IE80669B1 - A carburetor - Google Patents

Abstract

A carburetor which comprises, inter alia, a throttle shaft mounted in the carburetor body and projecting from respective opposite sides thereof, one end of the throttle shaft being connectable to an air valve or vane, the other end of the throttle shaft being connectable to a throttle actuating lever via a tension spring. The throttle actuating lever has a first position of use, which urges the throttle shutter into a closed condition of use, and a second position of use, which urges the throttle shutter into the open condition against the bias of the spring. Air movement against the vane results in rotation of the throttle shaft against the bias of the spring thereby urging the throttle shutter into the closed condition. Operatively associated with the throttle shaft is a friction engaging means for acting on the throttle shaft so as to retard but not prevent rotation of the throttle shaft relative to the carburetor body.

Description

A CARBURETOR This invention relates to a carburetor. In particular, it relates to a carburetor for use on a relatively small internal combustion engine. A carburetor generally comprises a main body portion defining a throttle means comprising a venturi and a throttle bore. The carburetor has an air intake side and an engine outlet side, a fuel pump, a fuel inlet supply channel for conveying fuel from the fuel pumps to the throttle means and a throttle shutter mounted within the throttle means between the air intake side and the engine outlet side.

In addition, there is provided a metering chamber for supplying fuel from the fuel pump into the throttle means via a main discharge port and at least one idle discharge port, the main discharge port opening into the throttle means on the air intake side of the throttle shutter.

A further feature of a known carburetor comprises a governing system which influences the throttle shutter position which in turn controls the engine speed.

It is known to employ carburetors having a governing system in lawn mowers, tillers etc. which system is directly related to engine load variation/requirements and prevents overspeeding of the engine. Such a typical system is shown in Fig. A and is described as follows: Fig. A comprises the following components and shows in schematic form a 25 known carburetor having a known governing system. 1. Engine fly wheel 2. Cooling fins 3. Air valve or vane 4. Throttle shaft . Throttle body (carburetor) 6. Throttle shutter 7. Throttle bore 8. Tension spring 9. Throttle actuating lever . Throttle lever 11. Linkage cable.

On rotation of the engine, the fly wheel 1 turns in a clockwise direction (arrow Z). The cooling fins 2 exert air pressure on the vane 3. This pressure pushes the vane 3 in a direction of the arrow x. The vane 3 is fixed fast to or is an integral part of the shaft 4. The air pressure, therefore, acting on the vane 3 moves the throttle shutter 6 so as to move the throttle shutter 6 towards the closed idle position.

The throttle lever 10 is connected to the throttle lever 9 via the linkage cable 11 and tension spring 8.

Figure A shows the system as the engine is in the idle mode (approx. 1500rpm). In this case the throttle actuating lever 9 is moved to the closed position in the direction of the arrow Y. Tension spring 8 becomes redundant, ie. ho force is acting on throttle lever 10. In the idling position the air pressure generated by the cooling fins 2 acting on vane 3, is the only force pushing the throttle shaft closed to idle position.

Figure B shows the system as the engine is operating at maximum rpm (approx. 6000rpm). The throttle actuating lever 9 is moved to the open position in the direction of the arrow Z. The throttle cable 11 expands the spring 8 which in turn pulls on the throttle lever 10 which in turn rotates throttle shaft 4 opening the throttle shutter 6. In so doing, the air vane 3 moves closer to the cooling fins 2. The shaft 4, throttle shutter 6, and vane 3 hold a fixed position which is related to a balance of forces between the tension spring 8 (tending to open the throttle shutter 6) and the air pressure on valve 3 (tending to close the throttle shutter 6). This balance of forces governs the engine rpm for any given load condition.

A common fault which can occur in such a known system is oscillation as it attempts to attain the zero balance point. A condition known as engine hunting results.

Accordingly, it is an object of the present invention to overcome these 3 0 disadvantages.

The invention, therefore, provides a carburetor which comprises a carburetor body defining a throttle means comprising a venturi and a throttle bore, the carburetor having an air intake side and ah engine outlet side; a fuel pump; a fuel inlet supply channel for conveying fuel from the fuel pump to the throttle means; a throttle shutter mounted within the throttle means between the air intake side and the engine outlet side; and a throttle shaft for controlling the movement of the throttle shutter, the throttle shaft being mounted in the carburetor body and projecting from respective opposite sides thereof, one end of the throttle shaft being connected to an air valve or vane, the other end of the throttle shaft being connected to a throttle actuating lever via a tension spring, and the throttle actuating lever being movable between a first position of use which allows the throttle shutter to assume a closed condition and a second position of use which urges the throttle shutter into an open condition via tension in the spring, wherein air movement against the vane results in rotation of the throttle shaft against the bias of the spring thereby urging the throttle shutter towards the closed condition; the carburetor further including at least one friction means located in a recess in the carburetor body around the throttle shaft so as to act radially on the throttle shaft, the friction means reducing any tendency of the throttle shaft to oscillate in use of the carburetor but not otherwise preventing rotation of the throttle shaft relative to the carburetor body.

Preferably, the friction means comprises a friction seal.

Preferably, the friction seal is in compression between the throttle shaft and the recess so as to provide a co-efficient of friction of between 2 and 5g/inch (0.07 and 0.20g/mm) The invention will be understood in greater detail from the following description of a preferred embodiment thereof given by way of example only and with reference to foe accompanying drawings in which: -4Figure A is a schematic view of a prior art carburetor in a first condition of use; Figure B is a schematic view of the carburetor of Figure A in a second condition of use; and Figure 1 is a perspective view of a carburetor according to the invention.

Referring now to the drawings, there is shown a carburetor 30 according to the invention which essentially comprises the components of Figures A and B above and in which like numerals are used for the same components in the three figures. Furthermore, a detailed description of the operation of the carburetor 30 will not be given as it is well known to those skilled in the art save to say that rotation of the throttle shaft 4 determines the movement of the throttle shutter 6 which in turn determines the rate of flow of fuel through the carburetor 30 which in turn controls the engine rpm.

As will be observed from Figure 1 of the drawings, the throttle shaft 4 is mounted in a bore 16 in the carburetor body 5 which throttle shaft 4 projects from opposite ends of the carburetor body enabling the air valve or vane 4 to be attached to one end of the shaft 4 while the other end has the throttle lever 10 attached thereto.

In the carburetor body 5 there is provided two recesses 14, 15 each of which is in communication with the bore 16. Into each of these recesses 14,15 is placed a respective friction seal 12,13 which acts radially against the shaft 4. Each friction seal 12,13 is in compression between the shaft 4 and the wall of each respective recess 14,15. The degree of compression and the nature of the material used in the friction seals 12,13 determines the co-efficient of friction acting radially on the shaft 4.

For a typical application, the friction co-efficient is desired to be of the order of between 0.07 and 0.20g/mm. The material of the seals 12,13 is preferably a polyurethane foam having 80-100 pores per inch (3.15 and 4.33 pores per mm) Nominal diameter compression on both seals 12,13 was 82. In -5 other words, the outside diameter of the seal reduced to 82% of its static diameter when compressed i.e. 18% compression (see graph on page 6). Per cent seal compression can be changed/calibrated depending on the required $ co-efficient of friction for a given application. The graph on page 6 plots the relationship between seal compression and co-efficient of friction for a . particular carburetor design.

The provision of the seal 12,13 will not normally inhibit the free movement of the shaft 4 thereby enabling the carburetor to enjoy the features and effects of the prior art carburetor having a similar arrangement without seals. However, with the seals 12,13 in position, so-called hunting or oscillation of the shaft is considerably reduced or even eliminated.

The invention is not limited to the embodiments described herein which may be modified or varied without departing from the scope of the invention.

Claims (4)

1. 5 1. A carburetor which comprises a carburetor body defining a throttle means comprising a venturi and a throttle bore, the carburetor having ah air intake side and an engine outlet side; a fuel pump; a fuel inlet supply channel for conveying fuel from the fuel pump to the throttle means; a throttle shutter mounted within the throttle means between the air intake side and the engine 10 outlet side; and a throttle shaft for controlling the movement of the throttle shutter, the throttle shaft being mounted in the carburetor body and projecting from respective opposite sides thereof, one end of the throttle shaft being connected to an air valve or vane, the other end of the throttle shaft being connected to a throttle actuating lever via a tension spring, and the throttle 15 actuating lever being movable between a first position of use which allows the throttle shutter to assume a closed condition and a second position of use which urges the throttle shutter into an open condition via tension in the spring, wherein air movement against the vane results in rotation of the throttle shaft against the bias of the spring thereby urging the throttle shutter towards the 20 closed condition; the carburetor further including at least one friction means located in a recess in the carburetor body around the throttle shaft so as to act radially on the throttle shaft, the friction means reducing any tendency of the throttle shaft to oscillate in use of the carburetor but not otherwise preventing rotation of the throttle shaft relative to the carburetor body.

2. A carburetor as claimed in claim 1 wherein the friction means is a friction seal.

3. A carburetor as claimed in claim 2 wherein the friction seal is in compression between the throttle shaft and the recess so as to provide a co5 efficient of friction of between 2 and 5g/inch (0.07 and 0.20g/mm).

4. A carburetor substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.