Technical Field of the invention

The present invention is comprised in the technical field of injection systems for gasoline combustion engines, and is especially applicable to gasoline combustion engines of the type which are used in vehicles such as motorcycles with a reduced cylinder capacity, mopeds and microcars, and in small stationary or transportable apparatuses such as electric generators, motor pumps, capstans, etc.

Background of the Invention

Currently, electronic injection systems for motorcycles with a four-stroke combustion engine and other apparatuses are essentially an adaptation of the systems applied in automotive vehicles and contain the same mechanical, electromechanical and electronic components. The injection systems used are generally of the indirect injection type, i.e., the gasoline is injected between the throttle valve and the gas intake valve of the engine.

Thus, for example, a typical electronic injection system for a high-medium power motorcycle usually comprises the following components for controlling the amount of intake gases, at the driver's will, measuring the admitted air flow and supplying the suitable amount of fuel for a correct operation of the engine:

- a throttle body, which frequently contains the injector distributing the gasoline downstream of the throttle valve or of the gas control valve and the sensor of its angular position which provides information of the load of the engine at any rotational speed;

- an electric pump in side the gasoline tank usually with a delivery of 20-35 l/h, 2-3 bar of pressure and a consumption of 1 .5A-3A at 12V, and driven by a direct current electric motor and with an internal gear pumping element or with a turbine, this latter pumping element not being self-priming therefore the pump needs to be located in the lower inner area of the gasoline tank;

- a 2-3 bar pressure regulator, with membrane, which regulates the pressure downstream of the throttle and which is normally located inside the gasoline tank to which it returns the excess gasoline flow;

- an electric injector which, when it is activated, electrically opens the obturator such that the injected gasoline flow depends on the outlet holes, on the difference of pressure on both sides of said holes, controlled by the pressure regulator, and on the electric activation time of the injector, the gasoline flow distributed by the injector depending, for a given injection system, only on the activation time of the injector;

- intake air and engine temperature sensors.

- an intake absolute pressure sensor which with the intake temperature signal allows calculating the intake density, which by the cylinder capacity gives the mass of admitted air and supplying in a suitable proportion the required gasoline; this sensor is only used in the most sophisticated injection, speed-density, systems, whereas in the most elementary systems the throttle-speed (a-n) angle is used, the speed and the phase being a piece of information arriving from an inductive sensors detecting the pitch of the teeth of a phonic wheel integral with the crankshaft;

- an auxiliary air inlet valve ("bypass") which is an electromechanical element controlling, by means of an electric activation, an air flow in parallel with the throttle to obtain an idling prefixed rotational speed at any temperature.

- an electronic control unit or central unit which processes the signals of the sensors and its memory and program data steers the actuators, the injector, the bypass and the gasoline pump to enable a correct operation of the engine.

Figure 1 shows a feed system of the state of the art for a four-stroke gasoline combustion engine (6) comprising a carburetor (4) conventionally arranged between an air filter (3), to which the carburetor (4) is connected by means of an air feed conduit

(5), and the intake elbow (7) of the engine (6), and connected through a feed tube (8) to a manual or automatic outlet valve (2) of the gasoline tank (1 ). The intake elbow (7) is connected to the intake (6a) of the engine (6) in which an intake valve (6b) is also conventionally arranged.

The possibilities offered by the electronic control allow optimizing the emissions of the engine by incorporating other components to the system such as ignition, the trivalent catalyst and Lambda probe, EGR valve and others.

The previously described injection system is currently used in high and medium power motorcycles, in which the cost of the injection system has a certain proportion with respect to the total cost of the vehicle. However, for low power motorcycles, about 50cc, commonly called mopeds, with an extremely low price, or for other low power four-stroke gasoline engines used for the applications of the type of those mentioned in the previous section, the previously described injection system becomes a very significant fraction of the total cost of the vehicle or apparatus. Therefore, low power combustion engines are currently fed by means of a carburetor. Nevertheless, given that the rules regulating their polluting emissions progress rapidly to more restrictive limits which engines provided with a carburetor will not be able to comply with, the electronic control of both the fuel feed and the anti-polluting components will be completely necessary in the near future.

To install a "classic" injection system of the type described above, in an engine fed with a carburetor, the modifications on the vehicle and apparatus would be rather substantial, given that it is necessary to:

modify the electric system of the vehicle by increasing the alternator power and the capacity of the battery to operate with a gasoline pump continuously consuming >2A to 12 V;

- install a frame inside the gasoline tank in which the level sensor, the gasoline pump and the gasoline pressure regulator with the tube connecting it with the intake manifold are fixed;

install a device deactivating the pump in the event of a collision when the engine stops to prevent fires, this device being able to have an inertial nature or a nature of steering the pump in the electronic central unit.

Therefore, these modifications would be complicated and expensive, both when first manufacturing the vehicles and apparatuses with an injection system of this type and when substituting the already existing carburetor feed system of a conventional vehicle or apparatus with this injection system.

Description of the Invention

The object of the present invention is to overcome the aforementioned drawbacks of the state of the art by means of an injection system for small gasoline engines defined in the attached independent claims.

Specifically, the electronic injection device for small gasoline engines of the invention comprises a throttle valve body, which internally has an air passage channel with an air inlet orifice and a mixture outlet orifice, a throttle valve being housed inside said channel. An electric gasoline injector is assembled in the body of the valve.

The device is characterized in that it comprises a sonic nozzle, with one or two throats, coupled with the outlet of the restriction of said electric gasoline injector, in a manner coaxial with the longitudinal axis of the restriction of the injector. The mentioned coupling between the nozzle and the restriction assures the perfect coaxial alignment between both elements, and therefore assures the suitable spraying of the gasoline.

The sonic nozzle is arranged to project a mixture of air and gasoline inside the channel downstream of the throttle valve which is added to the rest of the intake air.

An air inlet conduit is formed inside the body of the valve and arranged parallel to the longitudinal axis of the body of the valve, said conduit having an air inlet located upstream of the valve, and said conduit having an outlet which ends in an injection chamber supplying air to the inlet of the nozzle through openings allowing the air flow when said nozzle is coupled with the restriction of the injector.

One of the relevant features of the injection system of the invention consists of the implementation of a "doubly indirect" injection since the restriction of the injector discharges at the pressure of the injection chamber and then the gasoline passes to the intake conduit through the nozzle, a configuration which allows using the described injector with a low level of investments for its manufacture as well as reducing the electric consumption of the injection system.

Another consequence of this configuration is that it operates with an essentially cost-effective pressure regulator with sufficient functionality, since a variation of regulated pressure of 1 % added to a variation of the output of the pump of 15% causes a total variation of the injected gasoline flow of 1 %. This effect is also assured by the fact of using a 9V voltage regulator in the central unit to power the pump, thereby reducing the dispersion of its output and that of recirculation in the pressure regulator, as well as simplifying the fine-tuning of the application of this injection system in an engine, since it virtually eliminates the correction of the injection time by the variation of the voltage of the battery.

The present invention solves the drawbacks of the state of the art by providing a low-cost injection system with an excellent functionality and which furthermore allows the substitution of the carburetor with the gasoline injection system according to the present invention in a direct manner without needing mechanical or electric modifications both in relation to the design of vehicles or apparatuses manufactured for the first time and at the level of re-equipping already existing vehicles and apparatuses provided with carburetors, since it is enough to:

- substitute the gasoline valve in the outlet of the gasoline tank with a small gasoline pump of low pressure of, for example, 0.4-0.7 bar and consumption of, for example, 0.2A-0.4A at 9V powered from the electronic central unit; substituting the carburetor with a throttle body incorporating the injector, air bypass, pressure regulator with an obturator and spring in the return to the gasoline tank, sensor of the angular position of the throttle, engine/intake temperature sensor and, optionally, the electronic control central unit;

- only connect the electric power supply controlled by the ignition key and the ignition activation signal, normally an inductive sensor detecting the passage of a magnet integral with a wheel anchored in the shaft of the crankshaft, as a speed signal, therefore the phonic wheel is not necessary.

On the other hand, in a combustion engine with a low cylinder capacity, it is also not necessary to enhance the electric system since the maximum consumption of the injection system does not exceed 0.5 A at the maximum engine rotation speed, a figure less than the electric power consumption of the automatic starter device of the carburetor which usually exceeds 1 A, at 12 V. Finally, in the event of a collision, overturn, etc. with the stop of the engine experienced by the vehicle or of the apparatus, the pump stops working due to the absence of electronic central unit activation signal, therefore there is no fire risk and no need to incorporate other devices frequently used to prevent this risk.

If the negative pressure under throttle is greater than 0.1 bar, the injection system of the invention achieves that the difference of speed between the gasoline stream and the air flow is more than 300 m/s, inside the nozzle, which causes an intense nebulization of the injected gasoline stream. This is very beneficial for a good combustion of the air/gasoline mixture, since it reduces both the emissions of

CO and HC as well as the fuel consumption.

Negative pressures greater than 0.01 -0.02 bar occur in almost the entire operation field of four-stroke engines with sufficient nebulization quality of the gasoline, particularly one-cylinder engines of up to 150cc in relation to those in which the application of the present invention is particularly useful. Naturally, operating in stationary engines that are twice as slow, it can be applied to cylinder capacities that are twice as large without modifying the performance of the components of this gasoline injection system, an application which is highly adapted economically and functionally to this invention. Although two-stroke engines work with lower negative pressure in the intake manifold than four-stroke engines, it is also possible to apply this system to them with a suitable sizing of the parameters of the nozzle, reducing the unwanted effects of the intake-exhaust short circuit by operating with very poor mixtures and with programmed algorithms of fuel cut-off, of the damping of the idle return (dash-pot) and others.

According to that indicated above, inside the nozzle the relative speed of the gasoline with respect to the air is greater than 300 m/s, in almost the entire field of operation of the engine from the idle to areas close to full gas. In the case of a classic injection with a pump pressure of 3 bar this relative speed is of the order of 28 m/s with an electric consumption of about 2-3 A at 12V, i.e., with a minimum consumption of 24 W. The average electric consumption of the system proposed by the present invention is of 0.3A at 9V, i.e., about 3 W, i.e., the present invention has the advantage of a lower electric power consumption. On the other hand, the extremely high speeds with respect to air reached by the gasoline in the nozzle the present invention has the considerable advantage that, due to the effect of the shock wave when the engine works under a partial load, a high mixture homogeneity is generated which allows operating in a wide range of very poor air-gasoline ratios without problems of failures of combustion and low emission of unburnt hydrocarbons and carbon monoxide.

It must also be taken into account that for 125cc-150cc motorcycles the entire test of polluting emissions, of EURO 3 type, is carried out in conditions of negative pressure under throttle greater than 0.1 bar, therefore the injection system according to the present invention assures, in this type of test, a very satisfactory result of emissions in a wide field of fine-tuning the injection program.

Although in the system according to the present invention the pressure of the injection chamber, or area of entrance of air to the nozzle, varies slightly from one point of operation of the engine to another due to the pressure drop of the air filter, variable with the engine intake air flow, and acoustic effects in the intake of the engine, these variations of pressure only minimally affect the gasoline flow of the injector, since the jump of pressures through the restriction of the injector is modified, but they are repetitive at each point of operation of the engine and their effect is corrected upon assigning, in the program of the central unit, the injection time for obtaining the desired air-fuel ratio.

Although the present invention is especially useful for engines with a small cylinder capacity, as is inferred from the previous description, the developed injection system can also be implemented in combustion engines with various cylinder capacities and numbers of cylinders, it only being necessary for that purpose to adjust the output of the pump and pressure regulator to the maximum cylinder capacity and speed of the engine and the output of the injectors to the cylinder capacity of each cylinder, as well as the throats of the nozzles, associated with each injector, to the air flow of the idle.

For 50cc four-stroke engines, the injection system according to the present invention formed by the pump of low pressure, injector, injection chamber and convergent-divergent nozzle with two throats, coaxially coupled to the restriction, allows the operation with restriction of the injector of the order of 0.4-0.5 mm in diameter if the pressure determined by the pressure regulator is approximately 0.4-0.6 bar. In turn, when the system is applied to engines with a higher cylinder capacity, a restriction part of the injector of a larger diameter can be provided, or the pressure can be increased to close to 0.8 bar, maintaining the mentioned diameter of the restriction part.

This means that expensive series spark eroding processes for calibrating the restriction part of the injector are not needed and the precise methods of machining with successive bits are sufficiently suitable, which gives rise to a reduction amortization costs. This is particularly interesting for carburetor factories which already have this technology, although in no case is it a technical limitation and emergent technology precision drilling processes such as laser or the series spark eroding itself can be used if the evolution in terms of costs and process capacity makes them economically feasible, in which case the diameter of the restriction part would be smaller and the injection pressure higher, for one and the same engine. Nevertheless, one of the contributions of this invention consists of operating with low injection pressure in order to be able to use diameters of restriction parts of an injector made with a classic machining process with special lathes.

As inferred from the above, the injection system according to the present invention has, compared to conventional injection systems, a lower cost. This is due to the fact that investments in high-technology productive processes such as series spark eroding or precision grinding machines, as regards the process for manufacturing the injector the parts of which are obtained, for this injection system, by lathe machining with easily obtainable tolerances and finishes, are not necessary. The assembly process can contemplate the unitary fine-tuning of the run of the obturator and the tension of its spring to obtain the specified gasoline flows, for assigned injection times, in the area of the idle and maximum power, operations which can be easily automated.

Likewise, in this injection system the gasoline pump has a lower cost in view of the fact that it operates with low pressure which can be, in engines with a small cylinder capacity, considerably less than one bar, therefore its components can be manufactured with process for injecting plastics adapted for this function, such pump being able to be of the turbine type or of the positive displacement type, the latter being either a gear or a centrifugal vane type.

Finally and according to that indicated above, the use of the injection system according to the present invention in a 50cc moped with a four-stroke gasoline engine which has experimentally proved to not have difficulties for starting and working at temperatures between -20 ⁵ C and +50 ⁵ C. Furthermore, this moped repeatedly reached emissions less than 50% of the limits established by the EURO

2 standard for each pollutant, without any loss of performance, without altering the electric system of the original moped or its fixed ignition system, which proved that the injection system conferred exceptional anti-polluting qualities to the engine. Description of the Drawings

To complement the description which is being made and for the purpose of aiding to better understand the features of the invention according to a preferred practical embodiment thereof, a set of drawings is attached as an integral part of said description in which the following has been depicted with an illustrative and non-limiting character:

Figure 1 is a schematic side elevational view of a carburetor feed system of the state of the art for a low power four-stroke gasoline engine, in which the injection system according to the present invention can be installed.

Figure 2 is a view similar to that of Figure 1 which includes the injection system of the present invention.

Figure 3 is a schematic side longitudinal section view of an electric injector according to the invention.

Figure 4 shows in the top drawing a side elevational view of a sprayer according to the invention formed by a nozzle with two throats coupled to a restricting part. The bottom drawing is a longitudinal cross-section view according to section line A-A of the top drawing.

Figure 5 shows in the top drawing a side elevational view of a sprayer according to the invention formed by a nozzle with a throat coupled to a restricting part. The bottom drawing is a longitudinal section view according to section line A-A of the top drawing.

Figure 6 is an enlarged and cross-section view of a detail of the sprayer assembled in the body of the throttle.

Figure 7 is a longitudinal section view showing the arrangement of the injection device of the invention.

Figure 8 is a schematic partial outer perspective view of the arrangement shown in Figure 7.

Preferred Embodiment of the Invention

Figure 2 shows an embodiment of the injection system of the present invention in substitution of the carburetor feed system shown in Figure 1 , interconnecting a throttle body (1 1 ) between the air filter (3) and the intake elbow (7), and substituting the outlet valve in the gasoline tank (1 ) with an electric gasoline pump (10). The injector (9) is incorporated in a throttle body (1 1 ) with an inner air passage (1 1 a) in which there is a throttle valve (12), and with an air inlet (1 1 b) connected to the air feed conduit (5) and a gasoline/air mixture outlet (1 1 c) connected to the feed elbow (7).

The gasoline pump (10) is located in the outlet of the gasoline tank (1 ) and its outlet is connected to the gas supply inlet (1 1 e) of the injector (9) through the feed tube (8) leading the gasoline to an annular chamber (1 1 d) in the throttle body (1 1 ), this annular chamber (1 1 d) being located communicated with gasoline inlet holes

(23) of the injector (9).

The injector (9) is arranged in the throttle body (1 1 ) such that, through a sonic nozzle (16), it injects gasoline to the inner air passage (1 1 a) of the throttle body (1 1 ) between the throttle valve (12) and the mixture outlet (1 1c), i.e., downstream of the valve (12) and it is connected, at its upper area, to a pressure regulator (13) through which non-injected gasoline passes, which gasoline is returned to the gasoline tank (1 ) through a return conduit (14) connected to the tank (1 ). The gasoline returned to the tank (1 ) entrains with it all the gasoline bubbles which may have been generated by the high temperatures of the environment of the engine even if the ambient temperature is abnormally high, such as above 50 ⁵ C.

Integral with or separated from the throttle body (1 1 ) there is arranged an electronic central unit (15) comprising a first feed inlet (15a), a second inlet (15b) connected to a rotational speed sensor (not shown in the figures) and a third inlet (15c) connected to a temperature sensor (15d). The rotational speed sensor is the same sensor used for the ignition. The sensor of the angular position of the throttle, necessary for knowing the load state of the engine, is not shown in the figure.

The air by-pass valve, controlled by the central unit, is not depicted in Figure

2.

The gasoline pump (10) is of low pressure, its typical operating regime being 0.4-0.7 bar with an output which multiples by several times the maximum gasoline consumption of the engine (6), and with an electricity consumption of 0.2A-0.4A at 9V. Given its limited performance with a total efficiency of approximately 0.04, the gasoline pump (10) can be manufactured with suitable plastic components and with a very low cost.

The gasoline pressure regulator (13) is assembled in the throttle body, and comprises a cylindrical cavity containing a non-deformable conical obturator (39) at its end, arranged to close against a coaxial circular hole (40) by the action of a compression spring (44) also coaxial with the obturator. The pressure regulator (13) ends in a chamber (41 ) through which it is communicated with inlet holes (23) of the injector (9) through a conduit (1 1 f).

The injector (9), depicted in detail in Figure 3, comprises a ferromagnetic obturator (17) in the form of a piston housed in an inner axial cavity (18b) of a nonmagnetic sleeve (18). At one of its ends, the obturator (17) has a housing (17a) in which there is inserted with interference a sphere (19) pressed, in a closed position of the injector (9), by a spring (20) located in a cylindrical axial chamber (17b) of the obturator (17), against the edge of a circular passage hole (18d) formed by a constriction (18a) of the sleeve (18). The edge of the passage hole (18d) is concave and has a curvature complementary to the curvature of the sphere (19) which projects from the housing (17a) and which is pressed against said edge.

This complementary configuration can be formed, for example, by impacting, with a controlled load, a sphere of the same diameter as the sphere (19) on a sharp edge with sides at about 127 ⁵ , one of which is the generatrix of a cone tangent to the sphere at 80% of its diameter. The gasoline inlet holes (23) end in an inlet chamber (17c) located between the sleeve (18) and the end part of the ferromagnetic obturator (17) which is located close to said holes (23).

The obturator (17) is the mobile part of a magnetic circuit of a solenoid such that when the coil (21 ) surrounding a part of the sleeve (18) and contained in the casing (9a) is activated by means of an electric signal coming from the central unit (15), the ferromagnetic obturator (17) moves, overcoming the force of the spring (20), from its closed position shown in Figure 3 in which it presses the sphere (19) against the passage hole (18d) of the constriction (18a) towards an open position, performing a run (42), for example, of the order of 0.05 mm, in a direction opposite to the constriction (18a) such that the sphere (19) is separated from the passage hole (18d) of the constriction (18a).

In that open position, the gasoline supplied by the gasoline pump (10), after passing through the filter (22) and through the inlet holes (23) in the form of radial boreholes located in the sleeve (18), traverses the obturation area formed by the constriction (18d) and passes through the mouth (18c).

A threaded cylindrical part (25) forming part of the magnetic circuit in which the obturator (17) is supported when it completes its run, establishes the path of the obturator which can be regulated from the outside and is blocked by the action of two sealing O-rings (26), one of which eliminates, by axial compression, the axial play of the thread. In turn, the cylindrical part (25) internally houses in a coaxial manner a threaded cylinder (27), the first end of which contacts the spring (20) and the rotation of which in a first direction presses the spring (20) whereas its rotation in the opposite direction detensions the spring (20), which allows regulating and blocking the tension of the spring (20) of the obturator (17) additionally to the cylindrical part. This second cylindrical part (27) is blocked by the action of the O-rings (26'). With this mechanism the flow of the injector can be regulated at the specified values in its entire field of action with very restricted tolerances, eliminating the effects of the possible variations of flow capacity of the obturation area and of the final restriction part. The two threaded cylinders can subsequently be definitively blocked by providing them with a plastic resin in the rear cavity (28) made in a ferromagnetic sleeve (43) axially housed in the injector (9).

The present invention comprises a sprayer (33) shown in Figure 4, the function of which is to spray the injected gasoline coming from the injector (9). This sprayer consists of the sonic nozzle (16) with two throats and of a restriction (24), both elements being coaxially coupled to one another. More specifically, the restriction (24) is coupled with the inlet (16 a) of the nozzle (16), for which the nozzle has two half rounds (31 , 3Γ) inserted and elastically retained in a cavity (32) of the restriction (24) due to the elastic deformation thereof.

The restriction (24) is formed to be inserted inside the mouth (18c) of the injector (9), assuring the perfect axial alignment between the restriction and the throats of the nozzle. The restriction (24) furthermore has a narrowing (24a) for the passage of gasoline, the function of which is that of converting the pressure to which the gasoline is subjected into gasoline speed and by the effect of pressure drop, controlling the amount of injected gasoline when the injector is open.

Between said half rounds (31 ,31 ^' ) there are defined two diametrically opposite air inlets (34,34 ^' ), for the entrance of air in the nozzle from the injection chamber (29) and through the channel (30) coming from upstream with respect to the throttle.

The coupled injector and the sprayer can be seen assembled in the body of the valve in Figure 6, in which the outlet of the nozzle (16b) discharges in the intake conduit downstream of the throttle (12). It is observed in more detail how the channel (30) ends in the injection chamber (29), from which the air passes into the nozzle through the air inlets (34,34 ^' ).

Figures 7 and 8 show the circuits and fluidic-hydric components located in the throttle body (1 1 ). The gasoline inlet (1 1 e), coming from the pump, which connects with the radial holes of the injector, traverses its obturation area and is introduced by the restriction (24) of the sprayer from which it exits in the form of a stream directed with precision to the center of the throats of the nozzle (16). The conduit (30) provides air, coming from upstream of the throttle, to a transverse cylindrical cavity or injection chamber (29), at a pressure which is virtually equal to atmospheric pressure, and enters the nozzle (16) through its openings (34,34 ^' ). With negative pressures under throttle greater than approximately 0.1 bar, the throats of the nozzle reach the speed of sound and between them the speed of the air is supersonic. The speed of the air in the area comprised between the second throat and a normal shock wave which is formed in the divergent conduit of the nozzle is also supersonic, this area being larger the greater the negative pressure under throttle.

For a gasoline pressure established by the pressure regulator (13) of 0.4 bar, the speed of the gasoline stream coming from the restriction (24) of the sprayer is of about 10 m/s and the speed of air, in the same direction as that of the gasoline, being greater than 340 m/s in the entire area of the nozzle comprised between the first throat and the shock wave, the speed of the air with respect to the gasoline is greater than 300 m/s in said area, with the negative pressure under throttle being equal to or greater than the one mentioned above. This relative speed causes a very fine nebulization of the gasoline at the outlet of the nozzle which, mixed with the intake air generates a very homogeneous mixture which allows considerably reducing the emissions of CO and unburnt hydrocarbons as well as the gasoline consumption, feeding the engine with considerably poor mixtures and without problems of driving on roads.

For lower negative pressures of the order of 0.01 -0.02 bar, speeds of air close to 150 m/s are reached in the area of the two throats of the nozzle, sufficient to generate a good nebulization of the gasoline. In the case of a conventional injection as has been described at the beginning of this specification, the relative speed is of the order of 28 m/s, considerably less than the case of this invention.

The need for the sprayer (33), located between the outlet of the injector and the intake conduit downstream of the throttle, is justified by the convenience of the gasoline stream coming from the hole (24 a) of the restriction (24) not touching the inner walls of the nozzle, so that it is not decanted therein.

In an embodiment, for a 4-stroke 50 cc moped, it is established that the diameter of the gasoline stream, by assimilating it to the diameter of the restriction, allows for a circular crown of passage through the first throat of 0.2 mm in thickness, i.e., of difference of radii. With a configuration of the sprayer such as the one described, it is possible to manufacture its two components with current mass- production machining equipment, and therefore with normal manufacturing tolerances and economic criteria, assuring a sufficient concentricity between the gasoline stream and the throats of the nozzle and therefore a good nebulization of th e gasoline for each injection system designed and manufactured according to the description of this invention.

As can be seen in Figures 6 and 7, once the gasoline has passed through restriction (24) it is discharged at high speed in the form of a stream to a conical cavity (16c) formed at the inlet of the nozzle (16) and through the grooves of which there enters air coming from a cylindrical cavity made in the throttle body (1 1 ), which forms the injection chamber (29) of a small volume which is at atmospheric pressure or at a slightly lower pressure and which receives the air through the conduit (30), the inlet (30a) of which is in the wall of the inner passage (1 1 a) of the throttle body (1 1 ) between the air inlet (1 1 b) and the throttle (12) and which ends in the injection chamber (29).

The process for spraying droplets of liquid inside a gas stream is known. The average diameter of the droplets resulting from said spraying is smaller the larger the relative speed of the initial droplets of liquid with respect to the air. The time necessary for this process is proportional to the initial diameter of the droplets and inversely proportional to the mentioned relative speed. On the other hand, the diameter of the initial droplets is a certain fraction of the diameter of the gasoline stream, i.e., of the diameter of the restriction, since they come from the fractioning of said stream at a certain frequency. Given that the diameter of the restriction, and therefore that of the initial droplets, is relatively large as a consequence of the criterion of low electric consumption and easy manufacture of the restriction, it is very convenient to increase the transit time of the gasoline in a field of high speeds of air.

A solution provided by this patent against this approach is the nozzle (16) with two throats of Figure 4, it comprises a nozzle inlet (16c) and an ejection outlet

(16b) through which the gasoline is injected to an area located between the throttle (12) and the mixture outlet (1 1 c) of the inner air passage (1 1 a) of the throttle body. The nozzle inlet (16a) and the ejection outlet (16b) are communicated by an axial inner passage through which the gasoline stream passes and which comprises a convergent frustoconical segment (16c) into which the gasoline stream enters from the nozzle inlet (16a) and which narrows towards a first throat (35) in which the axial inner passage has its minimum cross-section. This throat is sized to block its air flow with 50-70% of the air flow of the idle. After this throat there is an increase of cross- section in a cylindrical segment (36) which narrows according to a frustoconical segment (38) finished in a second throat (37). A divergent frustoconical or stepped segment (16e) is arranged after the second throat (37) ending in the ejection outlet (16b).

The convergent frustoconical segment (16c) narrows by about 10-15 ^Q in the direction towards the first throat (35). The following cylindrical segment (36) has a section 15-30% greater than the first throat (35). The second throat (37) has a section 5-10% greater than the first throat (35). The divergent frustoconical segment

(16e) widens by about 2-5 ⁵ from the throat (16d) in the direction towards the ejection outlet (16b) of the nozzle (16). The divergent segment (16e) can be formed, as illustrated in the embodiment shown in the figures, by stepped segments with different diameters with inner edges (16f) aligned in a cone which successively form the mentioned widening towards the ejection outlet (16b). Said stepped segments allow reusing for the spraying most of the gasoline decanted in the inner wall of the divergent segment of the nozzle.

Another alternative proposed by this patent is injecting the gasoline into the intake through a nozzle with one throat according to Figure 5. Inserted, as has been previously described, in a cavity (32) of the restriction of the injector to form the sprayer, its geometric configuration arises from the nozzle with two throats by eliminating the cylindrical central segment (36) and sizing the resulting single throat (35) according to the described criteria. The divergent segment is formed by several stepped cylindrical cavities (161) such that they determine circular edges (16f), including that of the throat, aligned in a cone with a 2-5 ⁵ angle.

The nozzle with one throat is easier to manufacture than the nozzle with two throats but it is conceptually less efficient. In the nozzle with one throat, if the negative pressure under throttle is sufficient, supersonic speeds of air are generated from the throat until the shock wave in the divergent area, after which the speed is subsonic, the distance between the throat and the shock wave being greater the greater the negative pressure. In the nozzle with two throats, for the same negative pressure, the speed is supersonic from the first throat until the second throat, in which it becomes sonic and continues to be supersonic until the shock wave. It is evident that in the case of the nozzle with two throats the residence time of the gasoline in supersonic areas is much greater than in the case of the nozzle with one throat. According to the process for spraying the droplets of liquid inside a gas stream set forth above, the average size of the droplets will be smaller with the nozzle with two throats. For lower negative pressures, of the order of 0.01 bar, the comparative result is substantially equal but with subsonic speeds and lower spraying.

In addition to this argument, the EURO 2 emission control tests, on a 4- stroke 50 cc moped with various nozzle configurations, shows emissions of CO 20- 30% and a consumption 4-8% greater with the nozzle with one throat than with the nozzle with two throats, operating with considerably poorer mixtures than the stoichiometric mixture and without operation irregularity, differences which can be attributed to larger cycle-to-cycle richness variations with the nozzle with one throat. Summary of Features of this Injection System

The features of this injection system compared to the classic injection described at the beginning of this specification are set forth below:

- Lower cost of the injection system since investments in high-technology production processes such as precision grinding machines for manufacturing the injector or series spark eroding for its restriction are not needed.

- Lower cost of the gasoline pump due to operating at low pressure and therefore its parts can be manufactured with injected plastics adapted to their function, being able to be a turbine, gear or centrifugal vane pump.

- Lower cost of the pressure regulator due to having a linear configuration formed by a conical obturator closing on the sharp edge of a hole by the action of a spring, the regulation pressure being that determined by the force of the spring on the area of the hole.

- Without cost for adapting the vehicle or engine due to substituting the carburetor with this injection system in the aspect of mechanical modifications, need for other components or enhancing the electric system.

- Exceptional anti-polluting qualities compatible with satisfactory behavior on roads and performance.