GB2421543A

GB2421543A - I.c. engine fuel injection system with a positive displacement pump dispensing a fixed amount of fuel

Info

Publication number: GB2421543A
Application number: GB0516235A
Authority: GB
Inventors: Jeffrey Allen
Original assignee: Scion Sprays Ltd
Current assignee: Scion Sprays Ltd
Priority date: 2005-08-05
Filing date: 2005-08-05
Publication date: 2006-06-28
Anticipated expiration: 2025-08-05
Also published as: GB2421543B; GB2438456A; CN101238279A; GB2423119A; GB2423119B; GB2438456B; GB0606104D0; GB0522068D0; CN101238282A; CN101238282B; GB0516235D0

Abstract

An i.c. engine has a variable volume combustion chamber 13, an air intake system 18, 20, 21, an exhaust system 17 and a fuel injection system comprising an injector 19 which functions as a positive displacement pump. The fuel injector 19 comprises a fuel chamber 52 with inlet and outlet passages 50, 54 controlled by respective one-way valves 51, 53. A spring-biassed piston 55 having an end plate armature 58 is slideable in the chamber 52 and is surrounded by a solenoid 57 connected to ECU 23. Reciprocal movement of the piston 55 acts to draw fuel into, and force fuel from, the chamber 52. Since the piston moves between fixed end stops, the injector dispenses a fixed amount of fuel for each and every operation of the injector. Thus the total amount of fuel delivered per engine cycle is controlled by the ECU 23 by controlling the number of operation of the injector per cycle in response to engine load as sensed by the position of the throttle valve 21. The or each engine cylinder may be provided with two injectors dispensing unequal amounts of fuel. The simple fuel injection system is suitable for small, low-power engines, eg for lawn mowers or other garden equipment.

Description

A FUEL INJECTION SYSTEM FOR

AN INTERNAL COMBUSTION ENGINE

The present invention relates to a fuel injection system for an internal combustion engine.

Most internal combustion engines in automobiles currently use fuel injection systems to supply fuel to the combustion chambers of the engine. Fuel injection systems have replaced the earlier technology of carburettors because they give more control of delivery of fuel and enable the engine to meet emission legislation targets as well as improving the overall efficiency of the engine.

The injectors in current use are pulse width modulated.

This means that each injector is operated for a chosen period of time in each cycle of the engine, the length of time that the injector is open dictating the volume of fuel delivered to the combustion chamber in that cycle.

Typically, such pulse width modulation fuel injection systems use a fuel supply of a fixed pressure or an accurately known substantially constant pressure and on/off valves which can be activated for any predetermined time period under the control of an electronic controller. The result of such a combination of known pressure and variable, but controlled, opening times gives an injection of known quantities of fuel into the combustion chambers of the engine.

The above-described approach is taken for all gasoline injection systems (both port and direct injection systems) and also the new state-of-theart high pressure "common rail" diesel injection system. The latest common rail direct injection diesel fuel injection systems do sometimes use multiple injection pulses in order for better dispersal of fuel within the cylinder and better combustion results, S but each of these pulses is of a variable time (albeit a time much shorter than that of the single pulse earlier fuel injection systems) and the controller will set the opening time of the injector in each pulse in order to control exactly the amount of fuel delivered. All of the prior art systems therefore require a pump, a pressure regulator and an injector (which functions effectively as an on/off valve) and a sophisticated electronic control module to control the opening time of each injector. The injectors used in the fuel injection systems are very accurate and quick in their response (rather than the earlier fuel injectors which were slow in their operation and suffered from a lack of repeatability). The latest injectors are able to open and close in less than one millisecond.

Whilst the sophisticated and highly developed fuel injection systems currently available are ideal for use in internal combustion engines in automobiles, there are many other applications for internal combustion engines where such a level of sophistication is not appropriate and too costly. For instance, small single cylinder low power output engines as used for lawn mowers, chain saws, small generators, mopeds, scooters, etc are built to very tight cost targets and have low power outputs, so therefore cannot afford the cost of a sophisticated fuel injection system nor the power required to run a fuel pump which provides pressurised fuel as required by the available sophisticated fuel injection systems. To date, such small engines have used traditional carburettor technology. However, it is now the case that such small engines will face the same type of exhaust gas emission legislation as the engines in automobiles and must be modified in a way so as to meet the emissions targets. Therefore, a cheap and simple system of fuel injection is required for such small engines.

The present invention provides in a first aspect an internal combustion engine comprising a variable volume combustion chamber; an air intake system for delivering charge air to the combustion chamber; an exhaust system for relaying combusted gas from the combustion chamber to atmosphere; and a fuel injection system for delivering fuel into the charge air for combustion therewith in the combustion chamber; wherein the fuel injection system comprises a fuel injector which functions as a positive displacement pump and dispenses an amount of fuel which is fixed for each and every operation of the injector; and a controller which controls the operation of the fuel injector; characterised in that each of at least a majority of engine cycles the fuel injector is operated on a plurality of occasions by the controller; in response to an increasing engine speed and/or load the controller increases in amount the fuel delivered per engine cycle by increasing in number the occasions the fuel injector is operated per engine cycle; and in response to a decreasing engine speed and/or load the controller reduces in amount the fuel delivered per engine cycle by reducing in number the occasions the fuel injector is operated per engine cycle.

Preferred embodiments of the present invention will now be described with reference to the accompanying drawings, in which: Figure 1 is a schematic representation of an internal combustion engine with a fuel injection system according to the present invention; Figure 2 is a schematic representation of a first type of fuel injector suitable for use in the engine of Figure 1; Figure 3 is a schematic illustration of a second type of fuel injector suitable for use in the engine of Figure 1; Figure 4 shows the type of signal used in the prior art fuel injection systems to control the amount of fuel delivered to the combustion chamber in each engine cycle; Figure 5 shows the control signal used by the present invention to activate the fuel injector of Figure 1 (e.g. a fuel injector of the type of Figure 2 or of the type of Figure 3) in order to control the amount of fuel delivered into the combustion chamber in each operating cycle; Figure 6 shows at: Figure Ga a rotation signal taken from an engine cam shaft or crank shaft of the Figure 1 engine, Figure 6b a control signal generated for full load operation of the Figure 1 engine, Figure Gc a control signal generated for part load operation of the Figure 1 engine, Figure 6d a control signal generated for engine idling of the Figure 1 engine, and Figure 6e a control signal generated during starting of the Figure 1 engine; Figure 7 is a schematic representation of a second embodiment of internal combustion engine with a fuel injection system according to the present invention; Figure 8 is a schematic illustration of a fuel injector suitable for use with the engine of Figure 7; Figure 9 is a schematic illustration of the fuel injector of Figure 8 and its arrangement with a camming surface used to drive it; and Figure 10 is a schematic illustration of a second embodiment of fuel injector suitable for use in the Figure 7 engine in place of the fuel injector illustrated in Figure 7.

Turning first to Figure 1, there can be seen in the Figure an internal combustion engine 10 comprising a cylinder 11 in which reciprocates a piston 12 with the cylinder 11 and piston 12 defining between them a combustion chamber 13. The piston 12 is connected by a connecting rod 14 to a crankshaft 15, which in turn is connected to a cam shaft 16. A mechanism (not shown) such as a push-rod type mechanism, is used between the cam shaft 16 and two poppet valves 17 and 18 which are the exhaust and inlet valves of the engine. The cam shaft 16 will drive the inlet valve 18 and the exhaust valve 17 to open in timed relationship to the movement of the piston 12 in the cylinder 11 with return springs biassing the poppet valves 17 and 18 back into their valve seats. The engine 10 is a simple engine, a single cylinder engine of, for instance, a lawn mower or other garden equipment.

The engine 10 has a fuel injection system comprising a fuel injector 19 arranged to deliver fuel into an inlet passage 20 upstream of the inlet valve 18. A throttle valve 21 is placed in the inlet passage 20 to throttle the flow of charge air into the combustion chamber 13. A sensor is connected to throttle valve 21 and feeds back the signal via a line 22 to an electronic control unit 23, the signal indicating the rotational position of the throttle valve 21 and therefore engine load. The ECU 23 also receives a timing signal via a line 24, the timing signal being generated by a cam shaft sensor 25 (which could be replaced by a crankshaft sensor instead) . Having regard to the timing signal produced by the sensor 25 and the load signal produced by the sensor attached to throttle valve 21, the ECU 23 generates a control signal which is relayed via line 26 to the injector 19 and controls operation of the injector 19.

A first example of injector 19 is shown in Figure 2.

The injector 19 has a fuel inlet 30 in which a filter 31 is placed to remove any impurities from the fuel before it passes into the main body of the injector. The main body 32 of the injector has a cavity 33 in which is located a stack 34 of piezo-electric elements. The fuel introduced by the inlet 30 passes along a passage 35 through the stack 34. A flexible diaphragm 36 abuts a free end of the stack 34 and the diaphragm 36 incorporates in it a one- way valve 37 aligned with the passage 35 passing through the stack 34. A section 38 of the cavity 33 is defined by the flexible diaphragm 36 and leading from this section 38 there is a fuel outlet passage 39 which is opened and closed by a one- way reed valve 40. Downstream of the reed valve 40 is a high voltage electrostatic charging electrode 41 having apertures therethrough allowing passage of fuel. Downstream of the electrode 41 is a fuel outlet disc 42 having multiple fuel outlet orifices defined in it.

A simple gravity feed fuel delivery system (not shown) will relay fuel from a fuel tank (not shown) to the fuel inlet 30, the fuel then being filtered by the filter 31.

Fuel is then drawn into and expelled from the fuel injector of Figure 2 by the expansion of the stack 34 piezo-electric elements. When a voltage is applied to the piezo-electric elements of the stack 34, they expand and this expansion causes the stack 34 to grow in length and push on the flexible diaphragm 36. When this happens, the one-way valve 37 will close and fuel in the section 38 will be forced out of the section 38 by the flexing diaphragm 36, the diaphragm 36 flexing under the action of the stack 34. The one-way valve 40 will open to allow fuel to be expelled from the section 38 and the expelled fuel will then pass through the orifices in the charging electrode 41 and then through the orifices of the fuel outlet disc 42 into the air inlet passage 20 (shown in Figure 1). The fuel passing through the electrode 41 will receive an electrostatic charge and this electrostatic charge will help in the atomisation of the fuel passing out of the orifices of the fuel outlet disc 42.

Once the voltage is removed from the stack 34 of piezo- electric elements then the stack 34 will reduce to its original length and the flexible diaphragm 36, which is resilient in nature, will move back to its original position, thereby increasing the volume of the section 38 of the cavity in the injector. This in turn will cause the one- way valve 40 to close to seal off the section 38 from the fuel outlet, while the one-way valve 37 will open to allow fuel to flow through the passage 35 to fill the cavity 38. The cavity 38 can then be charged with fresh fuel charge ready for the next injection of fuel into the air inlet passage 20.

In Figure 2 the control line 26 can be seen connected electrically to the stack 34 of piezo-electric elements and also electrically connected to the high-voltage electrostatic charging electrode 41.

The fuel injector of Figure 2 differs from known fuel injectors in that it operates as a positive displacement pump, which, in each and every operation of the injector, dispenses the same amount of fuel. The volume of fuel delivered by the injector is constant for each operation.

This varies significantly from the injectors of the prior art where the injectors function as on/off valves controlling flow of fluid through them, the fluid supplied to them being supplied from a pressurised source. The prior art injectors then control the amount of fuel delivered by varying the opening time of the injector. There is no such variation of opening time with the injector of the present invention, instead it functions as a positive displacement pump and pumps out a set volume of fuel in each and every operation.

A second type of fuel injector suitable for the operation as the injector 19 of Figure 1 is shown in Figure 3. Its operating principle is the same as the injector of Figure 2, namely that in each and every operation a set amount of fuel is delivered and that the injector itself operates as a pump to positively displace a volume of fuel therefrom, the volume remaining constant across each and every operation of the -injector.

The injector of Figure 3 has a fuel inlet passage 50 which will be connected to a fuel tank (not shown) to receive fuel under a simple gravity feed arrangement (not shown) . A sprung-loaded one-way valve 51 controls flow of fuel from the inlet passage 50 into a fuel chamber 52 of the injector. A sprung-loaded one-way valve 53 controls flow of fuel out of the fuel cavity 53 to a fuel outlet pipe 54 through which the fuel can be delivered (directly or via a conduit to a remote spray nozzle) into the air intake passage 20.

A piston 55 is slidably located in the injector body.

It is acted upon by a biasing spring 56 and is surrounded by a solenoid 57. An end plate 58 is connected to the piston and extends radially outwardly from the piston across an end face of the solenoid 57. The solenoid 57 is connected by the line 26 to the ECU 23.

Starting from a condition in which the piston 55 is biased to its lowermost point by the biasing spring 56 (i.e. the point at which the fuel chamber 52 has its greatest volume), the fuel chamber 52 will be primed with fuel ready for injection. Energisation of the solenoid 57 then acts to pull the plate 58 into contact or near contact with the solenoid 57. The piston 55 moves upwards against the force of the biasing spring 56 to reduce in volume the fuel chamber 52. This causes the positive displacement of fuel from the fuel chamber 52, the one-way valve opening to allow the piston 55 to expel fuel from the fuel chamber 52 out of the fuel outlet 54.

- 10 - Once the solenoid 57 is de-energised, then the biasing spring 56 will force the piston 55 downwardly and the plate 58 away from the solenoid 57. The downward motion of the piston 55 will cause the fuel chamber 52 to increase in volume and this will have the effect of closing the one-way valve 53 and opening the one-way valve 51. The moving piston 55 draws fuel from the fuel inlet 50 into the fuel chamber 52 to fully charge the fuel chamber 52 ready for the next dispensing of fuel.

The injector is constructed so that the piston 55 has a set distance of travel in each operation. The piston 55 moves between two end stops. Thus, in each and every operation of the injector, the piston 55 displaces a set amount of fuel and a set amount of fuel is dispensed out of the fuel outlet 54. The amount of fuel dispensed by the injector is constant for each and every operation.

The control of the injectors of the present invention is quite different from the control of the injectors of the prior art, as will now be illustrated in Figures 4 and 5.

In Figure 4 there can be seen a graphic illustration of a control signal used to control a prior art injector. The mode of operation used is called pulse width modulation control. In solid lines can be seen a pulse of a chosen width and this corresponds to the duration of opening of a traditional fuel injector. The dotted lines show other greater pulse widths, i.e. greater opening durations of

traditional prior art injectors. With a set supply

pressure, the control of the pulse width gives exact control of the amount of fuel delivered by the fuel injector.

- 11 - Moving on to Figure 5, Figure 5 graphically illustrates the control signal generated by the ECU 23 to control the fuel injector 19 in the present invention. Instead of pulse width modulation, a form of control called pulse count injection is used. There can be seen in solid lines six different pulses. These are the pulses for a single cycle of engine operation, i.e. the delivery of charge fuel for a single combustion event in the combustion chamber 13. Each pulse represents one operation of the injector 19. As explained above, because the injector 19 in each and every operation delivers a set amount of fuel, the total amount of fuel delivered for combustion is controlled by controlling the number of operations of the injector for a particular engine operating cycle. In the case illustrated in solid lines, the injector 19 is operated six times to deliver a total quantity of fuel equal to six times the set amount delivered by the injector in each operation. This fuel is delivered into the air intake passage 20 for mixing with air to be delivered into the combustion chamber 13. The first operation of the injector 19 will take place whilst the inlet valve 18 is closed but it may be that the valve is open or has at least started to open by the time of the last operation of the injector 19.

In Figure 5 the dotted line pulses show that a greater amount of fuel can be delivered in the operating cycle by operating the injector a greater number of times. Figure 5 illustrates a total possible pulse count of 10 pulses, giving a total amount of fuel delivered of 10 times the set amount delivered by the injector in each operation.

- 12 - More detail is given in Figure 6. Figure 6a shows the cam shaft or crank shaft signal received on line 24 by the ECU 23. The pulses illustrated in the signal give an indication of the rotational position of the crank shaft or cam shaft. It will be seen that the ECU 23 times its own pulses in the control signal it generates to be synchronised with the pulses in the timing signal shown in Figures Ga. In fact, it is the pulses in the timing signal of Figure Ga which trigger the ECU 23 to generate its own control pulses, as shown in Figures 6b to 6e.

Figure Gb shows full load operation. Therefore, in each engine cycle (an engine cycle takes place between the chain dot lines in the Figure) the ECU generates a control signal shown at Figure Gb which comprises thirteen pulses which operate the injector 19 thirteen times. This represents the maximum amount of fuel that can be delivered for combustion in the combustion chamber 13.

Figure 6c shows the control signal generated in each engine cycle for part load operation. In this case, the control signal in each cycle comprises seven pulses which operate the injector 19 seven times in each engine cycle.

Thus, the amount of fuel delivered in each engine cycle is 7/13 of the total amount of fuel that is delivered in full load operation.

Figure 6d shows the control signal generated by the ECU through idle operation, i.e the time when the least amount of fuel is delivered in each engine cycle. Figure Gd shows that the injector 19 is operated only 4 times in each engine cycle.

- 13 - Finally, Figure Ge shows an exceptional condition of engine starting in which an over rich mixture of fuel and air is delivered into the combustion chamber 13 to enable starting of the engine. Seventeen pulse counts are shown for each engine cycle and this means that the injector 19 is operated seventeen times through each engine cycle at the time of starting the engine. The total fuel delivered is seventeen times the set amount that the injector delivers upon each operation.

It will be appreciated that the engine described above removes the need for a separate fuel pump,and a pressure regulator and dramatically simplifies the function of the ECU. The fuel injection system comprises a simple control system that counts the desired number of pulses into the engine for its correct operation. Whilst this does not give the degree of control possible with the prior art system (i.e. the total volume of fuel delivered cannot be varied continuously within a range, but only by set intervals or set amounts) this will be sufficient for a simple engine such as is used in a lawnmower. Putting it another way, the control possible with pulse count injection gives a coarser control of the amount of fuel delivered to the engine, but this will be sufficient for the simple engines involved.

As described above, the fuel delivered from the injector can be passed to a simple plain orifice or nozzle (see Figure 3) or can be passed through an atomising device such as a pressure spray nozzle (not shown) or an electrostatic charging unit (shown in Figure 2). The injector (or pulsing unit) can be close-coupled to the - 14 - atomising unit (as in Figure 2) or located elsewhere on the engine some distance away (i.e. the figure 3 embodiment could have a fuel outlet that led to a dispensing nozzle some distance away from the injectors shown) The volume of fuel delivered by the fuel injector will be to some degree dependent on engine size and the range of engine operating conditions. Typically, an injector will deliver between 0.05 mm3 and 0.1 mm3 per pulse. Typically the total volume delivered in each engine cycle will be between 0.1 and 0.5 mm3 If this is the case then the number of pulses required for correct engine operation will vary from five to ten pulses per engine cycle for engine idling and twenty to fifty pulses per cycle for a full load operation.

As the injector controls the quantity of fuel supplied itself, there is no need for a controlled fuel supply pressure and this means that fuel may be fed directly to the injector via a gravity feed system with no problem being caused by varying pressure due to the different head of fuel as the fuel level falls. Alternatively, a simple low pressure fuel pump could be used, as often used with carburettors. The only requirement is that sufficient fuel is delivered to the injector so that it can recharge itself for the next pulse.

The total quantity of fuel delivered to the engine in each cycle (every two strokes in a two-stroke engine or every four strokes in a four-stroke engine) is determined as a multiple of the volume of fuel dispensed in each operation of the injector and the number of times the injector is 15 - operated in the cycle. The engine management system can be simply constructed to deliver a different number of pulses in its control signal depending upon the load demand required of the engine, as measured by the sensor 21. A very simple electronic control unit can therefore be constructed from just a few I.C. chips which compare throttle position as measured by the sensor 21 (e.g. a throttle position potentiometer) with a look-up table giving the required number of pulse counts for that throttle position and with the ECU then generating pulses triggered by the timing signal on line 24 and counting the number of pulses until the correct number of pulses is reached. Then the pulse injector is switched off until the next engine cycle.

Figure 7 shows a second embodiment of engine according to the present invention, the engine having a mechanically powered injector which is controlled electrically, rather than an electrically powered injector as described previously.

In Figure 7 there can be seen an internal combustion engine 80 comprising a cylinder 81 in which reciprocates a piston 82 with the cylinder 81 and piston 82 defining between them a combustion chamber 83. The piston 82 is connected by a connecting rod 84 to a crank shaft 85 which in turn is connected to a cam shaft (not shown) having cams which by their camming action operate two poppet valves 87 and 88 which are the exhaust and inlet valves of the engine.

These valves are open and closed in timed relationship to the piston 82 and the cylinder 81. Return springs (not shown) will be provided to bias the poppet valves 87 and 88 - 16 - into their valve seats. The engine 80 is a simple engine, for instance a single cylinder engine of a lawnmower or other garden equipment. The engine 80 has a fuel injection system comprising a fuel injector 90 arranged to deliver fuel into an inlet passage 89 upstream of the inlet valve 88. A throttle valve 91 is placed in the inlet passage 89 to throttle the flow of charge air into the combustion chamber 83. A sensor is connected to the throttle valve 91 and generates a signal indicative of the position of the throttle valve 91 which is supplied as an electrical signal to an engine control unit 92.

The fuel injection system of Figure 7 comprises a camming surface 93 provided on a circumferential surface of a wheel 94 mounted on, and rotating with, the crankshaft 85.

A fuel injector 96 is driven by the camming surface 93 and is shown in greater detail in Figure 8.

In Figure 8 it can be seen that the fuel injector 96 comprises a fuel inlet 97 which receives fuel fed to it from a fuel tank (not shown) by a gravity feed system (not shown) . Fuel can pass from the fuel inlet 97 into a fuel chamber 98 with the flow of fuel controlled by a first sprungloaded one way valve 99. A second sprung-loaded one way valve 100 controls flow of fuel out of the fuel chamber 98 to a fuel outlet 101. The fuel outlet 101 is connected by a fuel line 120 (see Figure 7) to the delivery nozzle and atomiser 90.

A piston 102 is slideably mounted in a housing 103 of the injector 96 and is slideable in the fuel chamber 98. The piston 102 has a cam follower 103 which is a roller follower - 17 - rotatably mounted at one end of the piston 102. The roller follower 103 will engage with and follow the camming surface 93 (see Figure 7). The piston 102 and therefore the roller follower 103 are biased into engagement with the camming surface 93 by a biasing spring 104 which acts between the body 103 of the injector and a shoulder 105 provided to extend radially outward from the piston 102.

Also provided in the injector 96 is a control solenoid 106 which is controlled electrically by a signal provided on a line 107 along which pass control signals from the engine control unit 92. The solenoid 106 can act on an over-ride pintle 108 which comprises a rod 113 extending through the solenoid 106 and a disc 109 extending radially outward from the rod 113 over an end of the control solenoid 106.

In operation of the injector (and starting from a condition in which the piston 102 occupies a position in which the fuel chamber 98 has its greatest volume and assuming that the fuel chamber 98 is fully charged with a fresh fuel charge), the piston 102 will be pushed into the chamber 98 under the action of the camming surface 93. The piston 102 will therefore displace fuel from the chamber 98 which will flow out of the fuel outlet 101, the one-way valve 100 opening to permit dispensing of fuel from the fuel chamber 98, whilst the one-way valve 99 seals the fuel inlet 97 from the fuel chamber 98. The fuel forced out of the fuel chamber 98 will pass along the fuel pipe 120 to the delivery nozzle 90 to be delivered as a spray in the air intake passage 89. Subsequently, the piston 102 (following the profile of the cam surface 93 and under the action of the biasing spring 104) will move to increase in volume the - 18 - fuel chamber 98. This will have the effect of closing the one-way valve 100 whilst opening the one-way valve 99. Fuel will then be drawn into the fuel chamber 98 from the fuel inlet 97 until a maximum volume of fuel is reached, whereupon the process will start again.

In Figure 9 the injector 96 can be seen interacting with the camming surface 93 and it can be clearly seen that the cam surface 93 comprises pulse lobes such as 110 separated by base circle regions such as 111, the pulse lobes typically having a crest 0.1 to 0.5 mm greater in radius than the base circle. It is seen in Figure 10 that the wheel 94 has a total of twenty pulse lobes and also a section 112 of constant radius. When the roller follower 103 engages the section 112 then the pulse injector 116 is deactivated.

If the control solenoid 107 is kept deactivated throughout a whole engine cycle then each of the pulse lobes (e.g. 110) on the cam surface willresult in the dispensing of a quantity of fuel from the pulse injector 96. The injector 96 will dispense twenty separate pulses of fuel for each complete rotation of the wheel 94. It should be understood that each pulse lobe 101 will have a height relative to the base circle which is identical to all of the other pulse lobes, so that the piston 102 will in each operation move a set amount so that the amount of fuel dispensed by the injector 96 is the same for each and every operation of the injector 96, i.e. for each and every dispensing of fuel from the injector 96. The operating of the injector 96 twenty times for each rotation of the wheel 94 represents delivery of the maximum volume of fuel - 19 - possible to the engine in each operating cycle, such a condition being used for instance on engine start up.

The control solenoid 107 enables control of the injector 96. When the solenoid 106 is energised, then the pintle 108 will engage the one-way valve 99 and will force it open and will keep it open. When the one-way valve 99 is open then the motion of the piston 102 results only in the drawing into the chamber 98 of fuel from the fuel inlet 97 and then the expulsion of fuel from the chamber 98 back to the fuel inlet 97. No fuel is expelled from the chamber 98 via the one-way valve 100. Thus the ECU can control the operation of the injector 96 and can control how many pulses of fuel are delivered by the injector 96 and consequently the total amount of fuel delivered in each engine cycle (every two strokes in a two-stroke engine or every four strokes in a four- stroke engine) In Figure 10 there can be seen an injector 150 which could be used in the Figure 7 engine in place of the injector 96 illustrated in the Figure. The injector 150 comprises a fuel inlet 151 which receives fuel fed to it from a fuel tank (not shown) by a gravity feed system (not shown). Fuel can pass from the fuel inlet 151 into a fuel chamber 152 with the flow of fuel controlled by a first spring-loaded one-way valve 153. A second spring-loaded one-way valve 157 controls flow of fuel out of the fuel chamber 152 to a fuel outlet 154. The fuel outlet 154 will be connected by the fuel line 120 of Figure 7 to the delivery nozzle and atomizer 90.

- 20 - A resilient displacement diaphragm 155 seals the fuel chamber 152. The diaphragm 155 is provided with a cam follower contact pad 156. The contact pad 156 will engage with and follow a camming surface (not shown) . The contact pad 156 is biased into engagement with the camming surface by the resilience of the diaphragm 155. The camming surface will be variable in nature under the control of the ECU 92 in order to delivery a variable number of impulses to the contact pad 156. This will be achieved, for instance, by mounting a second control wheel alongside the cam wheel 94 rotatable with the cam wheel 94, but also rotatable with respect to the cam wheel 94 under the control of the ECU.

The control wheel could have, for instance, a first sector with a periphery of a constant radius equal to the radial distance to the peak of each lobe 110 of the cam wheel 94 and a second sector with a periphery of a constant radius equal to the radial distance to the bottom of each base circle region 111 of the cam wheel 111. At one extreme, the second sector of the control wheel aligns with all the lobes and base circle sections of the cam wheel 94 and they are all active in displacing the diaphragm 155. Then, as the control wheel and the cam wheel 94 are rotated relative to each other, the first sector of the control wheel aligns with some of the cam lobes 110 and the base circle sections 111 and "disables" them since the greater radial height of the control wheel "overrides" the base circle portions 111 of the cam wheel 94.

In operation of the injector 150 (and starting from a position in which the diaphragm 155 occupies a position in which the fuel chamber 152 has its greatest volume and assuming that the fuel chamber 152 is fully charged with - 21 - fresh fuel charge) the diaphragm will be flexed under the action of a cam 110 to reduce in volume the fuel chamber 152 and thereby displace fuel from the chamber 152 to flow out of the fuel outlet 154, the one-way valve 157 opening to permit dispensing of fuel from the fuel chamber 152, whilst the one-way valve 153 seals the fuel inlet 151 from the fuel chamber 152. The fuel forced out of the fuel chamber 152 will pass along the fuel pipe 120 to the delivery nozzle 90 to be delivered as a spray in the air inlet passage.

Subsequently, the diaphragm 155 (following the profile of the cam surface and due to its own resilience), will flex to increase in volume the fuel chamber 152. This will have the effect of closing the one-way valve 157 while opening the one-way valve 153. Fuel will then be drawn into the fuel chamber 152 from the fuel line 151 until a maximum volume is reached, whereupon the process will start again.

In each operating cycle of the engine the diaphragm 155 will be flexed to expel fuel from the fuel chamber 152 by each cam lobe operable in that cycle, the number of operable cam lobes being selected by the ECU, for instance, by rotating the above described control wheel relative the cam wheel.

As with the Figure 1 engine, the Figure 7 engine does not need a high pressure pump to pressurise the fuel supply or pressure regulator to control the pressure of the supplied fuel. Nor does the engine need a sophisticated ECU to control the operation of a fuel injector. Instead, the ECU can be constructed from simple I.C. chips, which together select the appropriate number of pulses for a given engine load (as sensed by the engine load sensor 91) and - 22 - then count the number of delivered pulses in an engine cycle before deactivating the injector by means of the solenoid 106.

With the Figure 7 engine it might even be possible to arrange for a mechanical control for the injector 96 by means of some linkage between the throttle and the injector 96.

In both of the embodiments of engine described above, only a single injector has been used for each working cylinder of the engine. However, the applicant envisages that each working cylinder could be provided with a plurality of injectors. This could have two advantages.

First, in order to deliver a given amount of fuel in each engine cycle the number of operations of each individual injector would be decreased and this could have practical benefits since each injector would not need to operate at such a fast speed in use. Secondly, if the injectors for a particular working cylinder were constructed so that they delivered a differing amount of fuel to each other, then the engine management system could control the operation of both in a way that would give a "finer" control of the amount of fuel delivered in each working cycle. For instance, if an engine is provided with a single injector which injects 0. 1 mm3 per pulse, then the total fuel injected per engine cycle will have to be a multiple of 0.1 mm3, i.e. 0.1 mm3, 0.2 mm3, 0.3 mm3 up to 0.5 mm3. However, if an engine is provided with two injectors, one which injects a pulse of 0.1 mm3 and the other which injects a pulse of 0.05 mm3 then the engine will be able to deliver in each engine cycle a total amount of fuel which could be 0.05 mm3, 0.1 mm3 - 23 - 0.15 mm3, 0.2 mm3 etc. This is achieved with a smaller number of injector operations than would be necessary if the working cylinder had only an injector capable of a pulse of 0.05 mm3.

Claims

- 24 - CLAI MS

1. An internal combustion engine comprising: a variable volume combustion chamber; an air intake system for delivering charge air to the combustion chamber; an exhaust system for relaying combusted gas from the combustion chamber to atmosphere; and a fuel injection system for delivering fuel into the charge air for combustion therewith in the combustion chamber; wherein the fuel injection system comprises: a fuel injector which functions as a positive displacement pump and dispenses an amount of fuel which is fixed for each and every operation of the injector; and a controller which controls the operation of the fuel injector; characterised in that: in each of at least a majority of engine cycles the fuel injector is operated on a plurality of occasions by the controller; in response to an increasing engine speed and/or load the controller increases in amount the fuel delivered per engine cycle by increasing in number the occasions the fuel injector is operated per engine cycle; and in response to a decreasing engine speed and/or load the controller reduces in amount the fuel delivered per engine cycle by reducing in number the occasions the fuel injector is operated per engine cycle.

2. An internal combustion engine as claimed in claim 1 wherein the fuel injector uses electrical power to dispense fuel therefrom and the controller is an electronic - 25 - controller which produces a pulsed control signal to control the fuel injector, each pulse causing the fuel injector to dispense fuel and the electronic controller varying the number of pulses per engine cycle to vary the amount of fuel delivered.

3. An internal combustion engine as claimed in claim 2 wherein the fuel injector comprises a stack of piezo- electric elements which on increasing in length force fuel out of the fuel injector.

4. An internal combustion engine as claimed in claim 2 wherein the fuel injector comprises an electrical coil and a piston moveable under the action of the electrical coil to force fuel out of the fuel injector.

5. An internal combustion engine as claimed in claim 3 or claim 4 wherein the fuel injector comprises a housing in which a fuel chamber is formed, from which chamber fuel is forced out of the fuel injector, the fuel injector having a fuel inlet for admitting fuel into the fuel chamber and a fuel outlet via which fuel is forced from the fuel injector, the fuel injector also having a first one-way valve which allows fuel to flow into the fuel chamber from the fuel inlet while preventing flow of fuel from the fuel chamber back to the fuel inlet and the fuel injector further having a second one-way valve which permits fuel to flow out of the fuel chamber to the fuel outlet, while preventing flow of fuel back into the fuel chamber from the fuel outlet.

6. An internal combustion engine as claimed in any one of claims 2 to 5 wherein a sensor is provided to monitor engine - 26 - load and to provide to the electronic controller a signal indicative of engine load, the electronic controller calculating how many pulses to produce in each engine cycle having regarding to engine load.

7. An internal combustion engine as claimed in claim 6 wherein a sensor is associated with a crankshaft or a camshaft of the engine and produces a timing signal related to rotation of the crankshaft or camshaft, which timing signal is used by the electronic controller to trigger the pulses generated thereby.

8. An internal combustion engine as claimed in claim 1 wherein the fuel injector is driven mechanically by a camming surface, the fuel injector comprising a piston biased into engagement with the camming surface by a biasing spring and the piston being displaceable by the camming surface to force fuel out of the fuel injector, the camming surface comprising a plurality of cam lobes each of which can interact with the piston during each engine cycle and the controller controlling how many of these cam lobes in each engine cycle cause the piston to force fuel out of the fuel injector.

9. An internal combustion engine substantially as hereinbefore described with reference to and as shown in the accompanying drawings. AW?,

9. An internal combustion engine as claimed in claim 8 wherein the fuel injector comprises a body having a fuel chamber and fuel outlet through which fuel is forced out of the fuel chamber by the piston, the fuel injector also having a fuel inlet through which fuel is introduced into the fuel chamber, the fuel injector further having a first one-way valve operable to allow fuel to flow into the fuel chamber from the fuel inlet while preventing flow of fuel - 27 back out of the fuel chamber to the fuel inlet and a second one-way valve operable to allow fuel to flow out of the fuel chamber to the fuel outlet while preventing flow of fuel back into the fuel chamber from the fuel outlet.

S

10. An internal combustion engine as claimed in claim 9 wherein the first one-way valve can be disabled by the controller and when disabled allows flow of fuel back out of the fuel chamber to the fuel inlet, the motion of the piston when the first one-way valve is disabled serving only to draw in fuel from the fuel inlet into the fuel chamber and then expel the fuel out of the fuel chamber back to the fuel inlet.

11. An internal combustion engine as claimed in claim 1 wherein the fuel injector is driven mechanically by a camming surface, the fuel injector comprising a flexible diaphragm displaceable by a camming surface to force fuel out of the fuel injector, the camming surface comprising a plurality of cam lobes which can each cause a flexing of the diaphragm during an engine cycle and the controller controlling how many of these cam lobes in each engine cycle cause the piston to force fuel out of the fuel injector.

12. An internal combustion engine as claimed in claim 11 wherein the fuel injector comprises a body having a fuel chamber and fuel outlet through which fuel is forced out of the fuel chamber by the piston, the fuel injector also having a fuel inlet through which fuel is introduced into the fuel chamber, the fuel injector further having a first one-way valve operable to allow fuel to flow into the fuel back out of the fuel chamber to the fuel inlet and a second - 28 - one-way valve operable to allow fuel to flow out of the fuel chamber to the fuel outlet while preventing flow of fuel back into the fuel chamber from the fuel outlet.

13. An internal combustion engine as claimed in claim 11 or claim 12 comprising cam control means capable of rendering one or more cam lobes of the camming surface inoperable, the controller using the cam control means to control how many cam lobes in each engine cycle cause the diaphragm to flex and force fuel out of the fuel injector.

14. A method of supplying fuel to a combustion chamber of an internal combustion engine, the method comprising: using a positive displacement pump to deliver to the combustion chamber in each engine cycle a plurality of pulses of fuel to all the other pulses; and varying in number the pulses of fuel from engine cycle to engine cycle in response to changes in engine speed and/or load to thereby control a total quantity of fuel delivered to the combustion chamber in each cycle.

15. A method as claimed in claim 14 wherein the number of pulses of fuel per engine cycle is kept at a first high level for a period immediately following starting of the engine and then reduced to lower levels for subsequent engine cycles until the engine is next started.

16. A method as claimed in claim 14 or claim 15 wherein the fuel displacement pump is electrically powered and controlled electrically by an electric or electronic controller generating a pulsed control signal, with each - 29 - pulse in the control signal causing the pump to deliver a pulse of fuel.

17. A method as claimed in claim 14 or claim 15 wherein the fuel displacement pump is mechanically powered and controlled electrically by an electrical or electronic controller which generates a control signal which suspends delivery of fuel by the pump for a chosen period in each engine cycle to thereby control the number of pulses of fuel delivered.

18. An internal combustion engine substantially as hereinbefore described with reference to and as shown in the accompanying drawings.

650345, AWP, CTF Amendments to the claims have been filed as follows

1. An internal combustion engine comprising: a variable volume combustion chamber; an air intake system for delivering charge air to the combustion chamber; an exhaust system for relaying combusted gas from the combustion chamber to atmosphere; and a fuel injection system for delivering fuel into the charge air for combustion therewith in the combustion chamber; wherein the fuel injection system comprises: a fuel injector which functions as a positive displacement pump and dispenses an amount of fuel which is fixed for each and every operation of the injector; and a controller which controls the operation of the fuel injector; wherein: in each of at least a majority of engine cycles the fuel injector is operated on a plurality of occasions by the controller; in response to an increasing engine speed and/or load the controller increases in amount the fuel delivered per engine cycle by increasing in number the occasions the fuel injector is operated per engine cycle; in response to a decreasing engine speed and/or load the controller reduces in amount the fuel delivered per engine cycle by reducing in number the occasions the fuel injector is operated per engine cycle; and the fuel injector comprises: a housing in which a fuel chamber is formed; an electrical coil; and a piston which slides axially in a bore in the housing under the action of the electrical coil to force fuel out of the fuel chamber, the piston sliding between two end stops which ensure that the piston has a set distance of travel in each operation.

2. An internal combustion engine as claimed in claim 1 wherein the fuel injector comprises a biasing spring acting on the piston.

3. An internal combustion engine as claimed in claim 2 wherein the electrical coil surrounds the piston.

4. An internal combustion engine as claimed in claim 3 wherein an end plate is connected to the piston and extends outwardly from the piston across an end face of the electrical coil.

5. An internal combustion engine as claimed in any one the preceding claims wherein the controller is an electronic controller which produces a pulsed control signal to control the fuel injector, each pulse causing the fuel injector to dispense fuel and the electronic controller varying the number of pulses per engine cycle to vary the amount of fuel delivered.

6. An internal combustion engine as claimed in any one of preceding claims wherein a sensor is provided to monitor engine load and to provide to the electronic controller a signal indicative of engine load, the electronic controller calculating how many pulses to produce in each engine cycle having regarding to engine load.

7. An internal combustion engine as claimed in claim 3 wherein a sensor is associated with a crankshaft or a camshaft of the engine and produces a timing signal related to rotation of the crankshaft or camshaft, which timing signal is used by the electronic controller to trigger the pulses generated thereby.

8. An internal combustion engine as claimed in any one of the preceding claims wherein the fuel injector has a fuel inlet for admitting fuel into the fuel chamber and a fuel outlet via which fuel is forced from the fuel injector, the fuel injector also having a first one-way valve which allows fuel to flow into the fuel chamber from the fuel inlet while preventing flow of fuel from the fuel chamber back to the fuel inlet and the fuel injector further having a second one-way valve which permits fuel to flow out of the fuel chamber to the fuel outlet, while preventing flow of fuel back into the fuel chamber from the fuel outlet.