GB2423119A

GB2423119A - I.c. engine fuel injection system with a positive displacement pump dispensing a fixed amount of fuel

Info

Publication number: GB2423119A
Application number: GB0606104A
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: 2006-08-16
Anticipated expiration: 2025-08-05
Also published as: GB0606104D0; CN101238279A; CN101238282B; GB2438456B; GB2421543B; GB0516235D0; GB2423119B; CN101238282A; GB2421543A; GB2438456A; GB0522068D0

Abstract

An i.c. engine has a variable volume combustion chamber 83, an air intake system 88, 91, an exhaust system 87 and a fuel injection system comprising a pump/injector 90, 96 which functions as a positive displacement pump and dispenses a fixed amount of fuel for each and every operation of the injector. The pump part 96 of the fuel injector comprises a housing 103 containing a fuel chamber 98 with respective inlet and outlet one-way valves 99, 100. A piston 102 is slideable in the chamber 98 and is spring-biassed into engagement with a camming surface to draw fuel into, and force fuel from, the chamber 98. The camming surface 93 may be provided on a wheel 94 that rotates with the crankshaft 85. An ECU 92 controls how many cam lobes (110, fig.3) of the camming surface 93 can cause injection of fuel by activating a solenoid 106 to displace a pintle 108 to prevent the inlet one-way valve 99 from closing. The ECU selects an appropriate number of pulses in response to engine load as sensed by the position of the throttle valve 91 and counts the number of injected pulses in an engine cycle before deactivating the inlet one-way valve 99. Alternatively, a mechanical linkage may be provided between the throttle 91 and the injector pump 96. The or each engine cylinder may be provided with two injectors 90 dispensing unequal amounts of fuel. The simple fuel injection system is suitable for small, low-power engines, eg for chain saws, lawn mowers, small generators, mopeds and scooters.

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, 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 S emissions targets. Therefore, a cheap and simple system of fuel injection is required for such small engines.

The present invention provides 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; 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 with 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 the cam lobes in each engine cycle cause the piston to force fuel out of the fuel injector; 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 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 onto the fuel chamber from the fuel outlet; and 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.

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 embodiment of internal combustion engine with a fuel injection system according to the present invention; Figure 2 is a schematic illustration of a fuel injector suitable for use with the engine of Figure 1; and Figure 3 is a schematic illustration of the fuel injector of Figure 8 and its arrangement with a camming surface used to drive it.

Figure 1 shows an 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 1 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 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 1 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 2 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 1) 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 rotatably mounted at one end of the piston 102. The roller follower 103 will engage with and follow the camming surface 93 (see Figure 1). 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 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 3 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 will result 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 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) The Figure 1 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 then count the number of delivered pulses in an engine cycle before deactivating the injector by means of the solenoid 106.

With the Figure 1 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.

- 10 - In the 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 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

- 11 - 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; 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; 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 with the piston being displaceable by the camming surface to - 12 - 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 the cam lobes in each engine cycle cause the piston to force fuel out of the fuel injector; 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 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 onto the fuel chamber from the fuel outlet; and 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.

2. 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 delivering charge air to the combustion chamber; - 13 - an exhaust system for relaying combusted gases 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 plurality of fuel injectors each of which functions as a positive displacement pump and dispenses an amount of fuel which is fixed for each and every operation of the injector, at least a first fuel injector of the plurality of fuel injectors dispensing an amount of fuel different to a second fuel injector of the plurality of fuel injectors; and a controller which controls operation of each of the plurality of fuel injectors; wherein: in each of at least a majority of engine cycles the fuel injectors are 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 injectors are 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 injectors are operated per engine cycle; each fuel injector is driven mechanically by a camming surface, each fuel injector comprising a piston biased into engagement with the camming surface by a biasing spring with 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 - 14 - controller controlling how many of the cam lobes in each engine cycle cause the piston to force fuel out of each fuel injector; each 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, each fuel injector also having a fuel inlet through which fuel is introduced into the fuel chamber, each 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 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 not the fuel chamber from the fuel outlet; and the first one-way valve of each fuel injector 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.

3. An internal combustion engine as claimed in claim 1 or claim 2 wherein the first one-way valve is provided with a control solenoid controlled electrically by the controller, the control solenoid acting on an override pintle which can engage the first one-way valve to force the first one-way valve open.

4. An internal combustion engine as claimed in any one of the preceding claims wherein all the cam lobes are of an identical height.

- 15 -

5. An internal combustion engine as claimed in any one of the preceding claims wherein the cam lobes are provided on a wheel which also has a section of constant radius.

6. An internal combustion engine as claimed in any one of the preceding claims wherein the piston of the/each injector has a cam follower which is a roller follower which engages and follows the camming surface.

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