US3738625A

US3738625A - Pumpless fuel system for small engines

Info

Publication number: US3738625A
Authority: US
Inventors: R Thompson
Original assignee: Briggs and Stratton Corp
Current assignee: Briggs and Stratton Corp
Priority date: 1970-12-10
Filing date: 1970-12-10
Publication date: 1973-06-12
Anticipated expiration: 1990-06-12

Abstract

In a pumpless fuel system for a small engine, having a suction tube extending down into a fuel tank from a carburetor venturi, a fuel inlet in the suction tube is large enough to provide the desired fuel flow rate when fuel in the tank is low, but a rich fuel-air mixture at high fuel levels. At high levels the inlet is restricted, to afford the desired flow rate, by a restriction valve element then maintained in operative position by an annular float surrounding and guided by the suction tube.

Description

D United States Patent 1191 1111 3,738,625 Thompson June 12, 1973 [54] PUMPLESS FUEL SYSTEM FOR SMALL 1,749,307 3/1930 Aseltine 123/119 UX ENGINES 1,778,868 10/1930 Schimanek 261/69 R x 2,120,975 6/1938 Hettler 261/72 R [75] Inventor: Robert G. Thompson, Milwaukee, 2,529,242 11/1950 Brown et a1 261/72 R X Wis. 2,614,581 10/1952 Russell 261/50 A X 2,627,852 2 1953 D'tt [73] Assignee: Briggs & Stratton Corporation, 1 mar R X Wanwatosa, Wis. FOREIGN PATENTS OR APPLICATIONS Dec- 10, Great Britain R [21] PP 96,879 Primary ExaminerTim R. Miles Attorney-lra Milton Jones [52] U.S. Cl. 2'61/68, 137/398 [51] Int. Cl. F02m 7/20 57 ABSTRACT [58] Field In a pumpless fuel system for a small engine, having a 8 4O 1 45 137595 & 429 suction tube extending down into a fuel tank from a 13 l u carburetor venturi, a fuel inlet in the suction tube is large enough to provide the desired fuel flow rate when [56] References cued fuel in the tank is low, but a rich fuel-air mixture at high UNITED STATES PATENTS fuel levels. At high levels the inlet is restricted, to af- 638,557 12/1889 Cary 261/68 ford the desired flow rate, by a restriction valve ele 947,639 l/ 1910 Hill et a1. ment then maintained in operative position by an annu- 1.335,390 3/1920 y lar float surrounding and guided by the suction tube. 1,432,935 10/1922 Wheeler..... 1,587,629 6/1926 Bates 261/120 3 Claims, 3 Drawing Figures I I L 1 u i l f 8 7 i 1 il H I 2* 1 1 F ii 1 I -18 2O L1 33 1 PUMPLESS FUEL SYSTEM FOR SMALL ENGINES This invention relates to fuel systems for internal combustion engines, particularly single-cylinder engines such as are used on power lawn mowers and the like; and the invention is more specifically concerned with a simple fuel system for such an engine, having no fuel pump but wherein fuel is instead sucked directly from a fuel tank into a carburetor mixing passage.

In gasoline engine fuel systems in which liquid fuel is sucked from a reservoir into a carburetor mixing passage or venturi, it has heretofore been considered necessary to maintain a substantially constant level of fuel in the reservoir in order to insure that at a given throttle setting there will be constant rate of fuel flow into the venturi. The rate at which fuel flows from the reservoir into the mixing passage should depend mainly upon the suction manifested in the venturi. However, the rate of fuel flow also depends upon the vertical distance through which the fuel must be raised in being sucked into the venturi, and therefore substantial variations in fuel level in the reservoir tend to result in substantial variations in the fuel-air ratio of the mixture fed to the engine.

To insure that the fuel drawn into the carburetor mixing passage would have a constant static head, it has heretofore been a general practice with large engines to provide a float bowl near the venturi, to serve as the reservoir from which it drew fuel. Fuel was pumped into the float bowl from the fuel tank, and the level of fuel in the bowl was maintained substantially constant by means of a float controlled valve that regulated admission of fuel into the bowl.

Since the float bowl structure comprised a number of parts, including a float controlled valve that had to be manufactured with some degree of precision, it was not well adapted to small, simple and inexpensive engines such as are used for powering lawn mowers and similar machines.

Many smaller engines have therefore been provided with a fuel system that eliminates theneed for a float controlled valve, wherein the bowl that provides the reservoir for fuel to the drawn into the venturi is mounted in the upper portion of the fuel tank and is provided with an overflow outlet through which excess fuel is returned to the tank. Fuel is pumped into this overflow bowl by means of a simple membrane pump actuated by the pulsing pressures in the carburetor throat. The rate of fuel flow into the bowl is maintained in excess of the rate at which fuel is burned in the engine, so that whenever the engine is running some fuel is always returning to the tank by way of the overflow; hence the fuel level in the bowl is always constant, at the elevation of the overflow outlet.

Although the overflow bowl arrangement is relatively simple and inexpensive, it still requires the provision of a fuel pump and a separate bowl or reservoir in the fuel tank. On the smallest lawnmower engines, therefore, where fuel consumption is low and where costs must be kept to the very minimum, it has become the practice to provide a relatively shallow fuel tank, mounted directly beneath the carburetor body, and a suction tube which extends down into the fuel tank from the carburetor body and through which fuel is sucked up directly from the tank. With this arrangement the carburetor has heretofore been adjusted to provide a normal fuelair mixture when the tank was about half full. The mixture was of course excessively rich when the tank was nearly full and was somewhat too lean when the tank was nearly empty, but because of the small depth of the tank these extremes were within the range at which the engine would operate. However, the excessively rich mixture resulted in a high percentage of air pollutants in the engine exhaust; the lean mixture likewise caused incomplete combustion as well as poor engine performance; and the arrangement imposed a definite limitation upon fuel tank capacity since it could not be used with a tank more than about two inches high.

The present invention has as its general object to proivde a very simple and inexpensive expedient for substantially overcoming the problem of varying fuelair mixture ratio in a gasoline engine fuel system in which fuel is sucked from the tank directly into the carburetor venturi.

More specifically, it is an object of this invention to provide, in a pumpless fuel system, very simple and inexpensive means for compensating for variations of fuel level in a tank mounted beneath a carburetor body, to insure that at any given throttle setting fuel will flow at a substantially constant rate through a suction tube that extends from the carburetor body down into the tank, to thus improve engine performance and provide for cleaner exhaust emissions from the engine at times when the tank is substantially more or less than half full.

It is also an object of this invention to provide a pumpless fuel system of the character described that makes possible, in cases where it is needed, the use of a deeper and substantially larger capacity fuel tank than has heretofore been. adaptable to such fuel systerns.

It is also a specific object of this invention to provide a pumpless fuel system for a simple engine, comprising a fuel tank mounted beneath a carburetor body and a suction tube that extends down into the tank from the carburetor body, in which fuel system a float controlled valve governs the effective size of a. metering orifice for fuel entering the suction tube, and the suction tube serves as a guide for the float actuator to constrain it to up and down motion with changes in the level of fuel in the tank.

With these observations and objectives in mind, the manner in which the invention achieves its purpose will be appreciated from the following description and the accompanying drawing, which are intended to exemplify the invention, it being understood that changes may be made in the specific apparatus disclosed herein without departing from the essentials of the invention as set forth in the appended claims.

The accompanying drawing illustrates one complete example of an embodiment of the invention constructed according to the best mode so far devised for the practical application of the principles thereof, and in which:

FIG. 1 is a view in side elevationof the fuel system of a single-cylinder internal combustion engine embodying the principles of this invention, with portions shown broken away, the apparatus being shown in its condition with the fuel tank nearly full;

FIG. 2 shows the fuel system in end elevation with portionsbroken' away, in'the condition in which the tank is nearly empty; and

FIG. 3 is a fragmentary view corresponding to FIG. 2 but on a larger scale.

Referring now more particularly to the accompanying drawings, the numeral 5 designates generally a fuel induction system for a single-cylinder internal combustion engine, embodying the principles of this invention and comprising, in general, a simple carburetor body 6, a fuel tank 7 mounted beneath the carburetor body, and a suction tube 8 which extends from the carburetor body down into the fuel tank. The fuel system requires no fuel pump and no fuel reservoir separate from the tank because fuel is drawn from the tank directly into the venturi 10 of the carburetor through the suction tube 8. A float actuated restriction valve 11 in the tank serves to maintain a substantially constant rate of flow of fuel from the tank to the carburetor venturi, as described and explained hereinafter.

As shown, the carburetor body 6 is substantially L- shaped, and the fuel tank 7 is secured to its underside to be supported by it. At its interior the horizontally extending portion of the carburetor body defines an induction or mixture passage that comprises the venturi 10 and in which the usual throttle butterfly 12 is movably mounted. The upwardly projecting portion 14 of the carburetor body provides for the mounting of an air cleaner (not shown) and defines an air inlet passage 15 that leads to the induction passage.

The upper end of the suction tube 8 is laterally spaced from the venturi 10 but is communicated therewith through a short passage 16 that is controlled by a needle valve 17 and provides'a fuel metering jet. Although the needle valve is adjustable to control the richness or leanness of the fuel-air mixture, the rate at which fuel is educted into the venturi depends not only upon the position of the throttle butterfly and the setting of the needle valve but also upon the pressure head of the fuel on the upstream side of the needle valve. It is the function of the restriction valve 11 to maintain this pressure head nearly constant despite substantial variations in the level of fuel in the tank.

The inlet to the suction tube is a concentric opening 18 at its lower end. This inlet is a metering orifice of such size as to provide substantially the desired rate of fuel flow to the carburetor venturi when the level of fuel in the tank is below the half-full mark. At its bottom the suction tube has a concentric, shallow, inverted cup-shaped foot 20, the rim 21 of which provides the seat for a disc-like valve element 22 that comprises a part of the restriction valve 1 l. The foot can also accommodate a fine-mesh screen 23, which is of course wholly located above the plane of the rim or valve seat 21.

The disc-like valve element 22 has a concentric orifree 24 therein that is smaller than the inlet orifice 18 in the suction tube. When the valve element is engaged with the valve seat 21, the small orifice 24 controls the rate at which fuel can be drawn up toward the needle valve and the venturi, and that small orifice is of such size as to maintain the desired rate of fuel flow when the tank is more than half-full.

The float controlled restriction valve 11 also comprises an annular float 25 by which the valve element 22 is maintained in its seat engaging position when the tank is more than half-full, and a plurality of light rods or pins 26 that provide a lost motion connection between the float and the valve element.

The float 25 is annular and surrounds the suction tube with a loose tit so that it can be guided by the suction tube for up and down motion with changes in the level of fuel in the tank. The rods 26, which extend parallel to the suction tube axis, are slidable in bores in the float and in aligned holes in edgewise projecting ears 27 on the disc-like valve element. As shown, each rod has an enlarged head 29 at its bottom end and has its upper end threaded to receive a nut 30.

To insure that the valve element will have good sealing engagement with its seat 21 when the float is in the higher portion of its range of motion, the rods 26 that connect the float with the valve element are preferably three in number and are circumferentially equispaced. In addition, a small, light compression spring 32 reacts between the head 29 on each rod and the underside of its ear 27 on the valve element, to compensate for possible differences in the lengths of the rods and for any tilting of the float. Good sealing engagement between the valve element and its seat is further assured by a gasket 33 of soft, resilient material such as neoprene, which is illustrated as secured to the disc, flatwise overlying the upper surface thereof.

So that the float can have sufficient volume for adequate bouyancy without requiring that the rods be excessively long and heavy, the float has upwardly opening slots 34 therein in which the nuts 30 on the rods are received.

To provide clearance for the valve element to drop down out of engagement with its seat when the tank is less than half full, the foot 20 on the suction tube must be spaced a distance above the bottom of the tank. However, the amount of unavailable fuel in the tank can be minimized by forming the bottom wall of the tank with a small well 36 beneath the foot in which the valve element can be received when unseated.

From the foregoing description taken with the accompanying drawings it will be apparent that this invention provides a pumpless fuel system for small gasoline engines whereby substantially constant fuel flow into the carburetor venturi can be obtained despite variations in the level of fuel in the tank.

Those skilled in the art will appreciate that the invention can be embodied in forms other than as herein disclosed for purposes of illustration.

The invention is defined by the following claims:

1. In an internal combustion engine having a carburetor venturi in which subatmospheric pressures normally prevail during engine operation, a liquid fuel tank beneath the venturi in which the.l'evel of fuel can vary over a substantial range, and a suction tube extending from the venturi down into the fuel tank and communicating the interior of the fuel tank with the venturi so that fuel can be sucked from the tank directly into the venturi to be mixed with air therein, means for maintaining a substantially constant ratio of fuel to air in the venturi during operation of the engine despite variations in the level of fuel in the tank, said means comprising:

A. the suction tube having an inlet at its bottom through which fuel can be drawn and which inlet is sufficiently large to provide fuel flow to the venturi at substantially a desired rate when fuel is below a predetermined level in the tank but at an excessively high rate when fuel is above said level, said inlet at the bottom of the suction tube being surrounded by a downwardly facing circumferential shoulder that provides a valve seat;

B. a float in the tank guided for up and down motion with changes in the level of fuel;

C. a valve element movable relative to the suction tube between a first position sealingly engaging said valve seat and a second position spaced from said valve seat, said valve element comprising a disc having an aperture that registers with said inlet at the bottom of the suction tube but is smaller than said inlet to restrict flow into the suction tube when the valve element is in its first position; and

D. means providing a connection between the float and said valve element whereby upward motion of the float moves the valve element towards its first position and downward movement of the float effects motion of the valve element towards its second position.

2. The internal combustion engine of claim 1, further characterized by:

E. the float being annular and surrounding the suction tube to be guided thereby for its up and down motion.

3. A fuel system for an internal combustion engine, of the type comprising a carburetor having a passage in which subatmospheric pressure normally prevails during engine operation, a liquid fuel tank beneath the carburetor in which the level of fuel can vary, and a suction tube extending from the carburetor down into the fuel tank and communicating the interior of the fuel tank with said passage so that fuel can be sucked from the tank directly into said passage to be mixed with air therein, said fuel system being characterized by:

A. the suction tube having at its bottom a downwardly facing valve seat surrounding an inlet to the suction tube which is sufficiently large to permit fuel to flow therethrough at a desired rate when fuel is below a predetermined level in the tank and entry into said inlet is not restricted, but which provides for excessive fuel flow when fuel is above said level;

B. an annular float surrounding the suction tube to be guided thereby for up and down movement with changes in the level of fuel in the tank; and

C. a valve element connected with the float to move therewith to and from engagement with the valve seat, which engagement is maintained when fuel in the tank is above said level, said valve element having a small orifice therein which registers with the inlet to the suction tube to provide a restricted entrance to the suction tube when the valve element is engaged with the valve seat, whereby the fuel flow into the suction tube is limited to substantially said desired rate.

Claims

1. In an internal combustion engine having a carburetor venturi in which subatmospheric pressures normally prevail during engine operation, a liquid fuel tank beneath the venturi in which the level of fuel can vary over a substantial range, and a suction tube extending from the venturi down into the fuel tank and communicating the interior of the fuel tank with the venturi so that fuel can be sucked from the tank directly into the venturi to be mixed with air therein, means for maintaining a substantially constant ratio of fuel to air in the venturi during operation of the engine despite variations in the level of fuel in the tank, said means comprising: A. the suction tube having an inlet at its bottom through which fuel can be drawn and which inlet is sufficiently large to provide fuel flow to the venturi at substantially a desired rate when fuel is below a predetermined level in the tank but at an excessively high rate when fuel is above said level, said inlet at the bottom of the suction tube being surrounded by a downwardly facing circumferential shoulder that provides a valve seat; B. a float in the tank guided for up and down motion with changes in the level of fuel; C. a valve element movable relative to the suction tube between a first position sealingly engaging said valve seat and a second position spaced from said valve seat, said valve element comprising a disc having an aperture that registers with said inlet at the bottom of the suction tube but is smaller than said inlet to restrict flow into the suction tube when the valve element is in its first position; and D. means providing a connection between the float and said valve element whereby upward motion of the float moves the valve element towards its first position and downward movement of the float effects motion of the valve element towards its second position.

2. The internal combustion engine of claim 1, further characterized by: E. the float being annular and surrounding the suction tube to be guided thereby for its up and down motion.

3. A fuel system for an internal combustIon engine, of the type comprising a carburetor having a passage in which subatmospheric pressure normally prevails during engine operation, a liquid fuel tank beneath the carburetor in which the level of fuel can vary, and a suction tube extending from the carburetor down into the fuel tank and communicating the interior of the fuel tank with said passage so that fuel can be sucked from the tank directly into said passage to be mixed with air therein, said fuel system being characterized by: A. the suction tube having at its bottom a downwardly facing valve seat surrounding an inlet to the suction tube which is sufficiently large to permit fuel to flow therethrough at a desired rate when fuel is below a predetermined level in the tank and entry into said inlet is not restricted, but which provides for excessive fuel flow when fuel is above said level; B. an annular float surrounding the suction tube to be guided thereby for up and down movement with changes in the level of fuel in the tank; and C. a valve element connected with the float to move therewith to and from engagement with the valve seat, which engagement is maintained when fuel in the tank is above said level, said valve element having a small orifice therein which registers with the inlet to the suction tube to provide a restricted entrance to the suction tube when the valve element is engaged with the valve seat, whereby the fuel flow into the suction tube is limited to substantially said desired rate.