GB2306198A

GB2306198A - Carburettor acceleration pump

Info

Publication number: GB2306198A
Application number: GB9613497A
Authority: GB
Inventors: Patrick Walsh
Original assignee: Barcarole Ltd
Current assignee: Barcarole Ltd
Priority date: 1995-10-13
Filing date: 1996-06-27
Publication date: 1997-04-30
Also published as: GB9613497D0; IES67434B2; IES950800A2

Abstract

The diaphragm 21 pumps extra fuel from the chamber 42 to the main nozzle chamber 14 in response to the reduction in manifold vacuum in the chamber 42 resulting from opening of the throttle valve 5.

Description

FLOAT TYPE CARBURETOR INCLUDING AN ACCELERATION PUMP This invention relates to a float type carburetor including an acceleration pump.

According to the present invention a float type carburetor includes an acceleration pump which operates in response to changes in negative pressure at the engine intake manifold.

Preferably the acceleration pump comprises a housing divided internally by a flexible membrane into two hermetically sealed chambers, one of the chambers being in communication with the engine intake manifold and the other of the chambers being in communication with the fuel flow path of the carburetor, the arrangement being such that a decrease in the negative pressure in the engine intake manifold tends to increase the volume of the said one chamber and correspondingly decrease the volume of the said other chamber whereby the pressure in the said other chamber and, correspondingly, in the fuel flow path is increased.

An embodiment of the invention will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a schematic cross-sectional diagram of the basic components of a known float type carburetor; Figure 2 is a schematic cross-sectional diagram of the basic components of a known float type carburetor including a known mechanical acceleration pump; and Figure 3 is a schematic cross-sectional diagram of the basic components of a float type carburetor including a vacuum acceleration pump according to the embodiment of the invention.

In the drawings the same reference numerals have been used for the same or equivalent components.

The construction and operation of a float type carburetor is well known in the art and will not be described in detail herein. Briefly, however, and referring to the known construction of float type carburetor shown in Figure 1, the carburetor includes a main body 1 with a passage therethrough defining a venturi 2. A fuel bowl 6 is attached to the underside of the body 1 and a hollow cylindrical fuel tower 10 within the fuel bowl 6 extends integrally from the body 1 down to the base of the fuel bowl 6. The upper rim 12 of the fuel bowl 6 is sealed to the underside of the body 1 and the lower end of the fuel tower 10 is sealed to the base of the fuel bowl 6, thereby defining a sealed fuel bowl chamber 9. An annular float 7 surrounding the tower 10 is disposed in the fuel bowl 6 in known manner.

A main fuel take-off jet 8 is set into the side of the tower 10 near its base so that fuel 13 in the chamber 9 can pass into the interior of the tower 10 at a region 14 near the base of the fuel bowl 6. A main nozzle tube 3 extends coaxially up through the tower 10 and also through the body 1, the top end of the tube 3 terminating in the venturi 2 and its lower end terminating just above the region 14. A throttle shutter 5 is located in the venturi 2 and is operated by a throttle shaft 4 in known manner. In use the carburetor body 1 is fixed to an engine intake manifold 11 as shown.

During operation of the carburetor, fuel 13 is drawn from the chamber 9 via the main jet 8 up the nozzle tube 3 and into the engine manifold 10. However, for certain engine applications such as a 4 stroke engine, when the engine is throttled from idle to wide open insufficient fuel is drawn from the carburetor which results in a lean condition giving poor acceleration.

This problem can be mitigated by the use of an acceleration pump 30 as shown in Figure 2. The pump 30 comprises a housing 40 whose interior is divided into two chambers 41 and 42 respectively by a flexible membrane 21. The chamber 42 is hermetically sealed, and is in communication with the region 14 in the fuel tower 10 via a pipe or tube 24 which is connected at one end to the chamber 42 and at the other end to a bore 43 formed in the carburetor body 1 and in the sidewall of the tower 10. A coil spring 22 maintained under compression in the chamber 42 between the membrane 21 and the facing wall of the chamber 42 biases the membrane 21 in a direction tending to increase the volume of the chamber 42.

The other surface of the membrane 21 is acted on by a piston 20 which is mechanically linked to the throttle shaft 4 via a lever or cam (not shown). When the throttle shaft 4 is set to the wide open position of the throttle shutter 5 (acceleration), the piston 20 moves in the direction X shown in Figure 2. This forces the flexible membrane 21 to the right (as seen in Figure 2) against the bias of the coil spring 22, causing a reduction in the volume of the chamber 42 and a consequent increase in the pressure in the chamber 42. This pressure is transmitted via the pipe 24 and bore 43 to the region 14 in the fuel tower 10. As a result additional fuel is forced up nozzle tube 3 and into the venturi 2. This additional fuel overcomes the lean acceleration condition.

Turning now to Figure 3, this shows an embodiment of the invention in which the carburetor has an acceleration pump 30 which is activated by engine manifold vacuum (negative pressure), eliminating the need for a mechanical linkage between the throttle shaft 4 and the pump 30.

In Figure 3, as before, the chamber 42 is hermetically sealed and in communication with the region 14 via the pipe 24 and the bore 43. However, in this case the chamber 41 is also hermetically sealed, and is in communication with the engine intake manifold 11 via a further pipe or tube 33. Further, the compression coil spring 22 is now located in the chamber 41 and acts on the opposite side of the membrane 21, thereby tending to push the membrane 21 to the right and decrease the volume of the chamber 42.

However, as will be described, in use the bias of the compression spring 22 is opposed by negative pressure in the engine intake manifold 11 which is transmitted through the pipe 33 to the chamber 41.

During engine idle condition a strong negative pressure exists in the engine intake manifold 11.

Typically this can be -100 ins./H20. This negative pressure is transmitted to the chamber 41 of the pump 30 via the pipe 33 (a one way valve 32 in the pipe 33 allows the negative pressure pulses only to be transmitted to the chamber 41). This negative pressure reduces the volume of the chamber 41 and thereby moves the membrane 21 in the direction X shown in Figure 3, against the bias of the coil spring 22.

When the throttle shaft 4 is set to the wide open position of the throttle shutter 5, the negative pressure in the manifold 1 drops accordingly, typically to -Sins./H20. This decrease in negative pressure is transmitted to the chamber 41 through the pipe 33. This allows the coil spring 22 to push the membrane 21 in the direction Y thereby causing a reduction in the volume of the chamber 42 and a consequent increase in the pressure in the chamber 42. As before, this pressure is transmitted via the pipe 24 and bore 43 to the region 14 in the fuel tower 10. Additional fuel is thereby forced up nozzle tube 3 and into the venturi 2.

This additional fuel overcomes the lean acceleration condition. When the engine returns to the idle condition the cycle begins again.

Claims

CLAIMS:

1. A float type carburetor including an acceleration pump which operates in response to changes in negative pressure at the engine intake manifold.

2. A float type carburetor as claimed in claim 1, wherein the acceleration pump comprises a housing divided internally by a flexible membrane into two hermetically sealed chambers, one of the chambers being in communication with the engine intake manifold and the other of the chambers being in communication with the fuel flow path of the carburetor, the arrangement being such that a decrease in the negative pressure in the engine intake manifold tends to increase the volume of the said one chamber and correspondingly decrease the volume of the said other chamber whereby the pressure in the said other chamber and, correspondingly, in the fuel flow path is increased.

3. A float type carburetor as claimed in claim 2, wherein the membrane is spring biassed in a direction tending to decrease the volume of the said other chamber, the spring bias being opposed by a negative pressure in the engine intake manifold.

4. A float type carburetor as claimed in claim 2 or 3, wherein the said one chamber is connected to the engine intake manifold via a pipe or tube containing a one-way valve such that only negative pressure pulses are transmitted to the said one chamber.

5. A float type carburetor including an acceleration pump, substantially as described with reference to Figure 3 of the accompanying drawings.