FR2613770A1 - Two-stroke internal combustion engine - Google Patents

Abstract

Two-stroke engine comprising two pistons 12, 13 which slide in a cylinder 8 belonging to a rotor integral with the output shaft of the engine, and between them defining a variable-volume combustion chamber 14. The pistons carry rollers 18, 19 which roll along a guide track 21 extending along a closed curve which has a large axis AA' and a small axis BB'. The pressure of gases exploding on the pistons rotationally entrains the rotor.

Description

Two-stroke internal combustion engine.

The invention relates to a new design of a two-stroke internal combustion engine.

Known two-stroke engines include at least one piston mounted sliding in a cylinder to define therein a combustion chamber of variable volume into which opens a fresh gas inlet opening and a burnt gas exhaust opening, each is released by the piston for part of the stroke thereof.

The fresh gases are first drawn into the sealed crankcase of the engine, opposite the combustion chamber with respect to the piston, and they are compressed by the movement of this so that they can then enter under pressure, through the opening. intake, into the combustion chamber by expelling the burnt gases contained in the chamber through the exhaust opening.

A spark plug is provided to cause an explosion of the gases in the combustion chamber, and the sliding movement of the piston under the thrust of the exploding gases is transformed into a rotary movement by a system of connecting rod and crank or crankshaft.

The principle of the two-stroke engine is too well known for it to be necessary to describe it further.

The drawbacks of this type of engine are also well known. In particular: - The torque produced is relatively low.

- The lubricating oil is mixed with the fuel and burns with it, which increases air pollution.

- If you want to avoid that at a high speed part of the fresh gases introduced into the combustion chamber come out directly through the exhaust opening, it is necessary to use complex means, the efficiency of which is up to 'here very limited.

The invention aims to avoid these drawbacks, and proposes a particularly efficient two-stroke engine.

The subject of the invention is a two-stroke combustion engine comprising at least one piston mounted sliding in a cylinder to define therein a combustion chamber of variable volume into which open a fresh gas inlet opening and an opening exhaust of burnt gases, each of which is masked by the piston over part of the stroke thereof, means for compressing the fresh gases to make them penetrate under pressure, through the intake opening, into the combustion by expelling the burnt gases contained in the chamber through the exhaust opening, ignition means for causing an explosion of the gases in the chamber, and conversion means for transforming the sliding movement of the piston under the thrust exploding gases in a rotational movement, characterized in that it comprises a second piston mounted sliding in said cylinder and associated with its own intake and exhaust openings, said chamber re combustion being between the two pistons, in that the cylinder and the pistons belong to a rotor whose axis of rotation is perpendicular to the sliding direction of the pistons, and in that the two pistons cooperate with a track of guide extending along a first non-circular closed curve symmetrical with respect to a center located on the axis of the rotor to constitute the conversion means, the pistons performing reciprocating movements symmetrically with respect to each other 'axis and the rotor making a half-turn for each period of movement of the pistons.

According to a characteristic of the invention, the compression means comprise at least a first compartment adjacent to the rotor and communicating with the intake opening therethrough and the volume of which varies periodically at a frequency twice that of rotation rotor.

In particular, the rotor may have a portion of external surface of revolution cooperating with a fixed wall to define a cavity symmetrical with respect to the axis of the rotor and the radial dimension of which varies between a value substantially zero in a first radial direction and a maximum value in a second radial direction perpendicular to the first, the cavity thus consisting of two halves separated from each other by the rotor, two oscillating spatulas symmetrical to each other with respect to the axis of the rotor, articulated on the rotor, extending from said surface portion to said fixed wall, each valve thus sharing, during the major part of a half-turn of the rotor, one of the halves of the cavity in said first compartment and a second compartment.

In this portion of surface of revolution advantageously open on either side of the articulation of each valve; a gas suction port in the second compartment and a gas discharge port out of the first compartment, communicating with an intake opening of the cylinder.

According to one embodiment, the fixed wall is cut by a plane perpendicular to the axis of the rotor according to a closed non-circular curve symmetrical with respect to a center located on the axis of the rotor.

This closed curve advantageously has in its plane two axes of symmetry.

According to a preferred embodiment, each piston carries a roller which is applied against the track and which can rotate freely around an axis parallel to the axis of the rotor to roll on the latter.

The invention also provides means for supplying lubricating oil to the interface between the spatulas and the fixed wall and from there to the pistons through the rotor, without entering the combustion chamber.

According to yet another characteristic, means are provided for closing an exhaust path for the burnt gases, downstream of the cylinder exhaust openings, for an adjustable fraction of the time for the latter to be released by the pistons. These means may include a diaphragm adjacent to the rotor having two symmetrical through passages with respect to the axis thereof and in front of which pass the exhaust openings during the rotation of the rotor, these being already with regard to the passages when the pistons release them and the diaphragm being able to pivot so that the exhaust openings remain opposite the passages over all or a variable fraction of the angle of rotation during which they remain released by the pistons.

Other characteristics and advantages of the invention will emerge from the detailed description given below of an exemplary embodiment, and from the appended drawings in which - FIG. 1 is a view in axial section of an engine according to the invention , according to line II of Figure 3, - Figure 2 is a sectional view along line II-II of Figure 1, - Figure 3 is a sectional view along line III-III of Figure 1, - Figures 4 and 5 are explanatory diagrams of the operation of the blower ensuring gas compression, - Figures 6 and 7 are explanatory diagrams relating to the adjustment of the exhaust time.

The engine shown comprises a casing formed by a ferrule 1 and two end flanges 2 and 3 screwed onto the ferrule. A rotor 4, integral with the output shaft 4 ′ of the motor, is mounted by two ball bearings 5 and 6 in central bores of the flanges 2 and 3 respectively.

The rotor notably comprises a part 7 pierced with a cylinder of revolution bore 8 whose axis 9 intersects the axis 10 of the rotor at right angles. The bore 8 opens at its two ends into the internal space 11 of the casing.

Two pistons 12 and 13 are slidably mounted in the bore or cylinder 8 and define therebetween, inside the latter, a chamber 14 sealingly separated from the open ends of the cylinder by annular seals 15 carried by the pistons . Each of the pistons 12 and 13 has two arms 16 directed opposite the axis 10 of the rotor and supporting the ends of a shaft 17 parallel to the axis 10. Two rollers 18 and 19 are mounted free to rotate respectively on the shafts 17 of the pistons 12 and 13. The rollers 18 and 19 can roll on a closed track 21 formed by the internal face of an annular part 20 immobilized in the shell 1. The track 21 has a cylindrical shape whose generatrices are parallel at the axis 10, cooperate with the generators of the rollers. The cross section of the track 21, obtained for example by the section plane of FIG. 2 and visible consequently in this figure, is a closed non-circular curve, symmetrical by relative to two axes of its plane, one of these axes 23 coinciding with the axis 9 of the cylinder 18 in the position as shown, and the other axis 22 being perpendicular to the first.

The curve 21 is composed of two complementary semicircles of the same diameter and of two straight segments tangent to these semicircles at their ends and connecting them to each other. This curve has no angular points. The distance between its points of intersection A and A 'with axis 23, or major axis, is greater than the distance between its points of intersection B and B' with axis 22. The distance between one points on the curve and the intersection 25 of axes 23 and 22, or radius, increases continuously when this point moves from point B to point A. This curve could also be an ellipse, or a curve whose radius varies sinusoidally depending on the angle.

I1 results from the shape of the track 21 that, when the rotor turns and the rollers 18 and 19 roll on the track, each of the pistons 12 and 13 slide in the cylinder 8 according to a periodic reciprocating movement, the distance between each piston and the axis 10 of the rotor and consequently the volume of the chamber 14, being maximum when the rollers are in contact with the points A and A 'of the track, and minimum when the rollers are in contact with the points
B and B '.

The rotor 4 has an axial bore 26 which extends on either side of the flange 2 of the casing and opens into the cylinder 8. In this bore is mounted a spark plug 27 whose electrodes 28 protrude into the cylinder and the body of which achieves a gas-tight separation between the bore 26 and the cylinder 8. In the bore 26 pass a cable 28 for the electrical supply of the spark plug and an insulating protective sheath 29 which surrounds it and comes into contact with the body of the candle. The sheath and the body of the spark plug internally limit in the bore 26 an annular passage 30 which communicates, outside the engine, with a source (not shown) of gaseous fuel mixture.

Around the part of the rotor 4 traversed by the bore 26 is disposed a fixed annular part 31 which extends axially between the flange 2 and another radial flange 32 located inside the casing. The part 31 has, in the direction of the axis 10 of the rotor, a cylindrical face 33 whose generatrices are parallel to the axis 10. The cross section of the surface 33, for example by the section plane of FIG. 3, is a closed curve completely similar to that defining the raceway 21 of the rollers of the pistons, and has a large axis A1, A'1 and a small axis B1, B'1 perpendicular to each other.

The rotor 4 has, opposite the surface 33, a cylindrical outer surface of revolution 34 which is tangent to the surface 33 along the generatrices passing through the points
B1 and B'1. The faces 33 and 34 therefore define, in cooperation with the flanges 2 and 32, a cavity formed by two halves 35 and 36 separated from each other by the generators of contact between the rotor and the part 31.

Figure 4 shows a position of the rotor 4 relative to the face 33 different from that of Figure 3. In Figure 4, the letter O indicates the center of symmetry of the closed curve constituting the cross section of the surface 33, c 'is to say the point of intersection of its axes A1, A'1 and Bl, B'l. M and N are the points of intersection of a radius from O with the surfaces 34 and 33 respectively. It is observed that the length of the segment M, N, that is to say the dimension of the cavity 35.36 in the radial direction, varies regularly between a value substantially zero in the direction of the axis OB1 at a maximum value in the direction of the axis OA1, perpendicular to
OB1.

Two spatulas 37 and 38 integral with the rotor 4 and diametrically opposite one with respect to the other are articulated by one of their ends 39 at the periphery of the part of the rotor defining the cavity 35, 36 so as to oscillate around axes parallel to axis 10 of the rotor. To this end, the ends 39 are thickened with respect to the body of the spatulas and are housed in surface recesses of the rotor, with which they cooperate by sliding surfaces of revolution. The spatulas 37 and 38 are biased away from the rotor by springs 40, so that their free ends 41 come to bear on the internal face 33 of the part 31. Furthermore, the spatulas extend axially from one to the other of the flanges 2 and 32, so that, in particular in the positions shown in FIGS. 3 and 4, each of the spatulas divides one of the cavity halves 35 and 36 into a first compartment 42 and a second compartment 43. The first compartment 42 is adjacent to the internal face of the spatula, which forms an obtuse angle with the wall 33, and the second compartment 43 is adjacent to the external face of the spatula, which forms an acute angle with the wall 33. The rotor 4 has flats 44 and 45 for receiving the internal faces of the bodies of the spatulas 37 and 38 respectively, which bodies are substantially planar, so that the spatulas, when they come into contact with the flats, do not extend beyond of the cylinder revolution outline d e the face 34 of the rotor. From the flats 44 and 45, recesses 46 (FIG. 4) are formed in the rotor over part of the axial length of the cavity 35, 36 to accommodate the springs 40 when the spatulas are folded down. on the flats.

Two gas inlet pipes 47 and 48 extend substantially radially, in diametrically opposite positions, between the bore 26 of the rotor and its external surface 34, so as to make the bore communicate with the cavity 35, 36. These pipes open into the face 34 in the immediate vicinity of the ends 39 of the spatulas, and on the opposite side of the latter relative to the flats 44 and 45 respectively.

Compressed gas discharge pipes 49 and 50, also provided in the rotor, open into the external face 34 at the flats 44 and 45 and / or recesses 46. These pipes 49 and 50 also lead to openings d 'admission of fresh gas into the cylinder 8 respectively 51 and 52. These openings 51 and 52 are closed respectively by the pistons 12 and 13 for part of the stroke of the latter and are only released by them when they are find in the vicinity of their position furthest from the axis 10 of the rotor, a position called bottom dead center by analogy with the operation of the conventional piston engine. In this position, recesses 53 formed in the face of the pistons facing the axis of the rotor receive the gases coming from the openings 51 and 52 and direct them towards the axis 10, according to a known arrangement in conventional two-stroke engines, however, that the burnt gases are expelled through exhaust openings 54 and 55 located approximately opposite the intake openings 51 and 52 respectively in the wall of the cylinder 8. Non-return valves 56 are provided in the pipes 49 and 50 to prevent the gases from being forced back into the cavity 35, 36 under the effect of the residual or expansion pressure prevailing in the combustion chamber 14.

The exhaust openings 54 and 55 of the cylinder 8 communicate with an annular exhaust manifold 57, itself connected to an exhaust manifold 58. The wall of the exhaust manifold 57 is defined by a fixed part 59 and by a disc-shaped part 60 which can pivot around the axis 10 of the rotor under the action of an adjustment member not shown. The disc 60 has two through openings 61 and 62 elongated in arcs of a circle centered on the axis 10 and symmetrical to each other with respect to this axis.

The operation of the engine will be described below, during which the rotor turns in the direction of arrow F3 in FIG. 3, the free ends 41 of the spatulas 37 and 38 being in front of their articulation ends 39 relative to this direction of rotation.

The elements represented in FIGS. 3 to 5 constitute a blower intended to send accelerated fresh gases into the combustion chamber 14. The device could also function as a compressor, by means of a modification of the gas passage sections, without the general functioning of the engine. be affected.

Figure 4 shows the start of a gas propulsion phase towards the combustion chamber. The orifices through which the suction pipes 47 and 48 open into the face 34 of the rotor have just crossed the points B'1 and B1 respectively and communicate with the cavity halves 35 and 36, which are each divided into two compartments 42 and 43 by the spatulas 37 and 38. The compartments 43 located behind the spatulas and communicating with the suction pipes 47 and 48 are very small, and the compartments 42 located in front of the spatulas and communicating with the drainage pipes 49 and 50 represent almost all of the cavity halves.

During the rotation of the rotor, the spatulas 37 and 38 move away from the points B'1 and B1 respectively, and the volume of the compartments 43 increases. Gases are therefore sucked into these compartments through the pipes 47 and 48. At the same time, the volume of the compartments 42 decreases and the gases which they contain are expelled through the pipes 49 and 50 towards the combustion chamber.

The end of the expulsion phase is shown in FIG. 5, where the free ends of the spatulas 37 and 38 reach points B1 and B'1 respectively, the spatulas coming to bear on the flats of the rotor. The volume of the compartments 42 communicating with the evacuation pipes 49 and 50 is zero, while the compartments 43 communicating with the suction pipes 47 and 48 represent all of the cavity halves 36 and 35 respectively. Then, the spatulas are raised again, putting the line 49 into communication with the half cavity 36 and the line 50 with the half cavity 35, which again give rise to large-volume compartments 42 filled with gas, and to from which a new expulsion phase can begin, the positions of the spatulas 37 and 38 being reversed with respect to Figures 3 and 4.

The explosion of the gases sent into the combustion chamber 14 is triggered by a spark produced by the spark plug 27 at a suitably chosen moment of the rotation of the rotor so that the pressure produced on the pistons by the explosion maintains the movement of the engine, the reciprocating sliding movement being transformed into a rotational movement of the rotor by the rolling of the rollers 18 and 19 on the track 21. The centrifugal force ensures permanent contact between the rollers and the track, of the compression springs 63 (or all equivalent means) may be provided to produce this contact as soon as the engine starts.

Figures 6 and 7 illustrate the scrolling of the exhaust openings 54 and 55 of the cylinder 8 in front of the inlet openings 61 and 62 of the exhaust manifold. There is shown, with horizontal hatching, the opening 61 as viewed in the axial direction from the exhaust manifold to the cylinder. During the rotation of the rotor, the exhaust openings 54 and 55 of the cylinder, of a circumferential length smaller than that of the opening 61, pass in front of it. It has been indicated under the reference 54-1, and with vertical hatching, the position occupied by the opening 54 for example when it has just been released by the piston 12. Similarly, the reference 54-2 indicates , also with vertical hatching, the position of this opening immediately before it is masked by the piston. The opening 61 is entirely superimposed on ranges 54-1 and 54-2 as well as those corresponding to all the intermediate positions of the opening 54.

The cylinder exhaust opening is therefore in communication with the exhaust manifold during the whole part of the piston stroke during which it is released by the latter.

In FIG. 7, the opening 61 has pivoted in the opposite direction to the direction of rotation of the rotor, indicated by the arrow F6.

The range 54-1 is always covered by the opening 61 but the range 54-2 is entirely external to the latter.

This means that the communication between the combustion chamber and the exhaust manifold is interrupted by the diaphragm 60 before the piston comes to close the exhaust opening 54 after its bottom dead center. Of course, the openings 55 and 62 being symmetrical with the openings 54 and 61 respectively with respect to the axis of the rotor, the scrolling of the opening 55 in front of the opening 62 takes place at the same time and under the same conditions as the scrolling of the opening 54 in front of the opening 61, and vice versa. The pivoting of the diaphragm 60 and the shortening of the exhaust time which results therefrom makes it possible to avoid, at high speed, the direct evacuation by the exhaust openings of the fresh gases introduced into the combustion chamber while the openings of exhaust are unmasked by the pistons. This pivoting can be done manually or automatically.

The engine lubrication system will now be briefly described. Oil is supplied through orifices not shown at the level of the face 33 of the part 31 to ensure lubrication of the contact between this face and the ends 41 of the spatulas 37 and 38. This oil is brought back towards the axis of the rotor by spiral grooves 64 formed in the face of the flange 32 facing the cavity 35,36.

The oil then passes through conduits 65 formed through the rotor and opening into the cylinder 8 through orifices separated from the combustion chamber 14 by the seals 15 of the pistons. The oil thus ensures the lubrication of the contact between the pistons and the cylinder, without entering the combustion chamber. Channels 66 are provided in the pistons to bring the oil from the wall of the cylinder to the spaces between the arms 16 of the pistons, so as to lubricate the rollers 18 and 19 in their rotation on the shafts 17 and in their rolling on runway 21.

From the latter, the oil falls into a bowl 67 formed in the lower part of the casing, from where it is brought back to the surface 33 by appropriate means.

We also see in the figures a turbine 68 integral with the rotor, intended to create a current of air through the motor for the cooling thereof.

In the example shown, the position of the rotor illustrated in FIG. 5, corresponding to the end of a propulsion phase of the blower, and for which the volume of the compartments 42 is minimal, in this case zero, is late d '' slightly less than 450 relative to the position of maximum spacing of the pistons, or bottom dead center, illustrated in Figures 1 to 3. This angular offset can be modified without difficulty by the skilled person in order to optimize the engine performance. It seems that a value between 25 and 300 is particularly satisfactory. The modification of this angle can be achieved, either by moving parts 20 and 31 relative to each other so that the corresponding closed curves do not no longer have their large axes and their small parallel axes respectively, or by modifying the rotor itself so that the plane containing the axes of pivoting of the spatulas does not pass through the axis of the cylinder.

It has been found that the engine according to the invention provides, at equal displacement and for the same sliding frequency of the pistons, a higher torque than conventional two-stroke engines. In addition, this sliding frequency corresponds to a rotation speed twice as low.

In fact, one revolution of the rotor corresponds to two back and forth movements of the pistons, whereas in a conventional engine one revolution of the crankshaft corresponds to two round trips of the piston.

The engine according to the invention can be used for all applications of two-stroke engines and in particular in two-wheeled vehicles.

Claims (11)

Claims 1. - Two-stroke internal combustion engine comprising at least one piston (12) slidably mounted in a cylinder (8) to define therein a combustion chamber (14) of variable volume into which open an opening (51) fresh gas intake and a burnt gas exhaust opening (54), each of which is masked by the piston over part of its stroke, means for compressing the fresh gases to make them penetrate under pressure, through the intake opening, into the combustion chamber, driving the burnt gases contained in the chamber through the exhaust opening, ignition means (27) to cause an explosion of the gases in the chamber, and conversion means for transforming the sliding movement of the piston under the thrust of exploding gas into a rotary movement, characterized in that it comprises a second piston (13) mounted to slide in said cylinder and associated with its own openings intake and exhaust nt (52,55), said combustion chamber being between the two pistons, in that the cylinder and the pistons belong to a rotor (4) whose axis of rotation (10) is perpendicular to the direction of sliding of the pistons, and in that the two pistons cooperate with a guide track (21) extending along a first closed non-circular and symmetrical curve with respect to a center situated on the axis (10) of the rotor to constitute the conversion means, the pistons performing reciprocating movements symmetrically to each other with respect to the axis and the rotor performing a half-turn for each period of the movement of the pistons. 2. - Motor according to claim 1, characterized in that the compression means comprise at least a first compartment (42) adjacent to the rotor and communicating with the intake openings (51,52) through the latter and the volume varies periodically at twice the frequency of rotation. 3. - Motor according to claim 2, characterized in that the angular position of the rotor for which the volume of the first compartment (42) is minimal occurs for a rotation of about 25 to 300 after the position for which the mutual separation of the pistons is maximum. 4. - Motor according to one of claims 2 and 3, characterized in that the rotor has a portion of external surface of revolution (34) cooperating with a fixed wall (33) to define a cavity (35,36) symmetrical by relative to the axis of the rotor and whose radial dimension (MN) varies between a substantially zero value in a first radial direction (OB1) and a maximum value in a second radial direction (OA1) perpendicular to the first, the cavity decomposing thus two halves (35,36) separated from each other by the rotor, two oscillating spatulas (37,38) symmetrical with each other with respect to the axis of the rotor, articulated on the rotor , extending from said surface portion to said fixed wall, each spatula thus sharing, for most of a half-turn of the rotor, one of the halves (35,36) of the cavity said first compartment (42) and a second compartment (43). 5. - Motor according to claim 4, characterized in that in said surface portion (34) open, on either side of the joint (39) of each valve, an orifice (47,48) of suction gas in the second compartment (43) and an orifice (49.50) for discharging gas from the first compartment (42), communicating with an inlet opening (51.52) of the cylinder. 6. - Motor according to one of claims 4 and 5, characterized in that said fixed wall (33) is cut by a plane perpendicular to the axis of the rotor according to a second closed non-circular curve symmetrical with respect to a center located on the rotor axis. 7. - Motor according to one of claims 2 to 6, characterized in that it comprises means for supplying lubricating oil to the interface between the spatulas (37,38) and the fixed wall (33) and from there to the pistons (12,13) through the rotor (4), without entering the combustion chamber (14). 8. - Motor according to one of the preceding claims, characterized in that the first closed curve, and / or where appropriate the second closed curve, has in its plane two axes of symmetry (AA ', BB'; AlA'l , BlB'l). 9. - Motor according to one of the preceding claims, characterized in that each piston (12,13) carries a roller (18,19) which is applied against the track (21) and which can rotate freely around a axis parallel to the rotor axis to roll inside of it. 10. - Engine according to one of the preceding claims, characterized in that it comprises means (60,61,62) for closing an exhaust path of the burnt gases, downstream of the openings (54,55) of exhaust of the cylinder (8), during an adjustable fraction of the time of release of the latter by the pistons. 11. - Motor according to claim 10, characterized in that the shutter means comprise a diaphragm (60) adjacent to the rotor, having two through passages (61,62) symmetrical to each other with respect to the axis (10) thereof and in front of which the exhaust openings (54, 55) pass during the rotation of the rotor, these being already opposite the passages when the pistons release them and the diaphragm being able to pivot by so that the exhaust openings remain opposite the passages over all or a variable fraction of the angle of rotation during which they remain cleared by the pistons.