US3685364A

US3685364A - Cam for control of combustion fuel-to-air ratio

Info

Publication number: US3685364A
Application number: US57985A
Authority: US
Inventors: Joseph L Turecek; Glenn D Craig; David T Feuling
Original assignee: Aqua Chem Inc
Current assignee: Aqua Chem Inc
Priority date: 1970-07-24
Filing date: 1970-07-24
Publication date: 1972-08-22
Anticipated expiration: 1989-08-22
Also published as: CA947634A

Abstract

Optimum fuel-to-air ratio over the entire operating range of a boiler fuel burner is obtained by having a motor, which is driven in response to boiler temperature or pressure changes, operate a damper and fuel valves simultaneously. A cam and follower reposition the fuel valves coordinately with a directly driven damper. Means are provided to adjust the cam contour over its length so optimum fuel-to-air ratios prevail for all positions of the damper. The follower is positively engaged with the cam.

Description

United States Patent Turecek et al.

3,685,364 1451 Aug. 22, 1972 [54] CAM FOR CONTROL OF COMBUSTION FUEL-TO-AIR RATIO [72] Inventors: Joseph L. Turecek, Brown Deer; Glenn D. Craig, Menomonee Falls; David T. Feuling, Beaver Dam, all

' of Wis.

[73] Assignee: Aqua-Chem, Inc.

[22] Filed: July 24,1970

[21 Appl. No.: 57,985

[52] US. Cl. ..74/55, 74/568 FS, 74/569 [51] Int. Cl ..Fl6h 53/00 [58] Field of Search ..74/55, 568 FS, 569

[56] References Cited UNITED STATES PATENTS 3,425,286 2/1969 Ellis ..74/568 3,344,685 10/1967 Grouzet ..74/569 1,525,052 2/ i 925 Spotz ..74/568 2,777,513

l/l957 Cooper "74/568 Primary Examiner--William F. ODea Assistant Examiner-Wesley S. Ratliff, Jr. Attorney-Ralph G. Hohenfeldt and Fred Wiviott 5 7 ABSTRACT Optimum fuel-to-air ratio over the entire operating range of a boiler fuel burner is obtained by having a motor, which is driven in response to boiler temperature or pressure changes, operate a damper and fuel valves simultaneously. A cam and follower reposition the fuel valves coordinately with a directly driven damper, Means are provided to adjust the cam contour over its length so optimum fuel-to-air ratios prevail for all positions of the damper. The follower is positively engaged with the cam.

4 Claims, 4 Drawing Figures PATENTEU M1822 1912 3,685,364

SHEET 1 [IF 2 //V VE N TOPS,

I JOSEPH L. TURECEK DAVID T. FEULING GLENN D CRAIG I H By Wwaw PAIENTEDmczzmz 3.685 364 sum 2 or 2 if? i 5% 7;. 25 i@ E :T:

INVENTORS,

JOSEPH L.TUYRECEK DAVID T. FEULING GLENN D. CRAIG BY wi ww Attorney CAM FOR CONTROL OF COMBUSTION FUEL-TO- AIR RATIO BACKGROUND OF THE INVENTION In connection with boilers, furnaces and other heating devices it is necessary to modulate the fuel combustion rate in accordance with the temperature that is desired. In a gas or oil fired boiler, for example, a transducer or a sensor may produce a force or signal which corresponds with pressure or temperature of the water or steam, respectively. This signal may act through a control to actuate a damper motor which adjusts the amount of air and, simultaneously, the amount of fuel required for optimum combustion efficiency.

It has been common practice to adjustfuel flow by letting the damper motor drive a variable contour cam whose follower actuates the fuel valves. To provide a fuel flow which matches the air flow for obtaining efficient combustion at all discrete settings, flexibility must be built into the system because the flow characteristics of the fuel valves are substantially different than those of the air dampers. For instance, a specific movement of the air damper will provide an air flow which is not necessarily compatible with the fuel flow resulting from the corresponding movement of the fuel valve. Thus, an adjustable contour cam is required with flexibility to rotate or otherwise actuate the fuel valves more or less so that the fuel-to-air ratio can be properly established for any combustion rate.

Fuel valve control cams whose contour or profile may be varied over increments of the length of the cam surface have been used before. However, prior types have some disadvantages. If there was some resistance to return movement of the fuel control valve linkages there was often insufficient force in the cam follower spring for the follower to be held in contact with the cam. The result was that fuel flow rate to the burner was not always held in proper proportion to the air flow for optimum combustion efficiency.

SUMMARY OF THE INVENTION An object of the present invention is to overcome the aforementioned and other disadvantages by providing a cam and follower assembly in which the cam contour or profile may be adjusted incrementally as desired and in which the follower is movably but positively engaged with the cam surface.

Another object is to provide a reliable, relatively simple and inexpensive fuel valve control cam assembly.

Briefly stated, one embodiment of the invention involves mounting an arcuate and bidirectionally movable cam segment on a journaled shaft for joint.rotation with a link that is driven from the damper motor. The arcuate cam segment has a pair of nominally concentric spaced apart metal cam strips which are engaged in their intermediate gap by a plurality of circumferentially spaced cam strip engaging members or heads. Each member is supported from the arcuate seg ment by an adjusting screw which may be turned to adjust the member and the segment of the cam which it engages to a preselected distance from the center of rotation. The cam strips may then have a generally uniformly curved profile but with minor undulations at incremental zones where correcting adjustments are made.

- The cam strips have exposed edge margins so that spaced rollers on a cam follower may positively engage the top and bottom surfaces of the cam strips and thereby be compelled to follow the cam strip contour and produce a positive lineardriving force on the follower.

How the foregoing and other more specific objects are achieved will appear from time to time in the ensuing description of an embodiment of the invention taken in conjunction with the drawing.

DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of a damper control motor and a fuel control valve which is operatively connected by the new cam assembly;

FIG. 2 is a side elevation view of the isolated cam and follower assembly;

FIG. 3 is an elevation view taken from the right'side of the assembly shown in the preceding figure; and

FIG. 4 isa fragmentary vertical sectional view of the cam adjusting screw and affiliated parts.

DESCRIPTION OF A PREFERRED EMBODIMENT FIG. 1 illustrates one type of conventional boiler fuel valve assembly comprising a body 10, some pressure gauges l1 and 12, and a pair of manual

flow control handles

13 and 14. The rate at which fuel is metered through the valve depends, in this example, on linear movements of a valve stem 15. Rotary valves are also used for metering gas or liquid fuels in some installations. On boilers that are adapted for switching from one type of fuel to another, both liquid and gas fuel valves may be present. The valves may be rotary or linear types and they may each be controlled by one of the new cam assemblies disclosed herein.

In the upper left of FIG. 1 the damper control motor 16 is illustrated. This motor responds to signals indicative of required changes in combustion conditions by rotation of its shaft 17. The shaft has pinned on to it an arm 18 which has several adjusting holes and is pivotally connected to a turnbuckle link 19. The turnbuckle link is pivotally connected to an arm 20 which is fixed on a jack shaft 21. An air damper may be driven directly by arms from jack shaft 21. The damper and arms are not shown.

The jack shaft is joumaled for rotation in a bearing 22 which is secured in a bearing bracket 23. Pinned on jack shaft 21 by means of a set screw 24 or other suitable means is a cam base 25 which has an arcuate longitudinally extending flange 26. A plurality of socketheaded screws 27 extend radially through the flange 26. These screws 27 are threaded in flange 26 in this embodiment.

Each screw 27 carries a cam contour adjusting head member 28 at the radially remote end of the screw. For brevity, these members will be called heads 28. The heads 28 have slots 29 on their opposite sides. A thin strip of metal 30, constituting a deformable-contour cam surface, is fitted into the corresponding slots 29 in a row on one side of the heads. There is another cam strip 31 similarly located in the row of slots on the other side of heads 28. These

parallel cam strips

30 and 31 have a gap 32 between them so that the center portion of heads 28 can pass between them. The ends of cam I strips 30 and 31 are tied together by a strap 33 which is secured to the cam strips by means of

screws

34 and 35. The cam strips 30 and 31 are similarly joined at both ends to fix them in parallel spaced relationship.

Because cam strips 30 and 31 are positively engaged by slots 29 in heads 28, it should be evident that increments of the contour or profile of the deformable cam strips can be changed or shaped with undulations by variously adjusting the radial distance of the individual heads 28 from the cam base flange 26. This is accomplished by turning adjusting screws 27 in or out with an Allen wrench. Thus, it is possible to establish the general contour of the cam strips 30 and 31 with adjusting screws 27 and it is also possible to change the profile of a selected cam strip length increment by ad justing a screw 27 in the head 28 that engages the cam strip where the profile of the increment is to be different than adjacent increments.

FIG. 4 shows how the contour adjusting screws 27 and the adjusting heads 28 are coupled. One may see that screw 27 has its diameter reduced in the region 36 so it passes through head 28 with a little clearance. The reduction in diameter results in formation of an annular shoulder 37 which prohibits axial upward movement of head 28. The terminal end 38 and screw 27 is countersunk and flared for retaining the head 28. A washer 39 is interposed between flared portion 38 and head 28 to provide a smooth bearing surface and to reduce friction when the screw is turned in the head to advance or retract it. Note in FIG. 4 that cam strips 30 and 31 extend laterally a considerable distance outside of slots 29 to provide upper and lower cam

follower bearing surfaces

40 and 41 which are marked only on cam strip 30.

Referring again to FIG. 1, one may see that the cam follower which drives fuel valve stem comprises a yoke which is generally designated 42. The yoke has a cross member 43 and a set screw 44 for fastening to it valve stem 15. The yoke also has a pair of spaced apart upstanding side members 45 each of which carries a pair of

rollers

46 and 47. The rollers are on stub shafts 48 the ends of which are threaded into side members 45. The peripheral surfaces of the adjacent roller pairs of spaced apart a distance that is substantially equal to the thickness of cam strips 30 and 31.

Rollers

46 and 47, therefore, follow faithfully all incremental undulations in the cam strip profiles. The fact that the cam strips are captured between the rollers results in follower 42 being driven forcibly in a vertical direction and the cam and follower cannot separate regardless of any resistance that may be offered by the valve stem 15 and its associated mechanism.

As stated earlier, arms extend from jack shaft 21 for operating the. damper. The damper and arms are not shown since they are not part of the novel subject matter and it is only necessary to recognize for present purposes that the damper is repositioned in response to changing boiler conditions. The fuel valve is readjusted correspondingly at the same time. With the new cam assembly, the cam contour may be adjusted so that optimum fuel-to-air ratios are obtained for all settings of the damper.

The new positive drive cam assembly is subject to some structural modifications without departing from the principles of the invention. For instance, the structure shown in FIG. 4 may be made conversely. That is,

the unthreaded portion 36 of the adjusting screws 27 may pass through a clearance hole in flange 26 and may be captured therein for rotation, and the threaded portion may be threadingly engaged with head 28. Rotation of screw 27 will still actuate the head radially inwardly or outwardly to change the cam strip profile.

The only limiting condition is that the cam follower must engage the cam surface by capturing it on both sides. The heads 28 could also be circularly slotted spools fastened to the screws 27 by turning and advancing and retracting with the screws.

In its broadest sense the invention requires a cam surface supporting member that is subject to rotational or translational movement relative to a follower which is positively engaged with the cam surface. The movement may be caused by any condition responsive force producing device. The cam surface is adapted for having increments of its length modified in profile so that the follower will move a distance which is disproportionate to the cam surface movement as may be predetermined at will. In the illustrative embodiment the cam surface members are mounted on heads which have individual adjusting screws extending from and threaded through anarcuate support. Various adjustable means other than screws could engage the heads and the heads or their equivalents could be replaced with other cam surface engaging means. Moreover, the cam surface could be mounted for translation in an angular plane in which case any incremental profile variations would still be transmitted to the follower.

Although a preferred embodiment of the invention has been described in detail, it will be understood that such description is to be considered illustrative rather than exclusive, for the invention may be variously embodied and is to be limited in scope only by interpretation of the claims which follow.

We claim:

1. A positive drive cam and follower assembly comprising:

a. a rotatable element having an arcuate part displaced radially from its axis of rotation,

b. a row of adjusting screw means extending radially from said arcuate part and turnable therein,

c. cam member supporting head means relatively rotatably mounted on said screw means,

. a cam member, increments of which are deformable in a radial direction, said cam member having radially opposed surfaces and being engaged at spaced intervals by head means in a row, said head means having laterally extending slot means receiving said cam member and positively engaging each of said opposed cam surfaces, whereby selective rotation of the adjusting screw means will positively deform increments of said cam member correspondingly radially toward or away from said rotatable element, and

e. a cam follower means including spaced apart roller means in positive contact engagement respectively with said opposite surfaces of the cam member so that the follower means are compelled to move in radial directions corresponding with the profile of the cam member.

2. The invention set forth in claim 1 wherein:

a. said cam member comprises a pair of metal strips which are similarly contoured and spaced apartin parallelism with each other,

b. the slot means of said head means snugly engaging and supporting each of said strips at spaced intervals along their lengths.

3. The invention set forth in claim 2 wherein:

a. said metal strips comprising the'cam member extend laterally outwardly in opposite directions from the slots to define the said opposed cam surfaces,

b. said follower means comprising yoke means on each side of which are pairs of roller means having parallel axes of rotation and which have their peripheries spaced part a distance that is substantially equal to the thickness of the metal strips, whereby the profile of the cam member strips that is presented continuously between the rollers due to cam rotation positively drives the cam follower means bidirectionally.

- 4. A cam assembly for closely coordinating the condition of the fuel and air flow control means of a burner wherein a cam follower means is driven in a positive manner bidirectionally to control the burner, comprismg:

a. a rotatable element having an axially projecting curved flange means,

b. a row of adjusting screw means radially threaded through the flange means and having unthreaded portions at their ends remote from the flange means,

c. a head means disposed on each unthreaded portion of the screw means and means retaining the head means thereon but permitting rotation of the screw means therein for individually advancing or retracting said head means radially,

d. said head means each having opposed laterally extending slots defining parallel opposed rows of slots, I

e. a pair of thin deformable continuous metal cam strips each having a corresponding edge spaced from and disposed in parallel with the other and with said edges being engaged in said respective rows of slots so that a cam profile is defined by the other edges of the strips which project from the slots, the said other edges having opposed cam surfaces,

f. a cam follower on which are mounted opposed pairs of rollers which have parallel axes of rotation, the peripheries of the rollers in a pair being spaced apart a distance that is substantially equal to the thickness of the cam strip, said roller peripheries in a pair being in contact simultaneously with said opposed cam surfaces for positively driving said follower linearly in correspondence with the cam profile increment that is presented between the rollers by rotation of the said rotatable element.

Claims

1. A positive drive cam and follower assembly comprising: a. a rotatable element having an arcuate part displaced radially from its axis of rotation, b. a row of adjusting screw means extending radially from said arcuate part and turnable therein, c. cam member supporting head means relatively rotatably mounted on said screw means, d. a cam member, increments of which are deformable in a radial direction, said cam member having radially opposed surfaces and being engaged at spaced intervals by head means in a row, said head means having laterally extending slot means receiving said cam member and positively engaging each of said opposed cam surfaces, whereby selective rotation of the adjusting screw means will positively deform increments of said cam member correspondingly radially toward or away from said rotatable element, and e. a cam follower means including spaced apart roller means in positive contact engagement respectively with said opposite surfaces of the cam member so that the follower means are compelled to move in radial directions corresponding with the profile of the cam member.

2. The invention set forth in claim 1 wherein: a. said cam member comprises a pair of metal strips which are similarly contoured and spaced apart in parallelism with each other, b. the slot means of said head means snugly engaging and supporting each of said strips at spaced intervals along their lengths.

3. The invention set forth in claim 2 wherein: a. said metal strips comprising the cam member extend laterally outwardly in opposite directions from the slots to define the said opposed cam surfaces, b. said follower means comprising yoke means on each side of which are pairs of roller means having parallel axes of rotation and which have their peripheries spaced part a distance that is substantially equal to the thickness of the metal strips, whereby the profile of the cam member strips that is presented continuously between the rollers due to cam rotation positively drives the cam follower means bidirectionally.

4. A cam assembly for closely coordinating the condition of the fuel and air flow control means of a burner wherein a cam follower means is driven in a positive manner bidirectionally to control the burner, comprising: a. a rotatable element having an axially projecting curved flange means, b. a row of adjusting screw means radially threaded through the flange means and having unthreaded portions at their ends remote from the flange means, c. a head means disposed on each unthreaded portion of the screw means and means retaining the head means thereon but permitting rotation of the screw means therein for individually advancing or retracting said head means radially, d. said head means each having opposed laterally extending slots defining parallel opposed rows of slots, e. a pair of thin deformable continuous metal cam strips each having a corresponding edge spaced from and disposed in parallel with the other and with said edges being engaged in said respective rows of slots so that a cam profile is defined by the other edges of the strips which project from the slots, the said other edges having opposed cam surfaces, f. a cam folloWer on which are mounted opposed pairs of rollers which have parallel axes of rotation, the peripheries of the rollers in a pair being spaced apart a distance that is substantially equal to the thickness of the cam strip, said roller peripheries in a pair being in contact simultaneously with said opposed cam surfaces for positively driving said follower linearly in correspondence with the cam profile increment that is presented between the rollers by rotation of the said rotatable element.