TWO-STROKE INTERNAL COMBUSTION ENGINE

Abstract: There is provided a two-stroke internal combustion engine which includes fuel injection means for direct injection of fuel into a cylinder. The injection means is so positioned within the cylinder to create turbulence and pre-mix the admitted air with the injected fuel before combustion. The injection means is also positioned so that heat from the exhaust port pre-heats the injected fuel.

Description: "Two-Stroke Internal Combustion Engine" The present invention relates to a two-stroke internal combustion engine which is particularly suited to use in motor cycles or mopeds, but is not limited to such use . Two-stroke engines are traditionally associated with the motor cycle industry as they offer considerable advantages over alternative power sources. Notwithstanding the simplicity of construction of a two-stroke engine when compared with a four-stroke, the weight of the two-stroke engine is considerably less and therefore the resultant power-to-weight ratio which a two-stroke engine affords is particularly suited to motor cycles. Two-stroke engines are often employed in other functions, such as in marine propulsion and motor-driven machinery, the latter category including lawn mowers, hedge-trimmers and the like. More generally, two-stroke engines find applications in a wide and varied field where the weight and size of an engine is of paramount importance such that restrictions and limitations on such govern the over- all design. However, two-stroke engines inherently suffer from being inefficient and therefore constitute a source of pollution. With the onset of European environmental directives which are soon to be introduced, the level of pollution which the two-stroke emits must be controlled and wherever possible reduced to comply with such directives, otherwise the use of two-stroke engines will effectively be prevented. Known designs of two-stroke internal combustion engines suffer from the inherent design flaw that during the intake of fuel, a substantial portion of the fuel is mixed directly with air which is expunged out the exhaust port, the port still being effectively open at this time. This large quantity of fuel provides a high degree of pollutant which is transferred directly to the atmosphere, without undergoing the combustion cycle within the cylinder. It is an object of the present invention to obviate or mitigate the above disadvantages by providing an improved two-stroke internal combustion engine which provides substantially equivalent power to those known in the art whilst effectively reducing the level of harmful emissions and improving the efficiency of the engine. According to a first aspect of the present invention there is provided a two-stroke internal combustion engine, said engine comprising a cylinder, said cylinder having an internal cavity adapted to have slidably and coaxially mounted therein a reciprocating piston, a cylinder head connected at one end of said cylinder and having an inwardly facing recess which forms a combustion chamber, said chamber directly communicating with said internal cavity, at least one inlet port, at least one exhaust port, injection means whereby fuel is injected directly into said internal cavity, said injection means being mounted in a side wall of said cylinder, characterised in that the position of said injection means in said side wall, relative to the position of said inlet port, is such that turbulence is created which premixes the admitted air with the injected fuel before combustion. Preferably, the position of said injection means is directly above said inlet port spaced at a distance therefrom along a substantially vertical axis and diametrically opposite said exhaust port along a substantially horizontal axis. Preferably, said injection means is upwardly inclined at an angle of between 0° and 40" to the horizontal axis, said angle most preferably being in the range of 18° to 22° . Preferably, said engine is further adapted to be controlled by an engine management system, wherein said management system can selectively control a plurality of engine parameters in response to feedback from a plurality of sensors. Preferably, said engine management system is controlled by a computer software program, said program being stored within an electronic storage and retrieval medium and being transferred to said medium using a micro-computer . Preferably, said at least one inlet port comprises an annular series of ports which are distributed around the inner surface of the cylinder wall. Preferably, said annular series of ports forms a symmetrical pattern about a vertical axis which bisects said exhaust port . According to a second aspect of the present invention there is provided a two-stroke internal combustion engine, said engine comprising a cylinder, said cylinder having an internal cavity adapted to have slidably and coaxially mounted therein a reciprocating piston, a cylinder head connected at one end of said cylinder and having an inwardly facing recess which forms a combustion chamber, said chamber directly communicating with said internal cavity, at least one inlet port, at least one exhaust port, injection means whereby fuel is injected directly into said internal cavity, said injection means being mounted in a side wall of said cylinder, characterised in that the position of said injection means in said side wall is such that heat from the at least one exhaust port preheats the injected fuel before combustion takes place. Preferably, the position of said injection means is directly above said at least one exhaust port at an angle substantially parallel to the horizontal and is most preferably positioned on a vertical axis which bisects said exhaust port. Preferably, said engine is further adapted to be controlled by an engine management system, wherein said management system can selectively control a plurality of engine parameters in response to feedback from a plurality of sensors. Preferably, said engine management system is controlled by a computer software program, said program being stored within an electronic storage and retrieval medium and being transferred to said medium using a personal computer. Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings in which : - Fig. 1 is a cross-sectional view of a two-stroke internal combustion engine according to a first aspect of the present invention; Fig. 2 is cross-sectional view showing the cylinder layout in more detail according to the first aspect of the present invention as shown in Fig. 1; Fig. 3 is a developed view of inlet and outlet ports according to both aspects of the present invention; Fig. 4 is a cross-sectional view of a two-stroke internal combustion engine according to a second aspect of the present invention; Fig. 5 is cross-sectional view showing the cylinder layout in more detail according to the second aspect of the present invention as shown in Fig. 4; and Fig. 6 is a schematic view of the present invention embodying an engine management system and associated sensors and electrical connections. Referring to Fig. 1 there, is shown a two-stroke internal combustion engine in the form of crankcase scavenged, single cylinder engine, generally depicted by the reference numeral 10. The engine 10 comprises a cylinder 12 which has an internal cavity 14. Housed within the internal cavity 14 is a reciprocating piston 16 which is coaxial with the major vertical axis of the cylinder 12 and mounted such that it may slide vertically within the internal cavity 14. It will be appreciated by those skilled in the art that said piston 16 will be provided with appropriate piston rings and the like to provide for an air-tight seal within the internal cavity 14. The movement of the piston 16 provides for sympathetic movement of a crank 18 housed within the crankcase 20, located at the lower end of the cylinder 12. A piston rod 22 is used to interconnect the piston 16 and the crank 18. The piston rod 22 is conventionally mounted on the crank 18 such that when the piston 16 is forced downwards by the internal combustion of an air/fuel mixture, the crank 18 rotates in a clockwise direction as indicated by the arrow in Fig. 1. Located at the opposite end of the cylinder 12 is the cylinder head 24 which is appropriately mounted using bolts (not shown) . The cylinder head 24 has an inwardly facing recess which constitutes what is commonly known as a combustion chamber 26. The combustion chamber 26 as shown in this particular embodiment is of the hemispherical chamber type as will be appreciated by those skilled in the art. It will also be appreciated that other types of chamber design may be incorporated within the scope of the present invention. A spark plug 28 is removably located through the cylinder head 24 such that the electrodes of the spark plug 28 are in direct communication with the combustion chamber 26. A reed valve 30 controls the air intake into the crankcase 20 in conjunction with an air intake system, the operation of which will be discussed in greater detail hereinafter. The admitted air is drawn in through the reed valve 30 and is forced into the internal cavity 14 within the cylinder 12 by the movement of the reciprocating piston 16. The air is passed through a number of conduits 32 (one of which is illustrated in Fig. 1) and is forced into the internal cavity 14 through an annular series of inlet ports 34, 36 and 38, as best shown in Fig. 3. Fig. 3 shows the displacement of the inlet ports 34, 36 and 38 in a two-dimensional plane as opposed to the actual displacement which would be on the curved inner surface of the cylinder 12. As will be appreciated, the inlet ports 34, 36 are arranged in pairs 34a, 34b, 36a, 36b which are symmetrical about a vertical line of symmetry 43 which bisects an exhaust port 42. A main inlet port 38 is located along a second line of symmetry 39 which bisects the main inlet port 38. The symmetrical positioning of the annular pairs of ports 34a, 34b and 36a, 36b provides a displacement of air within the cavity 14 which promotes the turbulence effect, further mixing the fuel and air. Fig. 3 also shows the exhaust port 42 which communicates directly with an exhaust pipe 44 through an exhaust manifold 46, as best shown in Fig. 1 and Fig. 4. Inlet port 38 is the main air inlet from the crankcase 20. In the embodiment shown in Fig. 1 and Fig. 2, the fuel injector 40 is located directly above the port 38, which is positioned such that when the fuel is injected into the internal cavity 14 through the injector 40, the air forced into the cavity 14 by the movement of the piston 16 creates a turbulence effect within the cavity 14 and provides premixing of the fuel and air before combustion. The fuel injector 40 is located directly above the main inlet port 38 and is located on the second line of symmetry 39 which bisects the main inlet port 38. Furthermore, the fuel injector 40 is located in such a position, and at an inclinational angle to be discussed subsequently, that when the fuel is injected under high pressure into the combustion chamber 26, the exhaust port 42 is at least partially covered by the piston 16. The precise timing of the injection is controlled and monitored by an engine management system which will be described in greater detail hereinafter. In this respect, the injected fuel is substantially prevented from being passed directly into the exhaust system without undergoing combustion, thereby reducing the level of harmful emissions from the engine 10. In use, the air/fuel mixture is compressed into the combustion chamber 26 by the upwardly moving piston 16 until the piston 16 reaches top dead centre (TDC) . As the air/fuel mixture is compressed, heating of the mixture takes place and an electric spark from the spark plug 28 causes the mixture to combust. This in turn forces the piston 16 downwards, and the exhaust gases are emitted through the exhaust port 42 and escape to the atmosphere through the exhaust pipe 44. As the piston 16 continues downward, clean air is pumped from the crankcase 20, the air then being forced through the conduits 32 into the internal cavity 14 through the annular series of ports 34a, 34b, 36a, 36b and 38, which further expunges the exhaust gases through the exhaust port 42. As will be appreciated by those skilled in the art, this cycle continues whereby air enters the crankcase 20 is forced into the internal cavity 14 where it is mixed with injected fuel. The mixture is then compressed, ignited and allowed to combust which forces the piston 16 downwards and allows the exhaust gases to escape. A fresh cycle then begins and the intake of air aids the process of expunging the exhaust gases, hence the term crankcase scavenged. In this type of engine 10 where crankcase scavenging is used, the crankcase 20 must be hermetically sealed so that it can function as a pump in association with the piston 16. It will be obvious to those skilled in the art that other means of scavenging the exhaust gases from the cylinder are known, such as fan-assisted methods and the like. The particular embodiment shown is by way of example only and is not limited to such. Referring now to Fig. 2 there is shown in greater detail the cylinder 12 of the engine 10 of Fig. 1. For simplicity, reference numerals which depict the same features as in Fig. 1 have been used wherever possible. The actual injector 40 has conveniently been omitted from Fig. 3 to allow for better interpretation, but it will be appreciated that the injector 40 is designed to be received within an aperture 41. In the embodiment of Fig. 1, the aperture 41 into which the injector 40 is located, is at upwardly inclined at angle of 20° to the horizontal. This inclinational angle gives the correct injection pattern of fuel to allow the turbulence effect created by the positioning of the annular series of inlet ports to achieve a substantial degree of premixing of the fuel and air before combustion so that the majority of the fuel which is injected into the engine is burnt during combustion. Another advantage offered by premixing is that in conventional two-stroke engines, a not insubstantial amount of the injected fuel passes directly out of the exhaust port and hence into the atmosphere. The turbulent effect created by the inlet ports prevents the fuel from doing so as the fuel is caught by the motion of the air. Furthermore, the inclinational angle of the aperture 41 and relevant positioning thereof allow the fuel to be precisely injected when the exhaust port 42 is substantially closed. The actual timing of this is controlled by the engine management system, to be discussed in detail subsequently. The closure of the exhaust port 42 is effected by the movement of the piston 16 into a position where it covers or at least substantially covers the exhaust port 42. Although the angle of the injector is shown as being 20° to the horizontal in this embodiment, it will be appreciated by those skilled in the art that this angle may be varied by as much as plus or minus 20° or more, whilst retaining the beneficial effects of creating the appropriate pattern of injected fuel to give the premixing required. Hence, the injector may be set at an angle either substantially parallel to the horizontal or inclined at an angle of about 40° to the horizontal. Referring now to Fig. 4 and Fig. 5 there is shown an alternative two-stroke internal combustion engine 100, according to the second aspect of the present invention. All reference numerals which are used to depict features different to those of the first embodiment, as in Fig. 1 and Fig. 2, have been prefixed with a "1." Otherwise, like reference numerals have been used wherever possible. In this embodiment, the aperture 141 for the injector 140 is situated above the exhaust port 42 as best seen in Fig. 5. As with the previous embodiment, the aperture 141 is located on the line of symmetry 43 which bisects the exhaust port 42. It will be appreciated that the design of the injector 40 will be the same as that for the injector 140 and that the use of a different reference number is to aid clarity only. The general operational cycle of the two-stroke engine 100 is the same in this embodiment, except that the fuel which enters the cylinder is preheated before combustion in addition to the advantages of premixing. This preheating is achieved through the positioning of the aperture 141 for the injector 140 above the exhaust port 42. As those skilled in the art will appreciate, a not inconsiderable amount of heat is irradiated from the exhaust system of any given engine. Hence, as the fuel is injected into the internal cavity 14, heat from the exhaust port 42 generally increases the temperature of the fuel before it is mixed with the air from the annular series of ports 34, 36 and 38. This preheating of the fuel allows the fuel to combust more completely in the combustion chamber 26, thereby reducing the amount of harmful emissions and providing a far greater efficiency from the engine 100. In this particular embodiment, there is no requirement for the exhaust port 42 to be closed before fuel is injected as the injector 140 is not directly facing the exhaust port 42. It will be appreciated that as a precaution to reduce the emissions from the engine 100, it is generally desirable to have the exhaust port 42 closed during the injection of fuel. Furthermore, the movement of the piston 16 will induce hot air from the exhaust port to mix with the injected fuel as it moves upwards. Referring now to Fig. 6 there is shown in schematic form an engine management system for use with a two- stroke internal combustion engine of the present invention. Here, the engine 10 is the equivalent of that shown in Fig. 1 and hence some reference numerals have been omitted to aid clarity. It will be appreciated that in the example shown in Fig. 6, the first aspect of the invention, as shown in Fig. 1 and Fig. 2, is illustrated in this embodiment. However, the engine management system is equally applicable for use with the second embodiment of the invention as depicted in Fig. 4 and Fig. 5. At the core of the engine management system is an engine management unit or EMU 48. A software program which controls the various functions of the engine 10, 100 is stored within a memory device being located as part of the EMU 48. Additionally, a plurality of electrical connections from a number of sensors are connected to the EMU 48 such that a closed-loop feedback path is made in order to afford accurate control over the engine parameters . The software program stored within the EMU 48 continually monitors the feedback values from the sensors. In response to this feedback, the controlling software adjusts various engine parameters in real-time for precise control of the engine 10, 100. Each of the control parameters will be discussed in greater detail below. All of these parameters are continually monitored and updated at very short intervals, up to 500,000 times a second, in real time. The fuel injection system of the engine 10, 100 comprises a fuel tank 54 which is fluidly coupled to a high pressure fuel pump 52 by way of an in-line fuel filter 56. The fuel pump 52 is electronically operated and controlled by the software program within the EMU 48 in response to the various control parameters. An electronically controlled, high pressure fuel injector unit 40 is fluidly connected to the pump 52 such that fuel from the tank 54 is pumped to the injector under high pressure for subsequent injection into the combustion chamber 26. The injector unit 40, 140 comprises an accumulator and control valve, an electronically controlled and operated injection pump and an injection nozzle. A fast acting solenoid-type valve is used to supply a fixed amount of fuel at high pressure and allows precise quantities of fuel to be delivered at the appropriate time under the control of the EMU 48. To achieve the performance of a standard two-stroke engine whilst reducing harmful emissions, the EMU 48 controls the width of the delivery pulse, the timing of the delivery and the fuel map. The air intake system of the engine 10, 100 comprises a butterfly valve 60 connected through an air conduit 62 to the reed valve 30 housed within the crankcase 20. The amount of air which is allowed to pass into the engine 10, 100 is controlled by the position of the butterfly valve 60. Specifically, the amount of air depends upon to what degree the valve 60 is open. The degree of opening is monitored by a sensor 58 housed within the valve 60 and is fed back to the EMU 48. The sensor 58 not only measures the position of the butterfly within the valve 60, but also the rate of flow of the air through the valve 60. The EMU 48 then translates these parameters into an input to be fed into the controlling software program. The EMU 48 controls the timing of the ignition and also the duration of the sparking of the spark plug 28. A signal is fed from the EMU 48 to a coil 64. This coil 64 in turn provides the necessary electrical current to the electrodes of the spark plug 28 such that a spark is induced across the electrodes and combustion of the fuel/air mixture takes place as is well known in the art. In order to control the level of emissions from the engine 10, 100, it is important to sample the levels of various gases which comprise the exhaust emission. A gas sensor array 66 is located at the exhaust manifold 46 and continually monitors the level of various exhaust gases and hydrocarbons such as oxygen, carbon monoxide and carbon dioxide. Also nitrous oxides in the emissions are monitored in addition to the foregoing. To enable the gas sensor array 66 to work effectively over the entire operating range of the engine 10, 100, a part dilution tunnel (not shown) is provided to sample the raw exhaust gases. This tunnel is located next to the exhaust 44 and ensures that the sensor array 66 can match all aspects of the engine performance. The dilution effect of using clean air ensures that the sensors are kept clean at all times and is created using a venturi effect on the main engine exhaust pipe 44. A signal is fed back to the EMU 48 which corresponds to the level of such gases which are contained in the exhaust emissions and the timing of the fuel injection, the width of the delivery pulse and the timing and width of the spark, along with the amount of air which is allowed to enter the engine 10, 100, is adjusted accordingly. This closed-loop feedback allows for very precise control of the engine 10, 100 such that harmful exhaust emissions are kept to an absolute minimum whilst ensuring efficient delivery of the available power output from the engine. In addition to the feedback loop which is employed in the engine management system, the EMU 48 may also control the injection of oil into the engine 10, 100 as an alternative to conventional engine structures which use a reservoir of oil within the crankcase 20. Oil is fed down from a separate oil reservoir 68, through a medium pressure oil pump 70 and injected into the engine 10, 100 using an oil injector 72. A second oil injector 74 dispenses oil to the outside of the crankcase 20 as necessary. As will be appreciated by those skilled in the art, oil is supplied to the crankshaft bearings, piston, piston rings and the like without using an air/oil mixture which is conventionally used. This arrangement allows the oil to be transported to the moving parts within the engine 10, 100 whilst minimising the amount of oil which is conveyed to the combustion chamber 26 thereby reducing the emissions. Consequently, the amount of oil required to lubricate the engine 10, 100 can be substantially reduced as it is under the precise control of the EMU 48 and is directly injected as required. The level of oil which is required for lubrication will obviously vary with the speed of rotation of the engine 10, 100. Hence another feature of the control system is that the position of the crank (and hence speed of rotation of the engine 10, 100) is monitored using a crank position sensor 76 located in the crankcase 20. A signal from the sensor 76 is fed into the EMU 48 to allow for this parameter to be converted into a suitable form for input into the control software. In addition to the parameters mentioned, the EMU is designed to monitor specific temperatures, internal pressures, voltage levels and relevant flow conditions as well as monitoring the solenoid valve status. In keeping with conventional software design techniques, the program allows for error diagnostics, monitoring of the system status and the ability to give information presentation. The latter of these utilises a graphical programming language to allow the various parameters as outlined above to be visually analysed and recorded in real time. Hence, the present invention provides an efficient engine which is precisely controlled by an engine management system. The management system uses a real- time continually updated sensor array to adjust the parameters of the engine, in conjunction with a complex software program, in order to deliver the maximum amount of output power available whilst ensuring that harmful exhaust emissions are kept within safe limits, as prescribed by European Directives.

Claims: CLAIMS 1. A two-stroke internal combustion engine, said engine comprising a cylinder, said cylinder having an internal cavity adapted to have slidably and coaxially mounted therein a reciprocating piston, a cylinder head connected at one end of said cylinder and having an inwardly facing recess which forms a combustion chamber, said chamber directly communicating with said internal cavity, at least one inlet port, at least one exhaust port, injection means whereby fuel is injected directly into said internal cavity, said injection means being mounted in a side wall of said cylinder, characterised in that the position of said injection means in said side wall, relative to the position of said inlet port, is such that turbulence is created which premixes the admitted air with the injected fuel before combustion. 2. An engine as claimed in Claim 1, wherein the position of said injection means is directly above said inlet port spaced at a distance therefrom along a substantially vertical axis and diametrically opposite said exhaust port along a substantially horizontal axis. 3. An engine as claimed in either preceding Claim, wherein said injection means is upwardly inclined at an angle of between 0° and 40° to the horizontal axis. 4. An engine as claimed in Claim 3 wherein said angle is in the range of 18° to 22°. 5. An engine as claimed in any preceding Claim wherein said at least one inlet port comprises an annular series of ports distributed around the inner surface of the cylinder wall. 6. An engine as claimed in Claim 5, wherein said annular series of ports forms a symmetrical pattern about a vertical axis which bisects said exhaust port . 7. A two-stroke internal combustion engine, said engine comprising a cylinder, said cylinder having an internal cavity adapted to have slidably and coaxially mounted therein a reciprocating piston, a cylinder head connected at one end of said cylinder and having an inwardly facing recess which forms a combustion chamber, said chamber directly communicating with said internal cavity, at least one inlet port, at least one exhaust port, injection means whereby fuel is injected directly into said internal cavity, said injection means being mounted in a side wall of said cylinder, characterised in that the position of said injection means in said side wall is such that heat from the at least one exhaust port preheats the injected fuel before combustion takes place. 8. An engine as claimed in Claim 7 wherein the position of said injection means is directly above said at least one exhaust port at an angle substantially parallel to the horizontal and is most preferably positioned on a vertical axis which bisects said exhaust port. 9. An engine as claimed in any preceding Claim and including an engine management system, wherein said management system can selectively control a plurality of engine parameters in response to feedback from a plurality of sensors. 10. An engine as claimed in Claim 5 wherein said engine management system is controlled by a computer software program, stored within an electronic storage and retrieval medium and transferred to said medium using a micro-computer.

Inventors: CAMPBELL TOM, CAMPBELL, TOM
Applicants: CAMPBELL TOM, GCUC LIMITED, CAMPBELL, TOM
Application year: 1998
Main classification: F02B25
IPC codes: F02B23, F02B25, F02B75