WO2006077439A2

WO2006077439A2 - A split carburettor with an improved throttle butterfly

Info

Publication number: WO2006077439A2
Application number: PCT/GB2006/000234
Authority: WO
Inventors: Stephen Glover; Stephen Morris
Original assignee: Ricardo Uk Limited
Priority date: 2005-01-22
Filing date: 2006-01-23
Publication date: 2006-07-27
Also published as: GB0501428D0; WO2006077439A3

Abstract

A carburettor comprising a throttle valve (20) , the throttle valve including a spindle mounting portion (70) , wherein the spindle mounting portion is provided with a threaded portion. The carburettor throttle disc further includes opposing closing surfaces and at least one hoop device arranged to protrude from one of the closing surfaces.

Description

A Split Carburettor with an Improved Throttle Butterfly

Field of the invention

The present invention relates to an intake passage and split carburettor and method of operation of an internal combustion engine.

More specifically the invention relates to a split carburettor where improved air and fuel management features are incorporated into the carburettor by modifications to the throttle butterfly and throttle spindle shaft.

Even more specifically the invention relates to a split carburettor and method of operation where during high power operation of the engine air and fuel is allowed to flow into the engine in sufficient quantities to allow the engine to produce correct and sufficient power.

Yet even more specifically the invention relates to a split carburettor and method of operation where the attachment of the throttle butterfly disc is made so that the engine is capable of producing correct and sufficient power and the throttle shaft and disc, when at substantially maximum throttle do not unnecessarily cause an obstruction to the air or fuel flowing into the said engine.

Background

One of the greatest challenges to current engine design is the increasing need for reduced engine emissions. This challenge continues to grow as the number of engines continues to climb and governments continually introduce more stringent emissions legislation.

Even small improvements in emissions levels of an engine are of very significant importance when multiplied across thousands or millions of engines.

It is also known that small two-stroke engines, particularly those for use with handheld products, are facing ever-stricter emission control legislation and durability requirements. Yet stricter legislation is expected in the USA in the near future and this legislation will be particularly severe for such small engines and will include limits not only on unburned hydrocarbons (HC) and carbon monoxide (CO) but also particulate emissions.

Therefore it is known that exhaust emissions may be reduced from small two stroke engines by the use of stratified charge techniques, even more specifically it is known that to reduce emissions from a stratified charge two stroke engine may be reduced even more substantially by using carburettors containing both substantially lean and substantially rich passages.

Commonly, in a related art, for example EP 1078151 B1 , which is incorporated in totality herein by reference, Figure 1 shows, a carburettor (18), employing twin passages consisting an upper passage (44), and a lower passage (42). In this carburettor the throttle disc (20) are so constructed and operated and the passages are so arranged that under low load or idling conditions, fuel is introduced into both the rich (42) and lean (44) inlet passages and therefore into both the rich and lean engine volumes of the engine (not shown). Whereas, under high load conditions substantially only air is delivered through the upper passage (44) and a fuel/air mixture is introduced into the rich passage (42).

It is important that small two stroke engines for hand held equipment must function correctly during progressive changes in the load under which the engine is operating, for example that is to start and idle whilst both cold and hot, and progress from idle to a lightly loaded condition in a smooth and correctly operating manner, and produce the correct and most suitable power for the size, dimensions and weight of the engine.

It is also of high importance that whatever method may be used to improve the emissions performance of an engine that this improvement should not significantly compromise in any way the power produced by the said engine.

Summary of the Invention

The present invention provides a carburettor arranged to supply fuel to an engine, the carburettor comprising an inlet duct, a throttling valve arranged to throttle the flow of air through the inlet duct, the inlet duct being divided over at least part of its length into at least a rich passage and a lean passage, which are arranged to communicate with a rich volume and a lean volume respectively of the engine, the carburettor and the throttle disc being adapted to supply, under high load operation, substantially all fuel into a first passage and to supply, under low load operation, substantially all fuel into a second passage; characterised in that the throttle disc is provided with a threaded portion. This provides an improved method of locating the throttle valve to the throttle spindle.

Further aspects of the invention are as defined in the accompanying claims.

The carburettor as shown in Figure 1 and disclosed in prior patent application EP1078151 is shown as a simple outline drawing only. The carburettor shown as Figure 2 is therefore a better representation of a real life carburettor as disclosed in the earlier application. It can be seen that in order to save space and provide a flat surface to affix a throttle disc (20) to a throttle shaft or spindle (70), the throttle shaft (70) may have a cross section that is half round or 'D' shaped. A single screw (72) is used to attach the throttle disc (20) to the shaft (70) by screwing into a threaded hole in the shaft (70). It can also be seen that when the throttle disc (20) is in the closed position shown in Figure 1 , the fixing screw (72) is readably accessible from the direction 'A' (shown in Figure 4) to allow for the fixing or unfixing of the screw and the throttle disc.

It is also important to note that the mechanical integrity of the throttle spindle (70) is a significant requirement. The shaft should withstand the significant wear and tear of normal use, and to ensure enduring trouble free operation a minimum diameter of approximately 5 mm is required. Figure 2 therefore shows a carburettor in which a round section shaft of approximately 5 mm diameter has been sectioned over a part of its length to provide a half round or 'D' section shaft (70) of approximately 2.5 mm section. This 'D' section allows the shaft (70) to be of appropriate strength to provide sufficient robustness and to provide a flat fixing surface for the throttle disc (20) and screw (72). It also reduces the obstruction to air flow that the full round section shaft (seen in Figure 1 on the prior art carburettor) would otherwise create.

It is therefore appreciated that the carburettor disc (20) and spindle (70) should not adversely reduce the airflow into the engine so allowing the engine to operate at an appropriate efficiency. Any significant reduction in airflow potentially reduces engine power and increases fuel consumption for a given task. It must also be appreciated that, during assembly it is imperative that the throttle disc (20) is allowed to centralise within the bore (22) of the carburettor to ensure a proper and effective seal between the throttle disc and the sidewall of the carburettor bore (22). In practice, this is achieved by a particular assembly technique. The throttle spindle (70) is first inserted through the sidewall of the carburettor, the throttle disc (20) and screw (72) are loosely assembled on to the spindle and the throttle spindle (70) is turned to the closed position as shown in Figure 1. The screw (72) is now tightened whilst the spindle (70) is held in the closed position. This ensures, due to the clearance hole that exists in the throttle disc, that the disc is centralised within the carburettor bore (22) and securely fixed to the shaft (70).

Whatever methods and improvements are therefore used to affix the throttle to the spindle, it is imperative that the aforementioned factors are taken into consideration.

The invention will now be more fully described by way of example and with reference to the following Figures:

Figure 1 is a line diagram of the prior art carburettor as found EP 1078151 B1 ;

Figure 2 is a cross section of a carburettor according to a first aspect of the invention showing a structural layout;

Figure 3a to Figure 3f is a diagram showing the first aspect of the invention;

Figure 4 is a cross section of a carburettor according to the first aspect of the invention showing a structural layout and an example of the use of the first aspect of the invention;

Figure 5a to Figure 5d is a diagram showing a second aspect of the invention in component parts;

Figure 6a and Figure 6b is a diagram showing the second aspect of the invention as an assembly; and

Figure 7 is a cross section of a carburettor as found in the second aspect of the invention showing a structural layout and an example of the use of the second aspect of the invention. An improved method of manufacturing the throttle disc is shown in Figures 3a to 3f. The blank disc 20' is first punched by a punch (110) to create an extrusion (120). The extrusion is further expanded and formed in Figure 3b where a second punch (130) both expands the extrusion and forms the recess (140). Further, in Figure 3c a third punch (150) removes the head of the extrusion and forms the parallel sides appropriate for threading. The threading operation is shown schematically in Figure 3d and the completed throttle disc with improved depth of threaded fixing is shown in Figure 3e. It can be seen in the illustrated embodiment in Figure 3f that the new improved fixing method allows an improved depth and security of thread (160) in the throttle disc 20'. It may also be appreciated in Figure 3f that the screw (72) can now be recessed into the 'D' shaped throttle shaft (70) so avoiding the reduction of airflow normally created by the screw head projecting into the air stream.

To further improve the induction of air in to the engine, and even more particularly to improve the air flow in the upper normally lean channel (44) it can be seen in Figure 4 that by relocating the 'D' section shaft (70) by 180 degrees when the throttle disc is rotated to substantially full or maximum throttle the top channel is predominately clear of obstruction normally found in other carburettors.

It is also seen that due to the screw (72) being rebated or countersunk into the shaft (70) it is still possible to access the screw for assembly and disassembly from direction 'A' allowing easy access.

To further improve the fixing of the carburettor throttle disc (20), another embodiment of the invention has been developed and shown in the illustrations of Figures 5 to 7. In this embodiment, an inlet throttle disc 20" is formed with stirrup shaped hoops (210). The hoops (210) that may be formed or pressed out from the base material of the throttle disc or attached as separate component parts suitably fixed to the throttle disc, are so shaped as to provide a flat surface (212). This surface is able to provide the locating face against which the rotational force of the spindle (213) is transferred.

Optionally, and as illustrated in Figure 5a, providing the 'D' shaped spindle (70) with one or more cut-outs or rebates (200) and the throttle disc 20" with corresponding sized and located hoops (210), the throttle disc may be slid over the spindle (70) allowing the hoops (210) to lock in to the rebates (200) and provide hinging on the throttle shaft. It may also be appreciated as illustrated in Figure (6a) and (6b), to allow assembly into the carburettor body (215) the throttle disc 20" must be placed into the carburettor bore (22) and the throttle shaft (70) inserted to pass through the carburettor body (215) and the throttle disc hoops (210) to the point where the hoops lock into the rebates (200). At this point, a round section-bearing surface (220) of the shaft (70) will be engaged into the carburettor body. An end cap (230) may then be inserted onto a pin (240) so forming the opposite bearing. The throttle disc may now be closed to centralise the disc in the carburettor bore (22), and the end pin (240) riveted over to clamp the throttle disc between the two faces (250) and (260) shown in Figure 5a of the end cap (250) and of the shaft (70) respectively.

In the illustrated embodiment of Figure 7 it is clearly shown that the invention provides a significant improvement in airflow in passage (44) with all the advantages of simple construction and assembly retained.

Claims

1. A carburettor comprising a throttle valve, the throttle valve including a spindle mounting portion, wherein the spindle mounting portion is provided with a threaded portion.

2. A carburettor as claimed in Claim 1 in which the throttle valve comprises a throttle disc.

3. A carburettor as claimed in Claim 1 or Claim 2 in which a throttle valve fixing screw is provided for passing through a throttle spindle to be located in the threaded portion of the said throttle valve, and in which a clamping force is provided to fixably locate the said throttle disc on a surface opposite that from which the screw (72) is insertable.

4. A carburettor arranged to supply fuel to an engine, the carburettor comprising an inlet duct, a throttling disc arranged to throttle the flow of air through the inlet duct, the inlet duct being divided over at least part of its length into at least a rich passage and a lean passage, which are arranged to communicate with a rich volume and a lean volume respectively of the engine, the carburettor and the throttle disc being adapted to supply, under high load operation, substantially all fuel into the rich passage and to supply, under low load operation, substantially all the fuel into a second passages; characterised in that the throttle disc comprises a spindle mounting portion that is provided with a threaded portion.

5. A carburettor throttle disc having a cross-section substantially as shown in Figure 3e.

6. A carburettor throttle disc having opposing closing surfaces, and characterised in that at least one hoop device is arranged to protrude from one of the closing surfaces.

7. A carburettor throttle disc as claimed in Claim 6, the disc comprising a butterfly valve.

8. A carburettor as claimed in Claim 6 in which the hoop device has one or more abutting surfaces arranged for location on a corresponding portion of a throttle shaft.

9. A carburettor as claimed in any of Claims 6 to 8 in which the hoops provide hinging, in use, on a throttle shaft.

10. A carburettor arranged to supply fuel to an engine, the carburettor comprising an inlet duct, a throttling disc arranged to throttle the flow of air through the inlet duct, the inlet duct being divided over at least part of its length into at least a rich passage and a lean passage, which are arranged to communicate with a rich volume and a lean volume respectively of the engine, the carburettor and the throttle disc being adapted to supply, under high load operation, substantially all fuel into a first passage and to supply, under low load operation, substantially all fuel into a second passage; characterised in that the throttle disc is provided with a hoop device with one or more abutting surfaces to locate a throttle shaft.

11. A carburettor throttle valve, substantially according to the projected views as shown in Figure 5b to 5d.