therefor are so arranged with the contact on the bimetal element engaging a fixed contact and upon a flexing of the bimetal that wiping of the contact located on the bimetal with the fixed contact is minimized due to a compensating movement introduced into the system.

These and other objects will become more apparent from a reading of the following specification and appended claims in which:

Figure 1 is a perspective view of an oil burner blast tube assembly with a heat sensitive device in the form of a flame detector attached to an oil tube;

Figure 2 is a sectional view of the flame detector including a slip friction arrangement and bimetal element associated therewith;

Figure 3 is a plan view of the arrangement of Figure 2 with the cover removed;

Figure 4 is a view of a portion of the slip friction arrangement and the bimetal element;

Figure 5 is a plan view of the arrangement of Figure 4;

Figure 6 is a view of the arrangement of Figure 4 taken along the lines 6-6 thereof; and

Figures 7-12 are views of the base of the flame detector showing the slip friction arrangement and the bimetal element during various stages of the cycle of the flame detector.

In Figure 1 of the drawing a blast tube 10 of an oil burner is shown. Within the shell of the blast tube 10 are located an oil tube 12 having an orifice 13, a pair of ignition electrodes 15 and 16, and a flame detector 20. The flame detector 20 is mounted on the oil tube 12 by means of a bracket 19. The flame provided by the burning oil is located beyond the opening 11 of the blast tube 10, and it is the radiation of this flame to which the flame detector 20 is responsive. The size of the flame detector 20 in relation to the inner cross sectional area of the shell of the blast tube 10 is such that it provides a minimum restriction to the free flow of air which is desirable due to the effect such free flow has on the efliciency of the oil burner blast tube and the flame pattern produced thereby.

It may be noted that the structure shown in the remainder of the figures is approximately twice actual size and has been so shown for purposes of clarity.

The flame detector 20 is more completely shown in Figures 2 and 3 wherein a base 22 and a cover 29 are held together by fastening means 25. A lime glass window 26, which is appropriately cemented in place, provides an opening through which radiation is allowed to pass to the interior of the flame detector 20. The base 22 and the cover 29 are formed from ceramic materials and the mating edges thereof are ground flat. By administering a coat of heat resistance varnish to the joint between the base 22 and the cover 29, after assembly, a substantially air tight container is provided.

r 2,882,371 I s r K A contact support member 30 is aflixed to the base by a first terminal member 31. To the contact support member 30, a contact 32 is aflixed and directly above the contact 32, an insulating member 34 is located. The contact 32 and insulating member 34 serve as stops for a flat bimetal member 35 and specifically a contact member 36 located .at its free end. The bimetal 35 is affixed at its opposite end to ,a portion 39 of a force input member in the form of a channel shaped yoke member 4t).

The yoke member -40 includes a pair of arms 41 and 4-2 extending in the same general direction and connected by a portion 43. The arms 41 and 42 are disposed between the arms 45 and 46 of the support member in the form of a bifurcated frame 47 which is affixed to the base 22 by means of a second terminal member 49. A bar or shaft 50 is disposed through oblong openings 44 of arms 41 and 42 :of yoke :member 40, the extremities of which bar are supported between the bendable ears of the arms 45 and 46 of the frame 47. It should be noted that the shaft 50 is cylindrical in shape throughout almost all its length to allow the yoke member 40 to rotate thereabout, but is oblong in shape where disposed in the arms 45 and 46 of the frame 47, as more clearly shown in Figure 9, so as to make it non-rotatable.

A resilient member in the form of a substantially V- shaped spring 53 includes a first arm 54 which is operatively fastened to the connecting portion 43 of the yoke member 40 and a second arm 55 which is bent over the top of connecting portion 43 and biased against the shaft 50.

Lead 58 is fastened to the lower surface of the bimetal 35 and to the uppermost portion of the second terminal member 49, thereby allowing for the establishment of a circuit across the first terminal member 31 and the second terminal member 4-9 upon the contact 36 of the bimetal 35 engaging the fixed contact 32.

In Figures 4-6 the bimetal 35 and yoke member 41 subassembly is separately shown. The shape and location of the oblong openings 44 of arms 41 and 42 is clearly shown in Figures 4 and 6. As is indicated in Figure '5, an extension 59 joining the portion 39 and the connecting portion 43 is necked down, so as to limit the transfer of heat between the bimetal 35 and yoke member 40, spring 53, shaft 50, and frame 47. This construction therefore acts to reduce the heat sink poten tialties of the aforementioned members which of course is desirable in a device such as described herein due to the lag introduced into the device by uninhibited heat transfer. In Figure 6, the relation of the necked down portion 59 to the remainder of the yoke member 40 is brought forth in a'clearer manner.

An examination of Figures 2-6 will indicate that the flame detector described is comprised of relatively easily formed elements, which elements require no close tolerances and which elements can be miniaturized. Further, the assembly of the elements is simple and straightforward. Thus, the shaft '50 need but be passed through the oblong openings 44 of the arms 41 and 42 of yoke member 40 and the subassembly dropped in place between the bendableears of the arms 45 and 46 of the frame 47 whereupon a consequent bending of the bendable ears of the arms 45 and 46 to the position shown in Figure 2 and the affixing of the complete assembly to the base 22 in cooperative relation with the contact support member 30 completes the device, except for fastening of the cover 29 thereto.

The slip friction arrangement of the flame detector is comprised of: the frame 47, the nonrotatable shaft '50, the yoke member 40, and the spring 53, interrelated as indicated above. An initial predetermined amount of force applied to the yoke member 43 by some means such as the bimetal 35 does not result in a rotational movement of the yoke member 40 about the shaft 50. This is becauseof the bias set up between the yoke member 40 and the shaft 50 by the spring 53. Upon a predetermined input force being :applied to the yoke member 40, rotation of the yoke member 40 about the shaft 50 occurs with the consequent slip friction between the yoke member 40 and the shaft 50 arising. Should the input force be removed from the yoke member 40 no movement of the yoke member 40 takes place due to the bias set up between the yoke member 40 and the shaft 50 by the spring 53. Further, a counter action will not cause rotation of the yoke member in the appropriate direction until a predetermined input force is obtained to overcome the aforementioned bias.

The operation of the flame detector will now be under taken and reference should be made to Figures 7-12.

In Figure 7, the arrangement is shown when cool and with the contact 36 of the bimetal 35 engaging the insulating member 34 with little or no loading of the slip friction arrangement. The bimetal 35 is so arranged that upon an increase in radiation being directed toward the flame detector, and hence an increase in temperature being sensed by the bimetal, the bimetal begins to flex and move downwardly toward the fixed contact 32 without a consequent movement of the slip friction arrangement, as shown in Figure 8. Upon a further increase in radiation, contact 36 of the bimetal 35 engages the contact 32 to close a circuit, as shown in Figure 9 thereby resulting in a control function taking place. Again, no movement of the slip friction arrangement takes place. Should the radiation continue to increase, increased flexure of the bimetal 35 occurs. This increased flexure results in a loading between contacts 32 and 36 and of the slip friction arrangement until a predetermined level is attained. Upon a further increase in radiation, the slip friction arrangement comes into play in that the bias provided by spring 53 is overcome and the yoke member 40 rotates clock-wise about the shaft 50, as is shown in Figure 10, thereby limiting the loading to which the contacts 32 and 36 are subjected.

Now, it will be noted that upon engagement between contacts 32 and 36, increased flexure of the bimetal 35 tends to cause relative movement between contacts 32 and 36 and movement of contact 36 toward shaft 50. However, due to the relation of the portion 39 of yoke member 40 with respect to shaft 50, rotation of the yoke member 40, and hence of the supported end of the bimetal 35 is in a direction so as to result in movement of the supported end of the bimetal toward the contact 32. 'These opposing, compensating movements result in a minimization of contact Wiping.

With a flame detector for use with an oil burner, it is of course necessary to almost instantly sense any reduction in radiation directed toward the flame detector. With the present device, a reduction in radiation results initially in a removal of the loading between the contacts 32 and 36 and of the slip friction arrangement and subsequently in a movement of the bimetal 35 and associated contact 36 away from the contact 32 toward the insulating member 34, as shown in Figure 11, to open the circuit, thereby resulting in a control function. It will be noted that the yoke member 40 does not rotate in the opposite direction under this set of circumstances due to the bias set up between the yoke member 40 and shaft 50 by the spring 53. The bimetal 35 is still flexed inasmuch as the radiation has been merely reduced and the temperature of the bimetal is still higher than that experienced by the device under the conditions of Figure 7. In Figure 12, the bimetal 35 is returned to the initial position so that contact 36 engages insulating member 34. However, the bimetal 35 is still flexed, again due to the fact that the radiation received by it is higher than when under the conditions of Figure 7. Should a continuing decreasein radiation be received by the device, the bimetal 35 would .approach the position shown in Figure 7, with a tendency to flex in the opposite direction to cause a counterclockwise rotation of the yoke member 40 about shaft 50 and to eventually cause a similar loading only in the opposite direction of the slip friction arrangement,

for the bimetal support structure to be effectively by-,

passed as a heat sink. While only one modification has been shown of the structure, other modifications are of course possible, and therefore, the scope of the invention is to be determined from the following claims in which I claim:

1. A flame detector of the radiation sensitive bimetal type for use with a flame producing unit, the combination comprising: a cover including a glass window for the passage of radiation; a base member affixed to said cover; a bifurcated support member located within the enclosure formed by said cover and said base and affixed to said base; a channel shaped yoke member including a pair of arms extending in the same general direction each having an oblong opening and a portion connecting said arms, said yoke member including an extension integral and connected by a necked down portion with the portion of said yoke member connecting the arms thereof; a shaft nonrotatably held by the arms of said support member, said yoke member being rotatably supported on said shaft by said oblong openings; a flat bimetal element having a first end portion operatively connected to the extension of said yoke member and located with respect to the window of said casing so as to be exposed to radiation passed therethrough, a second end portion of said bimetal element including a contact being associated with stop means including a contact supported by said base; and a substantially V-shaped spring member having a first portion operatively connected to the portion of said yoke member connecting the arms thereof and a second portion biased towards and engaging said shaft; initial flexure of said bimetal element resulting in the second end thereof being moved toward and engaging said stop means without consequent rotation of said yoke member due to the action of said spring member against said shaft and further flexure of said bimetal element after the contact of said stop means is encoun tered by the contact thereof resulting in rotation of said yoke member about said shaft; the extension of said yoke member and said stop means being located with respect to each other and said shaft so that upon flexure of said bimetal element and rotation of said yoke member the first end portion of said bimetal element moves toward said stop means thereby compensating for movement of the second end portion of said bimetal element toward said shaft caused by flexure of said bimetal element to reduce contact wiping.

2. A flame detector of the radiation sensitive bimetal type for use with a flame producing unit, the combination comprising: a cover including a glass window for the passage of radiation; a base member afiixed to said cover; a bifurcated support member located within the enclosure formed by said cover and said base and aflixed to said base; a channel shaped yoke member including a pair of arms extending in the same general direction and a portion connecting said arms, said yoke member including an extension integral with the portion of said yoke member connecting the arms thereof; a shaft nonrotatably held by the arms of said support member, said yoke member being rotatably supported on said shaft by openings located in said arms, a flat bimetal element having a first end portion operatively connected to the extension of said yoke member and located with respect to the window of said casing so as to be exposed to radiation passed therethrough, a second end portion of said bimetal element being associated with stop means supported by said base; and a spring member having a first portion operatively associated with the portion of said yoke member connecting the arms thereof and a second portion biased toward and engaging said shaft; initial flexure of said bimetal element resulting in the second end thereof being moved toward and engaging said stop means without consequent rotation of said yoke member due to the action of said spring member against said shaft and further flexure of said bimetal element after said stop means are encountered thereby resulting in rotation of said yoke member about said shaft.

3. A heat sensitive device comprising: a base; a bifurcated support member aflixed to said base; a channel shaped yoke member including a pair of arms extending in the same general direction and a portion connecting said arms; a shaft nonrotatably held by the arms of said support member, said yoke member being rotatably supported on said shaft by openings located in said arms; said yoke member including an extension integral with the portion of said yoke member connecting the arms thereof and displaced from the axis of rotation thereof; and a fiat bimetal element having a first end portion operatively connected to the extension of said yoke member and having a second end portion including a contact associated with stop means including a contact located on said base; the extension of said yoke member and said stop means being located with respect to each other and said shaft so that flexure of said bimetal element after the contact of said stop means is encountered by the contact thereof results in rotation of said yoke member about said shaft and movement of said extension and the first end portion of said bimetal element toward said stop means thereby compensating for movement of the second end portion of said bimetal element toward said shaft caused by flexure of said bimetal element to reduce contact wiping.

4. A heat sensitive device comprising: a base; a support member affixed to said base; a bar nonrotatably held by said support member; a force input member supported and rotatable about said bar; and a flat bimetal element having a first end portion operatively connected to said force input member displaced from the axis of rotation thereof and having a second end portion including a contact associated with stop means including a contact located on said base; said force input member and said stop means being located with respect to each other and said bar so that flexure of said bimetal element after the contact of said stop means is encountered by the contact of said bimetal element results in rotation of said force input member about said bar and movement of said force input member and the first end portion of said bimetal element toward said stop means thereby compensating for movement of the second end portion of said bimetal element toward said bar caused by flexure of said bimetal element to reduce contact wiping.

5. A slip friction arrangement comprising: a bifurcated support member; a channel shaped yoke member including a pair of arms extending in the same general direction each having an oblong opening and a portion connecting said arms, a shaft nonrotatably held by the arms of said support member, said yoke member being rotatably supported on said shaft by said oblong openings; and a substantially V-shaped spring member having a first arm operatively connected to the portion of said yoke member connecting the arms thereof and a second arm disposed between said yoke member and said shaft, said second arm being biased against said shaft thereby tending to force the yoke member to a position whereby said shaft engages one extremity of the oblong openings of the arms of said yoke member and further tending to retard rotation of said yoke member about said shaft.

6. A slip friction arrangement comprising: a bifurcated support member; a channel shaped yoke member including a pair of arms extending in the same general direction and a portion connecting said arms, a shaft nonrotatably held by the arms of said support member, said yoke member being rotatably supported on said shaft by openings located in said arms; and a spring member having a first 'portion operatively connected to the portion of said yoke member connecting the arms thereof and a second portion disposed between said yoke member and said shaft, said second portion being biased against said shaft thereby tending to retard rotation of said yoke member about said shaft.

7. A heat sensitive device comprising: a base, slip friction'means having a stationary mernber aflixed to said 10 base and rotatable means mounted on said stationary member having an axis of rotation, a substantially fiat bimetal element having a first portion mounted on said rotatable means and displaced a given distance from said axis of rotation, said bimetal element having a second portion including a contact assembly cooperating with stop 8 means including a stationary contact mounted on said b e, e leng h f id m l l m n e said firs and second portions being related to said given distance vof displacement so that continued flexure of said bimetal References Cited in the file of this patent UNITED STATES PATENTS 2,660,645 Deubel Nov. 24, 1953

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