US3161186A - Method and means for improving acceleration of small engines - Google Patents

Description

15, 1964 J. v. REICHENBACH ETAL 3,

METHOD AND MEANS FOR IMPROVING ACCELERATION OF SMALL ENGINES Filed April 5, 1965 2 Sheets-Sheet 1 1964 J. v. REICHENBACH ETAL 3,161,186

METHOD AND MEANS FOR IMPROVING ACCELERATION OF SMALL ENGINES Filed April 5, 1963 2 Sheets-Sheet 2 Jasgzvk 17 Ema/71 2mm United States Patent This invention relates to internal combustion engines, and refers more particularly to improvements in carburetion of small, simple gasoline engines not equipped with accelerating wells or accelerating pumps, to improve acceleration of such engines from slow idling or running speed.

It is well known that relatively fast opening of the throttle of an internal combustion engine, to cause the engine to accelerate quickly from a slow idling or running speed, requires enrichment of the fuel-air mixture being fed to the engine, and that the enrichment of the mixture should continue for a short time after throttle opening and until the engine has attained a speed substantially above idling.

One reason such mixture enrichment is needed is that the carburetor venturi is primarily designed for the conditions that prevail at the higher range of engine speeds. When the throttle butterfly is moved part way from its closed position, the increase in air flow rate through the carburetor throat does not produce an immediate corresponding decrease in air pressure at the fuel jet, or in other words, the suction by which fuel is educted into the combustion air does not increase at the same rate as the ilow of combustion air increases. The engine is therefore starved for fuel and cuts out unless additional fuel is in some manner added to the combustion air during and for a short period after opening of the throttle.

In large engines, such as those used on automobiles, it is conventional to provide an accelerating pump in the carburetor, by which an extra spurt of fuel is injected into the combustion air flowing to the engine whenever the throttle is opened abruptly.

On smaller engines, however, such as the single cylinder engines used on lawn mowers, garden tractors, portable sump pumps and the like, the provision of an accelerating pump is not practicable. For one thing, such an accessory would have to be of such small size as to require the maintenance of extremely close tolerances in its manufacture.

Another and perhaps more important consideration is that small engines are ordinarily equipped with overspeed governors, which would interfere with proper operation of an accelerating pump. The overspeed governor comprises an engine speed responsive element which is so linked to the throttle valve as to tend to close the same as engine speed increases, and which is spring biased in the direction to effect opening of throttle valve. The biasing force which the governor spring exerts upon the speed responsive element is regulated by means of a manually adjustable engine speed control member which is connected to the governor spring but has no other connection with the throttle valve. Hence when the speed control member is abruptly moved from its low speed to its high speed setting, the throttle valve opens substantially in unison with it, but as the engine comes up to speed, the speed responsive element of the governor begins to effect closure of the throttle to prevent overspeeding.

If an engine with such an overspeed governor were provided with an accelerating pump having its plunger actuated by a linkage to the throttle valve, the arrangement would result in an unstable hunting of engine speed. Upon initial opening of the throttle the acceleratin pump would provide sufiicient mixture enrichment to 3,161,186 Patented Dec. 15, 1964 brin the engine up to a high speed at which the governor would cause some closing of the throttle valve, whereupon the engine speed would again drop abruptly as the accelerating pump stoppedenriching the fuel-air mixture. This speed reduction would in turn bring about another opening of the throttle, initiating another cycle of engine acceleration and deceleration.

While the problem of hunting might be overcome by a direct linkage between the manually controllable speed adjusting member and the accelerating pump plunger, such a linkage would have to be tailored to each of the many different installations in which an engine might be used, and therefore would not be practical, especially since it would further add to the cost of the accelerating pump itself.

Heretofore the problem of poor acceleration characteristics in small engines equipped with overspeed governors has been solved by adjusting the engine to idle at a relatively high speed, sufiiciently fast so that special enrichment of the fuel air mixture is not needed upon abrupt opening of the throttle from its lowest speed position. Thus a conventional small engine is inherently capable of idling at 500-700 r.p.m., but heretofore if it had been permitted to idle at such a low speed it would have cut out whenever the manual speed adjusting control was moved from the idle to the high speed position with any degree or" rapidity. To avoid this, such engines were therefore adjusted to idle at about LOGO-1,200 r.p.m., with a somewhat rich mixture adjustment at the idle setting.

Operators of appliances powered by small gasoline engines have become conscious of the relatively limited speed range of such power plants. They know that the engines of their automobiles idle at relatively low speeds and accelerate rapidly when the throttle is opened, and it is only natural that they should expect somewhat the same speed range and acceleration characteristics from the small engines which power garden tractors, riding mowers, snow blowers and the like.

Heretofore the industry has accepted the limited practical speed range of the small engine as an inevitable sacrifice that was instilled by considerations of cost and expediency and which was not of any real consequence because a small engine is normally intended to be operated at its top speed whenever it is under load. Without in anywise implying that mere gratification of the consumers wishes is not sufiicient warrant for making changes, it is to be noted that there may be applications in which satisfactory provision for very low idling or runnin speed in a small engine is desirable or even necessary, so that the attainment of this objective Without incurring a substantial increase in engine cost is in every sense practical and useful.

Thus it is an object of the present invention to provide, in a small internal combustion engine not equipped with an accelerating pump, a very simple and inexpensive means for automatically enriching the fuel-air mixture during acceleration of the engine from a low idling or running speed, to thus achieve very smooth and rapid acceleration of the engine even though it is equipped with a governor, thereby permitting such an engine to be idled at speeds much lower than have heretofore been considered practicable.

Another important object of this invention is to improve the acceleration performance of a small engine equipped with an overspeed governor, to thus permit a substantial reduction of its practical idling speed and hence a substantial extension of its speed range, all without interfering in any manner with the overspeed governor or its operation and without entailing hunting of engine speed.

Still another object of this invention is to provide means for effecting enrichment of the fuel-air mixture being fed to an internal combustion engine during acceleration from a low idling speed, whereby enrichment of the mixture is diminished as the engine picks up speed, and at substantially the same rate as speed increases, to thus maintain the mixture ratio in step -withthe requirements of the engine during its acceleration.

It is also an object of this invention to utilize for the purpose of obtaining automatic mixture enrichment during acceleration; the choke butterfly that is conventional on small engines, without in any wise interfering with the normal operation of the choke in starting, andto provide wery simple and inexpensive mechanism that canbe installed on existing engine carburetors with only very minor modification thereof to effect the automatic operation of the choke butterfly by which such mixture enrich ment during acceleration is obtained.

With the above and other objects in view which will appear as the description proceeds, this invention resides in thenovel means substantially as hereinafter described and more'particularly defined by the appendedclaims, it being understood that suchlchanges in the precise embodiment of the hereindisclos'ed invention may be made as come within the scope of the claims.

The accompanying drawings illustrate one complete example of the physical embodiment of the invention con-.

structed according to the best mode so far devised for the practical'application of the principles thereof, and in which: a a

FIGURE 1 is a perspective view of a small gasoline engine having its carburetor equipped with means embodying the principles of this invention for automatically enriching fuel-air mixture during acceleration, portionsof the engine blower shroudrand carburetor being broken away, and the apparatus being shown in its idling condition;

a a of combustion air into, the mixing zone 11, thus increas- -ua1sqns a fi'u snao pus suoz fiurxrur s in uonons etp Eur tially larger proportion of fuel to be drawn into the comtiallyobstructing the combustion air passage upstream from the mixing zone whenever the engine is brought to FIGURE 2 is a fragmentary perspective view on an. en- 7 Referring now to the accompanying drawings, the I numeralS designates generally a small gasoline engine having a single cylinder 6 and a relatively simple car-' throttle valve or butterfly 13, near the top of the combus: tion air passageandabove the mixing zone, controls the rate at which combustion air mixed with fuel flows to the engine. a

- For simplicity no throttle actuating means is shown in the drawings, but it will be understood that the position of the throttle butterfly is manually adjustable in a conventionalmanner, as bymeans of the engine'speed responsive element of a mechanical governor (not shovm) which is linked to the throttle butterfly and which; is

biased toward the throttle closed position with a force;

that is controlled by a manual speed setting member.

In the inlet section 10 of the'combustion air passage there, is a choke valve or butterfly 14,-the position of which is controlled by a manually adjustable lever 15 that is movable betweendefined choke-open and chokeclosed positions. When'the choke butterfly is closed, as during engine .startingit very substantially restricts flow explained hereinafter.

such low speed,'and by decreasing the amount of such obstruction, upon subsequent opening of the throttle, at

V a rate substantially corresponding to the rate at which the engine speed increases and which is such as to substantially completely eliminate the obstruction when the engine attains a predetermined high speed (on the order of 1000-1200 r.p.m.) from which the engine can further accelerate satisfactorily Without the need for fuel-air mixture enrichment. 1

More specifically, the invention contemplatespartial closure of the choke butterfly 14 to provide such partial obstruction of the combustion air passage during sloW running or idling, and provides means for automatically swinging the choke toward its open position at a rate that is in step with increasing engine speed when the throttle is subsequently opened, so that the choke is brought to its fully open position when the engine reaches a speed in the neighborhood of 1000-1200 rpm.

The means for effecting such automatic actuation of the choke butterfly comprises a radially projecting counterweight arm 18 secured on the choke butterfly shaft 19, by which the butterfly is biased toward its closed position, and an air vane 20 projecting radially from the same shaft to be subjected to the stream of cooling air emanating from the flywheel blower 21 which is conventional on engines of the type here under consideration. The force of the blower airstream upon the vane 20 is of course substantially proportional to the speed of the engine, and is exerted in the direction to swing the choke valve against the biasing" force of the counterweight 18 and toward its open position. It will be apparent that the engine speed at which the choke valve is fully open depends upon the weight of the counterweight 18, and hence can be regulated by suitably changing the counterweight mass.

The end portions of the butterfly shaft 19, which are journalled in the opposite walls of the passage 8, project substantial distances outwardly beyond the carburetor air passage to accommodate the counterweight ,18 and vane 19. The vane is a flat piece of light metal, secured to one projecting end portion of the shaft 19 with its plane substantially on the shaft axis.

The manually adjustable choke positioning lever 15 is freely rotatably mounted on the other projecting end portion of the choke butterfly shaft and is confined against axial'displacement ofl? of the shaft by the counterweight arm 18, which is anchoredto the same end portion of shaft 19, outwardly of the lever. 1 The lever 15 has a disc-like hub portion 24 in which there is a coaxial arcuate slot 25, and has an'integral handle portion 26' which projects substantially radially from the choke valve shaft to facilitate manipulation of the lever. A pair of integral tabs or lugs 27 and 28 are bent outwardly from the hub portion of the lever, projecting substantially parallelto the choke shaft, to be engageable by and/ or with the counterweight arm 18 as Fastened to the bottom of the carburetor body is a bracket 29 having a flat plate-like wall 30 that underlies the disc-like hub portion 24 of the lever 15 and is perpendicular or transverse to the choke valveshaft which passes therethrough. Secured in the wall 30 of the bracket 29 is a stop screw or pin fit that extends through the arcuate slot 25 in the lever hub and cooperates with the ends of the slot to define chokeopen and choke-closed positions of the lever. A coiled compression spring 32, surrounding the shank of the stop screw and reacting against the underside of its head, bears against a washer 323 that flatwise overlies the disclike hub portion of the actuator. The hub portion of the lever is thus yieldingly clamped between the washer 33 and the wall 30 of the bracket 29, to frictionally hold the lever 15 in any position to which it may be adjusted.

The lever 15 is intended to be operated in any suitable manner, and to be placed in its choke-closed position for engine starting and in its choke-open or run position after the engine has started and is capable of running smoothly on its normal mixture.

The tabs or lugs 27 and 28 cooperate with the counterweight arm 18 to provide a lost motion connection between the lever 15 and the choke butterfly. When the lever is swung to its choke-closed position (see FIG- URE 2), the tab 28 on the hub portion of the actuator engages the counterweight arm to confine the choke butterfly in its closed position, for engine starting. When the lever is swung to its run position, the counterweight is permitted to have a limited range of swinging motion between the tabs 27 and 28. If no substantial force is imposed upon the vane 20, as when the engine is stopped or idling at low speed, gravity holds the counterweight engaged with the tab 27 and the choke butterfly is thereby maintained in a partially closed position (see FIGURE 3) at which it substantially increases suction in the mixing zone and enriches the mixture being fed to the engine. As engine speed increases above 700 r.p.m., the force of the blower airstream upon the vane 20 begins to overcome the gravity bias of the counterweight, swinging the butterfly farther open to an extent depending upon the speed of the engine. At engine speeds of about 1000 rpm. and upwards (see FIGURE 4) the force of the blower airstream upon the vane 20 completely overcomes the gravity bias of the counterweight and holds the latter engaged with the tab or lug 28, in which position of the counterweight the choke butterfly is fully open.

It will now be apparent that the operator uses the choke positioning lever in a normal and conventional manner for starting and normal running operation of the engine. However, once this lever is set in its run position, the choke butterfly automatically swings to its partially closed position whenever the throttle is closed and the engine drops down to low idling speed, and automatically swings toward its open position upon subsequent opening of the throttle. Since the position of the choke at any instant is a function of engine speed as manifested in the force which the blower airstream imposes upon the vane 20, the choke valve moves to its open position at a rate substantially corresponding to the rate at which the engine accelerates, diminishing the enrichment of the mixture accordingly.

From the foregoing description taken together with the accompanying drawings it will be apparent that this invention provides means for enriching the fuel-air mixture fed to a small engine during acceleration thereof from a slow running or idling speed, without the necessity for an acceleration pump or acceleration well and without interference with the overspeed governor with which such engines are normally equipped, thus permitting such engines to be satisfactorily operated at very low idling speeds and thereby substantially extending their speed ranges.

What is claimed as our invention is:

1. In an internal combustion engine having a blower which produces a stream of engine cooling air having a velocity that varies with engine speed, and a carburetor with a passage in the body thereof through which a combustible mixture of air and fuel flows to the engine with a throttle valve in said passage movable between open and closed positions for controlling the rate at which the combustible mixture flows to the engine:

(A) a choke valve in said passage to control the admission of air thereto, said choke valve being of the butterfly type and having a shaft which is journalled in the wall of said passage to mount the valve for free movement between defined closed and fully open positions;

(B) a weight eccentrically fixed to the choke valve shaft, gravity biasing the choke valve toward its closed position;

(C) a vane fixed to the choke valve shaft and located in the stream of cooling air to be responsive thereto and to move the choke valve toward its open position as the velocity of the air stream increases; and

(D) manually operable choke valve positioning means comprising (1) a lever mounted for rotation about the axis of the choke valve shaft, (2) a pair of angularly spaced apart opposing abutments on said lever, and (3) an arm fixed to the choke valve shaft with it free end portion between said abutments to be engageable thereby so that by the adjustment of the lever the position and range of adjustment of the choke valve may be set, adjustment of said lever in one direction to a first position effecting engagement between one of its abutments and said arm, to positively hold the choke valve in its closed position to facilitate starting, and adjustment of said lever in the opposite direction to a second position effecting engagement between the other abutment and said arm to move the choke valve to and hold it in a partially open low speed running position, to which position the choke valve freely moves in response to its gravity bias, whenever the engine slows down to its low running speed, so that the fuel-air mixture drawn into the engine upon sudden opening of the throttle valve while the engine is running at low speed, is sufficiently rich to enable rapid acceleration;

(E) means to limit the range of adjustment of said lever and define its said two positions; and

(F) means to releasably hold the lever in any position within its range of adjustment to which it may be manually moved.

2. The structure of claim 1, wherein the means to limit the range of adjustment of the lever comprises a wall fixed to the carburetor body transversely of the choke valve shaft and in position to have the lever swing across the wall,

a flat hub portion on the lever overlying said wall,

said hub portion having an arcuate slot concentric to the choke valve shaft, and a stop pin fixed to and received in said slot to collide with the ends thereof.

3. The structure of claim 2, wherein the means to releasably hold the lever in an adjusted position comprises a friction member on the stop pin and yieldingly pressed against said hub portion of the lever.

References Cited in the file of this patent UNITED STATES PATENTS 1,684,840 Mallory Sept. 18, 1928 1,759,153 Duffy May 20, 1930 2,548,334 Armstrong Apr. 10, 1951

Claims (1)

1. IN AN INTERNAL COMBUSTION ENGINE HAVING A BLOWER WHICH PRODUCES A STREAM OF ENGINE COOLING AIR HAVING A VELOCITY THAT VARIES WITH ENGINE SPEED, AND A CARBURETOR WITH A PASSAGE IN THE BODY THEREOF THROUGH WHICH A COMBUSTIBLE MIXTURE OF AIR AND FUEL FLOWS TO THE ENGINE WITH A THROTTLE VALVE IN SAID PASSAGE MOVABLE BETWEEN OPEN AND CLOSED POSITIONS FOR CONTROLLING THE RATE AT WHICH THE COMBUSTIBLE MIXTURE FLOWS TO THE ENGINE: (A) A CHOKE VALVE IN SAID PASSAGE TO CONTROL THE ADMISSION OF AIR THERETO, SAID CHOKE VALVE BEING OF THE BUTTERFLY TYPE AND HAVING A SHAFT WHICH IS JOURNALLED IN THE WALL OF SAID PASSAGE TO MOUNT THE VALVE FOR FREE MOVEMENT BETWEEN DEFINED CLOSED AND FULLY OPEN POSITIONS; (B) A WEIGHT ECCENTRICALLY FIXED TO THE CHOKE VALVE SHAFT, GRAVITY BIASING THE CHOKE VALVE TOWARD ITS CLOSED POSITION; (C) A VANE FIXED TO THE CHOKE VALVE SHAFT AND LOCATED IN THE STREAM OF COOLING AIR TO BE RESPONSIVE THERETO AND TO MOVE THE CHOKE VALVE TOWARD IST OPEN POSITION AS THE VELOCITY OF THE AIR STREAM INCREASES; AND

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