WO1998021463A9

WO1998021463A9 - Gaseous fuel supply control and fuel vaporiser

Info

Publication number: WO1998021463A9
Application number: PCT/AU1997/000776
Authority: WO
Filing date: 1997-11-11
Publication date: 1999-01-28

Abstract

There is provided a fuel system including a vaporizer of the 2 stage type, with a heat exchange chamber which is connected to the engine cooling system, an idle circuit (4), and a gas lock (5), controlled by safety switch that prevents the LPG from reaching the engine until cranked. A controller receives gas from the vaporizer and has a load block (31) mounting a power valve assembly (32) comprising a diaphragm (34) and piston (33) and operable by application of manifold vacuum. Mounted opposite the piston (33) is a trim valve assembly (40) comprising a solenoid operated piston (42) movable towards and away from the piston (33). The solenoid (41) is operable by controller (44), whereby the trim piston position is regulated in response to input from an oxygen sensor (45) and throttle position sensor (46) to the controller (44). In response to an idle condition, the controller pulses the idle solenoid (4) to achieve a selected range of values at the oxygen sensor (45).

Description

GASEOUS FUEL SUPPLY CONTROL AND FUEL VAPORISER This invention relates to a fuel system. This invention has particular but not exclusive application to a vehicle fuel system utilizing LPG or CNG, and for illustrative purposes reference will be made to such application. However, it is to be understood that this invention could be used in other applications, such as fuel systems for apparatus other than vehicles using gaseous or vaporizable fuels. Liquefied Petroleum Gas (LPG) and Compressed Natural Gas (CNG) are commonly used as fuel for high mileage vehicles, due to the relatively low cost of these fuels being able to offset the cost of the fuel system. The fuels are relatively less polluting. In conventional installations, a demand regulated vaporizer is adapted to receive LPG from a storage tank, the vaporizer being used to feed a demand air/fuel mixer and thence the engine. For CNG vehicles, a multistage fuel heater/pressure reduction apparatus similarly feeds an air/fuel mixer.

As air pollution becomes a more seriously treated problem, various legislative steps have been taken by governments in attempting to reduce vehicle emissions. One such design rule imposed on manufacturers is to utilize catalytic converters in exhaust systems, coupled with engine management which controls the oxygen balance of the induced charge to control the composition of gases in the exhaust manifold and in the catalytic converter.

In general, the rules for LPG and CNG vehicles specify that where a vehicle has an engine management system installed from the factory (OEM) the gas system shall also have an engine management system that gives gas emissions not inferior to the original system.

A problem with connection to the original petrol system is that this petrol system is trying to Control the engine emissions from the oxygen sensor to a preset stoichiometric air/fuel ratio (AFR) of approximately 14.5:1. The LPG system needs to run the engine at an induced charge ratio of approximately 15.5:1. This causes the engine management system to run lean on emissions.

To attempt to overcome this difficulty, it has been proposed to utilize a manifold vacuum operated power valve which had the effect of allowing a piston to be inserted or removed from the fuel flow according to engine demand. This system is effective, but recent modifications to the design rules require that the gas system be a closed loop, which renders the basic system unworkable. The solutions proposed to this additional regulatory requirement embody many differing concepts.

The main thrust of development has been to control the feedback by installing stepper motors operating a taper or shaped pistons to control the gas. The systems proposed to date have high end cost, lack reliability, and do not control as well as the original powervalve, whilst meeting the technical requirement of the standards.

The present invention aims to substantially alleviate at least one of the above disadvantages and to provide a fuel system which will be reliable and efficient in use.

With the foregoing in view, this invention in one aspect resides broadly in a fuel system including a fuel supply adapted to deliver gaseous fuel to an internal combustion engine and delivery regulating means comprising a valve operable according to engine demand and a trim valve responsive to engine emission status.

The fuel supply may take any suitable form in general determined by the selection of fuel or fuels to be utilized. For example, for LPG vehicles, the fuel supply may comprise vaporizer apparatus adapted to utilize waste heat from the engine cooling system or exhaust gases to vaporize the fuel . For CNG vehicles, the gas may be warmed by similar means adapted for this fuel tanked in the gaseous phase. The valve operable according to engine demand may comprise any suitable valve disposed in the gas flow such as a butterfly valve, gate valve, or the like disposed in a delivery line. The means for operating the valve in response to engine demand may utilize such arbitrary measure of demand as throttle position. However, it is preferred that the valve be operated by means responsive to engine manifold depression or vacuum, and functioning as a "power valve" in the language of the art. The power valve may comprise an operating diaphragm which reacts to engine vacuum and either adds or removes cross sectional area to a region of the gas line supplying fuel to the engine. The power valve may comprise an assembly of a load block having a flow passage therethrough which is selectively occludable by a piston mounted in a main body in the load block and operable by the diaphragm. As engine vacuum is directly proportional to engine demand this valve assembly may be made adjustable by screwing the main body directly into the load- block to a preset distance as required by the type of engine being fitted. The piston may be mounted in a bore in the main body which is substantially transverse to the direction of gas flow through the load block. The piston, in occluding the gas supply line blocking the path of gas, blocks the vacuum signal from the engine venturi thus creating less demand on the vaporizer. Preferably, this piston is spring biased to a normally-retracted position and can extend fully into the gas supply line at high Hg and retract into housing body proportional to the lower Hg. The maximum travel of this piston is preferably controllable so that the maximum demand of the engine can be catered for.

The trim valve responsive to engine emission status may be responsive to any selected measurable emission characteristic. For example, the trim valve may be responsive to carbon monoxide or nitrogen oxides content of a selected part of the exhaust gas flow. However, since conventional emission control apparatus for use in conjunction with the original petrol fuel system of most vehicles includes a residual oxygen sensor, this may be utilized to provide the primary input of emission status of the exhaust gas flow.

The powervalve piston is, in essence, the coarse control mechanism by which the vehicle may be set up to operate over substantially the full range of demand. The trim valve preferably provides fine control of the gas flow to a precision, based on exhaust emissions, not achievable with the powervalve. Preferably, the trim valve is formed as an assembly with the power valve. For example, the trim valve may include a further piston installed in the preferred load body and opposing the travel of the power valve piston. This second piston may be controlled by any suitable means responsive to the exhaust emissions monitored. For example, the piston may be controlled by a stepper motor, solenoid or the like under the control of microprocessor means or an output of engine management means. Preferably, the trim piston is electronically controlled by a solenoid under the operational control of a programmable controller unit which has pre-sets for the emission "window" to be achieved.

The electronic controller program may view the output received from the oxygen sensor and may react according to the pre-set programme to "pulse" the solenoid, moving the trim valve piston and thus trim the effective power valve actuation to the required emissions. The maximum travel of the solenoid shuttle is preferably limited by design to trim and control during the cruise mode where the solenoid shuttle will be pulsing in and out and have the maximum influence. In an idle situation where the two pistons will be closed face to face, a designed amount of leakage past the piston diameters may allow idle fuel as metered by the adjustable idle screw on the vaporizer to maintain idle, although it is envisaged that a separate idle system may be provided. During full power demand where the powervalve will be responding according to engine demand and opening to its maximum travel the solenoid shuttle will have no influence and will remain at full extension waiting to trim the mixture when required.

The combination vacuum powervalve/electronic trim solenoid control for cruise mode may incorporate in its control .means a mode for idle control in the idle range. Preferably, the idle circuit includes an on/off solenoid with electronic control from the controller which measures the oxygen sensor output and converts to a pre-controlled program within the controller to give an emission window within the set range. In idle mode this may be achieved by pulsing the idle solenoid as required to give a LP gas flow suitable for the engine conditions being monitored. In transition to the idle\cruise mode the idle solenoid preferably receives a signal from the throttle position switch that the cruise control situation is being entered and the electronic solenoid in the gas supply line trims the vacuum signal powervalve to the pre-set conditions. The requirements of the Australian Standard AS1425 and other standards generally require all vaporizers fitted to vehicles with OEM oxygen sensors to operate the LP gas systems under closed loop conditions, that is, under engine management control. The control is to be operating and effective in the "cruise" range of the vehicle and give emissions not inferior to the original OEM vehicle.

The present system uses a vacuum/electronic trim solenoid control in the cruise mode but also incorporates a pulse idle valve for idle control in the idle range. The design of the vaporizer idle circuit is an on/off solenoid with electronic control from the controller which measures the oxygen sensor output and converts to a pre-controlled programme within the controller unit to give an emission window within the set range. In idle mode this is accomplished by pulsing the idle solenoid as required to give a LP gas flow suitable for the engine conditions being monitored. In transition to the idle\cruise mode the idle solenoid receives a signal from the throttle position switch that the cruise control situation is being entered and the electronic solenoid in the gas supply line trims the vacuum signal powervalve to the pre-set conditions.

The present applicant has developed a system that uses the original powervalve concept in conjunction with an electronic trim control which has all the benefits of the original system, speed of operation, instant response, low initial cost and "fail to safe" in case of failure in the feedback system. An advantage of the above described apparatus is that in the event of solenoid or electronic failure, the limited travel of the shuttle will not effect a total shut down condition. The preferred powervalve, being vacuum operated, has a very high reliability rate. The vehicle could still be driven to a place of repair. Other types of controllers on the market either fail in the position they were last in or fail fully shut or fully open. In these circumstances, a vehicle could not be controllable and would have to be transported. By keeping the vacuum powervalve as the coarse control and relying on the solenoid valve to trim the resulting emissions it is a smoother and much faster reacting system than electronic designs that have stepper motors or vane valves. In the event of engine demand to full power requirements, the vacuum powervalve responds to engine demand and moves instantly (faster than a stepper motor) to full open position as set by the adjustable full power pre-set.

This has the result in allowing the engine to achieve a rich mixture on demand and not a delayed mixture that biases to the lean mixtures that could cause backfiring. As the powervalve piston has moved away rapidly from the solenoid shuttle, and the solenoid shuttle has a limited travel, an instant signal to the vaporizer occurs to supply the extra demand. With testing the benefits of the above apparatus operating in the "cruise" mode were established. It was determined that if the controller could be made to operate in the "idle" mode then an area of fuel usage that is in the excessive range could be brought under control at the same time. To achieve this the controller may include a function which incorporates an idle "pulsing system" that will control the emissions during the times that vehicles are stationary or in heavy traffic conditions. This is especially advantageous to vehicles such as Taxis and delivery vans which spend a high proportion of their life stationary.

The idle system of the apparatus as described may comprise allowing gas bypass of the powervalve piston and the solenoid trim shuttle. This bypass "leak" is usually controlled by an idle screw in the solenoid and is set to the engine's requirements. It has been determined that the same principal of operation for trimming cruise emissions can be applied to idle control. An idle control solenoid on the vaporizer may be pulsed in response to the controllers demands and in such fashion control the idle gas requirements to a much finer degree than a fixed aperture and adjustable screw can accomplish. To achieve this the input signal from the throttle position switch may be used to signal the controller that the engine throttle is in the closed position and sets the idle solenoid on the vaporizer to cycle in response to the pre-set program in the controller. In this situation it is possible to set the idle screw on the vaporizer a few turns richer (out) and allow the controller to control the emissions at idle, using the same oxygen sensor inputs as for cruise conditions.

In a further aspect this invention relates to a vaporizer apparatus suitable for use in fuel systems in accordance with the aforedescribed invention. Preferably, the main pressure reduction of the liquid is carried out in a first stage of the vaporizer. The flow of vapour LPG to the engine may be controlled in a second stage of the vaporizer. Between the first and second stage, situated both sides of the primary gas tract, there may be provided a heat exchange chamber which is connected to the engine cooling system, or other heat exchange means depending on the source of gas heating selected. The vaporizer preferably includes an electronically controlled idle circuit, for connection to the controller as described above. The idle circuit and the statutory gas lock on the LPG inlet are preferably controlled by an electronic safety switch that prevents the possibility of any LPG reaching the engine until the engine is being cranked.

The gas filter/lock off valves preferably communicate with a primary gas track through a primary valve held open by springs acting on a primary diaphragm, when the pressure in the primary gas track is low. As liquid LPG passes through the primary valve it will start to vaporise in the primary gas track as the pressure in this area is lower than the LPG cylinder pressure.

When the vaporising LPG has reached the primary pressure of about 22-26kPa the pressure in the primary track may act on the underside of the primary diaphragm overcoming the primary diaphragm spring pressure and forcing the primary valve to close. When the primary pressure drops to between 22-26kPa the primary valve will again open. This is a continuous cycle of the primary regulator whilst operating the vaporizer.

The main function of the second stage regulator is to control the amount of vapour LPG being supplied to the engine depending on the engine demand. It works in conjunction with a mixer venturi which is positioned in the inlet air stream of the engine. At idle a secondary valve may be held closed by a sensitivity spring, idle gas flowing through the idle lock into the secondary chamber and through a gas outlet . As engine revs increase, a vacuum signal from the mixer (venturi) may be applied to the secondary chamber of the vaporizer. The pressure difference created, atmospheric on one side of the secondary diaphragm and venturi vacuum in the secondary chamber may acts on a secondary lever, opposing the sensitivity spring and opening the secondary valve allowing LPG vapour to be drawn into the engine. As engine demand increases past a flow designed into the vaporizer flow through the primary gas track it will create a vacuum, by venturi effect in the boost tube, which in turn created more vacuum below the primary diaphragm further opening the primary valve which further boosts the pressure in the primary gas track from 22-26kPa up to 30kPa increasing the flow capacity of the vaporizer. This increase in flow provides a richer mixture for full power and acceleration.

The sensitivity spring adjustment is an important feature for providing preferred idle to part load progression. The spring pressure must be light enough so that the secondary diaphragm can overcome the spring tension with very low vacuum signal which is produced at part load to prevent a flat spot or sluggish progression of idle, but there must be sufficient spring pressure to maintain proper sealing of the secondary valve seat to prevent LPG leaking through on engine shut down causing hard starting or in the worst scenario, the possibility of a fire.

When the ignition is switched on both the LPG filter/lock and the idle lock solenoid will be opened by the safety switch ( external ) between 0.5 and 3 seconds depending on where the safety switch is set. This provides a small amount of LPG to prime the engine for easier starting and is similar in function to an automatic choke on a carburetor. If the prime time is too short, cranking time will be increased, if the prime time is too long the engine will flood and be hard to start.

Once the engine is cranking and the safety switch receives a pulse signal from the coil, both the LPG filter/lock and idle solenoid will remain open. At this time the LPG filter/lock and the idle solenoid are open and the secondary valve is closed so the amount of LPG required for idle flows through the idle circuit and is adjusted by an idle adjusting screw. When at idle on part load, the mixer venturi is starting to generate a vacuum signal which will act on the secondary diaphragm and start to open the secondary valve. Under part load, the vacuum signal generated in the mixer venturi increases applying a greater vacuum to the secondary diaphragm opening the secondary valve further supplying more LPG vapour on engine demand.

At full load, the mixer venturi has now generated its maximum vacuum which is pulling the secondary diaphragm down, further increasing the opening on the secondary valve increasing the vapour flow through the primary gas track as this flow increases a vacuum is being produced below the primary diaphragm opening the primary valve further increasing the venturi signal on the boost tube and the vacuum on the primary diaphragm increasing flow through the primary gas track producing more LPG vapour supply to the gas outlet ensuring a richer mixture needed for maximum power.

During deceleration the throttle will be closed, all but cutting off the air flow to the engine. This will lessen the vacuum signal generated in the mixer allowing the sensitivity spring pressure to return the secondary lever and secondary valve to the closed position so the only LPG vapour entering the engine now is the LPG from the idle circuit.

When the engine is stopped no vacuum signal will be generated in the mixer so the secondary valve will be closed. The ignition pulse to the safety switch will cease so likewise the power supply to the gas filter/lock and the idle solenoid will cease ensuring no LPG will flow to the engine.

In order that this invention may be more readily understood and put into practical effect, reference will now be made to the accompanying drawings which illustrate a preferred embodiment of the invention and wherein: FIG 1 is a section through vaporizer apparatus in accordance with the present invention; FIG 2 is a top view of the apparatus of FIG 1; and FIG 3 is a partial section through a fuel system in accordance with the present invention. In the figures there is provided a fuel system including a vaporizer of the 2 stage pressure reducing type which has a coolant system heat exchanger incorporated into its design. The main functions of the vaporizer is to reduce the tank pressure (usually 0.3-1.3 MPa) to a primary pressure of 14- 16kPa, to vaporise the liquid state of the LPG to vapour, and to control the flow of the vapour to the engine.

The main pressure reduction of the liquid is carried out in the first stage of the vaporizer ( 1 ) . The flow of vapour LPG to the engine is controlled in the second stage of the vaporizer (2). Between the first and second stage, situated both sides of the primary gas tract, is the heat exchange chamber which is connected to the engine cooling system, (usually to the cabin heater system). When installed correctly it will provide a good flow of hot coolant through the unit and the heat exchange plate will guarantee a complete and continuous vaporization of the LPG through the primary track (3). The vaporizer also has a separate electronically controlled idle circuit ( 4 ) , which with the gas lock ( 5 ) , is controlled by an electronic safety switch (external device), that prevents the possibility of any LPG reaching the engine until the engine is being cranked. The technical specifications of the illustrated vaporizer are as follows:

Maximum inlet pressure 2.6MPa

Vaporization capacity (unknown)

1st stage (primary pressure) 22-26kPa 1st stage pressure maximum (boost) 30kPa Heat exchanger water capacity 42ml Gas track capacity 30ml

After passing through the gas filter/lock off valve (5) the liquid LPG enters the 1st stage of the vaporizer, (the primary regulator) at the primary valve (6). While there is no pressure in the primary gas track ( 3 ) the primary valve ( 6 ) will be held open by spring pressure from the springs (8) acting on the primary diaphragm ( 9 ) and the primary pin ( 10 ) .

As liquid LPG passes through the primary valve ( 6 ) it will start to vaporise in the primary gas track (3) as the pressure in this area is lower than the LPG cylinder pressure.

When the vaporising LPG has reached the primary pressure of 22-26kPa the pressure in the primary trace (3) acts on the underside of the primary diaphragm ( 9 ) overcoming the primary diaphragm spring (8) pressure forcing the primary valve (6) to close.

When the primary pressure drops to between 22-26kPa the primary valve (6) will again open. This is a continuous cycle of the primary regulator whilst operating the vaporizer. The main function of the second stage regulator ( 2 ) is to control the amount of vapour LPG being supplied to the engine depending on the engine demand. It works in conjunction with a mixer venturi which is positioned in the inlet air stream of the engine. At idle the secondary valve (11) is held closed by the sensitivity spring (12), idle gas flows through the idle lock ( 13 ) into the secondary chamber and through the gas outlet (14). As engine revs increase, a vacuum signal from the mixer (venturi) is applied to the secondary chamber of the vaporizer (2). The pressure difference created, atmospheric on one side of the secondary diaphragm (15) and venturi vacuum in the secondary chamber (2) acts on the secondary lever (16), opposing the sensitivity spring ( 12 ) and opening the secondary valve (11) allowing LPG vapour to be drawn into the engine. As engine demand increases past a flow designed into the vaporizer flow through the primary gas track (3) it will create a vacuum, by venturi effect in the boost tube (17), which in turn created more vacuum below the primary diaphragm ( 9 ) further opening the primary valve ( 6 ) which further boosts the pressure in the primary gas track from 22-26kPa up to 30kPa increasing the flow capacity of the vaporizer. This increase in flow provides a richer mixture for full power and acceleration.

The sensitivity spring adjustment (18) is most critical in the idle to part load progression. The spring pressure must be light enough so that the secondary diaphragm can overcome the spring tension with very low vacuum signal which is produced at part load to prevent a flat spot or sluggish progression of idle, but there must be sufficient spring pressure to maintain proper sealing of the secondary valve seat to prevent LPG leaking through on engine shut down causing hard starting or in the worst scenario, the possibility of a fire.

When the ignition is switched on both the LPG filter/lock ( 5 ) and the idle lock solenoid ( 13 ) will be opened by the safety switch (external) between 0.5 and 3 seconds depending on where the safety switch is set. This provides a small amount of LPG to prime the engine for easier starting and is similar in function to an automatic choke on a carburetor. If the prime time is too short, cranking time will be increased, if the prime time is too long the engine will flood and be hard to start.

Once the engine is cranking and the safety switch receives ^■a pulse signal from the coil, both the LPG filter/lock and idle solenoid will remain open.

The LPG filter/lock (5) and the idle solenoid (13) are open the secondary valve (11) is closed so the amount of LPG required for idle flows through the idle circuit sand is adjusted by the idle adjusting screw (21).

When at idle on part load, the mixer venturi is starting to generate a vacuum signal which will act on the secondary diaphragm (15) and start to open the secondary valve (11). Under part load, the vacuum signal generated in the mixer venturi increases applying a greater vacuum ot the secondary diaphragm (15) opening the secondary valve (11) further supplying more LPG vapour on engine demand.

At full load, the mixer venturi has now generated its maximum vacuum which is pulling the secondary diaphragm (15) down, further increasing the opening on the secondary valve (11), increasing the vapour flow through the primary gas track ( 3 ) , as this flow increases a vacuum is being produced below the primary diaphragm ( 9 ) , opening the primary valve ( 6 ) further increasing the venturi signal on the boost tube (17) and the vacuum on the primary diaphragm ( 9 ) increasing flow through the primary gas track ( 3 ) producing more LPG vapour supply to the gas outlet (14) ensuring a richer mixture needed for maximum power. During deceleration the throttle will be closed, all but cutting off the air flow to the engine. This will lessen the vacuum signal generated in the mixer allowing the sensitivity spring (12) pressure to return the secondary lever (16) and secondary valve (11) to the closed position so the only LPG vapour entering the engine now is the LPG from the idle circuit.

When the engine is stopped no vacuum signal will be generated in the mixer so the secondary valve (11) will be closed. The ignition pulse to the safety switch will cease so likewise the power supply to the gas filter/lock (5) and the idle solenoid (13) will cease ensuring no LPG will flow to the engine. By installing a controller pre-programmed to LP-gas requirements the after market fitted gas fuel system will comply with the regulations and improve the operating efficiency of the engine. In the embodiment as it is illustrated in FIG 3, the gas outlet 14 from the vaporizer feeds gas to the engine via a feed pipe 30 having disposed therein a load block 31 having a gas passage therethrough. The load block 31 mounts a power valve assembly 32 comprising a diaphragm 34 mounting a piston 33 and operable by application of vacuum through pipe 35. Adjustment is provided by adjusting knob 36 acting on adjusting shaft 37 engaging the piston 33.

Mounted on the opposite side of the load block 31 is a trim valve assembly 40 comprising a solenoid 41 operating a piston 42 operable to move towards and away from the face of the powervalve piston 33. The trim piston 42 is biased out of engagement with the piston 33. The solenoid 41 is operable by control cable 43 by controller 44, whereby the position of the trim piston 42 is regulated in response to input from an oxygen sensor 45 to the controller 44.

The controller 44 is also adapted to receive input from a throttle position sensor 46 whereby an idle condition may be detected. In response thereto, the controller pulses the idle solenoid 4 to achieve a selected result or range of oxygen values at the oxygen sensor 45.

Apparatus in accordance with the foregoing embodiments have several advantages. The water jacket assembly of the vaporizer is able to be substituted by a heat tube. This has the advantage that the vaporizer can be converted with the substitution of a stainless steel tube to allow exhaust gas from the engine to heat the LP gas in place of the water system. This has advantages on air cooled engines.

The vacuum signal boost system of sensing the venturi effect through the secondary valve and using this signal to argument the bias of the primary diaphragm is unique in that both sides of the primary diaphragm are under control. The lower surface has vacuum supplied by the boost tube exposed venturi style to the flow through the secondary seat and the upper surface of the diaphragm has spring pressure resisted by the vacuum being supplied by the engine. This has the effect of not allowing the springs to overexert their influence on the primary diaphragm in a rush thus choking the gas inlet system. The secondary lever ratios are by design such that the travel of the diaphragm is transmitted to the secondary valve in such ration to be progressive with an acceleration ramp during the last stages of travel . The modular system of construction of the vaporizers allows the modular conversion from LPG to CNG vaporizers with the inclusion or removal of items building block style. For example, for air cooled engines, all of the features as described are retained but with the removal of the water heating chamber and the insertion of a stainless tube through the heating tunnel. This tube is for exhaust gas to be directed through the vaporizer from the vehicle thus heating the vaporizer.

For CNG vaporizers for water cooled engines, an added high pressure gas chamber may replace the primary diaphragm cover. This chamber has incorporated a heating tube for the engine water which is all the heat needed to be supplied to a CNG vaporizer. The original water plate is removed. This in effect converts the vaporizer to a three stage vaporizer for CNG use.

It will of course be realised that while the above has been given by way of illustrative example of this invention, all such and other modifications and variations thereto as would be apparent to persons skilled in the art are deemed to fall within the broad scope and ambit of this invention as defined in the claims appended hereto.

Claims

-CLAIMS

1. A fuel system including a fuel supply adapted to deliver gaseous fuel to an internal combustion engine and delivery regulating means comprising a valve operable according to engine demand and a trim valve responsive to engine emission status.

2. A fuel system according to Claim 1, wherein said fuel supply comprises vaporizer apparatus adapted to utilize waste heat from the engine cooling system or exhaust gases to vaporize the fuel.

3. A fuel system according to Claim 1, wherein said fuel system includes heater means adapted to heat fuel supplied from a CNG fuel tank.

4. A fuel system according to any one of Claims 1 to 3, wherein said valve operable according to engine demand comprises a valve disposed in the gas flow and selected from a butterfly valve, gate valve, or the like.

5. A fuel system according to Claim 4, wherein said valve operable according to engine demand forms with its operating means a power valve assembly.

6. A fuel system according to Claim 5, wherein said operating means is responsive to engine manifold depression or vacuum.

7. A fuel system according to Claim 6, wherein said power valve assembly comprises an operating diaphragm which reacts to engine vacuum and a load block having a flow passage therethrough which is selectively occludable by a piston mounted in a main body in the load block and operable by the diaphragm.

8. A fuel system according to Claim 7, wherein said power valve assembly is made adjustable by screwing the main body directly into the load-block to a preset distance determined by the type of engine being fitted.

9. A fuel system according to Claim 8, wherein said piston is mounted in a bore in the main body which is substantially transverse to the direction of gas flow through the load block, whereby the piston, in occluding the gas supply line blocking the path of gas, blocks the vacuum signal from the engine venturi thus creating less demand on the fuel supply.

10. A fuel system according to Claim 9, wherein said piston is spring biased to a normally-retracted position and can extend fully into the gas supply line at high Hg and retract into housing body proportional to the lower Hg.

11. A fuel system in accordance with any one of the foregoing Claims, wherein said trim valve is responsive to the residual oxygen sensor of conventional emission control apparatus supplied for use in conjunction with the original petrol fuel system of a vehicle to be converted to LPG or CNG.

12. A fuel system according to Claim 11, wherein the trim valve is formed as an assembly with said valve operable according to engine demand.

13. A fuel system according to Claim 12, wherein said valve operable according to engine demand comprises a conventional power valve and wherein said trim valve includes a further piston installed in the power valve load body and opposing the travel of the power valve piston.

14. A fuel system according to Claim 13, wherein said further piston is operated by a stepper motor, solenoid or the like under the control of control means selected from microprocessor means or an output of engine management means, in response to primary input received from the vehicle oxygen sensor.

15. A fuel system according to Claim 14, wherein said control means includes a pre-set programme to pulse the trim valve piston and thus trim the effective power valve actuation to the required emissions.

16. A fuel system according to Claim 15, wherein said powervalve and trim valve assembly includes idle regulator means .

17. A fuel system according to Claim 16, wherein said idle regulator means includes an on/off solenoid with electronic control from the control means of said further piston, whereby said idle regulator means is responsive to both oxygen sensor output and a pre-controlled program within said control means to give an emission window within a set range.

18. Vaporizer apparatus including: a first demand stage having an LPG inlet wherein main pressure reduction of liquid phase LPG is carried out; a second demand stage wherein the flow of vapour LPG to an engine outlet is controlled; a heat exchange chamber between said first and second stages ; idle regulator means controlling closed throttle fuel supply to said engine outlet; and a gas lock acting to close said LPG inlet until said engine is cranked.

19. Vaporizer apparatus according to Claim 18, wherein said idle regulator means comprise the idle regulator means of a fuel system according to Claims 16 and 19.

20. Vaporizer apparatus according to Claim 19, wherein said gas lock and said idle regulator means are closed by an by an electronic safety switch that prevents the possibility of any LPG reaching the engine until the engine is being cranked. AMENDED CLAIMS

[received by the International Bureau on 20 April 1998 (20.04.98); original claims 1-20 replaced by amended claims 1-16 (3 pages)]

1. A fuel system of the type including a fuel demand regulator adapted to deliver gaseous fuel to fuel metering means for an internal combustion engine, characterised in that the gas line between said regulator and said metering means includes a delivery regulating assembly comprising a valve operable according to engine demand and adapted to open with engine demand a flow passage incorporated in said gas line and a trim valve assembly responsive to engine emission status and adapted to moderate the flow passage opening.

2. A fuel system according to Claim 1, wherein said fuel demand regulator comprises vaporizer apparatus adapted to utilize waste heat from the engine cooling system or exhaust gases to vaporize the fuel.

3. A fuel system according to Claim 1, wherein said fuel demand regulator includes heater means adapted to heat fuel supplied from a CNG fuel tank.

4. A fuel system according to Claim 3, wherein said valve is operable in response to engine manifold depression or vacuum.

5. A fuel system according to Claim 4, wherein said power valve assembly comprises a load block having said flow passage therethrough, an operating diaphragm responsive to said engine manifold depression, and a piston mounted in said load block and operable by said diaphragm to selectively occlude said flow passage .

6. A fuel system according to Claim 5, wherein said power valve assembly is made adjustable by mounting in a bore in a main body which screws directly into the load-block to a preset distance determined by the type of engine being fitted. -7. A fuel system according to Claim 6, wherein said piston is mounted with its axis substantially transverse to the direction of gas flow through the load block, whereby the piston, in occluding the gas supply line blocking the path of gas, blocks the vacuum signal from the engine venturi thus creating less demand on the fuel supply.

8. A fuel system according to Claim 6, wherein said piston is spring biased to a normally-retracted position and can extend fully into the gas supply line at high Hg and retract into housing body proportional to the lower Hg .

9. A fuel system in accordance with any one of the foregoing Claims, wherein said trim valve is responsive to the residual oxygen sensor of conventional emission control apparatus supplied for use in conjunction with the original petrol fuel system of a vehicle to be converted to LPG or CNG.

10. A fuel system according to Claim 9, wherein said valve operable according to engine demand comprises a conventional diaphragm operated piston power valve and wherein said trim valve forms an assembly therewith including a further piston installed in the power valve load body opposite the power valve pi ston .

11. A fuel system according to Claim 10, wherein said further piston is operated by a stepper motor, solenoid or the like under the control of control means selected from microprocessor means or an output of engine management means, in response to primary input received from the vehicle oxygen sensor.

12. A fuel system according to Claim 11, wherein said control means includes a pre-set programme to pulse the trim valve piston and thus trim the effective power valve actuation to the required emissions.

13. A fuel system according to Claim 12, wherein said power valve and trim valve assembly includes idle regulator means.

14. A fuel system according to Claim 13, wherein said idle regulator means includes an on/off solenoid with electronic control from the control means of said further piston, whereby said idle regulator means is responsive to both oxygen sensor output and a pre-controlled program within said control means to give an emission window within a set range.

15. A fuel system in accordance with any one of the foregoing Claims 13 and 14, wherein said demand regulator comprises LPG vaporizer apparatus including: a first demand stage having an LPG inlet wherein main pressure reduction of liquid phase LPG is carried out; a second demand stage wherein the flow of vapour LPG to an engine outlet is controlled; a heat exchange chamber between said first and second stages; and a gas lock acting to close said LPG inlet until said engine is cranked.

16. Vaporizer apparatus according to Claim 15, wherein said gas lock and said idle regulator means are closed by an by an electronic safety switch that prevents the possibility of any LPG reaching the engine until the engine is being cranked.