Gas and liquid contact apparatus – Fluid distribution – Valved
Reexamination Certificate
2001-10-18
2003-05-13
Chiesa, Richard L. (Department: 1724)
Gas and liquid contact apparatus
Fluid distribution
Valved
C261S065000
Reexamination Certificate
active
06561496
ABSTRACT:
FIELD OF INVENTION
The present invention relates to throttle control mechanisms of carburetors for internal combustion engines, and more particularly to such a mechanism incorporating a detent mechanism for yieldably holding and positioning the throttle valve in one or more of a predetermined plurality of operational positions.
BACKGROUND OF THE INVENTION
Manually operated throttle valve control levers are typically provided on small carburetors designed for use with low displacement gasoline fueled engines, such as used on chain saws, weed whips, leaf blowers, and other small lawn, garden and forestry portable appliances. Although the throttle valve is typically operator manipulated for angular travel throughout an operable range from closed to wide-open, a throttle control detent mechanism is customarily provided for yieldably holding the throttle valve in a selected one of two or three predetermined operating positions, e.g., namely wide-open throttle (W.O.T.), idle and fully closed. On larger lawn and garden appliances the detent mechanism may be built into the throttle control linkage parts, such as a control knob protruding through a control panel slot having notches along the travel path of the control knob arm. However in very small lawn and garden appliances, such as weed whips and leaf blowers, the engines are typically of small size and of low displacement, and therefore typically are provided with a cubic-type diaphragm carburetor that may only be between one and two inches square in outside dimensions. The throttle control linkage may only consist of a single lever fixed at one end to the throttle shaft and protruding to a finger-grip free end located in an operator-accessible zone adjacent to the carburetor mounting location on the engine.
Heretofore the typical detent mechanism utilized in such small carburetor throttle control mechanisms consists of a conventional ball and spring detent. This type of throttle detent mechanism requires that a blind bore be provided in the carburetor body for receiving the compression coil spring as well as the hardened steel ball that seats against the free-end of the spring. The spring-biased ball rides against the throttle shaft circumference and is forced into whichever one of three throttle shaft pockets comes into registry with the ball during throttle shaft rotation.
Due to the minuscule dimensions of these detent mechanism parts involved in such tiny carburetors, and particularly the very small diametrical dimension of the throttle shaft, it is difficult in the first instance to machine the detent pockets on the throttle shaft, and even more difficult if not economically impossible to angularly locate the pockets to the sufficiently close manufacturing circumferential dimensional tolerances that would be required in order to accurately establish within close angular tolerances the predetermined positive position stops for the throttle valve at W.O.T., idle and closed valve settings.
In addition, there are the usual manufacturing and assembly costs involved in providing the spring and ball type throttle control detent mechanism, and these costs are particularly aggravated when producing very small cubic carburetors of the aforementioned type.
OBJECTS OF THE INVENTION
Accordingly, among the objects of the present invention are to provide an improved carburetor throttle control detent mechanism that eliminates the need for the aforementioned ball and spring type detent mechanism and yet is also built into the carburetor assembly and hence does not require any cooperative construction either on the engine or the appliance on which the engine is installed, that achieves reduced costs of manufacture and assembly and yet is capable of controlling the throttle valve clocking operation in very small and precise increments, and that allows a choice of a plurality of predetermined positive detent stop positions for the throttle valve throughout the range of throttle valve operation from W.O.T. to fully closed.
Another object of the invention is to provide an improved carburetor throttle control detent mechanism of the aforementioned character which, when employed on a carburetor having a choke valve shaft, is capable of utilizing the choke control shaft as one of the cooperative detent stops in the detent control mechanism.
A further object of the present invention is to provide an improved carburetor throttle control detent mechanism of the aforementioned character in which the throttle control lever and the detent cam member of the mechanism are combinable into one unitary piece part in order to further reduce overall cost of manufacture and assembly of the carburetor and associated throttle control mechanism.
SUMMARY OF THE INVENTION
In general, and by way of summary description and not by way of limitation, the invention fulfills one or more of the foregoing objects by providing a carburetor having a body with an air-fuel mixture passageway and a rotatable throttle valve in said passageway mounted for rotation on and with a throttle shaft that is journaled for rotation on a rotational axis in said body. The throttle shaft has a free end protruding exteriorly from an exterior side surface of the body. Typically the throttle shaft has a given diameter of relatively small dimension. A throttle lever detent arm is mounted on the throttle shaft free end for rotation therewith in an angular travel path about the rotational axis and adjacent the body exterior side surface. First detent means are provided on the body side surface located in fixed position adjacent the travel path of the detent arm and spaced radially away from the rotational axis a predetermined distance greater than the diameter of the throttle shaft by a multiple of the shaft diameter dimension, e.g., a distance about three times the shaft diametrical dimension. Second detent means are provided on the detent arm that likewise are generally spaced such predetermined distance radially away from the rotational axis. The detent means are constructed and oriented so as to be releasibly engageable with one another for thereby yieldable holding the detent arm and hence the throttle shaft and associated throttle valve in any one of a plurality of selected angular settings.
One of the primary features of the carburetor throttle control detent mechanism of the invention is providing engagement of the first and second detent means, regardless of their structural form, in an arc of mutual engagement along a detent arm cam travel path having a radial dimension, centered on the throttle shaft rotational axis, that is a multiple of the small diameter dimension of the throttle shaft, such as a multiple of three times the shaft diametrical dimension. This large radius of the travel path of the arcuate cam control surface thus allows the tolerance limits of the radial variations that are spaced circumferentially apart along the cam surface to be manufactured to the same manufacturing tolerance specifications that are otherwise normally employed in machining a detent ball seating groove in the throttle shaft when providing the prior art ball/spring detent mechanism.
Yet in so doing, and without tightening up prior manufacturing tolerance specifications, the angular tolerance variation on the set positions of the throttle valve blade as controlled by the detent cam surface is now approximately three times more precise, i.e. the tolerance limits for the detent controlled predetermined angular positions of the throttle valve are now rendered three times tighter than otherwise would be possible when utilizing the prior control detent pockets provided in the surface of the throttle shaft. Hence manufacturing tolerances do not need to be tightened up in order to achieve a three-fold improvement in operational tolerances of the carburetor throttle control detent mechanism. The invention thus provides a low cost throttle control detent mechanism that enables fine increment, positive stops at predetermined valve blade settings, such as the W.O.T. (wide-opened throttle), idle and closed valve po
Gliniecki Gary U.
Learman Paul S.
Pattullo George M.
Thomas David L.
Chiesa Richard L.
Reising Ethington, Barnes, Kisselle, Learman & McCulloch, P.C.
Walbro Corporation
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