GB1591050A

GB1591050A - Internal combustion engine

Info

Publication number: GB1591050A
Application number: GB3427177A
Authority: GB
Original assignee: Toyota Motor Corp
Current assignee: Toyota Motor Corp
Priority date: 1976-08-25
Filing date: 1977-08-16
Publication date: 1981-06-10
Also published as: SE431895B; DE2738391A1; IT1085383B; DE2738391C2; SE7709304L; CA1106765A

Abstract

Disclosed is an internal combustion engine capable of creating an active thermoatmosphere in the combustion chamber at the beginning of the compression stroke. The active thermoatmosphere continues to be maintained during the compression stroke when the engine is operating under a partial load. The self ignition of the active thermoatmosphere is caused in the vicinity of the top dead center.

Description

(54) AN INTERNAL COMBUSTION ENGINE (71) We, TOYOTA JIDOSHA KOGYO KABUSHIKI KAISHA, a Company of Japan organized and existing under the laws of Japan of 1, Toyota-cho, Toyotashi, Aichi-ken, Japan and Shigeru Onishi a Citizen of Japan residing at 31-12, Higashiyama 3-chome, Kanazawa-shi, Ishikawa-ken, Japan, do hereby declare the invention for which we pray that a Patent may be granted to us and the method by which it is to be performed to be particularly described in and by the following statement: The present invention relates to internal combustion engines and particularly to a method of firing an internal combustion engine and an engine able to carry out said method.

With regard to an internal combustion engine, for example, a 2-stroke engine, it is known that self ignition of the fresh combustible mixture can be caused in the combustion chamber of the engine without the fresh combustible mixture being ignited by the spark plug. The combustion caused by the above-mentioned self ignition is conventionally called an extraordinary combustion or a run on. In the attached Figures 1 and 2, A shows the region of occurrence of the extraordinary combustion which is caused in a 2-stroke engine. In Figure 1, the ordinate indicates a delivery ratio DR and the abscissa indicates an air-fuel ratio A/F. On the other hand, in Figure 2, the ordinate indicates a delivery ratio DR and the abscissa indicates the number of revolutions per minute N of the engine.In addition, Figure 1 shows the results of an experiment conducted under a constant engine speed of 2000 r.p.m. and Figure 2 shows the results of an experiment conducted under a constant air-fuel ratio of 15:1.

In a 2-stroke engine, when the engine is operating at a high speed with a low power output wherein the above-mentioned extraordinary combustion is caused, the amount of residual exhaust gas remaining in the cylinder of the engine is much larger than that of the fresh combustible mixture fed into the cylinder. Therefore, the fresh combustible mixture fed into the cylinder is heated until it is reformed by the residual exhaust gas, which has a high temperature, and as a result, the fresh combustible mixture produces radicals. An atmosphere wherein radicals are produced as mentioned above is hereinafter called an active thermoatmosphere.However, when an extraordinary combustion is caused, the active thermoatmosphere is extinguished at the beginning of the compression stroke, and a hot spot ignition, a mis-fire and an explosive combustion caused by a spark plug are alternately repeated, thus, causing a great fluctuation of torque. Since the extraordinary combustion has drawbacks in that a great fluctuation of torque occurs as mentioned above and, in addition, the piston may be damaged owing to the occurrence of the abovementioned hot spot ignition, such an extraordinary combustion is conventionally considered an undesirable combustion.

The inventor conducted research on extraordinary combustion and, as a result, has proven that, if the active thermoatmosphere which is caused in the extraordinary combustion at the beginning of the compression stroke can continue to be maintained until the end of the compression stroke, self ignition of the active thermoatmosphere is caused in the combustion chamber of an engine without the thermoatmosphere being ignited by the spark plug and, then, the active thermoatmosphere combustion takes place. In addition, the inventor has further proven that this active thermoatmosphere combustion results in quiet engine operation and can be caused even if a lean air-fuel mixture is used. This results in a considerable improvement in fuel consumption and a considerable reduction in the amount of harmful components in the exhaust gas.

Particularly in an engine for use in, for example, a vehicle, the engine operates for a majority of the operation time at a low power output. Consequently, if the abovementidned active thermoatmosphere combustion is carried out at a low power output, the fuel consumption is considerably improved and the amount of harmful components is considerably reduced.

The object of the present invention is to provide an internal combustion engine and a method of operation thereof which are capable of always creating a stable active thermoatmosphere independent of the number of revolutions per minute of the engine when the engine is operating with a low power output.

According to a first aspect of the present invention, there is provided a method of firing an internal combustion engine which is running with a low power output comprising the steps of: during the intake stroke of the engine restricting flow of a fresh combustible mixture into a combustion chamber of the engine; maintaining the Bow of fresh combustible mixture into the chamber at a low enough velocity to cause little turbulence within the chamber; suppressing the egress of burned gas from the chamber whilst the fresh mixture is flowing into the chamber; allowing the burned gas within the chamber to heat the fresh mixture so that the latter is reformed to produce radicals; maintaining the reformed atmosphere within the chamber by the mitigation of turbulence until the end of the compression stroke of the engine; and permitting self-ignition of the atmosphere within the chamber thereby firing the engine.

According to a second aspect of the present- invention there is provided a 2stroke internal combustion engine comprising: a cylinder block having a cylinder bore and a crank case therein; a piston having a substantially flat top surface and reciprobably movable in the cylinder bore, said cylinder bore and said piston defining a combustion chamber; an inlet passage having. an inlet port which opens into said combustion chamber and communicating said combustion chamber with said crank case for feeding a fresh combustible mixture into said combustion chamber, said inlet port being covered and removed by a reciprocal movement of the piston; an exhaust passage having an exhaust port opening into said combustion chamber for discharge of burnt gas from said combustion chamber; and restricting means disposed in said inlet passage at a position close to the entry of the inlet passage into the crank case for reducing the velocity of flow of the fresh combustible mixture into said combustion chamber.

According to a third aspect of the invention there is provided a 2-stroke internal combustion engine comprising: a cylinder block having a cylinder bore and a crank case therein: a piston having a substantially flat top surface and reciprocably movable in the cylinder bore, said cylinder bore and said piston defining a combustion chamber; an inlet passage having an inlet port which opens into said combustion chamber and communicating said combustion chamber with said crank case for feeding -a fresh combustible mixture into said combustion chamber; an exhaust passage having an exhaust port opening into said combustion chamber for discharge of burnt gas from said combustion chamber; at least one bypass passage which communicates said inlet passage with said crank case; and a switching valve for feeding the fresh combustible mixture into said combustion chamber via said bypass passage.

According to a fourth aspect of the present invention, there is provided an internal combustion engine wherein the fuel intake stroke is started after the exhaust stroke is completed, said engine comprising: a housing having a bore therein; a piston movable in said bore and defining therewith at least one combustion chamber; an intake passage for communicating said combustion chamber with a carburetor for feeding a supply of fresh combustible mixture into said combustion chamber an exhaust passage for said combustion chamber with exhaust means for egress of burnt gas from said combustion chamber; exhaust restricting means disposed in said exhaust passage for reducing the velocity of flow of the exhaust gas from said combustion chamber; ; restricting means disposed in said intake passage for reducing the velocity of flow of the fresh combustible mixture from the carburetor into said combustion chamber; and a bypass passage communicating the intake passage located upstream of said restricting means with the intake passage located downstream of said restricting means.

The present invention will now be described by way of example with reference to the accompanying drawings, in which: Figures I and 2 are graphs showing the region of the occurrence of an active thermoatmosphere combustion; Figure 3 is a cross-sectional side vew of a first embodiment of a 2-stroke engine according to the second aspect of the present invention.

Figure 4 is a cross-sectional view taken along the line IV-IV in Figure 3; Figure 5 is a cross-sectional view taken along the line V-V in Figure 4; Figure 6 is a graph showing the change in the opening area of a control valve and an exhaust control valve in the engine shown in Figure 3; Figure 7a is a diagram showing the scavenging and exhaust strokes of the engine shown in Figure 3; Figure 7b is a graph showing the velocity of the fresh combustible mixture flowing into the combustion chamber from the scavenging port and showing the actual scavenging time caused by the fresh combustible mixture in the engine shown in Figure 3; Figure 8 is a cross-sectional side view of another embodiment of a 2-stroke engine according to the second present aspect of the present invention;; -Figure 9 is a graph showing the specific fuel consumption and the concentrations of HC and NOX in the exhaust gas of the engine shown in Figure 8; Figure 10 is a graph showing the specific fuel consumption in the engine shown in Figure 8; Figure 11 is a cross-sectional side view of one embodiment of a 2-stroke engine according to the third aspect of the present invention;; Figure 12 is a cross-sectional side view of one embodiment of a 4-stroke engine according to the fourth aspect of the present invention Figure 13 is a cross-sectional side view of a further embodiment of a 4-stroke engine according to the fourth aspect of the present invention Figure 14 is a graph showing changes in the opening areas of the flow control valve, the exhaust control valve and the throttle valve of a 4-stroke engine according to the fourth aspect of the present invention.

Figure 15 is a cross-sectional side view of one embodiment of a rotary piston engine according to the fourth aspect of the present invention.

Figures 3 and 4 show the case wherein the present invention is applied to a Schnürle type 2-stroke engine. In Figures 3 and 4, 1 designates a cylinder block, 2 a cylinder head fixed onto the cylinder block 1, 4 a piston having an approximately flat top face and reciprocable in a cylinder bore 3 formed in the cylinder block 1 and 5 a combustion chamber formed between the cylinder head 2 and the piston 4; 6 designates a spark plug, 7 a crank case, 8 the chamber defined by the crank case 7, and 9 a balance weight; 10 designates a connecting rod, 11 an intake pipe, 12 an intake passage and 13 a carburetor; 14 designates a throttle valve of the carburetor 13, 15 a pair of inlet ports, 16 an inlet passage and 17 an exhaust port; 18 designates an exhaust pipe, 19 an exhaust passage and 20 a reed valve which permits the inflow of a fresh combustible mixture into the chamber 8 from the intake passage 12. The inlet passage 16 opens into the crank chamber 8 at an opening 21, on one hand, and is divided into two branches 16a, 16b which open into the combustion chamber 5 at inlet ports 15, on the other hand.

An arm 22 is fixed onto the throttle valve 14, and the tip of this arm 22 is connected via a wire 23 to an accelerator pedal 24 which is disposed in the driver's compartment. A control valve 25 is disposed in the passage 16 at a position near the opening 21 and is fixed onto a valve shaft 26 pivotably mounted on the cylinder block 1. A cam 27 is mounted on the valve shaft 26, and a wire 28 which is wound on the outer periphery of the cam 27 is connected to the accelerator pedal 24. Consequently, when the accelerator pedal 24 is depressed, the throttle valve 14 and the control valve 25 are opened.

Figure 6 indicates changes in opening areas of the throttle valve 14 and the control valve 25. In Figure 6, the ordinate X indicates a ratio of an opening area to the full opening area of the control valve 25, and the abscissa Y indicates a ratio of an opening area to the full opening area of the throttle valve 14. The relationship between the above-mentioned opening area ratios of the throttle valve 14 and the control valve 25 is shown by the curved line C in Figure 6. As is apparent from Figure 6, the control valve 25 when opened and is fully open before the throttle valve 14 reaches a position corresponding to the opening area ratio X of approximately 40 percent. In addition, the control valve 25 remains fully opened when the throttle valve 14 is further opened.

Consequently, in Figure 3, the cam 27 is connected to the valve shaft 26 in such a manner that the cam 27 rotates together with the valve shaft 26 until the time the acceleration pedal 24 is depressed to a particular extent and, then, when the acceleration pedal 24 is further depressed after the control valve 25 is fully opened, only the cam 27 rotates. As mentioned above, the inlet passage 16 is throttled by means of the control valve 25 when the engine is operating with a low power output so that the throttling operation of the inlet passage 16 is increased as the power output of the engine is reduced.

In operation, a fresh combustible mixture introduced into the crank chamber 8 from the intake passage 12 via the reed valve 20 is compressed as the piston 4 moves downwards. Then the fresh combustible mixture under pressure in the crank chamber 8 flows into the combustion chamber 5 from the inlet port 15 via the inlet passage 16 when the piston 4 opens the port 15. At this time, if the control valve 25 remains only slightly opened, the stream of the fresh combustible mixture flowing into the combustion chamber 5 from the crank chamber 8 via the passage 16 is restricted by the control valve 25. As a result of this, the velocity of flow of the fresh combustible mixture is reduced.

Since the velocity of the fresh combustible mixture is low throughout the inflow operation of the fresh combustible mixture, owing to the restricting operation of the control valve 25, the flow of the residual burned gas out of the combustion chamber 5 is extremely small and, as a result, the dissipation of the heat of the residual burned gas is prevented. In addition, at the beginning of the compression stroke when there is a low power output of the engine, a large amount of the residual burned gas is present in the combustion chamber 5. Since the amount of the residual burned gas in the combustion chamber 5 is large and, in addition, the residual burned gas has a high temperature, the fresh combustible mixture is heated until it is reformed by the residual burned gas to produce radicals and, as a result, an active thermoatmosphere is created in the combustion chamber 5.Further, since the flow of the gas in the cylinders is extremely small during the compression stroke, the occurrence of turbulence and the loss of heat energy is reduced. Consequently the active thermoatmosphere thus created continues to be maintained during the compression stroke and, as a result, the self ignition of the active thermoatmosphere is caused and the combustion is advanced while being controlled by the residual burned gas. As mentioned previously, this ignition is not caused by the spark plug 6. When the piston 4 moves downwards and opens the exhaust port 17, the burned gas in the combustion chamber 5 is discharged into the exhaust passage 19.

As mentioned above, in order to cause the active thermoatmosphere combustion, it is necessary to continue to maintain the active thermoatmosphere until the end of the compression stroke. However, it is impossible to continue to maintain the active thermoatmosphere until the end of the compression stroke by merely throttling the inlet passage 16 by means of the control valve 25 disposed in the passage 16. That is, if turbulence of the residual burned gas in the combustion chamber 5 is caused, the heat of the residual burned gas escapes into the cylinder wall. As a result of this, since the residual burned gas is cooled, it is impossible to continue to maintain the active thermoatmosphere until the end of the compression stroke.The fresh combustible mixture flowing into the combustion chamber 5 from the inlet port 15 has a great influence on the creation of the abovementioned turbulence of the residual burned gas. According to the experiments conducted by the inventor, it has been proven that the velocity of the fresh combustible mixture flowing into the combustion chamber, the inflow direction of the fresh combustible mixture and the turbulence of the fresh combustible mixture immediately before it flows into the- combustion chamber, have a great influence on the creation of turbulence in the residual burned gas.

Figure 7a is a diagram illustrating the opening and closing timings of the inlet and the exhaust ports of the 2-stroke engine shown in Figure 3. Figure 7b is a graph wherein the ordinate indicates the velocity V of the fresh combustible mixture flowing into the combustion chamber from the inlet port and the abscissa indicates the crank angle. In Figures 7a and b, EO indicates an opening timing of the exhaust port, SO an opening timing of the inlet, SC a closing timing of the inlet port and EC a closing timing of the exhaust port; P indicates a timing of the start of the inflow of the fresh combustible mixture into the combustion chamber from the inlet port 15 and Q a timing of the completion of said inflow of the fresh combustible mixture. In the crank angle between SO and P in Figures 7a and b, even if the inlet port is opened, since the pressure in the combustion chamber is lower than that in the inlet passage 16, the burned gas in the combustion chamber does not flows into the inlet passage 16. On the other hand, when the piston starts the upward movement after it reaches the bottom dead center, the pressure in the combustion chamber is again increased. As a result, in the crank angle between Q and SC in Figures 7a and b, since the pressure in the combustion chamber becomes higher than that in the inlet passage 16 and the gas in the combustion chamber flows backwards into the inlet passage 16. Consequently, the fresh combustible mixture flows into the combustion chamber from the inlet port 15 during the time period shown by the hatching in Figure 7a.In Figure 7b, the curved line E shows change in velocity V of fresh combustible mixture flowing into the combustion chamber from the inlet port in a conventional 2-stroke engine. As is apparent from Figure 7b, in a conventional engine, since the fresh combustible mixture flows into the combustion chamber at a high speed at the beginning of the inflow thereof, high turbulence of the residual burned gas in the combustion chamber is caused by the fresh combustible mixture and, as a result, it is impossible to continue to maintain the active thermoatmosphere until the end of the compression stroke.Contrary to this, by throttling the inlet passage 16 by means of the control valve 25 as indicated in Figure 3, the velocity V of the fresh combustible mixture flowing into the combustion chamber 5 from the inlet port 15 is low throughout the inlet operation caused by the fresh combustible mixture as shown by the curved line F in Figure 7b. In addition, as is shown by the point P' in Figure 7b, the start of the inflow operation of the fresh combustible mixture is delayed as compared to that, shown by P, in an conventional engine.

Consequently, since the fresh combustible mixture gently flows into the residual burned gas, it is possible to minimize the turbulence of the residual burned gas. In addition, in order to reduce the velocity of flow of the fresh combustible mixture entering into the combustion chamber 5 from the inlet port 15, it is preferable that the inlet passage 16 be so formed that the crosssectional area of the inlet passage 16 is gradually increased towards the inlet port 15. Furthermore, the arrangement of the control valve 25 would normally create turbulence in the fresh combustible mixture flowing in the inlet passage 16.However, by positioning the control valve 25 at a position as remote as possible from the inlet port 15, that is, at a position near the opening 21, the turbulence created by the valve 25 is mitigated in the inlet passage 16, and in addition, an approximately laminar flow of the fresh combustible mixture is created in the inlet passage 16. As a result of this, the fresh combustible mixture causing very little turbulence flows into the combustion chamber 5 from the inlet port 15.

In addition, the inlet port 15 is constructed so that, as is shown by the arrows G in Figure 4, the fresh combustible mixture flows into the combustion chamber 5 towards an approximately central portion of the combustion chamber 5 and, at the same time, as is shown by the arrow G in Figure 5, the fresh combustible mixture flows into the combustion chamber 5 in a slightly upward direction. That is, if the inlet port 15 is so constructed that the fresh combustible mixture flows into the combustion chamber 5 along the circumferential wall of the cylinder as shown by the arrow H in Figure 5, the fresh combustible mixture would cause turbulence of the residual burned gas prevailing in the region of the circumferential wall of the cylinder.As a result of this, since the heat of the residual burned gas in the combustion chamber easily escapes into the cylinder wall, it is difficult to continue to maintain the active thermoatmosphere until the end of the compression stroke.

By the above-mentioned preferred arrangements and construction of the control valve 25, the inlet passage 16 and the inlet port 15, the fresh combustible mixture flowing into the combustion chamber 5 from the port 15 does not cause turbulence of the residual burned gas and does not disperse in the combustion chamber 5 so that the dissipation of the heat of the residual burned gas is prevented. As a result of this, an active thermoatmosphere continues to be maintained until the end of the compression stroke, when the engine is operating with a low power output in the region shown by B in Figures 1 and 2, active thermoatmosphere combustion is carried out in out.

In addition, as is shown in Figure 3, it is preferable that the cylinder head 2 be so constructed that an annular squish area Z is formed between the cylinder head 2 and the peripheral portion of the top face of the piston 4 when the piston 4 reaches the top dead centre position. In this case, the propagation of the flame created by the self ignition of the active thermoatmosphere is controlled by the squish flow which is caused when the piston 4 reaches the top dead centre position, thus preventing the occurrence of a detonation. As a result of this, a stable active thermoatmosphere combustion can be carried out.

In the 2-stroke engine shown in Figure 3, as is shown by the curved line C in Figure 6, the control valve 25 remains fully open when the opening area ratio Y of the throttle valve is larger than 40 percent.

Consequently, when the opening area ratio Y of the throttle valve becomes larger than 40 percent, ordinary combustion which is caused by the spark plug 6 is carried out.

As mentioned previously, in order to continue to maintain the active thermoatmosphere until the end of the compression stroke, it is necessary to minimize the turbulence of the residual burned gas in the combustion chamber. Two other causes of turbulence of the residual burned gas are an abrupt blowing off operation of the exhaust gas discharging from the exhaust port 17 (Figure 3) and interference by the pulsating pressure of the exhaust gas. In order to prevent the above-mentioned abrupt blowing off operation and interference, as is shown in Figure 8, it is preferable that an exhaust control valve 29 be disposed in the exhaust passage 19. The exhaust control valve 29 is fixed onto a valve shaft 30 pivotably mounted on the exhaust pipe 18, and a cam 31 is mounted on the valve shaft 30.Similar to the scavenging control valve 25, a wire 32 is wound on the outer periphery of the cam 31 and is connected to the accelerator pedal 24. The relationship between the opening area ratios of the exhaust control valve 29 and the throttle valve 14 is shown by the curved line D in Figure 6. In addition, in order to appropriately prevent the exhaust gas from being abruptly discharged from the exhaust port 17, it is preferable that the volume of the exhaust passage 19 located between the exhaust port 17 and the exhaust control valve 29 be smaller than that of the combustion chamber 5 when the piston is positioned at the bottom dead centre position.

Figures 9 and 10 indicate the results of experiments conducted by using an engine as illustrated in Figure 8. The engine used had a single cylinder of 372 cc and an effective compression ratio of 7.9:1. In addition, the experiments related to Figure 9 were conducted under a constant engine revolution speed of 1500 r.p.m. and a constant airfuel ratio of 16:1 by changing the delivery ratio within the range of 5 to 2 percent. In Figure 9, the ordinate indicates specific fuel consumption be (gr/Ps-h), concentration of HC (ppm) and concentration of NOX (ppm), and the abscissa indicates a ratio OR(%) of an opening area to the full opening area of the exhaust control valve, and a delivery ratio DR(%).In addition in Figure 9, the curved broken lines I and indicate the specific fuel consumption be (gr/Ps-h) and concentration of HC, respectively, in a conventional 2-stroke engine while the curved solid lines K, L and M indicate the specific fuel consumption be, concentration of NOX and concentration of HC, respectively, in a 2-stroke engine according to the present invention. As is apparent from Figure 9, the specific fuel consumption be and the concentration of HC in an engine according to the present invention are considerably reduced as the load of the engine is reduced, that is, the delivery ratio DR is decreased as compared with that in a conventional engine. Figure 10 shows the specific fuel consumption of a 2-stroke engine according to the present invention.In Figure 10, the ordinate indicates the mean effective pressure Pme, and the abscissa indicates the number of revolutions per minute of the engine N(r.p.m.). In addition, in Figure 10, the numerals appearing in the graph indicate the specific fuel consumption (gr/Ps-h). Furthermore, in Figure 10, the region located beneath the solid line S is the region wherein the active thermoatmosphere combustion is carried out. As is shown in Figures 1, 2 and 10, active thermoatmosphere combustion is carried out when the power output of the engine is low over the entire range of the number of engine revolutions per minute and over a wide range of the air-fuel ratio.

As is indicated in Figure 11, active thermoatmosphere combustion can be carried out by using a lean air-fuel mixture having an air-fuel ratio of 16 through 21:1. Consequently, there is an advantage in that the amount of harmful HC, CO and NOX components in the exhaust gas can be simultaneously reduced.

Figure 11 illustrates a further embodimenu of a 2-stroke engine according to the present invention. Referring to Figure 11, a switching valve 34 having a through-hole 33 therein is disposed in the inlet passage 16 at a position near the crank chamber 8. A first bypass passage 35 and a second bypass passage 36 which have a cross-sectional area smaller than that of the inlet passage 16 are provided in addition to the inlet passage 16.

The switching valve 34 is fixed onto the valve shaft 37 pivotably mounted on the cylinder block 1, and the tip of an arm 38 fixed onto the valve shaft 37 is connected to the accelerator pedal 24 by means of a wire 39. When the accelerator pedal 24 is not depressed, that is, at the time of idling, the through-hole 33 of the switching valve 34 is aligned with the second bypass passage 36 as shown in Figure 11. On the other hand, when the acceleration pedal 24 is depressed, the switching valve 34 rotates in the counterclockwise direction as shown in Figure 1, and, as a result, the through-hole 33 of the switching valve 34 is aligned with the first bypass passage 35. After this, when the acceleration pedal 24 is further depressed, the through-hole 33 of the switching valve 34 is aligned with the inlet passage 16. When the switching valve 34 is positioned in the position shown in Figure 11, the fresh combustible mixture in the crank chamber is introduced into the scavenging passage 16 via the through-hole 33 and the second bypass passage 36. As is apparent from Figure 11, the length of the second bypass passage 36 is longer than that of the first bypass passage 35. In addition, in this embodiment, a 2-stroke engine has a plurality of cylinders, and the exhaust passages 19 of all of the cylinders are interconnected to each other via a passage 19' located upstream of the exhaust control valve 29.

As mentioned above, when the engine is operating with a low power output, as illustrated in Figure 11, the fresh combustible mixture in the crank chamber 8 is introduced into the scavenging passage 16 via the through-hole 33 of the switching valve 34 and the second bypass passage 36, and then, into the combustion chamber 5 via the inlet port 15. Since the second bypass passage 36 has a small cross-sectional area and a relatively long length in comparison with the first bypass 35, the velocity of the mixture flowing in the second bypass passage 36 is decreased and, as a result, the fresh combustible mixture flows into the combustion chamber 5 from the inlet port 15 at a low speed similar to the case wherein, in Figure 3, the control valve 25 is provided.In addition, when the engine is operating with a low power output, since the opening degree of the throttle valve 14 is small, the vacuum level in the intake passage 12 is large. Consequently, when the piston 4 moves upwards, a partial vacuum is produced in the crank chamber 8. Contrary to this, when the piston 4 moves downwards, the pressure in the crank chamber 8 is elevated. Thus, vacuum and increased pressure effects are alternately produced in the crank chamber 8. As a result of this, the fresh combustible mixture in the second bypass passage 36 is gradually introduced into the inlet passage 16 while reciprocally moving within the second bypass passage 36 owing to the above-mentioned alternate production of the vacuum and the pressure.

Consequently, since the fresh combustible mixture remains in the second bypass passage 36 for a long time, while reciprocally moving in the second bypass passage 36, the vaporization of the fuel in the passage 36 is promoted. In addition, a part of the fresh combustible mixture introduced into the combustion chamber 5 from the passage 36 is sucked back into the second bypass passage 36 when the vacuum is produced in the crank chamber 8 and at this time the vaporization of the fuel contained in the fresh combustible mixture is further promoted and the fresh combustible mixture is reformed owing to the heat exchanging operation which is taking place between the fresh combustible mixture and the residual burned gas in the combustion chamber.By providing the bypass passage as mentioned above, since the vaporization of the liquid fuel contained in the fresh combustible mixture is promoted and, at the same time, the reforming of the fresh combustible mixture is started before the fresh combustible mixture is introduced into the combustion chamber 5, it is possible to create an active thermoatmosphere in the combustion chamber 5. As a result of this, it is possible to ensure an active thermoatmosphere combustion when the engine is operating with a low power output.

As mentioned previously, when the accelerator pedal 24 is depressed and, thus, the power output of the engine is increased, fresh combustible mixture is introduced into the inlet passage 16 via the first bypass passage 35, which has a length shorter than that of the second bypass passage 36. On the other hand, when the acceleration pedal 24 is further depressed and the engine is operating with a high power output, the fresh combustible mixture in the crank chamber 8 is directly introduced into the inlet passage 16 via the through-hole 33 of the switching valve 34. Consequently, at this time, the flow resistance which the fresh combustible mixture is subjected to is reduced, whereby a desired high power output of the engine can be obtained.

Figure 12 illustrates the case wherein the present invention is applied to a 4-stroke engine. In Figure 12, 40 designates a cylinder block, 41 a piston reciprocally movable in a cylinder bore 42 formed in the cylinder block 40, 43 a cylinder head fixed into the cylinder block 40 and 44 a combustion chamber formed between the piston 41 and the cylinder head 43; 45 designates an intake passage, 46 an intake valve, 47 an intake manifold and 48 a carburetor; 49 designates a throttle valve of the carburetor 48, 50 an exhaust passage, 51 an exhaust valve, 52 an exhaust manifold, and 62 a spark plug. An arm 53 is fixed onto the throttle valve 49, and the tip of the arm 53 is connected to the accelerator pedal 55 via a wire 54.A flow control valve 57 is disposed in an intake passage 56, at a position located downstream of and near the throttle valve 49, and is fixed onto a valve shaft 58 pivotably mounted on the intake manifold 46. A cam 59 is mounted on the valve shaft 58 and a wire 60, which is wound on the outer periphery of the cam 59, is connected to the accelerator pedal 55.

An exhaust control valve 61 is arranged in the exhaust manifold 52. The valve 61 is caused to rotate by means of a wire 63 connected to the accelerator pedal 55.

The illustrated engine is additionally provided with a reed valve 64 only permitting the downward flow of the fresh combustible mixture is provided, and an accumulator 66 having a diaphragm 65 therein is provided.

An inside chamber 67 of the accumulator 66 is connected via a conduit 68 to the intake passage 56 upstream of the flow control valve 57 on one hand, while the inside chamber 67 is connected via a conduit 69 to the intake passage 56 downstream of the flow control valve 57 on the other hand. A small throttle valve 70 is disposed in the conduit 68 and is fixed onto a valve shaft 71 pivotably mounted on the conduit 68. A cam 72 is mounted on the valve shaft 71 and a wire 73 connected to the accelerator pedal is wound on the outer periphery of the cam 72.

Figure 14 shows the relationship between the opening area ratios of the throttle valve 49, the flow control valve 57, the exhaust control valve 61 and the small throttle valve 70. In Figure 14, the abscissa X indicates the ratio (%) of an opening area to the full opening area of the throttle valve 49, and the ordinate Y indicates the ratio (%) of an opening area to the full opening area of the flow control valve 57, the exhaust control valve 61 and the small throttle valve 70. In Figure 14, the curved line P indicates the relationship between the opening area ratios of the throttle valve 49 and the exhaust control valve 61, and the curved line Q indicates the relationship between the opening area ratios of the throttle valve 49 and the small throttle valve 70.In addition in Figure 14, the curved line R indicates the relationship between the opening area ratios of the throttle valve 49 and the flow control valve 57. The relationship between the opening area ratios of the throttle valve 49 and the exhaust control valve 61 which is shown by curved line P in Figure 14, is equal to the relationship between the opening area ratio Y of the throttle valve and the opening area ratio X of the exhaust control valve, which is shown by the curved line D in Figure 6. On the other hand, as is shown by the curved line R in Figure 14, the flowcontrol valve 57 remains fully closed when the opening area ratio of the throttle valve is less than 50 percent, while the flow control valve 57 is rapidly opened and then fully opened when the opening area ratio of the throttle valve becomes larger than 50 percent.In addition, as is shown by the curved line Q in Figure 14, the small throttle valve 70 is gradually opened as the throttle valve 49 is opened, and the small throttle valve 70 is fully opened when the flow control valve 37 is fully opened.

When the engine is operating with a low power output, the vacuum level in the intake manifold 47 is considerably large. On the other hand, since the pressure in the combustion chamber 44 and in the exhaust port 50 is larger than the atmospheric pressure at the end of the exhaust stroke, when the intake valve 46 is opened at the end of the exhaust stroke, the burned gas in the combustion chamber 44 blows back into the intake passage 45 via the intake valve 46. The more the timing of the opening operation of the intake valve 46 is advanced, that is, the more the duration of the valve overlapping is elongated, the more the amount of the burned gas blowing back into the intake passage 45 is increased.Since the flow rate of the exhaust gas is reduced by the exhaust control valve 61 when the exhaust control valve 61 is slightly opened, that is when the engine is operating with a low power output, the pressure in the combustion chamber 44 at the time of valve overlapping is greater than in the case wherein the exhaust control valve 61 is fully opened. As a result of this, a large amount of the exhaust gas can be caused to blow back into the intake manifold 47.

As mentioned above, since the flow control valve 57 remains fully closed when the engine is operating under a patial load, the fresh combustible mixture introduced into the intake passage 56 via the reed valve 64 is fed into the intake passage 56 located downstream of the flow control valve 57 via the small throttle valve 70, the conduit 68, the inside chamber 67 of the accumulator 66 and the conduit 69. The burned gas blowing back into the intake port 45 from the combustion chamber 44 is fed into the inside chamber 67 of the accumulator 66 via the conduit 69. Consequently, in the embodiment illustrated in Figure 12, the burned gas and the fresh combustible mixture are mixed with each other and, thus, the heat exchanging operation therebetween is carried out. As a result of this, the vaporization of fuel is promoted and, at the same time, the fresh combustible mixture is reformed.

In the embodiment illustrated in Figure 12, it is preferably that the volume of the inside chamber 67 of the accumulator 66 be larger than that of the combustion chamber 44 when the piston is positioned at its bottom dead centre position. That is, by setting the volume of the inside chamber 67 at the above-mentioned size, the unburned gas and the fresh combustible mixture can remain in the inside chamber 67 of the accumulator 66 for a long time, whereby the vaporization of fuel is further promoted and, at the same time, the combustible mixture is further reformed.

In addition, the promotion of the vaporization causes a uniform distribution of the fuel into the plurality of cylinders and also causes an improvement in the responsiveness of the engine with respect to the depressing operation of the accelerator pedal. If a uniform distribution of the fuel into the plurality of cylinders cannot be obtained as in a conventional engine, the air-fuel ratio of the fresh combustible mixture becomes irregular among the respective cylinders. Consequently, when a lean air-fuel mixture is used, the air-fuel ratio in one of the plurality of cylinders becomes large and is increased beyond the range wherein ignition can be caused. Consequently, in a conventional engine, in order to prevent the air-fuel ratio in all of the cylinders from being increased beyond the range wherein the ignition can be caused, it is necessary to use a fresh combustible mixture having a high fuel to air ratio. Contrary to this, in the present invention, since a uniform distribution of the fuel into the plurality of cylinders can be obtained, a lean air-fuel mixture can be used. Particularly at the time of idling and at the time when the engine is operating under a light load, wherein a satisfactory vaporizating operation of fuel cannot be obtained in a conventional engine, the distribution of the fuel into the plurality of cylinders becomes uniform in an engine according to the present invention. As a result of this, since a good combustion can be obtained in all of the cylinders, the fuel consumption is greatly improved.

Figure 13 illustrates a further embodiment of a 4-stroke engine. In the embodiment illustrated in Figure 13, a conduit 69' is elongated as compared with the conduit 69 illustrated in Figure 12, and an accumulator 66' has an inside chamber 67' having a volume which is smaller than the volume of the inside chamber 67 of the accumulator 66 illustrated in Figure 12. As mentioned above, the conduit 69' in the embodiment illustrated in Figure 13 has a considerably longer length than the intake passage 56 and, thus, the burned gas and the fresh combustible mixture are gradually fed to the intake passage 45 while reciprocally moving in the conduit 69'.In this embodiment, since the reciprocal movement of the unburned gas and of the fresh combustible mixture is created in the conduit 69', the vaporization of fuel is further promoted and, at the same time, the combustible mixture is further reformed as compared to the embodiment illustrated in Figure 12. In the 4-cycle engine illustrated in Figures 12 and 13, the flow control valve 57 remains fully opened when the engine is operating with a high power output. Consequently, when the engine illustrated in Figures 12 and 13 is operating with a high power output, the power output is similar to that which can be obtained in a conventional engine.

Figure 15 illustrates the case wherein the present invention is applied to a rotary piston engine. Referring to Figure 15, 80 designates a housing, 81 a rotor rotating in the direction T and having three corners which slide on the inner wall of the housing 80, 82 three combustion chambers, formed between the housing 80 and the rotor 81, and 83 a pair of spark plugs; 84 designates an intake port opening into the combustion chamber 82, 85 an intake branch passage connected to the intake port 84, 86 an intake manifold and 87 a carburetor; 88 designates a throttle valve of the carburetor 87, 89 an exhaust port opening into the combustion chamber 82, 90 an exhaust passage connected to the exhaust port 89 and 91 an exhaust manifold. An arm 92 is fixed onto the throttle valve 88 and the tip of the arm 92 is connected to the accelerator pedal 79 via a wire 93.A flow control valve 95 is disposed in an intake passage 94 located downstream of and near the throttle valve 88, and is fixed onto a valve shaft 96 pivotably mounted on the intake manifold 86. A cam 97 is mounted on the valve shaft 96 and a wire 98, which is wound on the outer periphery of the cam 97, is connected to the accelerator pedal 79. An exhaust control valve 99 is provided in the exhaust manifold 99. The valve 99 is cased to rotate by means of a wire 100 connected to the accelerator pedal 79.

The illustrated rotary engine is also provided with such a reed valve 101 only permitting the downward flow of the fresh combustible mixture, and an accumulator 66 having a diaphragm 102 therein. An inside chamber 104 of the accumulator 103 is connected via a conduit 105 to the intake passage 94 upstream of the flow control valve 95, on one hand, while the inside chamber 104 is connected via a conduit 106 to the intake passage 94 downstream of the flow control valve 95, on the other hand. A small throttle valve 107 is disposed on the conduit 105 and is fixed onto a valve shaft 108 pivotably mounted on the conduit 105.

A cam 109 is mounted on the valve shaft 108 and a wire 110 connected to the accelerator pedal 79 is wound on the outer periphery of the cam 109. The relationship between the opening area ratios of the throttle valve 88, the flow control valve 95, the small throttle valve 107 and the exhaust control valve 99, is equal to the relationship between the opening area ratios of the corresponding throttle valve 49, flow control valve 57, small throttle valve 70 and exhaust control valve 61 illustrated in Figure 12, which relationship is shown in Figure 14.

In this embodiment, in the same manner as described with reference to Figure 12, since the flow control valve 95 remains fully closed when the engine is operating with a low power output, the fresh combustible mixture introduced into the intake passage 94 via the reed valve 101 is fed into the intake passage 94 downstream of the flow control valve 95 via the small throttle valve 107, the conduit 105, the inside chamber 104 of the accumulator 103 and the conduit 106.

On the other hand, the burned gas blowing back into the intake branch passage 85 from the combustion chamber 82 at the end of the exhaust stroke is fed into the inside chamber 104 of the accumulator 103 via the conduit 106. Consequently, the unburned gas and the fresh combustible mixture are mixed with each other and, thus, the heat exchanging operation therebetween is started out.

As a result of this, the vaporization of fuel is promoted and, at the same time, the fresh combustible mixture is reformed. In addition, as is described with reference to Figure 12, in the embodiment illustrated in Figure 15, it is also preferable that the volume of the inside chamber 104 of the accumulator 103 be larger than the total volume of the combustion chambers 82. Furthermore, in the embodiment illustrated in Figure 15, the conduit 106 may be elongated similar to the conduit 69' illustrated in Figure 13.

In all of the embodiments hereinbefore described, when the engine is operating with a high power output, the operation of the engine according to the present invention is the same as that of a conventional engine.

Consequently, in all of the embodiments of the engine according to the present invention, the engine may be provided with an exhaust gas recirculating device for recirculating the exhaust gas into the intake system of the engine only when the engine is operating under with a high power output.

The active thermoatmosphere combustion causes the reduction in the amount of harmful HC components in the exhaust gas and also causes a considerable improvement in the fuel consumption. In addition, even if a lean air-fuel mixture is used, since an active thermoatmosphere combustion is caused, the amount of harmful NOX components can be reduced. Particularly in a multi-cylinder engine, since the distribution of fuel into the cylinders becomes uniform, a lean air-fuel mixture can be used as mentioned previously and, at the same time, a stable combustion can be obtained in all of the cylinders. As a result of this, the irregularity in the torque generated in the respective cylinders is extremely minimized and the vibration of the engine is reduced.

In addition, when the active thermoatmosphere combustion is carried out, the ignition delay does not occur and, as a result, a quiet operation of the engine can be effected at the time of idling and at the time when the engine is operating under a partial load.

WHAT WE CLAIM IS: 1. A method of firing an internal combustion engine which is running with a low power output comprising the steps of: during the intake stroke of the engine restricting flow of a fresh combustible mixture into a combustion chamber of the engine; maintaining the flow of fresh combustible mixture into the chamber at a low enough velocity to cause little turbulence within the chamber suppressing the egress of burned gas from the chamber whilst the fresh mixture is flowing into the chamber; allowing the burned gas within the chamber to heat the fresh mixture so that the latter is reformed to produce radicals; maintaining the reformed atmosphere within the chamber by the mitigation of turbulence until the end of the compression stroke of the engine; and permitting self-ignition of the atmosphere within the chamber thereby firing the engine.

2. A method as claimed in claim 1, wherein a squish flow is created in the combustion chamber at the end of the compression stroke for control of the combustion of the reformed atmosphere.

3. A method as claimed in claim 1, wherein the heating of the fresh combustible mixture by the residual burned gas is started before the fresh combustible mixture is fed into the combustion chamber when the engine is operating under a partial load.

4. A method as claimed in any one of claims 1 to 3, wherein said fresh combustible mixture is fed into the combustion chamber at a central portion of the combustion chamber.

5. A method as claimed in claim 1, wherein, in a 4-cycle engine and a rotarypiston engine, said fresh combustible mixture contains a large amount of burnt gas which gas is caused to blow back from the combustion chamber.

6. A 2-stroke internal combustion engine comprising: a cylinder block having a cylinder bore and a crank case therein; a piston having a substantially flat top surface and reciprocably movable in the cylinder bore, said cylinder bore and said piston defining a combustion chamber; an inlet passage having an inlet port which opens into said combustion chamber and communicating said combustion chamber with said crank case for feeding a fresh combustible mixture into said combustion chamber, said inlet port being covered and uncovered by a reciprocal movement of the piston; an exhaust passage having an exhaust port opening into said combustion chamber for discharge of burnt gas from said combustion chamber; and restricting means disposed in said inlet passage at a position close to the entry of the inlet passage into the crank case for reducing the velocity of flow of the fresh combustible mixture into said combustion chamber.

7. A 2-stroke internal combustion engine as claimed in claim 6, wherein said restricting means comprises a control valve.

8. A 2-stroke internal combustion engine comprising: a cylinder block having a cylinder bore and a crank case therein; a piston having a substantially flat top surface and reciprocably movable in the cylinder bore, said cylinder bore and said piston defining a combustion chamber; an inlet passage having an inlet port which opens into said combustion chamber and communicating said combustion chamber with said crank case for feeding a fresh combustible mixture into said combustion chamber;

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **.

103 be larger than the total volume of the combustion chambers 82. Furthermore, in the embodiment illustrated in Figure 15, the conduit 106 may be elongated similar to the conduit 69' illustrated in Figure 13.

In all of the embodiments hereinbefore described, when the engine is operating with a high power output, the operation of the engine according to the present invention is the same as that of a conventional engine.

Consequently, in all of the embodiments of the engine according to the present invention, the engine may be provided with an exhaust gas recirculating device for recirculating the exhaust gas into the intake system of the engine only when the engine is operating under with a high power output.

The active thermoatmosphere combustion causes the reduction in the amount of harmful HC components in the exhaust gas and also causes a considerable improvement in the fuel consumption. In addition, even if a lean air-fuel mixture is used, since an active thermoatmosphere combustion is caused, the amount of harmful NOX components can be reduced. Particularly in a multi-cylinder engine, since the distribution of fuel into the cylinders becomes uniform, a lean air-fuel mixture can be used as mentioned previously and, at the same time, a stable combustion can be obtained in all of the cylinders. As a result of this, the irregularity in the torque generated in the respective cylinders is extremely minimized and the vibration of the engine is reduced.

In addition, when the active thermoatmosphere combustion is carried out, the ignition delay does not occur and, as a result, a quiet operation of the engine can be effected at the time of idling and at the time when the engine is operating under a partial load.

WHAT WE CLAIM IS: 1. A method of firing an internal combustion engine which is running with a low power output comprising the steps of: during the intake stroke of the engine restricting flow of a fresh combustible mixture into a combustion chamber of the engine; maintaining the flow of fresh combustible mixture into the chamber at a low enough velocity to cause little turbulence within the chamber suppressing the egress of burned gas from the chamber whilst the fresh mixture is flowing into the chamber; allowing the burned gas within the chamber to heat the fresh mixture so that the latter is reformed to produce radicals; maintaining the reformed atmosphere within the chamber by the mitigation of turbulence until the end of the compression stroke of the engine; and permitting self-ignition of the atmosphere within the chamber thereby firing the engine.
2. A method as claimed in claim 1, wherein a squish flow is created in the combustion chamber at the end of the compression stroke for control of the combustion of the reformed atmosphere.
3. A method as claimed in claim 1, wherein the heating of the fresh combustible mixture by the residual burned gas is started before the fresh combustible mixture is fed into the combustion chamber when the engine is operating under a partial load.
4. A method as claimed in any one of claims 1 to 3, wherein said fresh combustible mixture is fed into the combustion chamber at a central portion of the combustion chamber.
5. A method as claimed in claim 1, wherein, in a 4-cycle engine and a rotarypiston engine, said fresh combustible mixture contains a large amount of burnt gas which gas is caused to blow back from the combustion chamber.
6. A 2-stroke internal combustion engine comprising: a cylinder block having a cylinder bore and a crank case therein; a piston having a substantially flat top surface and reciprocably movable in the cylinder bore, said cylinder bore and said piston defining a combustion chamber; an inlet passage having an inlet port which opens into said combustion chamber and communicating said combustion chamber with said crank case for feeding a fresh combustible mixture into said combustion chamber, said inlet port being covered and uncovered by a reciprocal movement of the piston; an exhaust passage having an exhaust port opening into said combustion chamber for discharge of burnt gas from said combustion chamber; and restricting means disposed in said inlet passage at a position close to the entry of the inlet passage into the crank case for reducing the velocity of flow of the fresh combustible mixture into said combustion chamber.
7. A 2-stroke internal combustion engine as claimed in claim 6, wherein said restricting means comprises a control valve.
8. A 2-stroke internal combustion engine comprising: a cylinder block having a cylinder bore and a crank case therein; a piston having a substantially flat top surface and reciprocably movable in the cylinder bore, said cylinder bore and said piston defining a combustion chamber; an inlet passage having an inlet port which opens into said combustion chamber and communicating said combustion chamber with said crank case for feeding a fresh combustible mixture into said combustion chamber;

an exhaust passage having an exhaust port opening into said combustion chamber for discharge of burnt gas from said combustion chanber; at least one bypass passage which communicates said inlet passage with said crank case; and a switching valve for feeding the fresh combustible mixture into said combustion chamber via said bypass passage.
9. A 2-stroke internal combustion engine as claimed in any one of claims 6 to 8, wherein said engine comprises exhaust restricting means disposed in said exhaust passage for reducing the velocity of flow of the exhaust gas from said combustion chamber.
10. A 2-stroke internal combustion engine as claimed in claim 9, wherein said exhaust restricting means comprises an exhaust control valve.
11. A 2-stroke internal combustion engine as claimed in claim 10, wherein the volume of said exhaust passage located between said exhaust port and said exhaust control valve is smaller than that of said combustion chamber when the piston is positioned at its bottom dead centre position.
12. A 2-stroke internal combustion engine as claimed in claim 6, wherein the cross-sectional area of said inlet passage is gradually increased in a direction towards the inlet port.
13. An internal combustion engine wherein the fuel intake stroke is started after the exhaust stroke is completed, said engine comprising: a housing having a bore therein; a piston movable in said bore and definin therewith at least one combustion chamber; an intake passage for communcating said combustion chamber with a carburetor for feeding a supply of fresh combustible mixture into said combustion chamber; an exhaust passage for communicating said combustion chamber with exhaust means for egress of burnt gas from said combustion chamber; exhaust restricting means disposed in said exhaust passage for reducing the velocity of the exhaust gas from said combustion chamber, restricting means disposed in said intake passage for reducing the velocity of flow of the fresh combustible mixture from the carburetor into said combustion chamber; and a bypass passage communicating the intake passage located upstream of said restricting means with the intake passage located downstream of said restricting means.
14. An internal combustion engine as claimed in claim 13, wherein said exhaust restricting means comprises an exhaust control valve.
15. An internal combustion engine as claimed in claim 13, wherein said restricting means comprises a flow control valve which can be gradually opened as the power output of the engine is increased.
16. An internal combustion engine as claimed in claim 13, wherein said restricting means is able to close completely said intake passage when the engine is operating under a partial load.
17. An internal combustion engine as claimed in claim 13, wherein said restricting means comprises a flow control valve.
18. An internal combustion engine as claimed in claim 13, wherein said restricting means is able to open fully said intake passage when the engine is operating with a high power output.
19. An internal combustion engine as claimed in any one of claims 13 to 18, wherein an accumulator is disposed in said bypass passage.
20. An internal combustion engine as claimed in any one of claims 13 to 19, wherein a flow control throttle valve is disposed in said bypass passage for controlling the velocity of flow of the fresh combustible mixture fed into the combustion chamber.
21. An internal combustion engine as claimed in claim 20, wherein said flow control throttle valve is located at a position near the position wherein said bypass passage opens into the intake passage located upstream of said restricting means.
22. An internal combustion engine as claimed in any one of claims 13 to 21 which is provided with said carburetor which has a throttle valve located in said intake passage at a position upstream of said restricting means, said bypass passage opening into said intake passage located between said throttle valve and said restricting means,
23. An internal combustion engine as claimed in claim 22 wherein a reed valve is disposed in said intake passage at a position located between said throttle valve and said restricting means.
24. A method of firing an internal combustion engine substantially as hereinbefore described with reference to any of Figures 3 to 15 of the accompanying drawings.
25. A 2-stroke internal combustion engine substantially as hereinbefore described with reference to any of Figures 3 to 11 of the accompanying drawings.
26. An internal combustion engine substantially as hereinbefore described with reference to any of Figures 12 to 15 of the accompanying drawings.