EP0133178A2 - Fuel injection device for a two-stroke engine - Google Patents

Abstract

A piston (20) is moved by a movable wall (21) which moves as a function of the air pressure prevailing in the precompression housing (3) of a two-stroke engine cylinder in order to draw up a perfectly determined dose. fuel when the air pressure increases in the precompression housing (3) and to discharge a determined dose of fuel to the injector (9) when the air pressure decreases in the precompression housing. This injection device is advantageously integrated into the engine cylinder in a compact construction.

Description

The present invention relates to a device for injecting fuel into a two-stroke engine with precompression in the crankcase and positive ignition.

One of the drawbacks of two-stroke petrol engines is their higher fuel consumption than that of four-stroke engines. To reduce the consumption of a two-stroke engine it is necessary to inject a rigorously metered quantity of fuel into the or each cylinder during or after the sweeping of the gases burned by the new air charge. Fuel injection is delicate and until now it requires expensive and expensive equipment which has limited its application mainly to four-stroke engines.

The object of the invention is to propose a fuel injection device of simple construction which makes it possible to dose the quantity of fuel injected in proportion to the quantity of air drawn into the engine at each cycle.

This object is achieved by an injection device characterized by a pump body comprising a first chamber in communication with the external atmosphere and communicating with the air intake pipe or the pipe. exhaust; a second chamber communicating with the precompression casing of the engine, said second chamber being separated from the first chamber by a movable wall secured to a support held by a spring; a piston pressing on the support and sliding axially in a channel when the movable wall moves the support; and a third chamber having an opening communicating with the fuel inlet pipe and an opening connected by a pipe to a fuel injector opening into the engine cylinder in a substantially radial direction so as to spray the fuel onto the stream or streams of scanning. The third chamber is arranged at the end of said channel so that when the movable wall moves the support, one end of the piston moves by varying the pressure prevailing in the third chamber in order to suck up a dose of fuel when the wall mobile compresses the spring and delivers a dose of fuel to the injector when the spring is relaxed. Means are provided for adjusting the stress of said spring in order to be able to adjust the injection device.

In an advantageous embodiment, the injection device is integrated into the engine cylinder in a compact construction. The pump body then has a generally cylindrical projection forming a housing for the injector and a discharge valve arranged coaxially in alignment with the longitudinal axis of the injection piston, said projection comprising means for fixing the device. injection on the engine cylinder in a substantially radial direction.

An alternative embodiment also incorporates a booster pump. This consists of a compact block screwed under the body of the injection device. The underside of the body of the injection device is formed with a cavity into which opens a duct which communicates with the air intake duct of the casing. The body of the booster pump is formed with a compartment which faces said cavity and is separated from it by a flexible membrane. The compartment of the booster pump body communicates with the fuel supply line by an intake valve closed by a movable tongue cut out from the flexible membrane. It also has a tab which closes a discharge valve communicating with the fuel supply pipe in the fuel chamber of the injection device.

Other particularities and variants will emerge from reading the description which follows.

The fuel injection device according to the invention makes it possible to obtain an appreciable reduction in fuel consumption and overload, a remarkable reduction in pollution which makes the two-stroke engine more attractive.

• . la figure 1 est une vue schématique d'un moteur à deux temps et d'un dispositif d'injection selon l'invention, servant à illustrer le principe du mécanisme de dosage et d'injection du carburant;
• . la figure 2 est une vue en coupe transversale d'un moteur et d'un mode d'exécution du dispositif d'injection selon l'invention;
• . la figure 3 est une vue en coupe axiale d'un détail d'exécution du dispositif d'injection selon l'invention;
• . la figure 4 est une vue en coupe axiale d'un mode d'exécution intégré d'un moteur et d'un dispositif d'injection selon l'invention;
• . la figure 5 est une vue en coupe verticale suivant la ligne V-V de la figure 6, dans un mode d'exécution du dispositif d'injection selon l'invention avec pompe de gavage intégrée;
• . la figure 6 est une vue en coupe horizontale suivant la ligne VI-VI de la figure 5.
• . les figures 7 et 8 illustrent deux variantes de réalisation du dispositif d'injection de la figure 2.

The invention is explained in more detail in the following with reference to the attached drawings in which:

• . Figure 1 is a schematic view of a two-stroke engine and an injection device according to the invention, used to illustrate the principle of the metering and fuel injection mechanism;
• . Figure 2 is a cross-sectional view of an engine and an embodiment of the injection device according to the invention;
• . Figure 3 is an axial sectional view of an execution detail of the injection device according to the invention;
• . Figure 4 is an axial sectional view of an integrated embodiment of an engine and an injection device according to the invention;
• . Figure 5 is a vertical sectional view along the line VV of Figure 6, in one embodiment of the injection device according to the invention with integrated booster pump;
• . FIG. 6 is a view in horizontal section along the line VI-VI of FIG. 5.
• . FIGS. 7 and 8 illustrate two alternative embodiments of the injection device of FIG. 2.

In Figures 1 and 2 we see a two-stroke engine cylinder 1 with its piston 2, the pre-compression housing 3, the transfer channel 4, the air intake port 6 communicating with the pipe intake 5, the exhaust pipe 8 of the combined gases and a fuel injector 9. The injector 9 is supplied with fuel by an injection device according to the invention designated as a whole by the reference 10 and which receives the fuel a reservoir 50 via a booster pump 30.Sur Figure 2 which shows an exemplary embodiment, the injection device 10 according to the invention, is attached to the ^p removed from the cylinder 1 and its arrangement is returned with respect to that of the schematic view of FIG. 1.

The injection device 10 is arranged to send to the injector 9 a rigorously controlled dose of fuel in proportion to the quantity of air drawn into the cylinder 1. This injection device comprises a body comprising a first chamber 11 which is located in communication with the outside atmosphere by a vent hole 14 and with the air intake pipe 5 by a tube 17 and a nozzle 18 which opens into the pipe 5 downstream of the adjusting butterfly valve 7. A second chamber 12, separated from the first chamber 11 by a sealed mobile wall 21, communicates with the precompression housing 3 by a conduit 19. A third chamber 13 receives the fuel from the booster pump 30 by the conduit 26 through a check valve. admission 25 and it communicates to through a discharge valve 27 with a pipe 28 supplying the injector 9 with fuel. The movable wall 21, which can for example simply be a flexible waterproof membrane, cooperates in its middle with a support head 22 held by a prestressing spring 15, the other end of which rests on a stop 16 cooperating with a screw. adjustment 42 used to adjust the spring preload 15.

Between the compression chamber 12 and the fuel chamber 13, the body of the injection device 10 comprises a channel 23 in which is housed a piston 20 having an end which is held against the support head 22 of the movable wall 21 or against the movable wall itself by the spring 24, this piston extending in the channel 23 so that its free end arrives in the fuel chamber 13.

When, during the expansion time, the piston 2 descends into the cylinder 1, it compresses the fresh gases in the casing 3 and creates an increase in pressure there which is proportional to the amount of air introduced into the cylinder during the previous cycle and which is in principle equal to the quantity of air in the cycle considered. The increase in pressure in the casing 3 is communicated in the compression chamber 12 of the injection device 10 via the conduit 19 and this increase in pressure is applied to the wall 21 which moves and compresses the spring 15 until the tension of the latter balances the pressure prevailing in said compression chamber 12. The displacement of the movable wall 21 causes the piston 20 which slides in the channel 23 creating in the fuel chamber 13, a depression which a fuel dose is drawn into the chamber as a function of the displacement of the piston 20 and therefore as a function of the quantity of air absorbed in the cylinder.

At the time of scanning, the piston 2 unmasks the light transfer and the pressure abruptly decreases in the casing 3. The pressure also decreases in the compression chamber 12, the spring 15 expands and the piston 20 moves towards the fuel chamber 13 while driving back to the injector 9 the dose of fuel which had been sucked up during the previous expansion time.

According to the calculation, if we consider the compression of the fresh gases in the crankcase 3 as being adiabatic, we see that the pressure prevailing in the crankcase, when the piston 2 is at bottom dead center, is indeed directly proportional to the amount of gas absorbed.

• V1: le volume du carter quand le piston est au point mort haut
• V2: le volume du carter quand le piston est au point mort bas
• Ω: le rapport volumétrique du carter = V1/V2
• P1: la pression régnant dans le carter quand le piston est au point mort haut
• P2: la pression régnant dans le carter quand le piston est au point mort bas
• P0: la pression régnant dans le carter quand le piston est au point mort bas et que le moteur tourne gaz coupés
• Cp: 5/2 R = 5 cal
• Cv: 3/2 R = 3 cal
• T1: la température régnant dans le carter quand le piston est au point mort haut (moteur chaud) = température ambiante
• T2: la température régnant dans le carter quand le piston est au point mort bas (moteur chaud) On a
  

Indeed, if

• V1: the volume of the crankcase when the piston is in top dead center
• V2: the volume of the crankcase when the piston is in bottom dead center
• Ω: the volumetric ratio of the casing = V1 / V2
• P1: the pressure prevailing in the crankcase when the piston is in top dead center
• P2: the pressure prevailing in the crankcase when the piston is in bottom dead center
• P0: the pressure prevailing in the crankcase when the piston is in bottom dead center and the engine is running gas cut
• Cp: 5/2 R = 5 cal
• Cv: 3/2 R = 3 cal
• T1: the temperature prevailing in the crankcase when the piston is in top dead center (hot engine) = ambient temperature
• T2: the temperature prevailing in the crankcase when the piston is in bottom dead center (hot engine) We have
  

From where:

• Cv log T + R log V = Cte
• Ou T^{3/2 R} . V^R = cte
• Ou T^3/2 V = cte
• Donc : T1^3/2. V1 = T2^3/2.V2
• Or ,
  
• Donc:
  
• 

Integrating:

• Cv log T + R log V = Cte
• Or T ^{3/2 R.} V ^R = side
• Or T ^3/2 V = side
• So: T1 ^3/2 . V1 = T2 ^3/2. V2
• Gold ,
  
• So:
  
• 

So the temperature always rises by the same proportion, whatever the pressure P1, that is to say whatever the operating conditions.

• Donc: P2 = H P1 avec H = constante
• R T1 Or ,
  
  avec T1, R, V1 constants
• Donc:
  
  où n est le nombre de moles de gaz absorbé H R T1 = cte si on suppose T1 constant. V1

Then applying the relation PV = n RT, we have:

• So: P2 = H P1 with H = constant
• R T1 Gold,
  
  with constant T1, R, V1
• So:
  
  where n is the number of moles of gas absorbed HR T1 = cte if we assume T1 constant. V1

So P2 is indeed directly proportional to the amount of gas absorbed.

doit être légèrement modifiée pour tenir compte de la chaleur cédée par le piston au gaz qu'il comprime dans le carter.It should be noted that the constant

must be slightly modified to take into account the heat given off by the gas piston which it compresses in the crankcase.

The injection device 10 according to the invention is adjusted by choosing the spring stress 15 and the active surface of the movable wall 21 so that, for a maximum value of the pressure in the precompression housing 3, the wall mobile 21 compresses the spring 15 so that the piston 20 causes the suction into the fuel chamber 13 of a dose of fuel which corresponds to a maximum opening of the gases. The adjustment is then made by adjusting the tension of the spring 15 using the screw 42 so that the force exerted by the spring 15 on the movable wall 21 exactly balances the pressure of the movable wall when the gases are cut. . The displacement of the piston 20 is then proportional to the pressure prevailing in the casing 3 and the dose of fuel injected is proportional to this pressure, that is to say to the quantity of air absorbed. Thanks to the nozzle 18 disposed in the communication pipe 17 connecting the chamber 11 to the air intake pipe 6, the dose of fuel injected is corrected as a function of the vacuum prevailing in said air intake pipe 6, which allows a possibility of correction of the richness of the fuel mixture and a better functioning of the engine at idle.

It is understood that the injector 9 must be chosen so that it can inject the entire dose of fuel delivered by the injection device 10 into the cylinder when the piston 2 of the engine masks the injector 9 in the cylinder.

To allow manual bleeding of the injection pump, the preload adjusting screw 42 is advantageously associated with a button 40 armed with a return spring 43 as shown in FIG. 3. The button 40 is integral with a rod 41 which passes axially through the adjusting screw 42. By pressing the button 40, the end of the rod 41 comes to bear on the support 22 against which presses the injection piston 20 and it displaces it in order to empty the fuel chamber 13.

FIG. 4 illustrates a preferred embodiment in which the injection device 10 is integrated into the engine cylinder in a compact construction. The body of the injection device 10 has a generally cylindrical projection 45 forming a housing for the injector 9 and for the discharge valve 27 which are arranged coaxially in alignment with the longitudinal axis of the injection piston 20. The projection 45 externally comprises a thread 46 for mounting a sleeve 47 intended to fix the injection device 10 comprising the injector 9 on the cylinder 1 of the engine in a substantially radial direction. This integrated embodiment greatly simplifies assembly since it eliminates the fittings and also significantly increases the thermal flywheel of the injector.

Figures 5 and 6 illustrate a particularly advantageous alternative embodiment. In this embodiment, the injection device 10 incorporates the booster pump 30. This consists of a compact block screwed below the body of the injection device 10 by means of screws 38 (FIG. 5). The underside of the body 10 has a cavity 31 into which opens a conduit 37 which communicates with the air intake duct of the casing 19. The body 30 of the booster pump is formed with a compartment 33 which faces to the cavity 31 and is separated from it by a flexible membrane 32. The compartment 33 communicates with the fuel supply line 28 by a conduit 34 and an intake valve 35 closed by a movable tongue cut out from the flexible membrane 32.

This membrane also has a cutout forming a tongue which closes a discharge valve 36 communicating with the conduit 25 intended to bring the fuel into the fuel chamber 13 of the injection device 10.

The functioning of the booster pump is conditioned by the displacement of the flexible membrane 32 in response to the pressure prevailing in the air compartment 31, which pressure is linked to the pressure prevailing in the casing 3. A decrease in pressure causes the opening of the intake valve 35 by detaching the movable tongue of the flexible membrane 32 downwards, that is to say towards the compartment 33, and fuel from the tank is then admitted into the compartment 33. An increase of air pressure causes the discharge valve 36 to open by detaching the tongue of the flexible membrane 32 upwards, and fuel is then discharged from the compartment 33 towards the suction valve 25 of the injection device 10.

The injection device according to the invention makes it possible to obtain an appreciable reduction in the fuel consumption of a two-stroke engine and, moreover, a remarkable reduction in pollution. These results have been demonstrated in the test stand rollers of a two-stroke engine cooling air of 250 cm ³ capacity. This engine was equipped with an injection device as described above provided with a movable wall 50 mm in diameter with a spring preload of 17 kg per millimeter of deflection. The fuel consumption and the CO content of the exhaust gases were measured at a speed of 90 km per hour with and without the injection device according to the invention.

• Consommation:
  • . avec carburateur 4,625 litres/100 km
  • . avec le dispositif d'injection 3,3 litres/100 km soit une économie de 28,6 %
• Teneur en CO
  • . avec carburateur 8,3 %
  • . avec le dispositif d'injection 0,75% soit un gain de 91 %.

The measurements gave:

• Consumption:
  • . with 4,625 liter / 100 km carburetor
  • . with the 3.3 liter / 100 km injection device, a saving of 28.6%
• CO content
  • . with 8.3% carburetor
  • . with the injection device 0.75%, i.e. a gain of 91%.

It was said above that the injector is chosen so that it can inject the entire dose of fuel delivered by the injection device into the cylinder when the engine piston masks the injector in the cylinder . Advantageously, the injector 9 is fixed in an injector holder 51 (FIG. 2) so as to open radially into the cylinder 1 at a certain distance from the top dead center and set back from the bore, thus providing a small cavity 52 in the bore. This arrangement has the effect of ensuring that the fuel is sprayed onto the sweeping stream (s) and that the fuel injection, rigorously metered by the injection device 10 as described above, is completed when the piston 2 goes into view of the injector 9. A ring 53 and a sleeve 54 made of insulating material, for example teflon, thermally insulate the injector holder 51 from the wall of the cylinder 1 so as to protect the injector against excessive heating by conduction of the heat of the cylinder.

By making the nozzle 18 (FIG. 2) which connects the chamber 11 of the injection device 10 to the air intake pipe 5, with variable opening, it is possible to adjust the back pressure prevailing in the chamber 11 depending on the depression in the pipe 5 and correct the air / fuel ratio so as to improve combustion.

FIG. 7 illustrates an alternative embodiment of the injection device 10 shown in FIG. 2. This alternative aims to adjust the quantity of petrol injected as a function of the accelerator control.

A first way of controlling the supply pressure of the injection pump, as a function of the throttle control, is to install an adjustable nozzle form 55 in the channel 19 between the precompression housing 3 of the engine and the chamber 12. The opening of this nozzle can be controlled by the engine speed or by the accelerator control or by both. The presence of this nozzle creates a pressure difference between the crankcase and the chamber 12.

Suppose the engine is supplied with air constantly and independently of the throttle. In this case, the quantity injected can only be acted on by direct action of the gas control on the injection pump.

By closing the adjustable nozzle 55 shown in the form of a rotary plug in FIG. 7, the pressure of the casing 3 is prevented from reaching the chamber 12 and therefore by acting on the membrane 21, determining a movement of the piston of the injection pump. By fully opening this plug 55, a maximum action of the pressure of the casing on the membrane 21 is allowed and the quantity injected is maximum.

Any intermediate position of the plug 55 determines an intermediate quantity of fuel injected between zero and the maximum.

The precompression cycle in the casing 3 then only serves to activate the pump and to synchronize it with the sweeping of the motor. First, a so-called "stratified" combustion is obtained, with excess air, the injector creating a rich mixture near the spark plug which initiates combustion.

To allow rapid emptying of the compression chamber 12 towards the precompression housing 3 at the time of injection, the variable nozzle 55 may be doubled with a conduit 56 provided with a valve 57 allowing easy passage of the air from the compression chamber 12 to the casing 3 and blocking the air passage from the casing 3 to the chamber 12. This emptying of the compression chamber 12 to the casing 3 determines the injection time: by delaying this emptying, the injection time in the cycle is delayed.

Another way of adjusting the quantity of petrol injected by means of the gas control is to link the rotation of the screw 42 to the gas control. By tightening the screw, we tighten the spring and we decrease the quantity injected of the volume: V = Surface of the injection piston x Pitch of the screw 42 x tightening angle (in degrees), divided by 360.

FIG. 8 illustrates another variant embodiment aiming to accelerate the injection process in a fast engine by using the pulse of the exhaust gases to increase the pressure supplied by the injection device 10 to the injector 9.

The chamber 11 communicates exclusively with the exhaust pipe 8 via a calibrated channel 58. The pressure wave of the exhaust then acts on the membrane 21 at the time of injection and is added to the force of the spring 15 to increase the injection pressure. To avoid deterioration of the membrane 21 by the heat of the exhaust gases, it is possible to interpose a protective flange 59 which receives the pressure of the exhaust gases.

Claims (12)

1. Fuel injection device for two-stroke precompression engine in the crankcase,
characterized by a pump body (10) comprising a first chamber (11) in communication (14) with the external atmosphere and communicating with the air intake pipe (5) or the gas exhaust pipe (8 ), a second chamber (12) communicating (19) with the precompression casing (3) of the engine, said second chamber being separated from the first chamber (11) by a movable wall (21) integral with a support (22) held by a spring (15); a piston (20) pressing on the support (22) and sliding axially in a channel (23) when the movable wall (21) moves the support (22); and a third chamber (13) having an opening (25) communicating with the fuel inlet pipe and an opening (27) connected by a pipe (28) to a fuel injector (9) opening into the engine cylinder in a substantially radial direction so as to spray the fuel onto the sweeping stream or streams, the third chamber being arranged at the end of said channel (23) so that when the movable wall (21) moves the support (22), one end of the piston (20) moves by varying the pressure prevailing in the third chamber (13) in order to d '' suck a dose of fuel when the movable wall (21) compresses the spring (15) and discharge a dose of fuel to the injector (9) when the spring (15) is relaxed. 2. Device according to claim 1, comprising means (42) for adjusting the stress of the preload spring (15). 3. Device according to claim 1 or 2, further comprising a member (40, 41, 43) which can be moved manually, arranged so that, when it is actuated, its end moves said support (22) against which the piston (20) rests so that the movement of said piston (20) causes the fuel chamber (13) to be drained . 4. Device according to claim 1, wherein the injector (9) opens into the cylinder (1) set back from the bore so as to form a cavity (52) in said bore. 5. Device according to claim 1 or 4, wherein the injector (9) passes through the engine cylinder in a sleeve (53, 54) of thermal insulating material. 6. Device according to claim 1, characterized in that the pump body (10) has a projection (45) of generally cylindrical shape forming a housing for the injector (9) and a discharge valve (27) arranged coaxially in alignment with the longitudinal axis of the injection piston (20), said projection (45) comprising means (46, 47) for fixing the injection device (10) on the engine cylinder in a substantially radial direction. 7. Device according to claim 1 or 6, characterized in that the communication conduit (19) between the casing (3) of the engine and the second chamber (12) of the injection device further communicates with a first compartment (31 ) separated from a second compartment (33) by a flexible membrane (32), the second compartment (33) communicating with the fuel supply line from the tank by an intake valve (35) which opens when the flexible membrane (32) is stretched by a depression prevailing in the first compartment (31) and of the second compartment also communicating with the fuel supply pipe (25) towards the fuel chamber (13) of the injection device by a discharge valve (36) which opens when the flexible membrane (32) comes off under the effect of the pressure prevailing in the first compartment (31). 8. Device according to claim 7, characterized in that the first compartment (31) is constituted by a cavity formed in the underside of the injection pump body (10), the second compartment (33) being constituted by a cavity formed in a second block (30), the second block being screwed under the injection pump body (10) with the interposition of a flexible membrane (32) to separate the cavities forming said first and second compartments (31, 33) , said flexible membrane cooperating with the inlet and outlet valves. 9. Fuel injection device according to claim 1, characterized in that said first chamber (11) is in communication with the air intake pipe (5) by a nozzle (18) with variable opening. 10. Device according to claim 1, characterized by means' (55) regulating the pressure in said second chamber (12) from the pressure in the housing (3) according to the accelerator control and thus allowing control direct of the quantity of fuel injected as a function of the accelerator; said means being placed in the channel (19) and doubled with a conduit (56) between said second chamber (12) and the casing (3), which conduit is provided with a valve (57) allowing the passage of the air from the chamber (12) to the housing (3) but blocking the passage of air from the housing (3) to the second chamber (12). 11. Device according to claim 1, comprising means (42) controlled by the throttle to adjust the stress of the spring (15). 12. Device according to claim 1, wherein the first chamber (11) is exclusively in communication (58) with the exhaust pipe (8) of the engine, a flange (59) protecting the movable wall (21) from heat exhaust gases.

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