Various apparatus have been used for the delivery of fuel into the combustion chambers of internal combustion engines, but most of these relate to fuels which are liquid at normal ambient operating conditions. With such fuels, either a carburettor or a fuel injection system is used. Particular problems arise, however, when the fuel is gaseous at normal temperatures and atmospheric pressure, but which may be stored in liquid form, under pressure.

One common form of such a fuel is liquefied petroleum gas (LPG). However, there are other equivalent fuels such as hydrogen, propane, and liquefied natural gas (LNG), also known as compressed natural gas (CNG). The present invention relates to the supply of such a fuel to an internal combustion engine, and throughout the description and claims of this application any reference to a particular example of such a fuel shall be taken as a reference to any equivalent fuel, and to any other gas, volatile gas or substance adapted to be used as a fuel for an internal combustion engine, which gas, volatile gas or substance is gaseous at normal temperatures and pressures, but which is normally stored in liquid form under pressure.

The efficient delivery of LPG-type fuels to internal combustion engines can be difficult. The usual method involves mixing the gaseous fuel and air before introducing this mixture to the engine. WO 97/47872 describes a method and apparatus for supplying LPG to an IC engine, utilising fuel injection. However, practical embodiments of that invention were not entirely satisfactory. Engines fitted with that fuel supply system often ran rough and/or failed to operate economically.

It is an object of this invention to provide an improved system for supplying gaseous fuel to an internal combustion engine.

The invention provides a fuel supply system for an internal combustion engine adapted to operate on a gaseous fuel, characterised in that said system includes a valve controlling the flow of gaseous fuel to a mixing point at which said fuel and air is caused to mix, said valve being operated in unison with a throttle associated with said engine.

The invention may also provide a method of operating an engine adapted to run on gaseous fuel, said method including the steps of operating a valve supplying fuel to said engine, and the throttle of said engine, in unison such that the optimum air/fuel ratio for the proper operation of said engine is obtained.

The invention further provides a fuel supply system for an internal combustion engine adapted to operate on a gaseous fuel stored in liquefied or gaseous form, characterised in that said fuel is drawn from a storage location in gaseous form.

Embodiments of the invention, which may be preferred, will be described in detail hereinafter with reference to the accompanying drawings, in which: Fig. 1 is a diagrammatic representation of one embodiment of a fuel supply system according to the present invention; Fig. 2 is an end elevation of a gas valve arrangement for use in the system of Fig.

1; and Fig. 3 is a partially-sectioned top plan view of the gas valve of Fig. 2.

The fuel supply system of Fig. 1 is applicable for both stationary IC engines, and IC engines which power vehicles. Preferably, the system is particularly suitable for small internal combustion engines from a capacity of about 1 Occ to that of about 500cc. In Fig. 1, the direction of movement of gas and air is shown by arrows.

The system of Fig. 1 includes a cylinder 10 containing LPG (12), although it is to be understood that the fuel in container 10 may be any of the fuels previously mentioned in this specification. Regulations in force in Australia require that not all

of a LPG cylinder be filled with liquefied petroleum gas: the top 20% of the volume of the cylinder 10 must only be filled with gas or vapour. In Fig. 1, that space is shown filled with LPG in gaseous form (14), which has"boiled off'the liquefied LPG 12.

The LPG in gaseous form 14 is drawn off the top of cylinder 10 and fed through gas line 16, in which a regulator 18 is located. Downstream of the regulator 18 is a lockoff arrangement 20, which is preferably an electronic gas lockoff system, more preferably incorporating an integral safety circuit or safety switch. Cable (s) 52 may supply electricity to the lockoff arrangement 20 and/or the safety switch.

Downstream of the lockoff arrangement 20 is a gas valve 22. The gas valve is operated by a first actuating lever 28, which is connected to a linkage arm 30, which will be described in detail later in this specification. Gas valve 22 has two adjusting means 24,26. Adjusting means 24 is an idle adjust, and adjusting means 26 is a high speed adjust. The lockoff arrangement may be incorporated in the valve 22.

The gas valve arrangement 22 of Figs. 2 and 3 may be used in the system of Fig.

1. In Figs. 2 and 3, reference numerals which are shared with Fig. 1 refer to the same features as designated in Fig. 1 by those reference numerals.

The gas valve arrangement 22 of Figs. 2 and 3 shows lever 28 adapted to operate a valve element 46. Safety switch 48 is also shown, located between lockoff valve and the body of valve arrangement 22, as is an outlet spigot 50, for communication with second gas line 40 (Fig. 1).

From gas valve 22, a second gas feed line 40 takes the gas to a vapour dispersion ring 42, positioned at the entrance to the body 36 of the throttle (not shown) of the IC engine (also not shown), where the gas 14 mixes with air 38. Mixture flow adjusting valve 34 in throttle body 36 is actuated by a second actuating lever 32, which is also connected to linkage arm 30. Second actuating lever 32 is controlled by the throttle control 44 of the IC engine, the throttle control being represented in Fig. 1 by a broken line leading from lever 32. Operation of the throttle control 44

controls the mixture intake at the entry 36, and also controls, through the interconnection of lever 28 and lever 32 by arm 30, the flow of gas through gas valve 22.

The operation and advantages of the fuel supply system of Fig. 1 will now be described. An idle bypass arrangement is provided by gas valve 22 being adapted to supply exactly the correct amount of gas 14 for the engine to operate smoothly at idle when the throttle 44 is closed. The idle adjustable jet 24 may be used to finely adjust the valve 22 to ensure the suitable operation of the engine at idle.

Because of the interconnection of the throttle 44 control of the throttle body 36 through valve 34, and valve 22, the fuel 14 in gaseous form is inducted (sucked) into the air valve throttle 36/34 in accordance with the engine demand, in unison with the operation of valve 22. Small variations may be absorbed by the elasticity of gaseous fuels, creating continuous gas vapour induction at correct air/fuel ratios. It should be noted that the fuel 14 in gaseous form is still under a pressure greater than atmospheric pressure, and that accordingly, under that greater pressure, it is drawn into the crankcase, cylinders and the like of the engine.

The vapour dispersion ring 42 does not restrict air flow when a dual-fuel engine is being operated on liquid fuel such as petrol or gasoline. Only a small reduction, if any, in power may be observed when an engine using the arrangement of Fig. 1 is running on a fuel such as petrol.

It can be seen that this invention provides an improved fuel supply system for internal combustion engines operating on gaseous fuels such as LPG. It should be noted that in comparison to the disclosure of WO 97/47872, the present invention, at least in the form of the embodiment of Fig. 1, omits such features as a non return valve, a heating chamber (because the fuel 14 is drawn from the cylinder 10 in gaseous form), and the injection of fuel into the carburettor, crankcase, transfer ports, cylinders or the like (because the fuel 14 in gaseous form is drawn or inducted into such engine elements). The entire contents of the description and drawings of Australian provisional patent application no. 2002951006, filed on 27 August 2002, are hereby incorporated into the specification of this application.

The claims form part of the disclosure of this application.