WO1995025883A1

WO1995025883A1 - Gas mixer

Info

Publication number: WO1995025883A1
Application number: PCT/AU1995/000142
Authority: WO
Inventors: Louie Doria; Edino Fabro
Original assignee: L & J Doria Pty. Ltd.; Fabro Engineering Pty. Ltd.
Priority date: 1994-03-18
Filing date: 1995-03-17
Publication date: 1995-09-28
Also published as: AUPM457194A0

Abstract

A gas mixer for mixing gaseous fuels such as liquid petroleum gas or compressed natural gas with air in the inlet tract of an internal combustion engine comprising an annulus (1) with a throat (4) placed in the air inlet tract and an axially sliding plunger (7) having an outwardly flaring skirt (18) which aligns with and restricts air flow through the throat (4) at idle. As air inlet velocity increases, pressure on the skirt (18) causes the plunger (7) to move axially and open the air passage through throat (4) while simultaneously opening a gas inlet valve (31) to admit more gas to the engine. Movement of the plunger (7) is dampened by an air chamber (26) formed between a bell (20) and a cylindrical block (10) to prevent unwanted vibration or fluttering of the plunger (7).

Description

GAS MIXER TECHNICAL FIELD This invention relates to a gas mixer and has been devised particularly though not solely for mixing gaseous fuels with air for induction into an internal combustion engine.

BACKGROUND ART

In the past some internal combustion engines such as those used in motor vehicles have been fuelled with various types of gaseous fuels such as liquid petroleum gas (LPG) or compressed natural gas (CNG) . Some such vehicles are equipped for so-called "dual fuel" applications where there is provided normal liquid fuel mixing apparatus, e.g. one or more carburettors or a fuel injection system and in addition a "gas mixer" which is used to mix the gaseous fuel with the incoming air to the engine when the engine is running on the gaseous fuel.

In some applications there is no provision for liquid fuel and there is simply the provision of a gas mixer for mixing the gaseous fuel with air for induction into the engine.

Although it is generally recognised that it is desirable to maintain the air to gas ratio at approximately 14.8 :1 when using gaseous fuels such as LPG and CNG, currently known gas mixers are unable to maintain this ratio over the full range of operating conditions. It is common for the engine to run excessively lean at various stages of operation and excessively rich during other phases of operation depending on the throttle opening in the inlet tract and the inlet manifold pressure depression (vacuum) .

DISCLOSURE OF THE INVENTION The present invention therefore provides apparatus for mixing gaseous fuels with air for induction into an internal combustion engine, said apparatus comprising an annulus adapted to be inserted into an induction tract of the engine, the internal surfaces of the annulus being configured to define a throat, a plunger having an outwardly flaring skirt and being mounted in one or more axial bearings so as to be slideably supported within the annulus, biasing means operable between the plunger and the annulus to bias the plunger into a position where the skirt is substantially in alignment with the throat, the plunger being arranged such that inlet air passing through the throat impinges upon the outwardly flaring skirt causing the plunger to move axially against the action of the biasing means, gas inlet means connected to a supply of gaseous fuel and arranged to direct that fuel to the downstream part of the plunger, the gas inlet means incorporating a gas flow control valve operable by movement of the plunger to deliver a predetermined flow rate of gaseous fuel to the downstream part of the plunger when the skirt is in alignment with the throat, and an increasing flow of gaseous fuel as the skirt moves away from the throat against the action of the biasing means.

Preferably the gas flow control valve is formed by a portion of the plunger sliding across an opening in a conduit forming part of the gas inlet means.

Preferably gaseous fuel passing through the gas flow control valve is directed to a chamber surrounding part of the plunger and passes from the chamber to the downstream side of the skirt through one or more apertures in the plunger.

Preferably movement of the plunger relative to the annulus is dampened by an air chamber containing a volume of air which varies upon movement of the plunger, the air being allowed to leak to and from the chamber at a controlled rate.

BRIEF DESCRIPTION OF THE DRAWINGS Notwithstanding any other forms that may fall within its scope one preferred form of the invention will now be described by way of example only with reference to the accompanying drawing which is an axial section through a gas mixer according to the invention. MODES FOR CARRYING OUT THE INVENTION In the preferred form of the invention a gas mixer particularly suitable for use in automotive internal combustion engines, but also applicable to other types of internal combustion engine is constructed as follows.

The gas mixer comprises an annulus 1 typically cast from a suitable metal such as aluminium alloy and adapted to be inserted into an inlet tract of the internal combustion engine with an upstream end 2 and a downstream end 3. The gas mixer would typically be installed immediately upstream of the throttle body of the engine but may be installed in other positions if desired.

The internal surfaces of the annulus are configured to define a throat 4 typically by providing a gradually inclined frusto-conical surface 5 terminating in the throat 4 followed by a more sharply inclined frusto- conical surface 6.

Mounted within the annulus 1 is a plunger 7 slideably mounted in axial bearings 8 and 9 machined in a support body 10 located coaxially within the annulus 1 by way of a post 11. The plunger typically has a rod-like shaft 12 being enlarged at a shoulder portion 13 to a body 14 which in turn enlarges outwardly through shoulder portions 15 to define a cylindrical portion 16 supported within the axial bearing surface 8. The cylindrical portion 16 in turn enlarges in diameter over shoulder portion 17 before terminating in an outwardly flaring skirt 18.

The plunger is typically turned or otherwise machined about a central axis 19 which in use is located on the axis of the annulus 1 by the configuration of the post 11 and the support body 10.

The shoulders 17 and 13 abut respective surfaces in the support body 10, causing the edges of the outwardly flaring skirt 18 to align with the throat 4 in the annulus 1.

The shaft 12 is further provided with a bell portion 20 which extends outwardly and downwardly from the end 21 of the shaft 12 where it is conveniently secured, e.g. by a split pin 22. The bell portion has a skirt 23 having a cylindrical machined inner surface 24 which aligns with and slides over a corresponding cylindrical surface 25 on the support body 10, defining an air chamber 26 within the bell portion.

Biasing means in the form of a compression spring 27 is provided operable between the underside of the bell portion 20 and the end 28 of the support body 10 to bias the plunger into the position shown in the accompanying drawing.

The surface 24 of the skirt 23 and the surface 25 of the support body 10 are machined to provide a predetermined clearance gap therebetween allowing leakage of air from the air chamber 26 to the surrounding annulus at a controlled rate.

The post 11 incorporates a conduit 29 adapted to be connected at its free end 30 to a supply of gaseous fuel. The conduit 29 terminates in the support body 10 in a location where it is partially closed off by the cylindrical portion 16 of the plunger 7 when the plunger is in the position shown in the accompanying drawing. A small opening 31 is however left between the shoulder portion 15 of the plunger 7 and the support body 10 allowing gaseous fuel to pass from the conduit 29 into chamber 34 defined within the support body. The gaseous fuel can then pass through one or more apertures 32 in the shoulder portions 15 to the downstream part of the plunger 7 where it can mix with air passing through the opening between the outwardly flaring skirt 18 and the throat 4.

In use, with the internal combustion engine at idle, gaseous fuel is mixed with air in the manner described above by passing up the conduit 29 through the opening 31 and into chamber 34 from where it passes through opening 32 to mix with the air moving through the annulus in the inlet tract of the engine and pass out through the downstream end of the gas mixer. As the throttle of the engine is opened, more air is induced to flow through the annulus 1, impinging on the outer surface 33 of the outwardly flaring skirt 18 and causing the plunger to move axially against the action of the spring 27. As the plunger moves axially, the opening 31 is enlarged causing more gaseous fuel to be admitted from the inlet conduit 29 and to mix with the air passing through the annulus.

The axial movement of the plunger is dampened, and prevented from chattering, i.e. the shoulders 17 and 13 bouncing against the respective surfaces of the support body 10, by the air within the air chamber 26. As the plunger moves axially, air is compressed within the air chamber 26 and leaks out into the annulus between the skirt 23 and the cylindrical surface 25. This leakage at a controlled rate dampens the axial movement of the plunger within the support body 10.

As the throttle of the engine is closed, the flow of air through the annulus reduces therefore reducing the pressure on the surface 33 of the outwardly flaring skirt 18. The spring 27 then causes the plunger to retract at least partially toward the position shown in the accompanying diagram reducing the flow of gaseous fuel into the engine by partially closing the opening 31. In this manner a gas mixer for an internal combustion engine is provided which automatically regulates the flow rate of gaseous fuel into the engine in a desired ratio to the volume of air being induced through the inlet tract.

Claims

CLAIMS:

1. Apparatus for mixing gaseous fuels with air for induction into an internal combustion engine, said apparatus comprising an annulus adapted to be inserted into an induction tract of the engine, the internal surfaces of the annulus being configured to define a throat, a plunger having an outwardly flaring skirt and being mounted in one or more axial bearings so as to be slideably supported within the annulus, biasing means operable between the plunger and the annulus to bias the plunger into a position where the skirt is substantially in alignment with the throat, the plunger being arranged such that inlet air passing through the throat impinges upon the outwardly flaring skirt causing the plunger to move axially against the action of the biasing means, gas inlet means connected to a supply of gaseous fuel and arranged to direct that fuel to the downstream part of the plunger, the gas inlet means incorporating a gas flow control valve operable by movement of the plunger to deliver a predetermined flow rate of gaseous fuel to the downstream part of the plunger when the skirt is in alignment with the throat, and an increasing flow of gaseous fuel as the skirt moves away from the throat against the' action of the biasing means.

2. Apparatus as claimed in claim 1 wherein the gas flow control valve is formed by a portion of the plunger sliding across an opening in a conduit forming part of the gas inlet means.

3. Apparatus as claimed in either claim 1 or claim 2 wherein gaseous fuel passing through the gas flow control valve is directed to a chamber surrounding part of the plunger and passes from the chamber to the downstream side of the skirt through one or more apertures in the plunger.

4. Apparatus as claimed in any one of the preceding claims wherein the internal surfaces of the annulus when considered in the direction of air flow therethrough comprise a converging frusto-conical surface terminating at the throat followed by a diverging frusto-conical surface.

5. Apparatus as claimed in claim 4 wherein the angle of convergence of the converging frusto-conical surface is significantly less than the angle of divergence of the diverging frusto-conical surface.

6. Apparatus as claimed in any one of the preceding claims wherein movement of the plunger relative to the annulus is dampened by an air chamber containing a volume of air which varies upon movement of the plunger, the air being allowed to leak to and from the chamber at a controlled rate.

7. Apparatus as claimed in claim 6 wherein the air chamber is formed from a bell portion mounted on and moving with the plunger, the bell portion incorporating a cylindrical skirt having its free inner end slideable engaged over a cylindrical block axially located within the annulus.

8. Apparatus as claimed in claim 6 wherein the clearance between the cylindrical skirt and the cylindrical block provides a predetermined amount of air leakage from the air chamber upon axial movement of the bell portion toward the cylindrical block.

9. Apparatus as claimed in either claim 7 or claim 8 wherein the biasing means comprises a compression spring operable between the bell portion and the cylindrical block.