Carburetor with accelerating device

Details Carburetor with accelerating device Carburetor with accelerating device

2000-01-20

2001-09-25

Chiesa, Richard L. (Department: 1724)

Gas and liquid contact apparatus

Fluid distribution

Pumping

C261S051000

Reexamination Certificate

active

06293524

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to carburetors for internal combustion engines and more particularly to an accelerator pump of the carburetor.
BACKGROUND OF THE INVENTION
Some carburetors for gasoline fueled small engines such as two-stroke engines for handheld power tools such as chain saws, weed trimmers, leaf blowers and the like have carburetors with an internal accelerator pump which supplies additional fuel to the operating engine as the throttle valve of the carburetor is opened from its essentially closed or idle position toward its completely wide open throttle position. This additional fuel is needed to smoothly and rapidly accelerate the engine without stumbling particularly when it is under a load. Many prior accelerator devices have a positive displacement pump with a piston actuated by rotation of a shaft of a throttle valve through a wide variety of mechanical cam and linkage arrangements. One problem with these positive displacement accelerator pumps is they supply an excess quantity of fuel producing an overly rich fuel mixture for the engine upon initial opening of the throttle from its idle position and particularly if the throttle is opened or advanced to only an intermediate position which is less than the wide open throttle position. This is particularly a problem with a handheld power tool because many operators tend to rather rapidly partially open and close the throttle several times before fully opening and maintaining the throttle at its wide open position for a period of time during which a power tool is in actual use and its engine is under a substantial load.
SUMMARY OF THE INVENTION
In a carburetor with a shaft rotatable to move a throttle valve in a fuel and air mixing passage between an essentially closed or idle position and a fully open or wide open throttle position, an accelerator pump which delivers most of the accelerating fuel only after the throttle has been partially opened to an intermediate position and is then further advanced toward its wide open position so that an excessively rich fuel mixture is not provided for accelerating the engine. Preferably, the accelerator pump has a piston slidably received in a cylinder bore and movable to an advanced position to dispense a quantity of accelerating fuel and to a retracted position to refill the cylinder with fuel. In response to rotation of the throttle shaft to move the throttle valve from its idle to its wide open position, the piston is advanced by a cam which is preferably a face on the throttle shaft engaging a ball received in the bore between the piston and the shaft. So that the extent to which the piston is advanced is small as to throttle valve and shaft are moved from the idle position to an intermediate position and the extent of travel is significantly greater as the shaft and throttle are further advanced from the intermediate position to the wide open throttle position, the axis of the cylinder bore and hence the piston and the path of travel of the center of the ball are all eccentric to or offset and spaced from the axis of rotation of the throttle shaft so that these axes do not intersect. Preferably, these axes are at right angle to each other and the piston is yieldably biased toward its retracted position and into engagement with the ball and the ball into engagement with the cam by a spring or other biasing means.
OBJECTS, FEATURES AND ADVANTAGES OF THIS INVENTION
Objects, features and advantages of this invention include providing a carburetor with an accelerator pump in which most of the accelerating fuel is delivered only as the throttle valve and shaft is advanced from an intermediate position toward its wide open position, supplies only sufficient fuel for accelerating an operating engine without providing an overly rich fuel mixture for acceleration, does not provide an overrich fuel mixture even when an operator rapidly moves the throttle valve between its idle and intermediate positions several times, is rugged, durable, reliable, of relatively simple design and economical manufacture and assembly and in service has a long useful life without any maintenance or repair.


REFERENCES:
patent: 2080569 (1937-05-01), Holley
patent: 2182393 (1939-12-01), Ball et al.
patent: 2190314 (1940-02-01), Firth
patent: 2214273 (1940-09-01), Fish
patent: 2223987 (1940-12-01), Firth
patent: 2478613 (1949-08-01), Weber
patent: 2989292 (1961-06-01), Marsee
patent: 3730495 (1973-05-01), Elam
patent: 5250233 (1993-10-01), Swanson
patent: 5554322 (1996-09-01), Kobayashi
patent: 5611312 (1997-03-01), Swanson et al.

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