US2408161A - Speed governor - Google Patents

Description

Sept. 24, 1946;;

c; DARNELL SPEED GOVERNOR I Filed June 9, 19 44 V 2 Sheets-Sheet 1 Se t. 24, 1946. v R. c, DARNELL r ,4

' SPEED GOVERNOR I Fi l ed June 9, 1944 I 2 Sheets-Sheet 2 1 3/ .41 r y v w i 1 Z9 W w 717 w Patented Sept. 24, 1946 isrnnn Gov-Emma I "RtexJCQDarnlhAnn Arbor, Mich, assignor to I Kmg-Seeley Corporation, -Ann Ar bonMich a corporation of Michigan Application-dune 9, 1944*,Serial No. 589,493

I fl his invention relates to speed governors vfor I internal combustion engines, and more particularlyjo governors -of the velocity.- or mixtureflow type. Such governors ,eonsist essentially of I a valve or throttle, plate mounted on rotatable shaft extendingitransverse'ly of the intake manifold -of the engine'to be governedi said shaft being off the center line of ithe manifold passage, whereby the forces exertedon the throttle plate bythe passage of :fuel-mixturethrough themani- I 1-fold tend to move the-plate 'fromopen' towards closed eposition, said gfOI'CES' having varying valnes as the plate changesrposi-tion. -A'reac'tance device in the form of a springorcombination of springsconnected to the-throttle :platej spindle I or shaft through a suitable-linkage, is employed to produce, a balanced condition :of theplate, in all positions-at governed speedjthepositions' of the throttle p lateand hence-the amount of fuel mixture-passing to theengine, -being dependent upon the load imposed upon the engine.

In all velocity type governors, :thereis-a ertain variation'hetween full load speed'and no load speed, which variation must be permitted. in,or-'

der tosecure proper functi'oning'of the governor, t

is well understoodin the-art. "This increase noPl'oad speed as compared with full load speed is *preferably less than 10% of the governed is-p'eed; and is known as the regulation of the :governor. inygovernedspeedbetweenfull load and no-load conditionsis-uniform, and-if plotted in terms of R.-- P,; M. Versus 'brakerhorsepower, would givea straight/line loadingm-urve or load speed -curve. i-lowever inypracti'ce, this desirable rewsultwhas been; achieved only in: part.

-I n a velocity type governor, the fforces acting uponthe throttle plate;-due-to the passage 'offuel mixture through the intake conduit have'been considered as 'tWo-fold',-namely, impingement of :the fueli mixture upon the difierential exposed areas-of the throttleplate, and the differencein rfiuid ,pressure upstream and downstream of the throttle plate. As is well known, the pressure upstream of the throttle {plate is substantially atmospheric whent-he carburetor-throttle valve "is-in op enposit-ion, as is-thec'a-se -when the engine isbeing operated under control :of the governon Ph'ei'pressure below or downstream, of the governor valve, at governed. speed, changes with -theload,varying from a valuein the neighb'orhoorl of 2" of Hg at ful-l loadto perhaps --20" of Hg :atn'ogload. Inth'e higher vacuum ranges, say'aboved'if'vof :Hg',"the=forces acting upon the I governor valve to -:move it towards F closed liOSif Theoretically, the rate of increase "1 is Claims. (01.137953) tion I change; but very little with an increase in -spE6d,'and for thisreason the-loading :curve or loading characteristic of such g overnors has, -i;n

the past, departed considerably from the desired straight linecurve under conditions ofelight load or no dead, resulting in -a considerableincrease of I speedunder such-light load or no loa d conditions.

This undesirable increase in'speed has, heretofore, been; tolerated as I essential to ,producef-the neeessary force to close the valve. I

' Ihe' general object-oi' the 'present invention; is the provision of I an improved :speed governor a of the velocity or mixture-flow ty-pe,- in which the force necessaryior proper-governor valve closure under 'no :load conditions =is-produced without resorting to engine speed increase, whereby-abetter loading I characteristic or load-speed curvei's obtained. a

- A= further objectis the provision or? algovernor I of the typedescribed in which, when the gover-nor {valve approaches closed i posi'tion due {to reductioniri-load, a forceinaddit'ion'to those normally actingupon the governor valve is employed for urging theJatter toward close d' position. I

-;Another object isthe :provision of -a governor of ;the type described-in which special Lrneans, lsubject to the engine vacuum below the governor 'valve are employed to move the valve toward closed-position.- I v -Another objectis the-provision of wanLimproved -governor -accordingto the last stated object, in

which the special-valve closing ineans are actuated only when theengine vacuumexceeds aprodete i -in'inedvalue. V a A further objectis the provision of agovernor of the type described in which the anti-steal piston usually associated with such gover orsis caused tome-actuated as theagove'fnor valveiapproachesclosed'position, to urge the valvejinf'a closing direction@ 7 o Another-abject is'the provision of a modified :form of the invention which .means operable upomamredeternfined decrease V in. external at.- inosph'eric I pressure are employed .Tfor' urging 'the governor valve towardolose'd position, "such modification being especiallyadapted {for use .at high altitudes asinthe caseof aircraft. I I

A further obj eetis --the provision ofIa governor such-as -described-in the last stated object in which the conventionalanti-steal I pistongis ,actuated at no "load -and upon a predetermined decrease inatmospheric pressure, to urge the governor va'lveinaclosinguirectiont 7 I "A fdrtherwbject is the: provision, imaegovernor according-tome last statedebject;in which means are provided for compensating said valve closing means for changes in temperature.

Other and further objects, features, and advantages will be noted from the description which follows, taken in connection with the accompanying drawings in which Figure 1 is a sectional view of a governor constructed in accordance with the present invention, on a plane including the axis of the fuel mixture passage and normal to the throttle valve.

Figure 5 is a sectional View, similar to Figure 1, 7

illustrating a modification of the present invention especially adapted for high altitude operation;

Figure 6 is a fragmentary sectional view showing a portion-of'Figure 5 on an enlarged scale;

Figure '7 is a detailed viewshowing the bimetallic temperature compensating device of Figure 6 in end elevation; and

Figure 8 is a detail view, in perspective, of one of the bi-metallic sprin s of the temperature compensating device of Figure 6.

In order to facilitate an understanding of the invention, reference is made to the embodiments thereof shown in the accompanying drawings, and detailed descriptive language is employed. It willnevertheless be understood that no-limitation of the invention is thereby intended and that various changes and alterations are contemplated such as would ordinarily occur to one skilled in the art to which the invention relates.

Referring now to Figure 4, the straight line ACD denotes a theoretically correct loading curve in which there is a slight, constant increase of speed with reduction in load. In practice, the actual loading curve ACB follows the line ACD as far as the point C, which corresponds roughly to an engine vacuum, below the governor valve, of 17 of Hg. From this point onward, as'the load is reduced, and due to the previously mentioned fact that the forces exerted upon the unbalanced governor valve by the mixture flow change but little with increasing speed in the higher vacuum ranges, the loading curve ACB departs at an increasing rate from the line ACD, the actual departure at no load varying from 200 R. P. M., in the case of well designed governors, to very much larger values in less carefully designed governors. The reason for this departure may bemore readily appreciated by consideration of Figure 3 which illustrates the values of engine vacuum below the governor valve, plotted against R. P. M. It will be seen that when the governor valve is wide open (i. e., the engine is running at below governed speed), the engine vacuum increases very slowly with increase in engine speed. As the engine approaches governed speed and the governor valve begins to close, the increase in vacuum with increase in R. P. M. occurs at a much higher-rate, the curve becoming nearly vertical. Thus, for a relatively slight increase in speed, at engine vacuums representing substantial loads on the engine, the forces acting on the throttle valve increase at a relatively high rate, thus increasing the forces acting on the governor valve accordingly and effecting proper governing action. On the contrary, as the governor valve approaches closed position and the engine vacuum increases further, the curve swings away from the vertical, indicating that such further increase in vacuum is achieved only through an undesirable increase in engine speed.

In order to overcome the described deficiencies in the velocity type governors heretofore used, the present invention employs an additive force,

derived from the engine vacuum below the governor valve, which force comes into play as the governor valve approaches closed position (i. e. in the higher vacuum range) which force, when added to those caused by mixture flow past the governor valve, serves to move the latter to closed position, thus eliminating the undesirable speed increase above noted.

Referring now to Figure 1, the embodiment there illustrated comprises a governor body Ill enclosing a fuel mixture conduit II. The governor body is intended to be inserted in the intake manifold between the carburetor and the engine, and with the conduit ll aligned with said manifold passage, the direction of flow of fuel mixture being indicated by the arrows in Figure 1. The governor valve consists of a throttle plate l2 secured upon a shaft l3 extending transversely through the fuel conduit. It will be noted that the shaft I3 is mounted eccentrically with respect to the fuel conduit, and the throttle plate I2 is mounted eccentrically with respect to the shaft I3, whereby the upstream portion of the throttle plate is considerably larger in area than the downstream portion. The shaft I3 is connected through suitable linkage to a spring balancing mechanism, which linkage and spring balancing mechanism are not shown for the reason that they are conventional and well understood in the art.

The throttle plate l2 is'provided with a projecting arm M, for cooperation with the end l5 of the piston rod l6 of the conventional anti-steal piston I! mounted in the cylinder l8 formed in the governor body. The piston I1 is subjected on its outer face to atmospheric pressure through the vent l9 and filter 2B, and on its inner face to the manifold vacuum above the governor valve through the groove 2| formed in the piston rod iii. The piston is normally maintained in its outward position by a light spring22. The groove 2| may be suitably contoured both transversely and longitudinally, to produce a variable controlled air bleed depending upon the position of rod l5.

The conventional functioning of the anti-steal piston iswell understood in the art and will not be described, except to point out that, ordinarily, the piston rod I6 is in physical engagement with the projecting arm M of the throttle plate l2 only when the latter is at or near full open position and the carburetor throttle is partly closed, thus introducing the engine vacuum to the space between the two throttle-plates. During the intermediate portion of the travel of the throttle plate 12, the piston rod [6 is normally retracted as shown in Figure l and, except for the present invention, the same would be true as the throttle plate approached closed position. However, in accordance with the present invention, the antisteal piston is made use of during the latter por 5 tion of the :throttle .plate travel toward closed position, .fr "exerting thera'dditiye iorceiheretoto the cylinder 18 through the passages Hand 23 is so :largely reduced. by air entering through a the groOVeZl as to be insufiicient to overcome the .force of spring 22. Accordingly, the governor operates in a normal manner, without hindrance from the piston rod 16. 1

However, as the load decreases and the throttle plate I2 aproaches closed position the vacuum below the plate increases and, at the sametirne, the passage 24-is, in effect, transferred from the upstream to the downstream side of the throttle plate and is subjected to the relatively high vacuum existing below the latter under such conditions. The vacuum thus communicated to the cylinder 18 is only partially reduced by the air entering through groove 2|, and is sufiicient to overcome the force of the spring 22 and to cause the piston I7 and the piston rod IE to move inwardly (to the left inF'igure 1), thus causing the .end l5 of the piston rod to impinge upon the arm M of the throttle .plate with a force urging the latter in the closing direction. In this way, the forces normally actin pon the throttle plate to close it are augmented suficiently' so that the undesirable speed increase represented by the lower po'rtionof the curve ACB of Figure 4 is avoided.

Figure 2 illustrates a modification in which .valving means are provided in order that the cylinder 18 shall not be subjected to the engine vacuum until the latter exceeds a predetermined value. In this way, the piston rod fl 6 is prevented from coming into contact with the throttle plate arm l4 during the intermediate ,portion of the throttle plate travel, i. e., under .normallload conditions. In order to effect this purpose, the petssage 24, which otherwise correspondsto th'epassage '24 ,of Figure 1, isprovided with a spring pressedball check valve 25, which is adapted to open only when the vacuumbelow the-throttle plate exceedsa predetermined value, .say '1 7 of Hg. The arrangements of both Figure 1 andE'igure 2 will serve functionally to meetthe requirements as set "forth above. However, it is believed that the arrangement of Figure 1, under certain operating conditions, might be more diflicult to calibrate than that of Figure 2, which latter may therefore possessadvantages' in certain circumstances.

Referring now to Figures "5 to 8 inclusive, .there is illustrated a modification of the invention which is especially .adaptedffor use with engines'operat ing athigh altitudes. It hasbeen recognized that the speed of an engine controlled by a velocity governor changes as the engine operates indifferent altitudes. Thus, 'bo'th'theIiull load and no load .speeds of an engine so governed increase with altitude. In the past,,n0 pa ticular importance has been attached to this phenomenon, it being considered, particularly insofar as ;'full load speed is concerned, actually to; be an ad vantage since such :increase in. speed automaticallyicompensated, toza .degree, the-loss of engine powerincidentrtosthe'reduction in. air density and atm'osph'eric pressure. J

Under 'ipres'ent :day conditions, however, in

whichlzhe-engine'speeds have become'higheriand .the manifold pressures and resultant'iuel velocizties change but slightly with speed, the reduction .in'atmosphericipressure and density with .alti- .tude-meduces the forces ranting-on the governor valve 'to'su'ch an extent :as to materially reduce :the'zelosingeffortenzthervalve,fandthusiincreases theme load speed tmaharm'ful extent. For example ,rit is' :kn'own. that'an engine equipped with a velocity 'type governorrsetioria'no'load speed at zse'at'levl of 130G09- RLtPJJM. to 320.0 R. tP. :M."will, Jat hi'ghaltitudes, reach am load speedas high .as 4ii0ll tb liil TB. M., aspe'ed :in the order-of 30% iii'gherithanithat at which the manufac'- turer'interrded" the engine to operate. Bymeans of -the'zp-resent invention, in the form now to described;'this "tendency is overcome so that the no load speed of an engine remaina'substantially :constant "regardless for the altitude at which it is operatirig.---:Atthe same time-since an increase in afull lo'ad speedxat 'high altitudes has some advantages, it-isrdesirabie that the correctionshall be confined to the *no "load eri'd'of the curve.

fR-eferrin now' to Figure -15, the governor "body '-Z6',.';fuel"-conduit 21,ithro'ttleplate 28, shaft 29, andstl-irottl' plate arm -84! correspond :exaotly'to thoseillustrated in Figure :1 and describedin con-- nection tl'zerewith; 'The bo'dy 26' is likewise pro- 'vided-with"a cylinder 33 corresponding to cylinder I 8 'of Figure 1',"whi'ch cylinder communicates 'at its :outer end with the external "atmosphere through"vent 32 and "filter 33. A piston 34 is :slidably mounted Within the cylinder 3i *and :is "provided wi'th aipis'ton rod. '35 adapted to make contact 11Hd1jCBIt8.in conditions with the throttleplate armifl; EIhe piston 34is'normally maintame-d; in its puterp'osition by aspring '36.

- :Ihe pistonwrod i'35'is 'formed with a groove 31 .providing' communication between the inner" end of'the ccy'linder 39 and the *fuel conduit upstream eff-thegovernor-valve. The piston rod is also :formed with a 'second groove 38, which, when the piston is-in its iinward position, as illustrated in Figure: :5; provides communication between the cylinder SI and thepassage 39 formed'inthe governor'body. The passage 39 communicates at its lower end with a passage M opening 'int'o' the fuel conduit '21- at 'a point downstream of the valve shaft 29 and so disposed .as to be downstream of the lower edge "of-the governor valve plate 28 when the latter is 'at or'near closed'position.

normally closed by means of a 'valve 'M "having a stem 4i which valve is normally held in closed position by a resilient devic 42, the latter being housed in a recess 43 formed'in the governor body. A sealed, gas-filled, expansible .cartridge 44 .is likewise housed within the recess :43, .one end of said cartridge being in engagement with the outer end of stem 4|'-of the'valve 4|. It is intended that the cartridg '54 be filled, in unstressed condition, with a gas such as air; at normal sea level atmospheric pressure. The recess i3 is open to the atmosphere bymeans of passages 45,15;

Aspreviously explained, the vacuum existing between the engine and the governor valve is of a rather high order, extending upto high as 18 to.20"v of Hg. at high 'speedszunder noload; 'ilt is proposedito'employ this .fOI'Ce'ltO create an addi- The open end of the passage 40 is maintained,

described conditions,

tive closing effort on the throttle valve under no load conditions when operating at high altitudes, which efforts, however, shall be removed at normal levels. Thus, when operating at normal levels under a no load condition when the engine vacuum will be of the order of 20" of Hg, the tendency of the valve 4| to open in response to such engine vacuum will be resisted by the spring 42, and the engine vacuum is thus prevented from being communicated to the cylinder 3 l. However, at relatively high altitudes, the entrapped air in the cartridge 44, being at a pressure higher than that existing in recess 43, will tend in conjunction with the high vacuum on the head of valve 4| to expand the cartridge 44, overcoming the force of the spring 42 and opening the valve 4|. The engine vacuum is thus communicated to the passage 39, groove 33, and cylinder 3|. The force thus exerted upon the piston 34 is communicated through the piston rod 35 to the throttle plate 3|] and becomes the above mentioned additive force for urging the throttle plate28 to closed position.

If, however, while operating under the above an additional load is thrown on the engine, the engine speed, will decrease somewhat, reducing the forces normally acting on the throttle valve, and the spring reactance will partially open the latter, forcing the piston rod 35 outwardly and interrupting communication between the groove 38 and passage 39. The cylinder 3| is thus cut off from the engine vacuum below the governor valve, and the additiv closing force thus removed from the latter, thus permitting the engine to run in a normal manner, even though the lower edge of the throttle plate is still above the valve 4|. As greater load is imposed on the engine, and the governor valve opens wider, the lower edge of the throttle plate 28 gradually passes below th valve 4|, transferring the latter to the upstream side of the throttle valve and enabling the spring 42 to retract the valve 4| on to its seat. The combination of the interruption of communication between groove 38 and passage 39, and the transfer of the valve 4| from the downstream to the upstream side of the throttle plate, enables the governor to operate at high altitudes, in the heavier load positions of the throttle plate in the same manner as at low altitudes.

It will, of course, be appreciated that in order to obtain a gradual transfer of forces it may be necessary to provide progressive areas of registration between the groove 38 and the passage 39 and also progressive areas of communication between the fuel conduit 21 and the groove 31 so as to eliminate sudden changes of force and produce, instead, a gradual transfer at such a rate as will bring about a proper functioning of the device as a Whole. This may be accomplished by suitably contouring the grooves 3! and 38 by empirical methods.

The foregoing description has not taken into account the effect of the variation in temperature upon the cartridge 44. It will be appreciated that if the cartridge is sealed at a normal outdoor temperature of say 70 F., as its temperature rises due to engine heat, the enclosed entrapped air will rise in pressure and the force acting to open the valve 4| will be thus increased. In order to offset this factor, the springs 42 are formed of bi-metallic strips of serpentine configuration, although otherbimetal arrangements would be familiar to those schooled in the art, secured in the governor body at their inner ends (46,, Figure 6) and connected at their outer ends by'a grooved washer 41 which also serves to connect them to the valve stem 45, the washer 41 being retained on the valve stem 4| by means of a clip 48. The springs 42 are so constructed that they tend to expand upon an increase in temperature, and are so calibrated as to exactly offsets the tendency of the cartridge 44 to expand upon a like increase in temperature.

Having thus described the invention, what is claimed as new and desired to be secured by Letters Patent is:

1. In a speed governor for internal combustion engines, a governor body enclosing a fuel mixture conduit, an unbalanced throttle plate pivoted in said conduit and having the larger of its unbalanced areas disposed upstream of its pivot axis, means including a pressure responsive element for urging said throttle plate toward closed position, and means for subjecting said element to the engine vacuum when said throttle plate is near its closed position.

2. In a speed governor for internal combustion engines, a governor body enclosing a fuel mixture conduit, an unbalanced throttle plate pivoted in said conduit and having the larger of its unbalanced areas disposed upstream of its pivot axis, means including a pressure responsive element for urging said throttle plate toward closed position, and means for subjecting said element to the engine vacuum when said throttle plate is near its closed position, said last means comprising a passage extending from said element to a point in said fuel mixture conduit downstream from said throttle plate.

3. In a speed governor for internal combustion engines, a governor body enclosing a fuel mixture conduit, an unbalanced throttle plate pivoted in said conduit and having the larger of its unbalanced areas disposed upstream of its pivot axis, means including a pressure responsive element for urging said throttle plate toward closed position, and means for subjecting said element to the engine vacuum when said throttle plate is near its closed position, said last means comprising a passage extending from said element to a point in said fuel mixture conduit, said last point being located below the downstream edge of said throttle plate when the latter is near its closed position.

4. In a speed governor for internal combustion engines, a governor body enclosing a fuel mixture conduit, an unbalanced throttle plate pivoted in said conduit and having the larger of its unbalanced areas disposed upstream of its pivot axis, means including a pressure responsive element for urging said throttle plate toward closed position, and means for subjecting said element to the engine vacuum When said throttle plate is near its closed position, said last means comprising a passage extending from said element to a point in said fuel mixture conduit downstream from said throttle plate, and valve means in said passage adapted to open when the engine vacuum exceeds a predetermined value.

5. In a speed governor for internal combustion engines, a governor body enclosing a fuel mixture conduit, an unbalanced throttle plate pivoted in said conduit and having the larger of its unbalanced areas disposed upstream of its pivot axis, means including a pressure responsive element for urging said throttle plate toward closed position, and means for subjecting said element to the engine vacuum when said throttle plate is near its closedposition, said last means comprising a passage extending from said element to a point in said fuel mixture conduit downstream from said throttle plate, valve means in said passage, and spring means for maintaining said valve in closed position during normal operation under load.

6. In a speed governor for internal combustion engines, a governor body enclosing a fuel mixture conduit, an unbalanced throttle plate pivoted in said conduit and having the larger of its unbalanced areas disposed upstream of its pivot axis, means including a pressure responsive element for urging said throttle plate toward closed position, and means for subjecting said element to the engine vacuum when said throttle plate is near its closed position, said last means comprising a passage extending from said element to a point in said fuel mixture conduit downstream from said throttle plate, valve means in said passage, spring means for maintaining said valve in closed position during normal operation under load, and meansfor opening said valve against the pressure of said spring when the barometric pressure of the surrounding atmosphere becomes substantially less than normal sea-level barometric pressure.

7. The combination defined in claim 6, said valve opening means comprising a sealed, gasfilled expansible cartridge, one wall of said cartridge operatively engaging said valve.

8. The combination defined in claim 6, said valve opening means comprising a sealed, gasfilled expansible cartridge, one wall of said cartridge operatively engaging said valve, and said spring being of temperature-compensating construction to counterbalance the effect of atemperature increase on said cartridge.

9. The combination defined in claim 6, said valve opening means comprising a sealed, gasfilled expansible cartridge, one wall of said cartridge operatively engaging said valve, and said spring being of serpentine, bimetallic construction to counterbalance the effect of a temperature increase on said cartridge.

10. In a speed governor for internal combus-' tion engines, a governor body enclosing a fuel mixture conduit, an unbalanced throttle plate pivoted in said conduit and having the larger of its unbalanced areas disposed upstream of its pivot axis, means including a pressure responsive element for urging said throttle plate toward closed position, and means for subjecting said element tothe engine vacuum when said throttle plate is near its closed position, said throttle plate having a projecting arm, and said pressure responsive element comprising a cylinder associated with said governor body, a piston in said cylinder and subjected to atmospheric pressure on its outer end, and spring means for urging said piston toward its outward position, said piston having a rod extending through and closely fitting a bore in said governor body and projecting into said conduit and adapted to engage said throttle plate arm.

11. The combination defined in claim 10, said piston rod being formed to provide a communicating passage between said cylinder and said conduit.

12. The combination defined in claim 10, said piston rod being formed to provide a communicating passage between said cylinder and said conduit, the cross-sectional area of said passage varying along its length, whereby the area of the opening between said rod and said body varies with movements of said piston.

13. In a speed governor for internal combustion engines, a governor body enclosing a fuel mixture conduit, an unbalanced throttle plate pivoted in said conduit and having the larger of its unbalanced areas disposed upstream of its pivot axis, said throttle plate having a projecting arm, a cylinder associated with said governor body, a piston in said cylinder subjected to atmospheric pressure on its outer end, said piston having an extension projecting into said conduit and adapted to engage said throttle plate arm, said extension being formed to provide a communicating passage between said cylinder and said conduit and a second passage extending from said cylinder into said governor body, spring means for urging said piston toward its outward position, a passage opening into said conduit at a point downstream from said throttle plate and extending in said valve body to a point adjacent said piston extension, whereby said last passage and said second passage intercommunicate when said piston is in an inward position, a valve in said last mentioned passage, spring means for maintaining said valve normally closed, and means for opening said valve against the pressure of said spring when the barometric pressure of the surrounding atmosphere becomes substantially less than normal sea-level barometric pressure.

14. The combination defined in claim 13, said valve opening means comprising a sealed, gasfilled expansible cartridge, one wall of said cartridge operatively engaging said valve.

15. The combination defined in claim 13, said valve opening means comprising a sealed, gasfilled expansible cartridge, one wall of said cartridge operatively engaging said valve, and said spring being of temperature-compensating con-- struction to counterbalance the effect of a temperature increase on said cartridge.

16. The combination defined in claim 13, said valve opening means comprising a sealed, gasfilled expansible cartridge, one wall of said cartridge operatively engaging said valve, and said spring being of serpentine, bimetallic construction to counterbalance the effect of a temperatuie increase on said cartridge.

REX C. DARNELL.

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