The present invention relates to a method of controlling fuel supply to a gas fuelled engine.

Two and three wheel motor vehicles are an important mode of transport used for commuting in and around cities. Such vehicles have engines operating on the two and four stroke cycle, employing petrol or other liquid fuel. As environmental laws become more stringent, emissions from such vehicles are required to reduce. One way of achieving lower emissions is to use gas fuelled internal combustion engines. Such gaseous fuel may be selected from LPG (Liquefied Petroleum Gas) or CNG (Compressed Natural Gas). While such gaseous fuels combust more efficiently than most liquid fuels, therefore reducing emissions, they also provide economic benefit since they are currently of lower cost than liquid fuels such as petrol.

Where supply of gaseous fuel is assured, vehicles may operate with only a gas fuel supply. However, as there may be regions where supply of gaseous fuel is less certain, vehicles may be fitted with a back-up liquid fuel system. Such vehicles are called dual fuelled vehicles. Typically, the back-up fuel is petrol since this is the easiest fuel to obtain, being available even in many remote regions.

The fuel supply for a gas fuelled vehicle comprises a pressurised fuel tank and, accordingly, as the pressure of the fuel tank is higher than can be handled by a gas fuelled internal combustion engine, a pressure regulator is required to control the gas fuel supply pressure to the engine through a gas fuel supply duct. Gaseous fuel at appropriate pressure is supplied to a mixer for mixing gas and air to form a combustible fuel mixture for delivery to the engine. To this end, the mixer is connected both to the gas fuel supply and an air intake system. The gaseous fuel pressure regulator includes an orifice for pressure regulation and its opening is controlled by a typical diaphragm operated lever mechanism. The orifice opening (even with engine in "OFF" condition) is controlled by force of a setting spring connected between body of the regulator and diaphragm operated lever. This diaphragm element being sensitive to pressure fluctuations moves to open and close the lever further as fuel is demanded by the engine while running. The pressure fluctuations are caused due to one side of the diaphragm element being subjected to engine vacuum and the other side subjected to atmospheric pressure.

It is also usual for a solenoid valve to be included within the gaseous fuel supply proximate the pressurised fuel tank. When the ignition switch is turned on, the engine control unit (ECU) causes this solenoid valve to open and deliver a flow of gaseous fuel through the pressure regulator towards the mixer and engine. Such a conventional solenoid valve, allows gaseous fuel flow towards the engine for a certain predefined duration (generally 1-3 seconds) and then the ECU turns the solenoid valve off.

A problem arises where, for one reason or another, the ignition switch is operated a few times (on/off) without starting the engine. In these circumstances, undue load is placed on the vehicle battery and gaseous fuel will still flow towards the engine causing either or both of the problems of engine flooding and wastage of gaseous fuel.
It is an object of the present invention to provide a method of controlling fuel supply to a gas fuelled engine which results in less potential for engine flooding and gaseous fuel wastage.

With this object in view, the present invention provides a method of controlling fuel supply to a gas fuelled engine comprising:

a) a gaseous fuel supply system comprising a gaseous fuel supply tank, a gaseous fuel pressure regulator and an electronically controlled valve located between the gaseous fuel supply tank and the gaseous fuel pressure regulator;

b) an ignition system including an ignition switch actuable to operate an ignition means of the engine; and

c) an engine control unit connected to the ignition switch and the electronically controlled valve wherein said electronically controlled valve is opened by said engine control unit to supply gaseous fuel to the engine when both of the conditions of ignition switch actuation and cranking of the engine are detected by the engine control unit. That is, the electronically controlled valve will not be opened at all, after the ignition switch is actuated, until the condition of engine cranking is sensed.

Cranking, or crankshaft rotation, of the engine may be determined in the following manner. When a crankshaft of the engine is sensed to rotate indicating engine cranking is imminent or in progress, a corresponding crank rotation signal

may be sent to the engine control unit. This signal may correspond with a pulse signal in the ignition system of the engine that is generated in a magneto of the engine with crankshaft rotation. At this point of correspondence between crankshaft rotation signal and pulse signal, the electronically operated valve will be caused to be opened by the engine control unit to supply gaseous fuel to the engine. Other means of detection of crankshaft rotation may be used, these including engine speed sensors, crankshaft encoders and so on. Assumption of cranking based on measurement of elapsed time from actuation of the ignition switch will not be used to sense engine cranking condition. The method, in this respect, is independent of measurement of elapsed time from actuation of the ignition switch.

The electronically controlled valve is conveniently a solenoid valve of conventional design enabling ready control over valve operation by an engine control unit. This solenoid valve may be actuated based on ignition state being "ON" condition. The present invention may also be applied to such designs wherein such solenoid valve allows gas flow only when both the conditions of engine ignition switch being turned "ON" and sensed pulse signal from crankshaft rotation are met.

Some engines include a second electronically controlled valve proximate the gaseous fuel pressure regulator.

In a further aspect, the present invention provides a gas fuelled engine comprising:

a) a gaseous fuel supply system comprising a gaseous fuel supply tank, a gaseous fuel pressure regulator and an electronically controlled valve located between the gaseous fuel supply tank and the gaseous fuel pressure regulator;

b) an ignition system including an ignition switch actuable to operate an ignition means of the engine; and

c) an engine control unit connected to the ignition switch and the electronically controlled valve wherein the electronically controlled valve is openable by the engine control unit to supply gaseous fuel to the engine when both of the conditions of ignition switch actuation and cranking of the engine are detected by the engine control unit.

In a still further aspect, the present Invention provides an engine control system for a gas fuelled engine comprising:

a) a gaseous fuel supply system comprising a gaseous fuel supply tank, a gaseous fuel pressure regulator and an electronically controlled valve located between the gaseous fuel supply tank and the gaseous fuel pressure regulator;

b) an ignition system including an ignition switch actuable to operate an ignition means of the engine; and

c) an engine control unit connected to the ignition switch and the electronically controlled valve wherein said engine control unit is programmed to open said electronically controlled valve to supply gaseous fuel to the engine when both of the
conditions of ignition switch actuation and cranking of the engine are detected.

The method, engine and engine control system of the present invention may be conveniently applied to two, three and four wheel gas fuelled automobiles or vehicles and such vehicles form a further aspect of the present invention. The engine may be spark ignited or dual spark ignited internal combustion engine and of any desired capacity. The method may be conveniently applied to a small capacity engine. The engine may be fuel injected or carburetted and may be single or dual fuelled allowing liquid fuel (petrol) as well as gaseous fuel operation.

Implementation of the method, engine and control system aspects of the invention may result in less fuel wastage and avoidance of engine flooding. Other advantages that may be achieved include improved engine starting and reduced load on a vehicle battery.

The method and control system for controlling fuel supply to a gas fuelled engine, as well as the gas fuelled engine itself, of the present invention may be more fully understood from the following description made with reference to the accompanying drawings in which:

Figure 1 is a schematic of one gaseous fuel supply system operated in accordance with the prior art.

Figure 2 is a schematic of another gaseous fuel supply system operated in accordance with the prior art.

Figure 3 is a schematic of a gaseous fuel supply system operated in accordance with one embodiment of the present invention.

Referring to Figure 1, the illustrated gaseous fuel supply system of spark ignited internal combustion engine is a liquefied petroleum gas (LPG) system for fuelling of a three wheel vehicle. LPG gas is stored at high pressure in the fuel tank in the form of gas cylinder 1. The solenoid valve 2 is fitted on to the cylinder 1 and is operated electronically by a control unit for the engine to start or stop the gas supply to engine 3 through gaseous fuel pressure regulator 4 in accordance with vehicle operating conditions. Solenoid valve 2 is actuated through vehicle ignition switch 5, as shown, in such a manner that it turns "ON" when the ignition switch is turned "ON". As a normal safety practice, the solenoid may remain in "ON" state for a couple of seconds, say for example 1 to 3 seconds. It operates again in the same sequence with repeated operation of ignition switch 5.

In all the above conditions, LPG gas fuel flows into the engine 3 through gaseous fuel pressure regulator 4, every time with ignition switch is actuated or switched "ON". This occurs irrespective of whether the engine 3 cranks or not so even though gas fuel flows into the engine 3, it Is not combusted to produce drive power for the vehicle. This flow of un-combusted LPG gas leads to wastage of gas and causes starting problems due to gas flooding.

To mitigate the above problems, attempts have been made to avoid unnecessary flow of gaseous fuel, to engine 3 by providing an orifice 8 in gas pressure regulator 12. This orifice 8 is closed against predetermined spring force till sufficient vacuum is generated due to cranking of engine 3 to open the orifice 8 and allow fuel flow to engine 3. This may be illustrated with reference to Figure 2, in which the orifice 8 provided in gas pressure regulator 12 is normally kept closed by a predetermined force of vacuum spring 6 connected at one end of lever 11, to overcome engine vacuum. The said vacuum spring 6 exerts more force in comparison to force exerted by setting spring 13. As vacuum is created in the engine 3, the vacuum diaphragm 9 is pulled downwardly due to the vacuum or negative pressure pulse received from the engine. This downward movement of vacuum diaphragm 9 compresses the vacuum spring 6 and relieves the additional force on one end of the lever 11. This ensures only setting spring 13 force on the lever 11, against which, the main diaphragm 14 opens or closes the orifice 8 depending upon the pulses received from engine through mixer 15 to enable the LPG fuel gas to be supplied to engine 3.

This mechanical arrangement does prevent unnecessary flow of gaseous fuel to the engine 3 when in non running condition. However, the arrangement has some disadvantages like complex design, difficulty in precisely tuning the engine and higher cost. Additionally, such a mechanical arrangement - having a number of components, is prone to malfunctioning.

To mitigate the problems noted in the gas fuel supply systems of Figures 1 and 2, as above described, the Applicant has designed a engine with a gaseous fuel supply system, and a method of controlling gaseous fuel supply to engine 3, to be described with reference to Figure 3. Here again, the gaseous fuel supply system, which has many features in common with the gaseous fuel supply system illustrated in Figures 1 and 2, supplies LPG gas fuel to the dual spark ignited engine 3 of a three wheel vehicle. As previously described, gas cylinder 1 is provided with an electronic solenoid valve 2, controlled by the engine control unit and which is actuated by ignition switch 5. However, in this case, before LPG gas fuel is allowed to flow through the solenoid valve 2 and into the engine 3, another criterion must be met in order to reduce risk of LPG gas fuel wastage and other problems such as engine flooding.

To this end, a pulse signal arrangement is provided which - through transmission of a pulse - communicates the engine condition "ON" or "OFF" to ignition switch 5 before allowing flow of LPG gas fuel to engine 3. This pulse signal corresponds with a pulse signal 10 in the ignition circuit that is generated in the magneto assembly of engine 3 only when the engine crankshaft is sensed to rotate indicating that engine cranking is imminent or in progress. When the ignition switch is turned to "ON" condition to energise Ignition means in the form of one or both of the spark plugs dependent on engine speed and acceleration conditions (for example in accordance with the Applicant's International Publication No. WO 2007032020 the contents of which are hereby incorporated herein by reference) and the pulse signal indicates engine state to be "ON", the engine control unit is programmed to instruct the solenoid valve 2 to open enabling supply of LPG gas fuel from gas cylinder 1 to the gaseous fuel pressure
regulator 4 and then to the engine 3 at the required pressure for efficient combustion under the particular operating conditions of engine 3.

On the other hand, if the ignition switch 5 is in "ON" condition and the pulse signal condition is in "OFF" condition, meaning that the crankshaft of the engine 3 is not rotating, solenoid valve 2 is not opened and no fuel is supplied to gaseous fuel pressure regulator 4 or to engine 3. It may be observed here that operation of the system is independent of the actual design of gas pressure regulator 4. For example, the gaseous fuel pressure regulator 4 of Figure 1 or 12 of Figure 2, or another gas pressure regulator, could be used.

Therefore, with the gas fuel system shown in Figure 3, it may be observed that LPG gas is allowed to flow into the engine 3 through gaseous fuel pressure regulator 4 only when the engine crankshaft rotates i.e. when the engine is about to start or is already running. Thus, use of this gas fuel system avoids wastage of gas and engine flooding.
The system also enables improved engine startability. The system also reduces load on the vehicle battery as the solenoid valve 2, which draws some current, say for example 1 ampere current, does not turn "ON" unless the engine crankshaft rotates. Additionally, the solenoid valve switches to "OFF" state immediately when the engine crankshaft rotation comes to a halt. This means it does not remain in "ON" state for any predetermined duration of time (as for 1~3 seconds in prior art). Accordingly, the solenoid valve 2 is only opened when necessary - that is with less frequency than in the prior art - which avoids unnecessary discharge of the vehicle battery and potentially enables longer battery life.

Modifications and variations to the method of controlling fuel supply to a gas fuelled engine, engine and engine control system of the present invention may be apparent to the skilled reader of this disclosure. Such modifications and variations are deemed within the scope of the present disclosure.

Claim:

1. A method of controlling fuel supply to a gas fuelled engine comprising:

a) a gaseous fuel supply system comprising a gaseous fuel supply tank, a gaseous fuel pressure regulator, and an electronically controlled valve located between the gaseous fuel supply tank and the gaseous fuel pressure regulator;

b) an ignition system including an ignition switch actuable to operate an ignition means of the engine; and

c) an engine control unit connected to the ignition switch and the electronically controlled valve
wherein said electronically controlled valve is opened by said engine control unit to supply gaseous fuel to the engine when both of the conditions of ignition switch actuation and cranking of the engine are detected by the engine control unit.

2. A method of claim 1 wherein the electronically controlled valve is not opened at all, after the ignition switch is actuated, until the condition of engine cranking is sensed.

3. A method of claim 1 or 2 wherein, when a crankshaft of the engine is sensed to rotate indicating engine cranking is imminent or in progress, a corresponding crank rotation signal is sent to the engine control unit, the crank rotation signal corresponding to a pulse signal in the ignition system of the engine that is generated in the magneto of the engine with crankshaft rotation, the correspondence between crank rotation signal and pulse signal causing the electronically operated valve to be opened by the engine control unit to supply gaseous fuel to the engine.

4. A method of any one of the preceding claims wherein detection of crankshaft rotation is independent of measurement of elapsed time from actuation of the ignition switch.

5. A method of any one of the preceding claims wherein said electronically controlled valve is a solenoid valve.

6. A method of claim 5 wherein said solenoid valve is actuated based on ignition state being 'ON" condition.

7. A method of claim 6 wherein said solenoid valve is actuated to allow gas flow only when both the conditions of engine ignition state being "ON" condition and sensed pulse signal for crankshaft rotation are met.

8. A gas fuelled engine comprising:

a) a gaseous fuel supply system comprising
a gaseous fuel supply tank, a gaseous fuel pressure regulator and an electronically controlled valve located between the gaseous fuel supply tank and the gaseous fuel pressure regulator;

b) an ignition system including an ignition switch actuable to operate an ignition means of the engine; and

c) an engine control unit connected to the ignition switch and the electronically controlled valve to supply gaseous fuel to the engine wherein the electronically controlled valve is openable by the engine control unit when both of the conditions of ignition switch actuation and cranking of the engine are detected by the engine control unit.

9. An engine of claim 8 wherein said electronically controlled valve is a solenoid valve.

10. An engine of claim 8 or 9 including a second electronically controlled valve proximate the gaseous fuel pressure regulator.

11 .An engine control system for a gas fuelled engine comprising:

a) a gaseous fuel supply system comprising a gaseous fuel supply tank, a gaseous fuel pressure regulator and an electronically
controlled valve located between the gaseous fuel supply tank and the gaseous fuel pressure regulator;

b) an ignition system including an ignition switch actuable to
operate an ignition means of the engine; and

c) an engine control unit connected to the ignition switch and
the electronically controlled valve wherein said engine control is
programmed to open said electronically controlled valve to supply gaseous
fuel to the engine when both of the conditions of ignition switch actuation
and cranking of the engine are detected.

12. A vehicle comprising the engine of any one of claims 8 to 10 or the engine control system of claim 11.