GB2227524A

GB2227524A - Carburettor idling fuel filter arrangement

Info

Publication number: GB2227524A
Application number: GB8928324A
Authority: GB
Inventors: Paolo Venturi; Domenico Cannone
Original assignee: Weber SRL
Current assignee: Weber SRL
Priority date: 1988-12-16
Filing date: 1989-12-14
Publication date: 1990-08-01
Also published as: IT8853601V0; FR2640693B1; BR6902585U; IT215053Z2; GB8928324D0; FR2640693A1; DE3939824A1

Abstract

A filter cartridge 14 is located in a duct 13 supplying idling fuel to a chamber 11 where it is mixed with air from a duct 22, 23, 25. The cartridge 14 includes a mesh 42 supported at one end by a head 43 located by the blind end of the duct 13 and at the other by a tubular head 41 located and sealed by bushes 56, 62. The bush 56 has a hole (57, Fig. 2) for fuel flow into the chamber 11. <IMAGE>

Description

CARBURETTOR WITH IMPROVED IDLING FILTER DEVICE The present invention relates to a carburettor provided with a device of improved type for the supply of an idling engine.

It is known that a carburettor essentially comprises a chamber or tank from which the engine sucks air which is mixed with the fuel in a diffuser. A butterfly valve located downstream of the diffuser regulates the flow of the mixture to the engine cylinders. The device for supplying the engine during idling comprises a duct which discharges downstream of the butterfly valve and via which the engine sucks a sufficient quantity of fuel to keep running. Obviously the engine also sucks a predetermined quantity of air through this duct which is mixed with the fuel before reaching the idling mixture outlet hole. An idling mixture regulation screw is also installed along this hole.

The main drawback of the carburettor described above is that, during idling, any impurities in the carburettor, for instance, those which may have been formed during the machining of the carburettor components, can travel along the corresponding duct.

The object of the present invention is to provide a carburettor equipped with a device for the supply of an idling engine which prevents the impurities present in the carburettor from travelling into the engine.

According to the present invention, there is provided a carburettor with a device of improved type for the supply of an idling engine comprising a first duct for supplying fuel to a mixing chamber, a second duct for supplying air to said chamber and a third duct which discharges downstream of a flow regulation valve disposed along the mixture supply duct for supplying the fuel/air mixture from said chamber to the engine, a filter cartridge installed in a portion of the first duct and having means by which it can be centred in said portion, the cartridge being adapted to retain impurities carried by the fuel and which may be present in the carburettor.

Preferably, the first duct comprises a blind hole which has a substantially conical base wall, the centring means comprising a lower head having a substantially frustoconical lower portion engaging with said base wall, the cartridge having a tubular upper head, a cylindrical filter mesh and a lower cylindrical head which comprises an upper portion supporting the mesh, a central portion with a smaller diameter than the upper portion and the lower centering portion, an outlet of a fuel supply duct being provided at the location of the central portion so that the fuel is not subjected to constriction as a result of the smaller diameter of this central portion, the diameter of the upper portion being such that the area defined between this portion and the inner wall of the blind hole is greater than the area of the outlet of the fuel supply duct.

In a preferred embodiment, the cartridge is pressed against the base wall by a bush pressed by a threaded shank of a member screwed along an upper threaded portion of said blind hole, said bush being adapted to communicate internally with the interior of the cartridge and having an intermediate portion in which there is provided a calibrated hole for the discharge of fuel whose outer surface defines the mixing chamber with the inner portion of a central section of the blind hole.

Preferably, hydraulic sealing means are located between the mixing chamber and a lower section of the blind hole which houses the cartridge so that the fuel flows only into the interior of the bush and is discharged therefrom to the mixing chamber only via the calibrated hole.

Preferably, the filter mesh is supported by at least two uprights provided between the heads of the cartridge.

Conveniently, a carburettor mounting is provided in which there is provided the mixture supply duct and a cover in which the first and second ducts and part of the third duct are formed.

A preferred embodiment of the present invention will now be described, by way of example only, with reference to the attached drawings, in which Figure 1 is a partial sectional view of a carburettor fitted with a filter device of the invention, Figure 2 is a sectional view on an enlarged scale of part of the device of Figure 1, Figures 3 and 4 are side views at two different angles of a filter cartridge, and Figures 5 and 6 are sections along the lines V-V and VI-VI-of Figure 3 respectively.

Referring to Figure 1, there is shown a carburettor 1 which comprises a carburettor mounting 2 in which a duct 3 is formed for the supply of fuel to an internal combustion engine (not shown). A butterfly valve 4 is located in this duct 3 and actuated by a known mechanism in order to regulate the flow of the air and fuel mixture which has been formed downstream of this valve 4 in a diffuser 5. The carburettor mounting 2 is provided with a cover 6 in which at least one chamber is provided and houses an emulsifier of known type. A second body 7 in which the diffuser 5 is provided is located between the carburettor mounting 2 and the cover 6.

With reference to Figures 1 and 2, the carburettor 1 comprises a device 8 which enables the supply of fuel to an idling engine (not shown). This device 8 comprises a duct supplying the fuel to a chamber 11, a duct supplying air from outside to the chamber 11 in which the air and fuel is mixed, a duct supplying the fuel/air mixture to the duct 3 immediately downstream of the butterfly valve 4 and an idling mixture regulation screw 12 via which the flow of this mixture is regulated.

The first duct requires the provision on the cover 6 of a blind hole 13 whose axis is parallel to the axis of the duct 3. A filter cartridge 14 adapted to retain any impurities carried by the fuel and present in the carburettor 1 as a result of the machining of its components is located in this blind hole 13. From its top downwards, the hole 13 has a first threaded section 15, a second non-threaded section at which location the chamber 11 is formed, a third section 16 of reduced diameter which thus forms an annular shoulder 17 with the second section, and a conical base wall 18. A duct 21 connected to the fuel tank (not shown) discharges the fuel into the hole 13 in the vicinity of this wall 18.

The second duct requires the provision on the cover 6 of a second blind hole 22 of a smaller longitudinal extension to the side of the hole 13. A calibrated bush 23 by means of which air is taken in from atmosphere is mounted at the top of this hole 22. A duct 24 for the supply of air to the tank or to the diffuser 5 starts from the hole 22 and a duct 25 which discharges into the chamber 11 starts from the opposite side.

The third duct requires the provision of a duct 26 which starts from the chamber 11 and discharges into the duct 3 downstream of the butterfly valve 4. This duct 26 has a first section 27 formed in the cover 6 and which starts from the chamber 11 coaxially with the duct 25, a second smaller section 28 formed in the cover 6 and which is parallel to the hole 13, a third section 31 formed in the body 7 coaxially with the section 28, a fourth section 32 formed in the carburettor mounting 2 coaxially with the section 31 and a fifth smaller section 33 perpendicular to the section 32 and which discharges into the duct 3. A seat 34 is formed coaxially with the section 33 in the carburettor body 2, to receive the conical point 35 of the idling mixture regulation screw 12 which regulates the flow of the mixture into the section 33.

Immediately downstream of the butterfly valve 4 there is a hole 36 which places the ducts 26 and 3 in communication with each other. This hole 36 is normally called a progression hole since it enables a quantity of mixture allowing a uniform increase in the angular speed of the engine, starting naturally from idling, to be supplied during the opening of the butterfly valve 4.

As shown in Figures 2 to 6, the filter cartridge 14 comprises a tubular upper head 41, a cylindrical filter mesh 42 and a lower head 43 formed by a solid cylindrical body shaped so that it can be centered, and thereby centre the cartridge 14 in the hole 13. The filter mesh 42 has an upper end which engages within the head 41 and a lower end which engages in an annular seat provided in the head 43. Two uprights 44 through which the mesh 42 passes and which therefore form a support for this mesh are provided between the heads 41 and 43. The head 43 has an upper portion 45 in which the seat for the lower end of the mesh 42 is provided, a central portion 46 of smaller diameter and a lower portion 47 of the same diameter as the portion 45 and having a frustoconical end section.In operation, the lower portion 47 engages with the conical base wall 18 of the hole 13 thereby allowing the cartridge 14 to be centered therein. The central portion 46 is then opposite the outlet of the duct 21. The diameter of the portion 46 is calculated so as to prevent the flow of fuel supplied by the duct 21 from being constricted, while the diameter of the portion 45 is calculated so that the extension of the area defined between this portion and the inner wall of the section 16 of the hole 13 is greater than the extension of the area defined by the outlet of the duct 21.

With reference to Figures 1 and 2, the filter cartridge 14 is retained in the hole 13 and more precisely in its section 16 by a cylindrical bush 51 pressed against the head 41 of a cylindrical body 52. The bush 51 in particular has a hollow interior and has, from the top downwards, a first portion 53, a second smaller portion 54 of greater diameter which defines, together with the portion 52, an annular shoulder 55, a third portion 56 which is located opposite the chamber 11 and which has a calibrated through radial hole 57, a fourth smaller portion 58 of a diameter greater than the diameter of the portion 56, and a frustoconical end portion 61. A second bush 62 which has an outer annular shoulder 63 which abuts against the shoulder 17 is force-fitted at the location of the head 41 of the filter cartridge 14 between the latter and the inner wall of the hole 13.

The bush 62 is suitably dimensioned so that a respective hydraulic seal is formed between this bushing and the head 41 and between this head and the inner wall of the hole 13. The frustoconical portion 61 of the bush 51 presses, during operation, on the inner corner of the upper end of the bush 62 thereby exerting a pressure on the cartridge 14 via the bush 62 and forming a hydraulic seal between the interior of the cartridge 14 and the chamber 11. The body 52 has a portion 65 outside the hole 13 and a tubular portion 66 which is externally threaded so that it can be screwed along the section 15 of the hole 13. The upper portion 53 of the bush 51 is therefore within the portion 66 and the end of the tubular portion 66 abuts against the shoulder 55 thereof.

In operation, when the engine is idling, a drop in pressure or depression is created downstream of the butterfly valve 4 which causes the air and fuel mixture to be sucked along the duct 26 and thus causes fuel to be sucked from the duct 21 and air to be sucked via the calibrated bush 23. The fuel enters the hole 13 at the location of the central portion 46 of the head 43 of the cartridge 14. The fuel then passes through the filter mesh 42 which retains the impurities conveyed by the fuel and is introduced into the chamber 11 via the bush 51 and the hole 57 thereof. A predetermined quantity of air is mixed with the fuel supplied to the chamber 11 via the bush 23, the hole 22 and the duct 25 and this forms a fuel/air mixture which is sucked through the duct 26. During idling, the butterfly valve 4 is in a position which substantially obstructs the duct 3.The fuel/air mixture is thus supplied to the duct 3 solely via the section 33 of the duct 26.

The advantages which can be achieved with the illustrated embodiment of the present invention should be evident from the above description. However, in particular, a filter is provided which makes it possible to retain impurities carried by the fuel and present in the carburettor 1 as a result of the machining of its components which is located along the duct for the supply of fuel to the idling engine. As is evident, this filtering will protect the engine from any damage these impurities can cause. In addition, the filter cartridge 14 is shaped so that it can be securely and efficiently centered along its housing seat. The dimensions of the head 43 of the cartridge 14 are calculated so that they do not constrict the flow of fuel. It should be noted that the filter cartridge 14 is installed on the cover 6 of the carburettor 1 and is thus in a position which facilitates its installation and replacement. It should be noted lastly that simple components allowing the cartridge 14 to be held in position and at the same time providing hydraulic seals between the section 16 of the hole 13 and the chamber 11 are provided along the hole 13.

Claims

1. A carburettor with a device of improved type for the supply of an idling engine comprising a first duct supplying fuel to a mixing chamber, a second duct supplying air to said chamber and a third duct which discharges downstream of a flow regulation valve disposed along the mixture supply duct for supplying the fuel/air mixture from said chamber to the engine, a filter cartridge installed in a portion of the first duct and having means by which it can be centered in said portion, the cartridge being adapted to retain impurities carried by the fuel and which may be present in the carburettor.

2. A carburettor as claimed in claim 1, wherein the first duct comprises a blind hole having a substantially conical base wall, the centering means comprising a lower head having a substantially frustoconical lower portion engaging with said base wall.

3. A carburettor as claimed in claim 2 wherein the cartridge has a tubular upper head, a cylindrical filter mesh and a lower cylindrical head which comprises an upper portion supporting the mesh, a central portion with a smaller diameter than the upper portion and the lower centering portion, an outlet of a fuel supply duct being provided at the location of the central portion so that the fuel is not subjected to constriction as a result of the smaller diameter of this central portion, the diameter of the upper portion being such that the area defined between this portion and the inner wall of the blind hole is greater than the area of the outlet of the fuel supply duct.

4. A carburettor as claimed in claim 3 wherein the cartridge is pressed against the base wall by a bush pressed by a threaded shank of a member screwed along an upper threaded portion of said blind hole, said bush being adapted to communicate internally with the interior of the cartridge and having an intermediate portion in which there is provided a calibrated hole for the discharge of the fuel whose outer surface defines the mixing chamber with the inner portion of a central section of the blind hole.

5. A carburettor as claimed in claim 4, wherein hydraulic sealing means are located between the mixing chamber and a lower section of the blind hole which houses the cartridge so that the fuel flows only into the interior of the bush and is discharged therefrom to the mixing chamber only via the calibrated hole.

6. A carburettor as claimed in any one of claims 3 to 5, wherein at least two uprights supporting the filter mesh are provided between the heads of the cartridge.

7. A carburettor as claimed in any one of the preceding claims comprising a carburettor mounting in which there is provided the mixture supply duct and a cover in which the first and second ducts and part of the third duct are formed.

8. A carburettor including a device of improved type for the supply of an idling engine as described and illustrated with reference to the attached drawings.