GB2207192A

GB2207192A - Carburettor

Info

Publication number: GB2207192A
Application number: GB08717014A
Authority: GB
Inventors: William Richard Davison
Original assignee: Ford Motor Co
Current assignee: Ford Motor Co
Priority date: 1987-07-18
Filing date: 1987-07-18
Publication date: 1989-01-25
Also published as: GB8717014D0

Abstract

A fixed-venturi carburettor has a booster venturi 14 mounted in the barrel 10 to increase the depression. At the lower end of the booster, an auxiliary plate 20 is fitted, extending generally in the direction of flow through the barrel and extending at least partially around the barrel axis. Various shapes and plate dimensions are disclosed. <IMAGE>

Description

CARBURETTOR This invention relates to a carburettor for a motor vehicle internal combustion engine, to a retro-fit accessory for fitting in an existing carburettor and to a carburettor booster venturi for fitting in an existing carburettor.

The demands on carburettors in terms of fuelling performance are particularly high as a result of the movement towards low exhaust emission engines. When low emissions are achieved by operation with an air/fuel mixture with a high air:fuel ratio (so-called lean burn engines), then the carburettor has to ensure that the small fuel quantity being introduced is introduced at the right place, at the right time and in the right form.

Failure to achieve these criteria may result in emission levels not being met, or in poor "drivability", i.e. in a car fitted with the engine not running smoothly.

According to the invention, there is provided a fixed venturi carburettor having a throttle barrel containing a venturi, a throttle plate and a booster venturi mounted centrally in the barrel upstream of the throttle plate wherein an auxiliary plate is mounted in the barrel between the throttle plate and the booster venturi, which plate extends generally parallel to the barrel axis and extends at least partially around the axis.

By "generally parallel", we mean that the basic direction of the walls is in line with the axis of the barrel, but a draft necessary for production may be present, and an inclination of the wall to the axis of up to about 15 to 200 may be acceptable.

Preferably the auxiliary plate either touches or is close to the wall of the booster venturi and either touches or is in close proximity to the wall of the barrel.

If the auxiliary plate does touch the booster venturi wall, then the area of contact should be as small as possible and small enough not to affect the depression created by the venturi.

The carburettor is preferably a downdraught carburettor, although the principle of the invention could also be applied to a sidedraught carburettor.

It has surprisingly been found that the presence of an auxiliary plate as set forth above can provide a substantial improvement in drivability in an engine running on a lean air/fuel mixture (e.g. a mixture varying, depending on throttle opening and load of between 16:1 and 22:1).

The plate is preferably curved with a radius of curvature greater than that of the booster venturi cylindrical wall and preferably occupies an arc greater than 600 and less than 1800. A preferred arc is about 1050.

Because of the need to avoid a reduction in the depression created by the booster venturi, a complete circle is not likely to be possible as this would have contact with the venturi wall over a relatively large arc. However a closed shape around the venturi axis is possible. One example of such a shape ' is a three-cornered shape based on an equilateral triangle but with the sides curved rather than straight.

Where the plate is curved in one or more arcs, the axis from which the or each arc is generated will normally be parallel to (but spaced from) the axis of the venturi booster.

The plate does not have to be curved; it may be of rectilinear form with the shape imposed by bending of the plate at one or more positions along bend lines which lie parallel to the venturi axis.

The plate preferably extends at least 5mm below the bottom of the booster venturi, and must not interfere with the movement of the throttle plate. Good results have been obtained with a plate which extends 8 mm below the bottom of the venturi.

In a twin barrel carburettor, an auxiliary plate may be provided in the primary barrel only.

The auxiliary plate can be supported in the carburettor either by attaching it to the downstream end of the booster venturi, or by providing it with a mount by which it can be separately supported in the carburettor barrel.

Accordingly, a second aspect of the invention provides a carburettor booster venturi unit comprising a tubular central passage, means for supporting the passage in the barrel of a carburettor and for introducing fuel into the passage, and a plate fitted to the downstream end of the barrel and extending at least partially around the axis of the carburettor barrel and generally parallel to the said axis.

A third aspect of the present invention provides an auxiliary plate for mounting in the barrel of a carburettor, the plate comprising an operative surface and means for supporting the operative surface in a carburettor barrel so that at least part of the surface extends between a booster venturi and a throttle flap mounted in the barrel, the surface extending generally parallel to the axis of the barrel and extending at least partially around the axis.

The invention will now be further described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a sectional view through a carburettor according to the invention; Figure 2 is a cross-section on the line A-A from Figure 1; Figure 3 is a cross-section on the line -A-A from Figure 1 but showing an alternative embodiment to that of Figure 2; and Figure 4 is a perspective view of a booster venturi for a carburettor according to the invention.

The carburettor shown in Figure 1 has a conventional barrel 10 with a neck 12 which forms a venturi. Supported within the barrel is a booster venturi 14 in the form of a tube coaxial with the barrel 10. The booster itself is shown in more detail in Figure 4. A fuel inlet 16 communicates with the internal space of the booster. At the bottom of the barrel. a conventional throttle flap 18 is fitted.

An auxiliary plate or shroud 20 is attached to the lower end of the booster and, as can be seen from Figures 2 and 3, extends around the booster passage, is in contact with the barrel walls and touches the booster at one point 22.

In Figure 2, the plate 20 is arcuate and occupies an arc (Figure 4) of about 1050.

In Figure 3, the plate has three faces, each of an arcuate form, each touching the booster 14 at one point and each touching the internal barrel wall. As shown, the outer ends of the faces also meet each other at the point where they touch the barrel wall.

The purpose of the booster 14 is to increase the depression in the carburettor barrel, and to this end the lower end of the booster is aligned with the neck 12. If the lower edge of the booster is interfered with, the designed depression may not be achieved. It is therefore important that any contact between the plate 20 and the lower edge of the booster be limited to the smallest possible area.

At the same time however, it appears necessary for the plate to approach as close as possible to the booster. The two forms of plate shown in Figures 2 and 3 provide two forms which have been found to work in practice.

In one practical embodiment, where the invention was put into effect in a-Weber TLDM carburettor, the dimensions shown in Figure 4 had the following values: A = 12 mm B = 8 mm C = 1050 These specific values are not to be regarded as limiting in any way, and numerous other shapes and dimensions may be employed in putting the invention into practice.

Claims

1. A fixed venturi carburettor having a throttle barrel containing a venturi, a throttle plate and a booster venturi mounted centrally in the barrel upstream of the throttle plate , wherein an auxiliary plate is mounted in the barrel between the throttle plate and the booster venturi, which plate extends generally parallel to the barrel axis and extends at least partially around the axis.

2. A carburettor as claimed in Claim 1, wherein the auxiliary plate either touches or is in close proximity to the wall of the booster venturi and either touches or is in close proximity to the wall of the barrel.

3. A carburettor as claimed in Claim 1 or Claim 2, and being a downdraught carburettor.

4. A carburettor as claimed in any preceding claim,.

wherein the auxiliary plate is curved with a radius of curvature greater than that of the booster venturi cylindrical wall.

5. A carburettor as claimed in Claim 4, wherein the auxiliary plate occupies an arc greater than 600 and less than 1800.

6. A carburettor as claimed in Claim 4 or Claim 5, wherein the auxiliary plate occupies an arc of about 1050.

7. A carburettor as claimed in any preceding claim, wherein the auxiliary plate forms a closed shape around the venturi axis.

8. A carburettor as claimed in Claim 7, wherein the shape is a three-cornered shape based on an equilateral triangle but with the sides curved rather than straight.

9. A carburettor as claimed in any preceding claim, wherein the auxiliary plate is curved in one or more arcs, and the axis from which the or each arc is generated is parallel to, but spaced from, the axis of the venturi booster.

10. A carburettor as claimed in any one of Claims 1 to 3, wherein the auxiliary plate is of rectilinear form with the shape imposed by bending of the plate at one or more positions along bend lines which lie generally parallel to the venturi axis.

11. A carburettor as claimed in any preceding claim, wherein the plate extends at least 5mm below the bottom of the booster venturi.

12. A carburettor as claimed in Claim 11, wherein the auxiliary plate extends 8 mm below the bottom of the venturi.

13. A carburettor as claimed in any preceding claim with twin barrels, wherein an auxiliary plate is provided in the primary barrel only.

14. A carburettor as claimed in any preceding claim, wherein the auxiliary plate is supported in the carburettor by attaching it to the downstream end of the booster venturi.

15. A carburettor as claimed in any one of claims 1 to 13, wherein the auxiliary plate is provided with a mount by which it can be separately supported in the carburettor barrel.

16, A carburettor as claimed in any one of Claims 1 to 13, wherein the auxiliary plate is cast integrally with the carburettor barrel.

17. A carburettor booster venturi unit comprising a tubular central passage, means for supporting the passage in the barrel of a carburettor and for introducing fuel into the passage, and a plate fitted to the downstream end of the barrel and extending at least partially around the axis of the carburettor barrel and generally parallel to the said axis.

18. An auxiliary plate for mounting in the barrel of a fixed venturi carburett-or; the plate comprising an operative surface and means for supporting the operative surface in a carburettor barrel so that at least part of the surface extends between a booster venturi and a throttle flap mounted in the barrel, the surface extending generally parallel to the axis of the barrel and extending at least partially around the axis.

19. A fixed venturi carburettor substantially as herein described with reference to any embodiment shown in Figures 1 to 3 of the accompanying drawings.

20. A booster venturi unit substantially as herein described with reference to Figure 4 of the accompanying drawings.