TECHNICAL FIELD

The present disclosure relates generally to a fuel charge forming device for an engine such as a carburetor having an adjustable valve and a limiter for the adjustable valve.

BACKGROUND

Government agencies of an increasing number of countries are applying exhaust emission control regulations to protect the environment. These regulations are being applied to all gasoline fuel combustion engines including engines used in marine, lawn and garden and recreational equipment such as outboard motors, garden tractors, chain saws, lawn mowers, hedge trimmers, snowmobiles and personal watercraft. One means of limiting excessive exhaust emissions in a small engine is to restrict the maximum amount of fuel delivered to the combustion chamber by a charge forming device such as a carburetor. This maximum fuel amount is pre-set on each individual engine by the engine manufacturer with the understanding that the end user requires some adjustment capability to meet changing work conditions and environmental factors such as altitude and ambient temperature. The higher the altitude and temperature, the lower the air density, and thus the amount of fuel mixed with the air must be decreased to maintain the proper oxygen to fuel ratio necessary to efficiently operate the engine. The user of the engine must therefore be able to adjust the fuel to air mixture ratios and may do so via low and high speed needle valves protruding from the carburetor.

Not only is it desirable to limit the richness of the fuel-to-air mixture because of exhaust emission regulatory concerns, but the engine manufacturer of a two-cycle engine product also wants to restrict minimum amounts of fuel, or the leanness of the fuel to air mixture. Often a user will desire more power from a two-cycle engine and will attempt to operate the engine in an ultra-lean state. This will cause a two-cycle engine to operate at a temperature higher than its design temperature and may decrease its useful life and lead to service and warranty concerns. Therefore, known limiter caps are designed not only to restrict the carburetor to a maximum amount of fuel, but also to restrict the carburetor to a minimum amount of fuel.

Limiter caps secured to the projecting ends of the low and high speed needle valves are commonly used to restrict the end user from demanding too much fuel from a carburetor which could exceed regulatory emission limits. The user purchases the engine already factory set to a desired fuel amount, adequate for efficient operation in low lying areas. Should the engine be utilized in a high altitude area, the user can still decrease the amount of fuel supplied to compensate for the low air density and/or ambient temperature.

In a conventional needle valve, the valve has an enlarged metallic head having an outward end face that defines a diametric recess or slot for receipt of a tool or blade of a screwdriver to rotate the valve to adjust fuel flow. The limiter cap has a similar diametric recess or hole in an end wall for access of the screwdriver, and a continuous inner surface defining a bore for receipt of the head. The inner surface may have serrations which axially mate with serrations on the head so the limiter cap when in a user assembled state rotates in unison with the head. Typically, a peripheral side or outer surface of the limiter cap has at least one radially projecting tab which engages at least one stop of the carburetor body in both the fuel rich and fuel lean directions and thereby limits fuel adjustment capability by the end user.

Due to carburetor and engine design and manufacturing tolerances, a manufacturer's setting of a specific carburetor to an optimum fuel amount prior to use on a specific engine, or within a specific environment such as altitude, is not practical. The limiter cap assembly is therefore supplied in a non-engaged mode in which the cap is not mated to the needle valve head and is often separate from the carburetor itself. Unfortunately, supplying a carburetor with unassembled parts contributes to manufacturing or assembly inefficiencies and possible regulatory violations if the caps are never actually fully engaged to the valves.

Other needle valve assemblies, such as that disclosed in U.S. Pat. No. 6,467,757, to Douyama, and incorporated herein by reference, have a limiter cap which is pre-engaged to the carburetor body by the carburetor manufacturer for delivery to the engine manufacturer who then engages and locks the limiter cap to the valve head after final adjustments are made during operation on a specific engine. Three axially spaced projections disposed on the outer surface of the limiter cap are required to press-fit and hold the cap in the pre-engaged position and then to press-fit and lock the cap in the engaged position. When pre-engaged, the limiter cap projects outward from the carburetor body and the valve head, and the unmated serrations of the valve head are spaced axially away from the serrations of the limiter cap. When the limiter cap is pre-engaged, a screwdriver blade is inserted through the cap hole for factory rotational adjustment of the needle valve while the limiter cap is unmated from the needle valve. Upon adjustment completion, the caps are press fitted directly over the needle valve head, mating the serrations and received in the carburetor body. Once engaged to the valve head, the end user has restricted adjustment of the needle valve by rotating the limiter cap which, in turn, rotates the needle valve.

Unfortunately, during factory adjustment, if a worker employee misses the elongated hole with the screwdriver, the limiter cap may inadvertently be pushed-in axially into engagement with the needle valve head and thereby prevent factory adjustment without destroying the cap by forcibly removing it. Furthermore, the press-fit between the cap projections and the carburetor body requires that the cap be made of a resilient synthetic resin material such as nylon or other resilient thermoplastic material.

SUMMARY

A charge forming device may have a rotatable fuel adjustment valve received in a passage of a body of the device. A limiter cap may be received on the valve with a driving feature engageable with a drive feature on the valve and having a first position permitting rotation of the valve relative to the limiter cap and a second position permitting only lesser rotation of the valve than that of the first portion.

The limiter cap may have a tamper restraint feature that retains the lesser range of rotation. The tamper resistant feature may include one or more flexible fingers defining a cavity with a volume that decreases when the cap is moved to its second position to inhibit access to the valve. The cap may include a stop which in the second position limits rotation of the valve even if the fingers are tampered with or broken off and removed.

A clasp and a plug may be received in a carburetor cavity each with an opening through which a limiter cap at least in part may be received. A head of a needle valve may be received in the carburetor cavity and may be rotatably disengaged from the cap when the cap is in its first position and engaged with the cap when in its section position for lesser rotation of the valve.

The clasp may have a one or more fingers with a free end engageable with a first shoulder of the limiter cap when in its first position to inhibit removal of the cap from the cavity and engageable with a second shoulder of the cap when in its second position to inhibit movement of the cap toward its first position.

In at least some implementations, a limiter cap assembly for a carburetor having a cavity in which one or more adjustable valves are received, includes a plug adapted to be received within a cavity of the carburetor and having an opening and a cavity aligned with the opening, a clasp engageable with the plug and having at least one retention feature and an opening aligned with the opening of the plug, and a limiter cap received within the opening of the plug and engaged with the retention feature of the clasp. Removal of the limiter cap from the plug opening is prevented by engagement of the retention feature with the limiter cap and by engagement of the clasp with the plug.

In at least some implementations, the limiter cap includes a first shoulder that is engageable by the retention feature in a first position of the limiter cap relative to the plug, and the limiter cap includes a second shoulder engageable with the retention feature in a second position of the limiter cap relative to the plug.

In at least some implementations, the plug includes a base and a wall extending from the base, the wall has a free end spaced from the base and the wall defines part of the cavity, and wherein the clasp includes a base engageable with the free end of the wall. The wall may be part of a sheath section of the plug, and the sheath section may include a gap extending radially through the wall, and the retention feature may be received at least partially in the gap and at least partially within the cavity. The clasp may include a leg extending from the base, and the retention feature may be a foot defined by a bend in the leg.

In at least some implementations, the base of the plug includes an outer surface arranged to face outwardly from the cavity of the carburetor, and an inner surface adapted to face inwardly in the cavity of the carburetor, and wherein the retention feature engages the limiter cap closer to the inner surface than to the outer surface. In at least some implementations, the retention feature engages the limiter cap between the base of the plug and the base of the clasp.

In at least some implementations, the clasp includes a base and multiple legs, each leg having a first end connected to the base and a free end spaced from the base, the legs being angled relative to the base so that the free ends of the legs are closer together than are the first ends of the legs. At least one retention feature may include multiple retention features with a separate retention feature on each leg, and with each retention feature located at least partially within the cavity and engaged with the limiter cap.

In at least some implementations, the opening in the plug is a first opening, the plug includes a second opening and the plug includes a partition wall located between the openings, and a rotation limiter is carried by the partition wall and extends into the cavity to limit rotation of the limiter cap. In at least some implementations, the limiter cap substantially fills the opening in the plug, and the limiter cap and the outer surface of the plug prevent access to the retention feature from within the opening of the plug.

In at least some implementations, an assembly includes a carburetor body having a void, a plug adapted to be received at least partially within the void, the plug having an opening and a cavity aligned with the opening, a clasp engageable with the plug and having at least one retention feature and an opening aligned with the opening of the plug, an adjustable valve received at least partially within the void, aligned with the opening and cavity, and a limiter cap received at least partially on the adjustable valve and within the opening of the plug and engaged with the retention feature of the clasp. Removal of the limiter cap from the plug opening is prevented by engagement of the retention feature with the limiter cap and by engagement of the clasp with the plug.

In at least some implementations, the limiter cap includes a first shoulder that is engageable by the retention feature in a first position of the limiter cap relative to the plug, and the limiter cap includes a second shoulder engageable with the retention feature in a second position of the limiter cap relative to the plug.

In at least some implementations, the plug includes a base and a wall extending from the base, the wall has a free end spaced from the base and the wall defines part of the cavity, and wherein the clasp includes a base engageable with the free end of the wall. The wall may be part of a sheath section of the plug, and the sheath section may include a gap extending radially through the wall, and the retention feature may be received at least partially in the gap and at least partially within the cavity. The clasp may include a leg extending from the base, and the retention feature may be a foot defined by a bend in the leg. The at least one retention feature may include multiple retention features with a separate retention feature on each leg, and with each retention feature located at least partially within the cavity and engaged with the limiter cap.

In at least some implementations, the opening in the plug is a first opening, the plug includes a second opening and the plug includes a partition wall located between the openings, and a rotation limiter is carried by the partition wall and extends into the cavity to limit rotation of the limiter cap.

In at least some implementations, the retention feature engages the limiter cap between the base of the plug and the base of the clasp.

