WO2001009505A1

WO2001009505A1 - Direct injection system for internal combustion engines and method thereof

Info

Publication number: WO2001009505A1
Application number: PCT/IB2000/000776
Authority: WO
Inventors: Giuliano Cozzari
Original assignee: Giuliano Cozzari
Priority date: 1999-06-11
Filing date: 2000-06-13
Publication date: 2001-02-08
Also published as: EP1218634A1; AU4943600A

Abstract

A direct injection system for internal combustion engines, which system comprises means (19) for pumping fuel at a first pressure (P0) from a tank (18), electric driven injection means (11) directly associated to relevant combustion chambers (17), means (13) for applying a second pressure (P1) to the fuel supplied to said injection means (11), said second pressure (P1) being much higher than said first pressure (P0) and substantially prevailing with respect to a third pressure (P2) available in the combustion chamber (17), said means (13) for applying said second pressure (P1) to the fuel being located upstream the injection means (11). According to the present invention, means (12) are provided for takin g the third pressure (P2) available in the combustion chamber (17) and transmit it to means (21) for amplifying the third pressure (P2), which are comprised in the means (13) for applying the second pressure (P1), in order to generate said second pressure (P1).

Description

DIRECT INJECTION SYSTEM FOR INTERNAL COMBUSTION ENGINES AND METHOD THEREOF

DESCRIPTION

The present invention relates to a direct injection system for internal combustion engines, which system comprises means for pumping fuel at a first pressure from a tank, electric driven injection means directly associated to relevant combustion chambers, means for applying a second pressure to the fuel supplied to said injection means, said second pressure being much higher than said first pressure and substantially prevailing with respect to a third pressure taken from the combustion chamber and said means for applying said second pressure to the fuel being located upstream the injection means.

In particular, direct injection methods, such as GDI (Gasoline Direct Injection) are primarily featured by injector devices, which inject the fuel directly into the cylinder instead of mixing it with air in the intake manifold. Obviously, direct injection inside the cylinder requires application of a high pressure to the fuel, which should prevail on the high pressure available inside the cylinder. In general, existing direct injection systems employ a low pressure pump for conveying fuel to a high pressure pump from the tank. This electric operated high pressure pump is apt to exert pressures up to over 100 bar on the fuel. Therefore, the fuel is conveyed under high pressure to a manifold, also called fuel rail, which supplies the electromechanical injectors placed on each cylinder.

Such a system has some drawbacks. First of all, an expensive pump has to be provided for applying and managing the high pressure required. Moreover, said pump has to be power supplied, thus requiring a power take-off from the engine through a belt loop or a similar arrangement. This will imply constructive complications and a consequent lower engine efficiency.

However, another way for direct injection is to inject either during the compression stage or intake stage or during the same intake-compression cycle, so as to have three different conditions, i.e. low load, medium load and high load. It is the object of the present invention to solve the above drawbacks and provide a direct injection system for internal combustion engines and/or a method thereof, having a more efficient and improved performance with respect to existing solutions. In this frame it is the main object of the present invention to provide a direct injection system for internal combustion engines and/or a fuel injection method for internal combustion engines, which do not require a high pressure injection pump to be electric operated or through the energy taken off the engine.

A further object of the present invention is to provide a direct injection system for internal combustion engines and/or a fuel injection method for internal combustion engines, which allow injection in the combustion engine at least during intake and/or compression cycles. In order to achieve such aims, it is the object of the present invention to provide a direct injection system for internal combustion engines and/or a fuel injection method for internal combustion engines, incorporating the features of the annexed claims, which form an integral part of the description herein.

Further objects, features and advantages of the present invention will become apparent from the following detailed description and annexed drawings, which are supplied by way of non limiting example, wherein:

Figure 1 shows a basic schematics of a direct injection system for internal combustion engines according to the present invention;

Figure 2 shows a diagram of a first detail of the direct injection system for internal combustion engines according to the present invention;

Figure 3 shows a basic schematics of a first embodiment of the fuel injection system for internal combustion engines represented in figure 1 ; - Figure 3a shows a quality operation diagram of the fuel injection system represented in figure 3 ;

Figure 4 shows a basic schematics of a second embodiment of the fuel injection system for internal combustion engines represented in figure 1 ;

Figure 4a shows an operation diagram of the fuel injection system represented in figure 4. According to the present invention, in order to generate the fuel injection pressure, the fuel direct injection system for internal combustion engines is based on the principle of using the compression energy of the air contained in the cylinder into which fuel will be injected. through appropriate multiplying operations of said pressure and time modulation . In Figure 1 there is shown a basic schematics of a fuel injection system according to the present invention.

A fuel intake line 14 from a fuel tank 18 is shown, which is pressurized by a pump 19 at a first pressure PO. The fuel intake line 14 is provided with a one-way valve 16, then the fuel intake line 14 will reach the input of a pressurizer 13. The fuel intake line 14 will then exit the pressurizer 13 and feed an injector 1 1 , which injects the fuel into a cylinder 17. A pressure modulating device 30 is provided on the fuel intake line between the pressurizer 13 and injector 11, from which a fuel recirculating duct 31 is departing to the tank 18. The cylinder 17 has a pressure intake element 12 to take the air pressure contained in the cylinder 17, which is connected to an intake duct 15 connected on its other end to the pressurizer 13.

Operation of the injection system is as follows: the pump 19 will transfer fuel at a first pressure PO to the pressurizer 13. The pressurizer 13 receives a pressure P2 taken from the cylinder 17 by the pressure intake element 12 and intake duct 15, and transfers it according to an amplification ratio to the fuel contained in the pressurizer 13, so that the fuel exiting the pressurizer 13 to the injector 11 will have an injection pressure PI . Since this amplifying ratio is greater than one. the resulting injection pressure PI will be higher than the pressure P2 taken from the cylinder 17. thus determining the pressure head required for injection into the cylinder 17. The one-way valve 16 is provided for hindering the fuel to flow back to the pump 19 due to the action of the pressurizer 13.

The function of the pressure modulating device 30 is to accumulate the injection pressure PI generated by the pressurizer 13 and supply it during time in the form of a modulated injection pressure PI " to the injector 11 , either during the intake stage or compression stage, or both stages according to the chosen injection strategy, as better explained in the following.

The fuel recirculating duct 31 is used, in fact, to let the fuel having a modulated injection pressure PI ^' value, which is excessive for performing any of the above strategies, to flow- down to the tank 18 and allow control of the modulated injection pressure PI ^'. Adopting the pressure modulating device 30 it is possible to store the injection pressure PI determined by the pressure taken from the cylinder P2 in a stage of the engine cycle, and return it in the form of a modulated injection pressure PI ' to another stage with a pressure value suitable for said stage. For example, if the modulated injection pressure PI ' is injected through the pressure modulating device 30 during the intake stage, it will be set at a first value, whereas if injected during the compression stage, said modulated injection pressure PI ^" will be set at a second higher value than the first one.

The injector 11 is an electromechanical injector, i.e. with a solenoid controlling the axial movement of a pin for plugging a nozzle. The solenoid is controlled by a system driving the pin opening-closing motion according to the timing of the thermodynamic cycle. The pressurizer 13 is shown in detail in Figure 2. This is substantially an hydraulic press, consisting of a cylindrical housing 20 made from metallic material, capable of supporting the pressures generated inside the cylinder 17 during the compression stage, and of a floating piston 21 coupled to the housing 20 by means of springs 26. The housing 20 comprises internally two chambers, i.e. an upper chamber 24 with a large diameter, connected on its top to the air duct 15, and a lower chamber 23 with a smaller diameter, bearing both the inlet and outlet of the fuel line 14 in its lower section. The floating piston 21 consists of two parts: a cylinder 27 with a section SI in its lower part, whose diameter will let it slide freely in the lower chamber 23. Said floating piston 21 also bears a plate 22 on its upper side, whose section SI is equal to the section of the upper chamber 24, so that said section SI has a larger section than section S2.

Therefore, when the fuel enters the lower chamber 23 through the fuel intake line 14, it will receive from the floating piston 21 through the cylinder 27 the injection pressure PI . which is equal to the pressure P2 taken from the cylinder 17, multiplied for the ratio from the section SI to section S2. i.e. the above amplification ratio. So, PI = P2 x (S 1/S2).

The floating piston 21 has appropriate seal rings 25 both on the plate 22 and cylinder 27. which ensure a tight seal on the upper chamber walls 24 and lower chamber 23 during longitudinal sliding. A vent 28 is provided in the lower chamber 23 hindering that the air trapped therein may oppose the movement of the floating piston 21. It should be noted that during the intake and discharge stage of the cylinder 17 a vacuum is generated, which, trasmitted through the intake duct 15, will bring the floating piston 21 back to its stroke start. The springs 26 have mainly the purpose of adjusting the oscillating frequency of the floating piston 21. Figure 3 shows a detail of the pressure modulating device 30, which comprises a one-way valve 35 hindering the fuel to flush back inside the pressurizer 13. This pressure modulating device 30 has a pressure storage device 32 downstream said valve 35, as well as a modulating valve 33 obtained through an electric controlled solenoid valve, in particular by means of the injection system, which operates the fuel recirculating duct 31. Said fuel recirculating duct 31 departs downstream the pressure storage device 32 and upstream the injector 11. The pressure storage device 32 is manufactured in the usual way, for example through an elastic deformable element containing a membrane or spring loaded piston, which bents under the injection pressure PI supplied by the pressurizer 13 and goes back to its position when the injector 1 1 opens for discharging said injection pressure PI . It should be noted in Figure 3 how the pressure intake element 12 consists in this case of an intake lumen 36, i.e. a hole on the side wall of the cylinder 17, placed at such a height that the piston 19 obstruct said hole during the explosion stage, thus avoiding that any undesired overpressures may reach the pressurizer 13 through the intake duct 15. In Figure 3a there is represented a diagram of the pressure P2 taken from the cylinder 17 and operating on the floating piston 21, as a function of the crank angle, i.e. of the position of the engine shaft.

In this diagram, as for the diagram represented in Figure 4a. PMS indicates the top dead centre reached by the piston 19. whereas PMI indicates the bottom dead centre. ALP indicates the opening instant of the intake lumen 36 letting the pressure flow P2 to the floating piston 21. CLP, vice-versa, indicates the closing instant of said intake lumen 36. Consequently, the hatched area indicates the time, expressed as crank angle, wherein said lumen is open and the pressure P2 being exerted on the floating piston 21 follows the pressure inside the cylinder 17. It should be remembered that the intake stage occurs from 0° to 180°. compression stage from 180° to 360°, explosion stage from 360° to 540° and discharge stage from 540° to 720°; also the diagram shown in Figure 3 represents a complete four-stages cycle.

Figure 3a indicates an atmospheric pressure Patm, as well as a calibration pressure P35. which is the opening pressure of the one-way valve 35. In fact, when a higher injection pressure PI than said calibration pressure P35 is exerted on the one-way valve 35, the latter will open and let the fuel flow from the line 14 to the accumulating device 32.

The diagram should be interpreted as follows: when the piston 19 goes over the bottom dead centre PMI, the pressure P2 taken from the cylinder 17 will increase according to the compression operation in course and also the injection pressure PI increases proportionally through the floating piston 21. The one-way valve 35 should be calibrated at a calibration pressure value P35. which is lower than the highest injection pressure value PI reached during the compression stage before the closure of the intake lumen 36, so as to obtain opening of the one-way valve 35 during the compression stage. When the calibration pressure value P35 is exceeded, the one-way valve 35 opens to let the fuel flow to the accumulating device 32. During these operations the injector 1 1 as well as the modulating valve 33 are conveniently closed, so that the pressure P2, multiplied to injection pressure PI will collect in the accumulating device 32 with no outburst possibility. When, during the compression stage, the piston 19 obstructs the intake lumen 36 (instant CLP). the pressure P2 remains fixed at a substantially contant value, the same as for the injection pressure PI . Development of the explosion stage will determine a sudden pressure increase inside the cylinder 17, which reflects on the pressure P2 only when the piston 19, descending to the bottom dead centre PMI, will release the intake lumen 36 (instant ALP). The pressure P2. after a sudden initial excursion, will follow the quick pressure decrease in the cylinder due to the expansion stage. A stored pressure Ps (represented in Figure 3a by a hatched curve) remains stored in the pressure accumulating device 32 substantially near to the greatest pressure value P2. This stored pressure Ps may then be modulated through the modulating valve 33, so as to reach the desired value of the modulated injection pressure PI ^*. This modulating pressure, equalling a discharge of some pressure Ps stored in the fuel recirculating duct 18, is performed in the available time before the opening of the injector 1 1. Said opening of the injector 1 1 occurs during the subsequent intake stage, so that the pressure modulating device 30 operates over two engine cycles as represented by the diagram in Figure 3a. The accumulating device 32, in fact, will collect the pressure Ps stored by the injection pressure PI in a first cycle as the one indicated in Figure 3a. and supply the modulated injection pressure PI ' from the stored pressure Ps during a second subsequent cycle, in particular during the intake stage of said second cycle. Alternatively, the one-way valve 35 may also be calibrated to have the one-way valve 35 opening only after the intake lumen 36 has opened following the explosion stage of the second cycle, so as to allow the pressurizer 13 to operate and supply the injection pressure PI to the pressure modulating device 30. This second solution, which is performed with the calibration pressure P35 greater than the maximum pressure P2 obtainable during the compression stage, allows for extending the time during which the injection can be performed. Vice-versa, the modulation valve 33. as mentioned above, is apt to optimise the modulated injection pressure PI ^" as a function of the engine and injection stage needs. This result is obtained by the modulation valve 33 through a reduction of the pressure Ps stored in the storage device 32 by discharging the fuel in the fuel recirculating duct 31 and utilizing for the operation the time interval from the explosion stage to the discharge stage during the first cycle of the engine and the compression stage during the second cycle of the engine. Figure 4 shows a pressure modulating device 40, which is an implementation of the pressure modulating device 30 shown in Figure 3. This pressure modulating device 40 comprises two branches, i.e. an intake branch Al and a compression branch A2, respectively, which have pressure accumulating devices 42 and 42', respectively. On the intake branch Al downstream the pressure accumulator device 42, a first intercepting valve 45 is also arranged, which is obtained through a solenoid valve remotely controlled by the injection system, whereas on the compression branch A2. downstream the pressure storage device 42' a second intercepting valve 44 is arranged, also a solenoid valve, electronic controlled by the injection system. For the rest, the pressure modulating device 40 is like the similar device shown in Figure 3. The function of both branches Al and A2 is to allow injection both during the compression stage and intake stage. The first intercepting valve 45, the second intercepting valve 44 and the modulation valve 33 remain closed, the same as for the injector 1 1 , whereas in the compression stage during the first cycle, both storage devices 42 and 42' will fill up with fuel and become pressurized having overcome the calibration pressure P35, i.e. the stored pressure Ps follows the injection pressure PI set by the pressurizer 13.

When, during the expansion stage consequent to explosion, the injection pressure PI decreases to become lower than the stored pressure Ps, the one-way valve 35 will close. leaving the storage devices 42 and 42^* pressurized by said stored pressure Ps, like to what is shown in Figure 3a.

For a better understanding, reference is now made to Figure 4a representing an operating diagram of the pressure modulating device 40. On the ordinate, which is always as a function of the crank angle, there are defined X, Z, Zl, W and Wl points related to as many time instants during the engine cycle. The four diagrams refer, respectively, to: opening/closure time of the modulation valve 33; opening/closing time of the second intercepting valve 44; opening/closing time of the first intercepting valve 45; - opening/closing time of the injector 1 1.

The time instant X relates to the instant, during the explosion stage, when the piston 19 frees the intake lumen 36 and the injection pressure PI reaches its peak, which is stored as stored pressure PS. The time instant Z relates to the opening instant of the injector 11 in the intake stage. The time instant Zl relates to the closing instant of the injector 1 1 during the intake stage. The time instant W relates to the opening instant of the injector 1 1 during the compression stage. The time instant Wl relates to the closing instant of the injector 1 1 during the compression stage.

The valves 33. 44. 45 open in the time interval from X to Z. The empty bar shown in Figure 4b indicates the opening of said valves 33 and 44 in order to modulate the modulated injection pressure PI ^", i.e. opening according various time functions, bringing the pressure in the storage devices 42 and 42' to their optimal values.

During this time interval, lasting from the instant X to the instant Z. the injector 1 1 remains closed. Operating the valves 33, 44 and 45. and utilizing the presence of two branches Al and A2. a higher pressure than the one stored in the device 42 can be stored in the storage device 42".

Following the instant Z, the modulation valve 33 and the second intercepting valve 44 are closed by the system and both the injector 1 1 and first intercepting valve 45 open, the latter injecting during the intake stage and receiving the modulated injection pressure PI ^" from the intake branch Al .

From the instant Zl . during which the injector 1 1 is closed, to the instant W. wherein the injector 1 1 opens, the valves 33 and 44 may open again for modulating the pressure of the compression branch A2. The first interception valve 45, located on the intake branch Al downstream the device 42 remains closed and will hinder the greater pressure stored on the compression branch A2 from flushing back into the intake branch Al .

At the instant W the modulating device 33 is closed, whereas the second intercepting valve 44 will stay open to allow injection during the compression stage in the time interval from W to Wl . The injector 1 1 will open at the same time. With this system the injection pressure PI is time modulated as a function of the optimal combustion requirements, depending on the number of revs and engine load. Therefore, all opening strategies of the injector 1 1 can be operated, in particular the stratified injection opening strategies, which provide pre-injections during the intake stage, a main injection and post-injections during the compression stage. A distinction is possible, for example, between three operating conditions as already done for the systems equipped with a high pressure pump or injector/pump, i.e. a low load condition with the injection during compression stage, a medium load condition with the injection during intake stage and a full load condition with the injection during the intake-compression stage. From the above description the features of the present invention as well as the relevant advantages thereof are clear.

The direct injection system and/or direct injection method for internal combustion engines according to the present invention provides advantageously a flexible injection system appropriate for all injection strategies, as it will eliminate an expensive high pressure pump either separated or obtained through a pump injector as well as an engine power take-off through a belt loop or similar arrangement. The pressurizer 13. in fact, will convert the pressure taken from the cylinder directly, with no need for energy from other sources. Even if no special independent high pressure pump is available, it is anyway possible, as said above. to perform all required injection strategies as required in present engines, such as a stratified injection to optimise engine output and reduce pollution, by virtue of the injector drive releasing this operation from the injection pressure excursions.

This, advantageously, because the direct injection system and/or direct injection method for internal combustion engines according to the present invention provides upstream the injector a pressure time modulating device to improve the performance of the injection strategies requested by present engines and allow injection both during the intake stage and compression stage. The pressure modulating device will store pressure advantageously and release it during the time according to the desired strategy and appropriate values for the engine cycle stage wherein the injection is performed. The direct injection system and/or direct injection method for internal combustion engines according to the present invention can be advantageously utilized both in two-stroke engines and four-stroke engines.

The use of an intake lumen sideways the cylinder is particularly advantageous because the intake duct can be automatically plugged during the explosion stage, without having requiring any additional devices for its occlusion.

It is obvious that many changes are possible for the man skilled in the art to the direct injection system for internal combustion engines and/or to the fuel injection method in internal combustion engines described above by way of example, without departing from the novelty spirit of the innovative idea, and it is also clear that in practical actuation of the invention the components may often differ in form and size from the ones described and be replaced with technical equivalent elements.

The direct injection system and/or direct injection method for internal combustion engines according to the present invention may be adopted based on some most spread techniques for injection improvement. For example, as described above, the system may also be used for fuel supplying diesel engines by appropriately sizing their fuel pressurization system, or a pre- chamber connected to the cylinder may be obtained, on which the injector and a spark plug are inserted, or alternativelya hot point may be obtained. Such a pre-chamber is like the one utilized for diesel engines. Thus, a rich fuel mixture can be obtained in the pre-chamber, or pre-combustion be provided in the pre-chamber through the proper spark plug favouring the passage of an inflamed leaner mixture in the cylinder during the expansion stage, where according to Lean Burn technique combustion is completed in a poor environment. Various fuel types may also be used for injection through the direct injection system and/or the direct injection method for internal combustion engines according to the present invention, such as also direct injection in diesel or hot-head systems.

In a likely embodiment, the pressurizer or small hydraulic press may be assembled directly on the cylinder wall, in correspondence with the cylinder pressure intake hole, so as to minimize the duct length and consequently reduce system inertia when reacting to pressure changes in the cylinder.

Moreover, without departing from the inventive idea, it is also clear that other energy contributions can be added to the energy obtained from the cylinder, such as cooperating with the floating piston movement by means of an electromagnetic solenoid when particular necessities in applying pressure to the fuel are required .

Claims

1. A direct injection system for internal combustion engines, which system comprises means (19) for pumping fuel at a first pressure (PO) from a tank (18). injection means (1 1 ) electric driven injection means (18) directly associated to relevant combustion chambers (17). means (13) for applying a second pressure (PI) to the fuel supplied to said injection means (1 1 ). said second pressure (PI) being much higher than said first pressure (PO) and substantially prevailing with respect to a third pressure (P2) taken from the combustion chamber (17), said means (13) for applying said second pressure (PI) to the fuel being located upstream the injection means (11), characterized in that it provides means (12) for taking the third pressure (P2) available in the combustion chamber (17) and transmit it to means (21) for amplifying the third pressure (P2). which are comprised in the means (13) for applying the second pressure (PI), in order to generate said second pressure (PI) .

2. A direct injection system for internal combustion engines, according to claim 1. characterized in that the means (13) for applying the second pressure (PI) are manufactured in the form of an hydraulic press.

3. A direct injection system for internal combustion engines, according to claim 1 or 2, characterized in that it also comprises time modulating means (30;40) of said second pressure (PI).

4. A direct injection system for internal combustion engines, according to claim 3, characterized in that said time modulating means (30;40) are located upstream the injection means (11) and supply a modulated injection pressure (PI ') to said injection means (1 1 ).

5. A direct injection system for internal combustion engines, according to claim 4, characterized in that said time modulating means (30;40) comprise storing means (32; 42, 42") for the second pressure (PI) in an stored pressure (Ps).

6. A direct injection system for internal combustion engines, according to claim 4, characterized in that said time modulating means (30;40) comprise fuel intercepting means (33: 44, 45).

7. A direct injection system for internal combustion engines, according to claim 6, characterized in that said intercepting means (33; 44, 45) comprise a valve (33) operating on a fuel recirculating (31).

8. A direct injection system for internal combustion engines, according to claim 7. characterized in that said time modulating means (40) comprise at least two parallel branches (Al , A2). including respective storing means (42. 42") and/or intercepting means (44;45).

9. A direct injection system for internal combustion engines, according to claim 8. characterized in that the means (12; 36) for taking the third pressure (P2) from the combustion chamber (17) consist of an intake lumen (36) obtained on the side wall of said combustion chamber (17).

10. A direct injection method for internal combustion engines, which system provides pumping the fuel at a first pressure (PO), applying a second pressure (PI) to the fuel before injecting the fuel directly in the combustion chambers (17), said second pressure (PI ) being higher than said first pressure (P0) and substantially prevailing with respect to a third pressure (P2) available in the combustion chamber (17), characterized by taking said third pressure (P2) from the combustion chamber (17). multiplying said third pressure (P2) for obtaining the second pressure (PI ) and by injecting the fuel independently from the behaviour of the second pressure (P2).

11. A direct injection method for internal combustion engines, according to claim 10. characterized by the steps of taking said third pressure (P2) from the combustion chamber (17). multiplying said third pressure (P2) for obtaining the second pressure (PI), time modulating said second pressure (PI) in a modulated injection pressure (PL) and injecting the fuel independently from the trend of the second pressure (P2).

12. A direct injection method for internal combustion engines, according to claim 1 1. characterized in that the fuel is injected according to the stratified injection method.

13. A direct injection method for internal combustion engines, according to claim 1 1. characterized in that the fuel is injected during the intake stage with the engine in a medium load condition, that fuel is injected during the compression stage with the engine in a low load condition, that fuel is injected both during the intake stage and compression stage with the engine in a high load condition.

14. A direct injection method for internal combustion engines, according to claim 1 1, characterized in that it takes said third pressure (P2) from the combustion chamber (17) in a first engine cycle and that fuel is injected during a second cycle of the engine.

15. A direct injection method for internal combustion engines, according to claim 1, characterized in that it provides time modulation of said second pressure (PI) to a modulated injection pressure (PL), operating said modulation during the first cycle of the engine.

16. A direct injection method for internal combustion engines, according to claim 14, characterized in that it provides time modulation of said second pressure (PI) to a modulated injection pressure (PL), operating said modulation during the second cycle of the engine, immediately subsequent to the first cycle of the engine.

17. A direct injection system for internal combustion engines, according to claim 2. characterized in that the means (13) for applying the second pressure comprise a housing (20) including in turn an upper chamber (24) associated to the means for taking the third pressure (12;45;52). and a lower chamber (23) associated to the means (19) for pumping the fuel at a first pressure (PO) to the injection means (1 1).

18. A direct injection system for internal combustion engines, according to claim 17, characterized in that the lower chamber (23) is located on a fuel intake duct (14), which connects the means (19) for pumping the fuel at a first pressure (P0) to the injection means (11).

19. A direct injection system for internal combustion engines, according to claim 18, characterized in that the means (21) for amplifying the third pressure (P2) comprise a floating piston (21) sliding in the upper chamber (24) and in the lower chamber (23).

20. A direct injection system for internal combustion engines, according to claim 19, characterized in that said floating piston (21) comprises an upper side (22) with a section (SI) substantially congruent with the section of the upper chamber (24) and a lower side (25) having a second section (S2) substantially congruent with the section of the lower chamber (23).

21. A direct injection system for internal combustion engines, according to one or more or the previous claims, characterized in that the means (13) for applying a second pressure (PI) to the fuel also comprise energizing means independent from the third pressure of the cylinder (P2), in particular an electromagnetic solenoid.