GB2224776A

GB2224776A - I.c. engine carburetted mixture atomiser

Info

Publication number: GB2224776A
Application number: GB8923911A
Authority: GB
Inventors: David John Buckingham
Original assignee: Individual
Current assignee: Individual
Priority date: 1988-10-25
Filing date: 1989-10-24
Publication date: 1990-05-16
Also published as: GB8923911D0; GB8824985D0

Abstract

A synthetic rubber membrane 10 about 1mm thick with a central hole 18 bounded by a multiplicity of radial petals 16 is installed between a carburettor and an inlet manifold. Flow through the hole 18 bows the petals 16 resiliently, thus increasing the size of the hole 18 and providing a tapered lead-in. There may be an annular channel (38, Fig. 2) for feeding air inwardly downstream of the membrane 10. Holes 22 provide some mixture flow to prevent stagnation downstream of the membrane. <IMAGE>

Description

INTERNAL COMBUSTION ENGINE This invention relates to an internal combustion engine including a device for promoting the mixing of fuel and air, which may thus improve the fuel economy of the engine. In another aspect it relates to a method of producing such an engine by the installation of such a device.

A known economy device for an internal combustion engine comprises a ring with a tapering bore, or just an annular plate, which is fitted in the passage between the carburettor and the inlet manifold of the engine. It provides a restricted orifice in the passage and directs any layer of liquid fuel from the wall of the outlet passage of the carburettor into the centre of the inlet manifold to improve mixing of the fuel and air and to improve atomisation of the liquid fuel.

The present invention provides in a first aspect an internal combustion engine including a carburettor communicating with an inlet manifold for feeding a fuel/air mixture thereto, and wherein the communication is via a device for promoting the mixing of fuel and air, comprising an obstruction in the flow path for said communication, the obstruction having a generally central orifice therethrough, the size of which orifice is variable and is arranged to increase in use with the rate of flow of fuel and air along said path. Preferably the obstruction is provided (at least when fuel and air are flowing) with a portion with a tapering bore which forms a tapered lead-in to the orifice.

In a preferred form, the obstruction is provided by a plurality of inwardly extending segments of a resiliently flexible material, whereby an increase in flow rate deflects the segments to provide or increase in size a central orifice defined by the segments. The segments in their deflected condition will then form the tapered bore portion. Although the segments could completely close the passage when there is no flow, so that there is no orifice, it is preferred that they still define an orifice when there is no flow. The resiliently flexible material could be any such material which is resistant to attack by the air/fuel mixture, for example nitrile rubber.

Preferably the obstruction is provided with peripheral holes. Some of the air/fuel mixture will therefore flow through the peripheral holes, and prevent the formation of a stagnation region downstream of the obstruction.

In one embodiment, an air jet is directed into the centre of the passage for fuel and air from the periphery thereof, so as to enhance the lifting of any fuel layer from the wall of the passage. Suitably this peripheral air jet is located downstream from the obstruction.

In a second aspect the invention comprises a method of producing an engine according to the first aspect by installing a device as defined above between a carburettor and an inlet manifold so as to obstruct variably a fuel/air flow path between them.

Internal combustion engines embodying the invention will now be described by way of example, with reference to the accompanying drawings, in which: Fig. 1 is a plan view of a device for use in one embodiment; and Fig. 2 is a sectional view of a modified embodiment of engine including such a device.

The device seen in Fig. 1 comprises a membrane 10 of a resiliently flexible material such as synthetic rubber (e.g. nitrile rubber) of a thickness of about lmm or a little less. The membrane has an external shape which corresponds to the shape of the mounting flange of the carburettor of the engine to which it is to be fitted, and in use the membrane is fitted in place of the conventional sealing gasket between the carburettor mounting plate and the engine inlet manifold. For this purpose, the membrane has two opposed mounting holes 12 to accommodate the mounting bolts of the carburettor.

The drawing shows a typical external shape and arrangement of mounting holes 12; however modifications can easily be made to suit any given carburettor and inlet manifold.

In the centre of the membrane, within a region which in use is bounded by the wall of the outlet passage of the carburettor (shown by a dotted line 14 in Fig. 1), are a plurality of inwardly extending segments 16, forming a petal-like structure. In the very centre of the device, these segments 16 define a circular orifice 18. At the root of each slit 20 between adjacent segments there is a smaller circular hole 22, all of which are at the periphery of but within the wall 14 of the carburettor.

When applied to a carburettor with two (or more) choke tubes, the membrane will conveniently conform to the shape of the sealing gasket between the engine inlet manifold and the carburettor; there will be two (or more) regions bounded by the outlet of each choke tube and containing a plurality of inwardly extending segments for each of the choke tubes of the carburettor.

In use, with the device fitted as described above, when air and/or petrol flows from the carburettor to the inlet manifold, the segments 16 are resiliently deflected in the direction of flow from their normal radial positions, increasing the size of the orifice 18 and so reducing the obstruction which the segments cause to the flow. Clearly, the greater the flow the larger will the orifice 18 become. Because the segments are deflected in the direction of flow, they form a tapered lead-in to the orifice 18. This forces the air/fuel mixture towards the centre of the passage from the carburettor to the inlet manifold, and in particular petrol which may have formed in a layer on the wall of the carburettor outlet passage is deflected into the middle of the flowing air/fuel mixture, thus improving the atomisation of the fuel and thoroughly mixing it with the air.This leads to more efficient operation of the engine.

The holes 22 allow the passage of some of the fuel/air mixture near the periphery of the carburettor walls, and thus help to prevent the formation of a stagnation region downstream of the membrane. In addition, these holes 22 reduce the stress which would otherwise be present at the root of the slits 20, thus helping to prevent tears in the material of the membrane from occurring in the region of these roots.

It will be possible to devise other means for providing a variable orifice. For example, a variable iris structure (of the type used to vary the apertures of camera lenses) might be used, with direct mechanical control coupled to the throttle of the carburettor.

The modified device shown in Fig. 2 uses the same membrane 10 as seen in Fig. 1, mounted between the mounting flanges 24,26 of the carburettor 28 and engine inlet manifold 30 by means of bolts 32. The fuel/air mixture flows in the direction of arrow A. Also sandwiched between the membrane 10 and the inlet manifold flange 26 are a spacer plate 34 and a jet-forming member 36, both of which are annular. The jet-forming member has an annular channel 38 in the face abutting the plate 34, which forms an air inlet gallery, and the inner side wall 40 of this channel is slightly reduced in height so as to form a continuous peripheral jet 42 with the spacer plate 34. Air is led into the channel 38 through a conduit (not shown) at atmospheric pressure or slightly above, and because of engine vacuum forms a jet into the inlet manifold downstream of the membrane 10, as a continuous sheet indicated by arrows B. Instead of a continuous sheet, a large number of discrete jets could be provided. This air jet serves to assist the lifting of any fuel layer on the wall of the inlet manifold and further enhance mixing of the fuel and air. If desired, it could be provided upstream of the membrane 10 instead of downstream.

Claims

1. An internal combustion engine including a carburettor, communicating with an inlet manifold for feeding a fuel/air mixture thereto, said communication being via a device for promoting the mixing of fuel and air, said device comprising an obstruction in the flow path for said communication, the obstruction having a generally central orifice through it whose size is variable and is arranged to increase in use with the rate of flow of fuel and air in the passage.

2. An engine according to claim 1 wherein the obstruction is arranged to provide, at least in use when fuel and air are flowing through the orifice, a portion with a tapering bore which forms a tapered lead-in to the orifice.

3. An engine according to claim 1 or claim 2 wherein the obstruction is provided by a plurality of inwardly extending segments of a resiliently flexible material, whereby an increase in flow rate deflects the segments to provide or increase in size a central orifice defined by the segments.

4. An engine according to claim 3 wherein the segments are arranged so that they still define an orifice when there is no flow.

5. An engine according to any preceding claim wherein the obstruction is provided with peripheral holes.

6. An engine according to any preceding claim comprising a membrane of a resiliently flexible material.

7. An engine according to any preceding claim which has a plurality of fuel/air inlet tubes leading to an inlet manifold, and a said device installed at the input side of the inlet manifold and having a respective one of said obstructions for each said inlet tube.

8. An engine according to any preceding claim wherein said carburettor and inlet manifold have respective opposing flange portions, and the device has a peripheral mounting region which surrounds said obstruction and is sandwiched between the opposing flange portions.

9. An engine according to claim 8 wherein means are provided in the flow passage adjacent the obstruction for directing an air jet into the centre of the passage for fuel and air from the periphery thereof, so as to enhance the lifting of any fuel layer from the wall of the passage.

10. An inlet arrangement according to claim 9 wherein the peripheral air jet is located downstream from the obstruction.

11. An internal combustion engine including a carburettor and a device for promoting the mixture of fuel and air and being substantially as described herein with reference to and as illustrated in the accompanying drawings.

12. A method of producing an engine according to any preceding claim compriC.ing installing between a carburettor and an inlet manifold a device for promoting the mixing of fuel and air, said device providing a said obstruction in a flow path between the carburettor and the inlet manifold.