US2475717A - Automatic spark advance mechanism - Google Patents

Description

JulyiZ, 1949. I w. OSTLING 2,475,717

AUTOMATIC SPARK ADVANCE MECHANISM Filed Feb. 20, 947 2 Sheets-Sheet l I N VEN TOR.

h il liam' Osilin A T TORNZ Y- vacuum July 12, 1949. OSTUNG 2,475,717

AUTOMATIC SPARK ADVANCE MECHANISM Filed Feb. 20, 1947 2 Sheets-Sheet 2 TEK'.

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' 7 BY ,'l iam Osilz'hg Patented July l2, 1949 UNITED STATES PAT OFFICE AUTOMATIC SPARK ADVANCE ISM William Ostling, .Los Angeles, cans, 'ass ignor to California Machinery and Supply Company, Ltd., Los Angeles, 'Calif., a corporation of'Dlaware Application February 20, 1947, Serial No.1729i688 4 Claims. v1

As :is well recognizedin this art, the spark =timing has a major effect upon the efficiency of operation of a spark ignition engine. .In order to obtain maximum power, ignition must occur =before-the compression stroke is completed, that is, before top dead center is arrived at by the piston, because the combustion process requires a finite time and it is desirable that the maximum pressurebe developed in the cylinder before the expansion of the power stroke begins.

As will be :seen laterand as well knownin this art, the higher the engine speeds, that is the higher the linear velocity-of the piston, theearlier must be the spark, in order that the combustion process have sufficient time to generate the maximum pressure by the time the piston reaches top dead center. The optimum position for the spark in relation to the stroke is determined by laboratory experimentation, as will be more .fully set forth below.

Theinterval between the time of the spark and the arrival of the piston at top dead center is termed the spark advance. The earlier the spark is generated in the compressionstroke of the engine, the more advanced is the spark, and the nearer to the time of arrival of the piston at top dead center, the more retarded is the spark. The degree of spark advance may be measured interms of the crank angle.

While the degree of spark advanceis a function of engine speed, it is alsoa function-of throttle position. Thus, at any engine speed the degree of spark advance desirable for part-throttle operation is greater than that required for full throttle operation. The adjustment of .thespark the form of a nut with lobes equal in number to the vnum'ber of cylinders fired by the distributor. Surroundingthe cam shaft and concentric therewith .isa non-rotating breaker plate upon which ,Iismounted a breaker, the function of which is to open. the circuit of the-i nition system so that the condenser discharges across the cylinder -plug points. The angular relationship between the breaker and the cam determines the point in the stroke of the piston rwhenthe breaker points will separate and the spark will jump.

The term fullload refers to that load .which it is rimposed upon the engine at full open throttle position at any given speed. In other words, it is people of average sizewhendriving on a straight road without acceleration. "This ratherarbitrary loading correspondsto -about a B5'"throttle opening at speeds ofabout MOO'RJP. R-oadload 'maythus be stated as the load imposed "on an engine operating "at 3400 R. P. at sea level with'the'throttle, for example, at from fully closed. With such road load "imposed on the engine, as the throttle isopenedbeyond 35 the engine speeds up under such-=constant road load, and as the throttle is closed the engine slows down.

In order to-=deterrriine the best spark position for all conditions ofoperation ofthe engine, the engine is tested under load eitherzin a dynamometer or onthero'ad and the sparkis set manually by adjusting the brea ker plate for ail conditions "of throttle "position andrspeed to establish :what

is known -a'srthe aideal *spark advance curves for *full load and road load positions. If the spark is controlled to advance aalong these 'curves at full load and road iloaditheytwill 'iaisoibe adequate'at intermediate load conditions. :Such curves and spark advance settingsare hereafter referred to as ideal or optimum ourves or. settings.

During cranking .andisidling the spark for best operation is :retarded. When operating atroad load, the wsparke'should be advanced, the degree of advanc'eibeingigreaterzas the:speed 'atrroad load operations is higher. the throttle is opened wider to iull throttle position lfor full load: operations the sparkis best rretarded, but at full throttle operation thetspark should be :more advanced the higherrthe speed at full load, i. e.,-wide open irottle.

Spark ignition internal combustion engines,

particularly those used in the automotive -field,

have devices forautomaticallyadjusting the spark advance inrelation to engine speed and alsoin relation .to the throttle ,position at such engine speed. One method employed is to attach the cam to centrifugal weights which are rotated by the cam shaft. As the engine speed increases the weights move out under centrifugal force and rotate the breaker cam relative to the drive shaft, thus advancing the spark. However, since at part throttle operation a greater spark advance at any engine speed is desirable than that for full throttle operation, it is desirable that the spark advance mechanism at part throttle operation advance the spark an amount in addition to that which is obtainable from the centrifugal spark advance mechanism. In one standard type of such device now employed the breaker plate is advanced above that obtainable from the centrifugal weight by means of a link connected to a pneumatically operated power means for actuating the link. This means is conventionally a diaphragm positioned in a chamber which is in turn connected to an orifice positioned at the throttle in the air fuel induction system.

In another form of such automatic spark advance, such as represented by the Vanderpoel and Ostling Patent No. 2,249,446, the centrifugal weights are omitted and the entire advance is pneumatically controlled.

In addition to the orifice positioned at the throttle, an orifice is placed either at the main carburetor Venturi or at an auxiliary Venturi, as described in the co-pending application Serial No. 694:, 266, filed August 31, 1946, by Garth L.

Young and William Ostling. A by-pass is pro-v vided between the two orifices which are in turn connected to the pneumatic power means,

specifically the diaphragm chamber similar to that described above. If desired a check valve may be placed in this by-pass. arrangement the centrifugal weights may be entirely omitted and the spark advance may be obtained entirely by the rotation of the breaker plate by means of a stem connected to the diaphragm in the diaphragm chamber.

With such an arrangement at idling position the throttle orifice is on the carburetor side of the throttle and the velocity is so low that the vacuum generated is low. It is insuflicient to advance the spark. When the throttle is opened to part throttle position the throttle orifice is on the manifold side of the throttle and is subjected to the vacuum of the intake manifold but this vacuum is in part bled through the Venturi orifice which is, of course, at a higher pressure,

' i. e., lower vacuum, and this modifies the excessive vacuum thus created by the manifold and the spark is advanced. When the throttle is opened to full open position, such as in the full load operation, the manifold vacuum drops substantially and is at practically atmospheric, but due to the velocity of the gases through the Venturi there is a vacuum at the Venturi orifice which prevents the spark from being retarded to the degree it would have been if it had only been subjected to the manifold vacuum.

By positioning the check valve when the pressure at the Venturi is lower than at the throttle orifice, as it is in full throttle position, the check valve closes so that the vacuum generated at the Venturi is not bled by the higher pressure in the manifold, and thus the advance of the spark is increased over that which would have been obtained if the check valve had not been present.

It is an object of my invention to improve the operation of such spark advance mechanisms.

As is generally well recognized in this art, with I such devices the suction exerted at road load (part throttle operation) may be excessive,

With such an especially at intermediate engine speed, and over advance the spark if the advance at full load is any where near that which is desired at full load.

Additionally, vacuums at road load in the diaphragm chamber, where the spark advance mechanism is employed with carburetors having but a throttle orifice and no Venturi orifice, fall rapidly as soon as engine speeds reach an upper limit, for example, about 1000 to 2000 R. P. M. This causes a retardation of the spark, i. e., an insuificient advance at such engine speeds. In order to obviate these excessive high vacuums, especially at lower and intermediate speeds, speeds under road load conditions, auxiliary bleeds have been introduced to bleed down the vacuum attained at the throttle orifice.

The difficulty with such bleeds is that they are non-selective in that they bleed at all positions of the throttle at low and intermediate engine speeds. Thus, while they will bleed the excessive vacuums at low engine speeds under road load conditions, they will also bleed the insufficient vacuums attained at high engine speeds under .road load conditions.

In another form of such device, the bleed orifice is positioned in the throat of the main carburetor Venturi as in the Vanderpoel-Ostling Patent No. 2,249,446 or in an auxiliary venturi as in the improved modifications of the Vanderpoel-Ostling type disclosed in the above copending application Serial No. 694,266.

The Vanderpoel-Ostling type of spark advance control avoids this excessive bleeding at high engine speeds by positioningthe throttle orifice bleed at the throat of the carburetor Venturi so that the pressures created in the throat at the high engine speeds do not excessively bleed the suctions created at the throttle orifice at high engine speeds under road load operations. Additionally a check valve may be introduced into the bleed by-pass to shut off the throttle orifice when the throttle opens so widely that the pressures at the throttle orifice are actually greater than at the Venturi orifice.

In this manner while the excessive vacuums at low engine speeds are bled down to prevent an over advance at low engine speeds, the pressures created at the throttle orifice at higher engine speeds are not bled down but the effective suctions are actually higher than that occurring at the throttle orifice. But even with this type of bleed the suctions created at road load speeds may, for some engine designs, be excessive to give an over advance of the spark if the advance at full load is of satisfactory character.

It is desirable that the automatic spark advance mechanism approximate as closely as possible the spark advance curve obtained both at full load and road load over all engine speeds under 0 laboratory conditions, i. e., the ideal or optimum spark advance curve.

In the case of the governor controlled spark advance of the prior art, this may be accomplished by adjusting the advance caused by the governor with increase in engine speed and also by adjusting the retarding spring tension in order to determine the advance obtained by the vacuum. In this way the rate of advance with engine speed caused by the governor is controlled and the rate of advance with increase in vacuum is also controlled. It is usually possible by these controls to establish the full load spark advance curve in close approximation to the ideal curve. However, the difficulty is much greater when the road load 5 advance curve is considered. Since the adjusteliminated by the use of the auxiliary throttle orifices. These throttle orifices are positioned so that at full open throttle all of the throttle orifices are on the manifold side of the throttle.

The throttle orifices are also on the manifold side of the throttle when it is in the position at road load necessary to give the upper engine speed selected for such throttle position at such road load.

When the throttle is at idling position all of such throttle orifices are on the carburetor side of the throttle. At all intermediate positions of the throttle some of the orifices are on the manifold side of the throttle and an orifice or orifices are on the carburetor side of the throttle. The result of this construction is that the auxiliary throttle orifices on the carburetor side of the throttle bleed the throttle orifices on the manifold side of the throttle at all positions of throttle opening under road load operations in which the engine speed is below a predetermined upper limit.

The greatest retard is attained at the lowest speeds. These orifices will also reduce the degree of retard as the speeds increase and will cause no additional retarding action over the effectof a single orifice at the high engine speeds but will all act together as a single throttle orifice.

This invention and the objectives thereof will be more fully understood by reference to the accompanying drawings, in which Fig. 1 is a view partly in section of a carburetcr construction of the Vanderpoel-Ostling type including the improvements of the present invention, and of a spark advance mechanism suitable for use in connection therewith;

Fig. 2 is a fragmentary view taken along line 2-2 of Fig. 1, showing the position of the throttle at idling;

Fig. 3 is a similar view with the throttle at a to an air supply. Air passes through passageway 2 past fuel nozzle 3 in the venturi 4. The throttle 5 is positioned in the air fuel passageway '6. A bore forming chamber 1 farmed in the wall of the passageway 6 into which bore open a plurality of orifices formed in the wall of the passageway 6. Three in number, 8, 9, and H], are shown, although I may employ two or more than three, as will be understood by those skilledin this art from the present description of my invention.

All of the orifices open into chamber 1. The position of the orifice 3, and therefore of 9 and I0, is such that when the throttle is in idling position. shown solid in Fig. 1, the orifices 8, 9, and H1 are on the Venturi side of the throttle. The distance between. centersof the orifices 8, 9, and I9 measured parallel to, i. e., along the longitudinal axis of 6, is such as to place all of the orifices on the manifold side of the throttle when the throttle is in road load position as illustrated at 5'. The distance between centers of the orifices measured in. a direction perpendicular to the axis of 6 is dictated by the necessity of leaving sufficient metal between the orifices and also by degreeof bleed required at various iii throttle openings. It will be observed that the closer the orifices 9 and I0 are placed to the axis of 6 when measured as a projection on the plane passed through the carburetor perpendicular to the pivotal axis of 5 (see Fig. 1) the less the throttle opening upon which they will be placed on the manifold side of the throttle.

The spacing of the orifices and their diameter will be further described in connection with the discussion of Fig. 7.

The chamber 1 is connected by by-pass [2 to the orifice II which is positioned at the throat of the venturi 4. The ball check valve I3 is positioned in line I2 and is held again-st the seat l5 by the spring 14, which is just sufiicient to overcome gravity, and thus holds the ball 13 against its seat when pressure is equalized on both sides of the valve, i. e., in chamber 1 and at the orifice II.

The by-pass I2 is connected to the pneumatically operated spark advance mechanism (of construction forming no part of my present invention) by line 56 which connects to chamber [1 in which is the diaphragm [8. Chamber H is at the vacuum generated by the carburetor. The chamber l9 underneath the diaphragm is at atmospheric pressure. The retarding spring 11' holds the diaphragm down and the mechanism in full retard. The advance is caused by the motion of the diaphragm which is connected by rod 28 to the breaker plate 2| carrying the circuit breaker 22 which cooperates with the breaker cam 23 rotated at half engine speed by the cam shaft The plate 21 carries a hole 25 which cooperates with a pin 26 positioned on an angularly adjustable bracket in the case of the device whereby the initial advance setting, when vacuum in IT is zero and the maximum permissible advance irrespective of the magnitude of the vacuum in l1,'is obtained,.as is conventional in this type of spark advance construction.

Referringto Fig. 7, line A gives the variation in vacuum (measured as the difference in pressure in inches of mercury between 17 and atmospheric) occurring on the vacuum side of the diaphragm chamber I! for full load, i. e., wide open throttle operation at speeds ranging from 400 up to 3400 R. P. M. The consequent full load advance for a particular case, chosen to explain and illustrate the principles of my invention, is illustrated in B. The initial advance setting was at 5, the vacuum being 0 at speeds up to 600 R. P. Since at full load operation, 1. e., wide open throttle, the auxiliary orifices 8, 9, and II! have substantially no difierential effect upon the total vacuum, the full load advance is substantially the same where the auxiliary orifices 8, 9, and ID are employed as when a single orifice of area approximately equal to the area of the throttle orifices 8, 9, and I0 is employed.

The effect of these auxiliary orifices 8, 9, and II] upon the spark advance is, however, illustrated by reference to curves C and D. Curve (3' gives the vacuum in the diaphragm chamber [1 in the Vanderpoel-Ostling type of mechanism where only a single throttle orifice of the same character as 8 is employed. It will be observed that in the case illustrated this vacuum rises sharply from low speed up to 1400 R. P. M., this being in the region where the throttle is opened sufficiently to pass the throttle orifice from the carburetor side to the manifold side of the throttle.

The advance for the particular chosen case is shown in curve D. It will be seen that the advance is very rapid dueto the rapidly increas= vacuum existing. in the. throttle orifices.

result is a very rapidandsharp advance. Since etspeeds of about 1400.12.31. M. the throttle is sufficiently wide open. so that the total vacuum nolonger increasesnas rapidly as engine speed l-but flattens asis evident. from curve C, the rate of spark advance with increasing speed also. diminishes until when at a speed of about. 2150 M., whenthevacuuinin l.l is9 inches, the advanceof the plate 2t comes against the stop 2.5 at a spark advanceof 5.0."... It is thus maintained at substantially the same point until a speed of about 3.100R. P... M. is obtained, during which. period. the vacuumisgreater than 9 inches, as is seen from curve C. When the throttle has become so wide open at speedsabove about 3200 .R. P. .M. the manifold pressure. starts dropping .slimciently to cause the total vacuum in the diaphragm chamber to .drop below 9 inches and the spark isretarded from 50. to 48 at 3400 R. P. M. It. will .be noted,fho.wever, that the vacuum peak is. at speeds above about 2400 R. P. M. and that drop in vacuum at higher speeds is. prevented from becoming excessively sharp, as would be the result. iflit were controlled entirely by the throttle orifice, because at this point the manifold pressure has become less than the pressure at the jVenturi orifice and the check valve is closed. The vacuum is therefore controlled entirely by the Venturi orifice and. is prevented from dropping to a low value, so that the spark advance is maintained at the high point indicated by curve D.

A reference to curve E, willv show, however, that in such case the spark. is excessively advanced. Curve E. represents the ideal advance curve, for the particularly chosen illustrative case, such as. is obtained by manual adjustment under laboratory conditions, giving the ideal road. load advance. at various engine speeds- It will be observed that the spark advance, curve D, has been made. to.- match the ideal advance curveat high engine speeds, but that it is over advanced at all other speeds. Curve B corresponds to the. so-calledideal full load curve, showing that the tensionof spring l1 and the orifices havetbeen. made. to. obtain the desired full load advance.

The effect of the auxiliary orifices 9 and. H) onthe vacuum. in. t1 tocorrecttthe over advance at lower engine speedsis evident-by reference to curve F. As the throttle moves from idling positiontolpartthrottleposition at a Speedof L400 R. P. M. orifice. 8 is placedonthe manifold side of-the throttle, while orifices 9. and 10 are. on the carburetor side. of thethrottle, as.is,,ot course, the. Venturi orifice. The high vacuum of the manifold is not. tully exerted underneath. the valve l3, since it is modified by the higher pres.- .sure existing in. theair f-uel. passage on. the car- .buretor side of. the throttle at. orifices: 9 and I0. Since, however, the. total pressure. thus effected in. the chamber. 1 is. less than that. exerted at theLVenturi orifice Ilf,.the. valve I'3 remains open. However, the .net of this. combination is to createavacuumin the chamber 1. which is less than would have been exerted had only orifice 8 been employed, the other orifices 9 and lfl being. omitted] as in the, original Ostling-Vanderpoel arrangement. The net vacuum. thus produced in chamber 1 at 1400 R. P. M. .isshown at. curve which shows. that. when this situation has oocurred at. about 1400B. P. M., the total vacuum is. 2.5 inches as. compared to 5.8 inches when only one throttle orifice. has been employed. The advance resulting is '38 whi'ch corresponds to the ideal advance at. such speed and throttle posisition, as given in curve E. As the throttle is opened widerthev space between. the periphery of the throttle and the. conduit wall is increased and the vacuums at. the throttle orifices rise due to inereaseinspeed of theengine until at a speed of .2200. PQM. the. throttle is opened sufficiently to place orifice 9 on the manifold. side of the throttle, leaving only orifice. ID on the carburetor side of the. throttle. Because of the bleeding effect of orifice l0, as well as that of the Venturi orifice III, the vacuum generated in the chamber [1 is not. as. great as occurred in the original Vanderpoel-Ostllng. arrangement. As is seen from curve Elf-the vacuum thus generated at 2200 R. corresponds to 4.5 inches instead of 9.2 inches of mercury (curve C) and the advance thus obtained at this R. P. M. corresponds. to 461, and this will be. seen to be the ideal advance atthi's speed (curve E). As the speed is increasedby the further opening of the throttle at 33200311. P. M.,.the third orifice I0 is now placed on the manifold side of the throttle. Therefore, since all three orifices are now on the manifold side of the throttle, the vacuum generated corresponds to that generated when only one orifice it is employedli. e.,.9 inches, and corresponds to 50.. The advance thus. obtained. is that obtained under thev operation according to curve C which, it will be seen, is coincident with that of curve F. At this. point the throttle. is substantially at road" load position, i. e.,. part throttle position and allofthefthrottle orifices 8, 9, and [0- are on. the. manifold sideof the throttle. The curve Fis shown dotted, indicating that the intervals between 4 and. 1400. R. P. M. and between .1400 and 22003.. P. M., and between. 2400 and 3200 R. P. M. need not necessarily be a straight line as indicated onF. However, the advance curve. obtained with the orifices 8,. 9, and I0 fits the ideal curve at the speeds 1400, 2200and. 3200 R. P. M. and. will fit quite. closely at intermediate speeds.

It willthus be seen. that where, as in. the Vanderpoel-Ostling type of spark advance control, the advance is excessive at. low engine speed and approximates more closely the desired advance at high engine. speeds I amable. to modify the advance. at low engine speeds Without disturbing the advance at high engine speeds and thus am able to fit. theadvance to the ideal advance curve throughout the range. of engine speeds without affectingthe full load advance- It willbe recognized. that since. at full load the throttle is wide open all three orifices function in substantially the same way as a single orifice. The check valve, if one is employed..closes, as in the case of the Vanderpoel-Ostling device employing a check valve, permitting the full vacuum existing at the venturi to be exerted in the diaphragm chamber and to give the full. load advance which is thus obtained with a single or a plural type ofthrottle orifice construction, i. e., the vacuum of line A and the advance of line B; In the case of the plural throttle orifices employed with a V'andeipol-Ostling device without check valve,a similaraction obtains.

By altering the size of the orifices, their number and distribution at the throttle, the effeet at various enginespeeds at various throttle positions may bealtered to modify the total vacuum generated at any engine speed at road load operation in the desired manner to fit the advance obtained to that desired. Thus, by providing a number of orifices at the throttle so that as the throttle is opened wider and wider the orifices are shifted from the carburetor side of the throttle to the manifold side of the throttle, the net vacuum existing in the diaphragm chamber may be controlled to the desired variation with engine speed to give the desired degree of advance with variation in engine speed at road load operations.

rom what has been said above, it is apparent that the auxiliary orifices act to cause a retardation of the spark above that which is attainable with a single throttle orifice and their utility is therefore of primary value where the spark advance mechanism employing such throttle orifice causes an over advance of the spark at all engine speeds at road load below an upper engine speed at which the single orifice gives the desirable advance. Such a situation is particularly the case in the Vanderpoel-Ostling type of control mechanism for certain motor designs. In such construction the bleed of the single throttle orifice by means of the Venturi orifice is supplemented by the auxiliary throttle orifices which also bleed the manifold vacuum at throttle openings which are less than that setting required to obtain the aforementioned engine speed chosen as the definition of road load conditions.

In Fig. 6 is shown a slot which in effect is cut through the orifices 8, 9, and Ill and acts in the same manner as the auxiliary orifices 8, 9, and H! except instead of the effect being discontinuous, represented by the stages of bleed as the throttle traverses each orifice serially, the bleed changes continuously as the proportion of the slot, on the manifold side of the throttle to that on the Venturi side of the throttle, changes as the throttle is opened wider and wider until at road load operation at high speeds all of the slot is on the manifold side of the throttle, whereas at idling speed the slot is entirely on the Venturi side of the throttle.

The specific values of the vacuums and advance as shown in Fig. 7 and as described in the specification discussing said figure, and the specific values of throttle position and speed and loading chosen to describe road load, are employed as illustrative only and not as a limitation of my invention. The specific values of the vacuums and of the advance and their variation with engine speed will vary with engine design and with the values of the throttle opening, speed and loading chosen as the definition of road load. The positioning of, sizes and number of throttle orifices which are desired will depend on the above factors and upon the specific nature of the carburetor construction. However, by applying the principles described above, those skilled in the art will be able to produce the desired spark advance variation with speed desired at full load and at that degree of loading (throttle position and speed) chosen as road load.

While I have described a particular embodiment of my invention for the purpose of illustration. it should be understood that various modifications and adaptations thereof may be made within the spirit of the invention as set forth in the appended claims.

I claim:

1. An automatic spark advance mechanism for spark ignition engines, comprising a carburetor including an air inlet and a fuel inlet to said carburetor, an air passageway, a venturi in said passageway, an orifice at said venturi, a throttle in said passageway, means for attaching said passageway to the intake manifold of a spark ignition engine, a plurality of orifices positioned in the wall of said passageway at said throttle, said orifices being disposed at said throttle longitudinally of the axis of said first mentioned passageway and spaced along said wall in relation to said throttle to be on the carburetor side of said throt tle when said throttle is in idling position and all of said throttle orifices are on the manifold side of said throttle when said throttle is in road load position, at part open throttle at a predetermined upper engine speed, a conduit connecting said orifices at said throttle and said orifice at said venturi, and a tube for connecting said conduit to a pneumatic spark advance mechanism.

2. An automatic spark advance mechanism for spark ignition engines, comprising a carburetor including an air inlet and a fuel inlet to said carburetor, an air passageway, a venturi in said passageway, a throttle in said passageway, an orifice at said venturi, a conduit connected to said air passageway at said venturi and at said throttle, the connection at said throttle extending longitudinally of said passageway forming an inlet into said conduit at a plurality of points along said passageway said throttle being positioned in respect of said connection of said conduit at said throttle so that when the throttle is in closed position said last-named point of connection is between the throttle and the air inlet and when the throttle is in part open position the conduit is connected to the air passageway at a point between the throttle and the air inlet and also beween "the throttle and the intake manifold connection, a tube connected to said conduit and adapted for connection to a pneumatic spark advance mechanism.

3. An automatic spark advance mechanism for spark ignition engines, comprising a carburetor including an air inlet and a fuel inlet to said carburetor, an air passageway, a venturi in said passageway, an orifice at said venturi, a throttle in said passageway, means for attaching said passageway to the intake manifold of a spark ignition engine, a plurality of orifices positioned in the wall of said passageway at said throttle, said orifices being disposed at said throttle longitudinally of the axis of said first mentioned passageway and spaced along said wall in relation to said throttle to be on the carburetor side of said throttle when said throttle is in idling position and all of said throttle orifices are on the manifold side of said throttle when said throttle is in road load position, at part open throttle at a predetermined upper engine speed, a conduit connecting said orifices at the throttle and venturi, a tube adapted for connecting to a pneumatic spark advance mechanism connected to said conduit.

4. An automatic spark advance mechanism for spark ignition engines, comprising a carburetor including an air and fuel inlet to said carburetor, an air passageway, a venturi in said passageway, a throttle in said passageway, an orifice at said venturi, a conduit connected to said first passageway at said venturi and at said throttle, the connection at said throttle to said conduit extending longitudinally of said passageway to provide an elongated connection of said conduit to said passageway said throttle being positioned in respect of said throttle connection of said conduit so that when the throttle is in closed position said 14 last-named point oi connection is between the REFERENCES CITED throttle and the air inlet and when the throttle is in part open position the conduit is connected y igg gi z are of record in the to the first passageway at a point between the v p throttle and the air inlet and also between the 5 UNITED STATES PATENTS throttle and the intake manifold connection, a Number Na tube connected to said conduit and adapted for 2249 446 vandeggel et a1 81941 connection to a pneumatic spark advance. 2:335:424 Schachenman l 1943 WILLIAM OSTLING.

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