Classifications

• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
  • F02B—INTERNAL-COMBUSTION PISTON ENGINES; COMBUSTION ENGINES IN GENERAL
  • F02B25/00—Engines characterised by using fresh charge for scavenging cylinders
  • F02B25/14—Engines characterised by using fresh charge for scavenging cylinders using reverse-flow scavenging, e.g. with both outlet and inlet ports arranged near bottom of piston stroke
  • F02B25/18—Engines characterised by using fresh charge for scavenging cylinders using reverse-flow scavenging, e.g. with both outlet and inlet ports arranged near bottom of piston stroke the charge flowing upward essentially along cylinder wall adjacent the inlet ports, e.g. by means of deflection rib on piston
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
  • F02B—INTERNAL-COMBUSTION PISTON ENGINES; COMBUSTION ENGINES IN GENERAL
  • F02B25/00—Engines characterised by using fresh charge for scavenging cylinders
  • F02B25/14—Engines characterised by using fresh charge for scavenging cylinders using reverse-flow scavenging, e.g. with both outlet and inlet ports arranged near bottom of piston stroke
  • F02B25/145—Engines characterised by using fresh charge for scavenging cylinders using reverse-flow scavenging, e.g. with both outlet and inlet ports arranged near bottom of piston stroke with intake and exhaust valves exclusively in the cylinder head
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
  • F02B—INTERNAL-COMBUSTION PISTON ENGINES; COMBUSTION ENGINES IN GENERAL
  • F02B75/00—Other engines
  • F02B75/02—Engines characterised by their cycles, e.g. six-stroke
  • F02B2075/022—Engines characterised by their cycles, e.g. six-stroke having less than six strokes per cycle
  • F02B2075/025—Engines characterised by their cycles, e.g. six-stroke having less than six strokes per cycle two
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
  • F02B—INTERNAL-COMBUSTION PISTON ENGINES; COMBUSTION ENGINES IN GENERAL
  • F02B3/00—Engines characterised by air compression and subsequent fuel addition
  • F02B3/06—Engines characterised by air compression and subsequent fuel addition with compression ignition

Definitions

• the present invention generally relates to a two-stroke internal combustion engine with at least one cylinder containing a reciprocating piston, in particular but not exclusively of the Diesel type, and more particularly relates to a valve device, incorporated exclusively in the cylinder head , which allows the replacement of burnt gases by the fresh air necessary for combustion.
• the invention also relates to a cylinder head, for internal combustion engines, which is equipped with said device, as well as to the various applications and uses resulting from its use.
• the prechamber opens into the cylinder through an orifice of restricted section so as to allow the mixture of air and fuel to penetrate therein in the form of a compact jet and the rod of the or each inlet valve crosses the delimited space in the cylinder head by the geometric extension of the cylinder wall, which gives rise to a throttled and asymmetrical flow of the mixture admitted to the cylinder.
• criterion (b) is respected, due to the introduction at high speed of the air particles into the cylinder towards the piston, on the other hand, criterion (c) is not respected: the introduction of air particles at high speed into the cylinder is made, due to the arrangement of the intake valve, within the mass of gas - especially when the intake valve is at the start of opening - causing an intense mixture of l fresh air and burnt gases. In addition, this arrangement leaves dead areas, not scanned, which further reduces the efficiency of scanning. Due to the presence of the orifice of restricted section, the permeability of the cylinder head to flow (criterion a) is very poor.
• US-A-2,061,517 is confirmed in the third paragraph of US-A-4,616,605 (KLINE) which was not published until October 14, 1986.
• US-A-2,222,134 (AUGUSTINE) , there is described a two-stroke internal combustion engine having an intake valve and an exhaust valve whose axes are parallel to that of the cylinder and whose opening movements are directed in opposite directions.
• the seat of the intake valve opens from bottom to top in a prechamber which itself opens from top to bottom in the cylinder through a crescent-shaped orifice, arranged tangentially to the cylinder.
• the geometry of the prechamber is such that there is a strong turbulence around the intake valve, causing disorientation of the particles of fresh air entering the cylinder, causing a strong short circuit (criterion b not respected), and that the air is preferentially directed into the upper surface of the elbow connecting the prechamber to the cylinder, which will cause the air particles to penetrate within the mass of gas, giving rise to a significant mixture of fresh air with flue gases (criterion c not met).
• the invention aims to improve the operation of a two-stroke internal combustion engine, in particular but not exclusively of the Diesel type, with at least one cylinder with reciprocating piston and with device gas exchange provided exclusively by at least one intake valve and at least one exhaust valve arranged in the cylinder head at the head of the associated cylinder, so as to allow a scavenging that meets both the three defined criteria above.
• the main object of the invention is therefore, in an engine of the aforementioned type, to increase the efficiency of the exchange of gases, that is to say to drive the residual burnt gases to the maximum by replacing them by a corresponding volume of fresh air, while preventing or, at least, minimizing any risk of direct passage of fresh air from the intake valve to the exhaust valve and simultaneously avoiding, as much as possible , any creation of a zone for mixing fresh air and burnt gases, with minimal energy expenditure.
• the objective of the invention is therefore to achieve a compromise between good sweeping and combustion efficiency with the simplest technology while retaining the above advantages as much as possible while reducing the drawbacks mentioned above.
• the position of the cylinder is such that its axis is vertical and that thus the cylinder head occupies the upper or upper position and the piston the lower or lower position.
• the present invention solves the aforementioned technical problems by providing a two-stroke internal combustion engine, with at least one cylinder with reciprocating piston, with gas exchange device entirely incorporated in the cylinder head and comprising a group of at least one valve.
• each intake valve having its seat arranged in the wall of a combustion and sweeping prechamber
• said gas exchange device having a plane of symmetry passing through the cylinder axis and common at the disposal of the group of at least one inlet valve, at the disposal of the group of at least one valve exhaust, and to the configuration of the interior surface of the prechamber and of the cylinder head sky as well as to the configuration of the face of the piston, characterized in that the prechamber communicates with the cylinder by a transfer channel, the walls are at least partially substantially parallel to the axis of the cylinder and whose cross section perpendicular to this axis opens out in a substantially oblong shape tangentially to the cylinder, and in that the or each intake valve cooperates with the side wall of the prechamber, practically without play with this in the upper part of said valve so that the intake air circuit, upstream of the valve, opens directly into the transfer channel downstream of the valve, including during the first moments of valve lift.
• the axis of each intake valve has a direction which is not parallel to the axis direction of the cylinder and makes, with the latter, an angle preferably comprised between approximately 45 ° and approximately 90o.
• the seat associated with each intake valve, is located in a wall portion of the prechamber extending at least approximately the wall portion of the transfer channel tangent to the surface of the cylinder.
• a single intake valve and a single exhaust valve are provided.
• the gas exchange device has two inlet valves parallel to each other.
• the gas exchange device has two exhaust valves parallel to the axis of the cylinder.
• the motor is characterized in that the cross section of the channel transfer opening into the cylinder develops over a circular sector with an angle at the center between 60 ° and 110 ° and represents an area whose ratio to that of the cross section of the cylinder is preferably between 0.10 and 0.20 and more particularly between 0.13 and 0.17.
• the bottom wall of the sweeping and combustion prechamber substantially opposite the transfer channel opening into the cylinder is formed by a cylinder portion; of coaxial revolution with each intake valve, substantially tangent to each valve head, so that the radial clearance between said wall and the head of each intake valve has a minimum value such that each intake valve flows directly and essentially on its sector oriented towards the transfer channel, to direct almost all of the air flow emerging from each intake valve directly to the transfer channel.
• the engine is characterized in that the radial clearance is as reduced as possible between the upper part of each intake valve and the side wall, cylindrical and coaxial with the corresponding valve, of the prechamber in the angular sector substantially opposite to the transfer channel.
• the invention also relates to a cylinder head of two-stroke internal combustion engines, arranged in accordance with the characteristics set out above.
• the invention provides, among others, the following important advantages:
• the sweeping efficiency is improved because, while ensuring high permeability, it makes it possible to obtain a high sweeping efficiency with very good use of the sweeping air, minimizing any risk of direct passage of fresh air from the cylinder to the exhaust valve, thanks to the confinement of the stream which is accelerated towards the piston without being able to deviate towards the exhaust valve, including during the first moments of the opening of the valve of admission.
• Experimental development for obtaining good efficiency. scanning is considerably simplified due to the low number of parameters acting on the formation of the air stream. In fact, for the first part of the valve lift, therefore at a low sweep rate, the shape of the walls delimiting the prechamber and leading to the transfer channel is predominant for orienting the air stream on the wall of the liner.
• a single intake valve prohibits any asymmetry of the purge air stream relative to its plane of symmetry defined above, which is always difficult to avoid when there are for example two intake valves due to a possible evolution in operation of their respective clearance or their respective fouling state.
• the significant contribution of the geometry of the transfer channel which represents a fixed geometry as opposed to the variable geometry of the intake valve, in the formation of the purge air stream, allows an air stream to be produced high stability sweep in all cases of load and engine operating speed.
• the transfer channel contributes, if necessary, to restoring better symmetry of the gas stream.
• the invention ensures a successive sweep of the prechamber and the cylinder, so that, even in the case of a very small amount of sweeping air, the volume of the prechamber is scanned and almost exclusively filled with fresh air before the compression stroke (unlike unswept combustion pre-chambers). This has the consequence that, in the extreme case described corresponding to a partial load operation, the volume of combustion air is located in the upper part of the prechamber after being discharged - by the residual gases from the cylinder during the stroke of compression.
• the fuel introduction (injector) and / or ignition means will preferably be located in the part of the prechamber opposite the seat of the intake valve. -
• the movement of the piston at the end of its upward stroke that is to say in the vicinity of its top dead center, causes the transfer of the charge of fresh air from the cylinder to the prechamber and thus induces a field turbulence all the more intense as the dead space between the preferably flat piston head and the cylinder head bottom where the valve head is flush with the closed state exhaust is reduced.
• the turbulence prevailing in the combustion prechamber at the time of fuel injection, in the period immediately preceding the top dead center position of the piston, can be strongly influenced by the residual turbulence of the vortex from the direction scanning phase opposite to the turbulence field induced by the piston rising.
• the horizontal or inclined arrangement of the intake valve allows it to be actuated by a very direct control, in particular by lateral camshaft disposed in the upper part of the engine block, in the case of engines polycylindrical with individual cylinder heads, or by overhead camshaft in the case of single cylinder engines.
• This configuration thus allows, due to the low masses in movement, to achieve very high acceleration values when opening and closing the intake valve without exceeding the admissible contact pressure limits at the cam, which is very favorable since the opening diagram of the intake valve is very short (of the order of 100o to 140o of rotation of the crankshaft) and shorter than that of the exhaust valve (of the '' order of 20 to 40 ° crankshaft rotation).
• This arrangement promotes the achievement of larger intake valve lifts than is common in known engines (the ratio between the maximum lift and the inside diameter at the valve seat can reach and exceed double the normal) for compensate for the fact that the intake valve only flows in its lower part, taking into account its radial clearance, almost zero in its upper part, with the lateral surface of the prechamber opposite the transfer channel.
• the geometrical configuration of the sweeping and combustion prechamber makes it possible to achieve very high volumetric ratios, which can reach and even exceed 20, and this also in the case of stroke / bore ratios close to the unit. This fact facilitates the starting conditions of very small diesel engines, for example for automotive application.
• the invention will be better understood and other objects, characteristics, details and advantages thereof will appear more clearly in the course of.
• FIG. 1 is a fragmentary view, in cross section, of the only elements relating to the invention, that is to say of the head of a cylinder and the associated cylinder head portion of a two-stroke diesel engine with distribution by an intake valve and an exhaust valve mutually perpendicular and both shown open during the scanning and filling, near the bottom dead center of the piston;
• - Figure 2 is a horizontal cross-sectional view along line II-II of Figure 1, showing the outlet of the transfer channel in the cylinder;
• - Figure 3 is a sectional view along line III-III of Figure 1;
• - Figure 4 is a sectional view, similar to that of Figure 2, of an embodiment with two inlet valves parallel to each other;
• - Figure 5 is a sectional view, similar to that of Figure 2, of an embodiment with two exhaust valves parallel to each other;
• FIG. 6 shows, on a larger scale, a preferred variant of the embodiment of Figures 1 to 3;
• FIG. 7 is a sectional view along the line VII-VII of Figure 4.
• FIG. 8 shows the diagram of the opening periods of the intake and exhaust valves as a function of the angle of rotation of the crankshaft;
• Figures 9a to 9h show the different phases of the operating cycle of the variant subject of Figures 1 and 2;
• - Figure 10 shows another embodiment of the invention according to a fragmentary view similar to that of Figure 1, in which the control of the valves by a single common overhead camshaft is clearly represented.
• the reference 1 designates ⁇ m cylinder of a diesel engine with one or more cylinders operating according to a two-stroke cycle, with a geometric axis 2 represented here in a substantially vertical position and containing a reciprocating piston 3 shown in a position close to its bottom dead center.
• the upper end or head of the cylinder is surmounted and closed by a cylinder head 6, which contains an exhaust valve 7 controlling a conduit 8 for exhausting the burnt gases communicating with an exhaust path 9, in particular forming an exhaust manifold, as well as an intake valve 10 controlling an intake conduit 11 fresh oxidant air communicating with an intake manifold 12.
• the intake valve 10 opens, and the intake duct 11 opens, in the direction of flow of the purge air, into a prechamber of sweeping and combustion 13 which is formed in the cylinder head 6 and which is open towards the cylinder 1 by communicating with the latter by a transfer channel 14.
• the arrangement of the intake 10 and exhaust 7 valves preferably admits a symmetry plane e, corresponding moreover to the plane of FIG. 1 and passing through the axis of the exhaust valve 7, the axis of the intake valve 10 and the axis 2 of the cylinder 1, these three axes being indicated by dashed line in Figure 1.
• the axis of the exhaust valve 7 is substantially parallel to the axis 2 of the cylinder and offset with respect to the latter so that in the open position, the head of this exhaust valve 7 is of a side (on the left side of FIG. 1) relatively close to the corresponding adjacent side wall of cylinder 1 and, on the other side (on the right side in FIG. 1), relatively distant from the outlet of the transfer channel 14.
• L the axis of the intake valve 10, opening in the prechamber 13, is not parallel, and is shown here preferably at least approximately orthogonal, to the walls of the cylinder 1, therefore to the axis of the valve d 'exhaust 7 and axis 2 of the cylinder.
• the rod 17 of the valve 10 moves away from this axis 2, in the above plane of symmetry.
• the exhaust valve 7 cooperates with a fixed seat 15 provided in the cylinder head 6.
• the intake valve 10 cooperates with a fixed seat 16 provided in the cylinder head 6.
• the transfer channel 14 has a wall
• the transfer channel 14 also has, in cross section perpendicular to the axis 2 of cylinder 1, a substantially oblong shape tangential to cylinder 1, as is clearly visible in FIG. 2.
• the cross section of the transfer channel 14 opening into cylinder 1 preferably develops on a circular sector with an angle at the center of between 60 ° and 110 ° and represents an area whose ratio to that of the cross section of the cylinder 1 is preferably between 0.10 and 0.20 and, more particularly, between 0 , 13 and 0.17.
• the prechamber 13 has, from the seat 16 of the intake valve 10, a portion of cylinder of revolution 18, coaxial with the intake valve 10, substantially tangent to the head 10a of the valve 10 and whose dimension is: such that there is practically no air flow at the upper part of the head 10a of the intake valve 10.
• This portion of cylinder 13 therefore constitutes in practice the top or the back wall of the prechamber 13.
• the wall part 14a of the transfer channel 14 is connected to the lower part of the valve seat 16 by an arcuate profile 22 allowing a direct flow of air to the transfer channel 14, from the start of the opening the inlet valve 10.
• the part of the cylinder of revolution 18 substantially coaxial with the intake valve 10 leaves between this wall 18 and the head 10a of the intake valve 10, a radial clearance 32 having a minimum value preventing the creation of a significant air stream around the upper part of the head 10a of the intake valve 10. Consequently, almost all of the air flow emerging from the intake valve 10 flows around the lower part of the head 10a of the intake valve 10 towards the transfer channel 14, as symbolized by the flow arrows 28 in FIG. 3.
• FIG. 7 there is shown a second embodiment of the invention according to which there are two intake valves designated respectively by 100 and 110, at the top of each of which is provided, as in the case in Figure 3, a minimum radial clearance 32 just sufficient for the passage of the heads of these valves.
• this makes it possible to inject fuel into the aforementioned plane of symmetry, and also, as will be explained below, to take advantage of the organized turbulence caused by the flow, coming from cylinder 1 resulting from the piston rising.
• a single exhaust valve 7 has been provided.
• FIG. 5 another embodiment of the invention has been represented, according to which two exhaust valves have been provided, designated respectively by 107 and 117, with a single intake valve 10.
• the single valve either exhaust 7 or intake 10 is located in the above-mentioned plane of symmetry.
• FIG. 8 represents the diagram of opening of the intake and exhaust valves of the preferred embodiment of FIGS. 1, 2 and 3.
• the intake opening is designated by OA, by OE the exhaust opening, by FA the intake closing, by FE the exhaust closing, by TDC top dead center and by PMB bottom dead center.
• the opening period of the exhaust valve 7 represents approximately 160 ° of rotation angle of the crankshaft while the opening period of the intake valve 10 represents approximately 140 ° of rotation angle of the crankshaft. It will be observed in this connection that the opening period of the exhaust valve 7 begins well before the opening period of the intake valve 10, respectively 60 ° and 30 ° before the bottom dead center.
• FIGS. 9a to 9h various sequences of the operating cycle of this engine have been shown.
• FIG. 9a represents the expansion phase for which the intake valve 10 and the exhaust valve 7 are closed and the piston 3 moves towards bottom dead center, as symbolized by the arrow F.
• FIG. 9b has shown the following sequence for which the exhaust valve 7 has just opened while the intake valve 10 is still closed, the piston 3 continuing its downward movement towards bottom dead center, which will allow, d in a manner known per se, to lower the pressure in the cylinder 1 to the level of the scanning pressure.
• FIG. 9c represents the following sequence in which the exhaust valve 7 is almost completely open, the piston being at the start of its upward stroke as shown in the reverse direction of the arrow F, while the intake valve 10 is already practically open and thus allows the flow of the air stream which has been designated for example by 23 in FIG. 3.
• This flow 28 is transformed into a single flow of air 40 bearing on the vertical wall of the cylinder following the transfer channel 14, which discharges, during its penetration into the cylinder 1, a corresponding volume of burnt gases 42.
• FIG. 9d represents the following sequence corresponding to the scanning of the cylinder 1 and showing the maximum liftings of the exhaust valve 7 and of the intake valve 10 respectively.
• this maximum lift of the valve d intake 10 is larger than that of conventional two-stroke engines.
• the valve lift is calculated in such a way that the lateral surface of the geometrical cylinder limited between the valve seat and the transverse surface of the valve is equal to or slightly greater than the free section of the valve seat. valve open. In the case of the invention, it is only about half of the lateral surface of the aforesaid geometrical cylinder which allows the fresh air to pass through and it is therefore necessary to compensate for this loss of surface by increasing the lift of the intake valve 10 or intake valves 100, 110.
• the ratio between the maximum lift of the or each intake valve 10 and the internal diameter of the seat 16 of said intake valve is greater than 0, 35.
• FIG. 9e represents the end of scanning sequence for which the exhaust valve 7 has just closed, the inlet valve 10 being partially open before it is completely closed.
• the piston 3 continues to rise in the cylinder 1 and causes a partial discharge of the air in the direction of the intake manifold 12.
• Figure 9f shows the following sequence compression for which the two exhaust valves 7 and inlet 10 are closed.
• the continued ascent of the piston in the cylinder therefore not only causes compression but also a progressive discharge of the air towards the prechamber 1.3, which induces a large field of turbulence, symbolized by the arrow 50, conducive to phase d injection of fuel and its mixture with the combustion air in the following sequence.
• FIG. 9g represents the fuel injection phase just before top dead center, symbolized by a jet of fuel 52.
• FIG. 9h represents the last sequence relating to the combustion of the mixture thus prepared with the piston being at its top dead center. Thanks to the structure described and to this operation, all the technical advantages mentioned in the introductory part of the description are obtained.
• the head 10a of the intake valve 10 has an approximately planar surface 19 intended to cooperate with a mating surface 20, also approximately planar, of the seat 16.
• the opposite face 21 of the head 10a which is preferably approximately conical, is arranged so as to enter a recess 30, of conjugate shape, formed in the wall, opposite from the prechamber 13, the assembly being such that the inlet valve 10, when it is raised maximum, penetrates almost completely into, this recess by driving out the burnt gases.
• the intake duct 11 is advantageously provided with a lip 33, immediately below the seat 16 and on its lower part, intended to accelerate gradually, by a nozzle effect, the fresh air entering the prechamber 13 , upon opening, of the intake valve 10.
• the fuel is introduced under pressure into the prechamber 13 by an injector 120 arranged, not at the top of this prechamber as shown diagrammatically in FIG. 1, but in the axis of the inlet valve 17, which improves the homogeneity of the mixture of air and fuel admitted into the cylinder.
• an injector 120 arranged, not at the top of this prechamber as shown diagrammatically in FIG. 1, but in the axis of the inlet valve 17, which improves the homogeneity of the mixture of air and fuel admitted into the cylinder.
• an injector 120 arranged, not at the top of this prechamber as shown diagrammatically in FIG. 1, but in the axis of the inlet valve 17, which improves the homogeneity of the mixture of air and fuel admitted into the cylinder.

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• Engineering & Computer Science (AREA)
• Chemical & Material Sciences (AREA)
• Combustion & Propulsion (AREA)
• Mechanical Engineering (AREA)
• General Engineering & Computer Science (AREA)
• Combustion Methods Of Internal-Combustion Engines (AREA)
• Valve-Gear Or Valve Arrangements (AREA)

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• 1985
  • 1985-12-31 FR FR8519506A patent/FR2592430B1/fr not_active Expired - Lifetime
• 1986
  • 1986-12-31 JP JP62500487A patent/JPH0711248B2/ja not_active Expired - Lifetime
  • 1986-12-31 KR KR1019870700785A patent/KR940008265B1/ko not_active IP Right Cessation
  • 1986-12-31 DE DE8787900178T patent/DE3667810D1/de not_active Expired - Lifetime
  • 1986-12-31 US US07/072,244 patent/US4854280A/en not_active Expired - Fee Related
  • 1986-12-31 AU AU68324/87A patent/AU594997B2/en not_active Ceased
  • 1986-12-31 EP EP87900178A patent/EP0252935B1/de not_active Expired
  • 1986-12-31 WO PCT/FR1986/000451 patent/WO1987004217A1/fr active IP Right Grant
• 1987
  • 1987-06-23 IN IN491/CAL/87A patent/IN166067B/en unknown
  • 1987-08-25 FI FI873667A patent/FI873667A0/fi not_active IP Right Cessation
• 1989
  • 1989-08-07 US US07/390,207 patent/US5014663A/en not_active Expired - Fee Related

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