EP1149238A1

EP1149238A1 - Internal combustion engine injector device and injection method thereof

Info

Publication number: EP1149238A1
Application number: EP99973097A
Authority: EP
Inventors: Giuliano Cozzari
Original assignee: Individual
Current assignee: Individual
Priority date: 1998-12-02
Filing date: 1999-12-02
Publication date: 2001-10-31
Also published as: AU1401700A; ITTO981015A0; WO2000032927A1; ITTO981015A1; KR20010090859A; IT1303195B1; JP2002531752A

Abstract

Fuel injection device for internal-combustion engines, which device is apt for injecting the fuel reaching a first pressure from a tank in a gaseous phase including air, which is conveyed through air feed ducts to the combustion chambers. According to the invention means for spraying liquid microjets (14; 45) associated to the air feed ducts (2; 7) are provided, said means for spraying liquid microjets (14; 45) comprising at least a pressure microchamber (21) for receiving the fuel, a micronozzle (23) and means for applying a second pressure (24) to the fuel contained in the pressure microchamber (21).

Description

INTERNAL COMBUSTION ENGINE INJECTOR DEVICE AND INJECTION METHOD THEREOF

DESCRIPTION

The present invention relates to a fuel injection device for internal-combustion engines, which fuel injection device is apt for injecting the fuel reaching a first pressure from a tank in a gaseous phase including air, which is conveyed through air feed ducts to the combustion chambers. Endothermic reciprocating engines with spark ignition, also including turbo engines, are fed through an air-fuel mixture obtained upstream the combustion chamber. Such an air-fuel mixture is usually obtained drawing the fuel from the tank through a proper motor pump and feeding it to an electroinjector. The electroinjector will inject the fuel atomizing it inside the induction duct wherein air is flowing. The air-fuel mixture is then fed to the combustion chamber through the induction duct. Such an injection method is called Single Point Injection (SPI); also an injection method called Multi Point Injection (MPI) is known, where each cylinder is fitted with an electroinjector near the input of said cylinder.

Both SPI and MPI injection methods use electromagnetic actuated electroinjectors, which consist of a needle sliding in a body wherein fuel is flowing in. The needle has a shutter on its end portion, the displacement of which will either allow fuel outflow under pressure from an outlet nozzle or not. Since actuation is electromagnetic, the needle has a magnetic anchor in its middle area, whereas a proper solenoid is arranged in the injector body for magnetic actuation of the needle according to a known scheme for solenoid valves. Electromagnetic injectors reach flow rates ranging from 200 to 750 cm³/min, obtaining drops whose size exceeds 50 μ. Injection frequency is ranging from 100 to 200 Hz, with an injection time from 1,7 to 2,5 ms.

A main drawback for such injectors is the poor atomization of the fuel drops obtained when the air-fuel mixture is formed, since the smaller the fuel drops the better the air-fuel mixture for combustion purposes. Additionally, accurate adjustment of the air-fuel ratio is difficult to obtain due to the low operation frequency and flow rate of said electroinjectors,.

Another drawback is also due to the requirement for electroinjectors to have fuel maintained at a high pressure, so that an adequate fuel pump and adequately sized hydraulic circuit for a pressure of several bars are needed, with resulting higher costs. A further drawback is caused by the overall dimensions of present electroinjectors having 50 to 70 mm length and a weight from 50 to 150 g, which require special measures for their arrangement inside the engine feed system.

It is the object of the present invention to solve the above problems and provide a fuel injection device for internal-combustion engines, having an improved and more efficient performance with respect to the solutions already known.

In this frame, it is the main object of the present invention to provide a fuel injection device for internal-combustion engines and/or a fuel injection method in internal-combustion engines, which provide for fuel micronization when the feed air-fuel mixture is formed. A further object of the present invention is to provide a fuel injection device for internal- combustion engines, which allows an accurate adjustment of the air-fuel ratio in the feed mixture.

A further object of the present invention is to provide a fuel injection device for internal- combustion engines, allowing application of a lower pressure to the fuel than according to known systems.

A further object of the present invention is to provide a fuel injection device for internal- combustion engines, which has restricted overall dimensions and weight, obtaining a more rational arrangement of the fuel injection points along the air path up to the combustion chamber. In order to achieve such aims, it is the object of the present invention is to provide a fuel injection device 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 fuel injection system for internal-combustion engines according to the present invention;

Figure 2 shows a basic schematics of a fuel injection device for internal-combustion engines according to the present invention; - Figure 3 shows a basic schematics of a detail of the fuel injection system for internal- combustion engines represented in Figure 1 ; Figure 4 shows a basic schematics of a second detail of the fuel injection system for internal-combustion engines represented in Figure 1 ;

Figure 5 shows a basic schematics of an implementation to the fuel injection system for internal-combustion engines represented in Figure 1 ; - Figure 6 shows a schematic prospective view of a fuel injection device for internal- combustion engines according to the present invention in a different assembly embodiment. A basic schematics of a fuel injection system for internal-combustion engines 1 according to the present invention is shown in Figure 1, i.e. representing an induction manifold 2, which feeds the combustion mixture with the required air from the motorvehicle air intakes, the latter not shown here. The induction manifold 2 has an interponed air filter 3, which has a throttle housing 4 downstream, comprising a throttle valve 5. An air plenum is located downstream the throttle housing 4, wherefrom a plurality of induction ducts 7 are departing and ending in a cylinder head 8. The elements described above are all known and will not be described in detail. A fuel tank 9 is provided, wherefrom departs a fuel feed hydraulic circuit 10 represented by a thicker line. Said fuel feed hydraulic circuit 10 is actuated by a fuel pump 1 1 with a fuel filter 12 downstream. Also the arrangement of these elements is known as such. Downstream the fuel filter 12, the hydraulic circuit 10 departs in a first branch 10a comprising a metering device 13, which has some microinjectors 14 arranged downstream. Moreover, the metering device 13 is connected through an air duct 27 to the induction manifold 2. Said microinjectors 14, which will be further detailed with reference to Figure 2, are arranged in windows 15 obtained on the surface of the induction manifold 2. The microinjectors 14 pertaining to the first branch 10a are arranged downstream the filter 3 and upstream the throttle housing 4. Various microinjector pairs 14 are represented in Figure 1 , which are positioned tangentially to the induction manifold 2 and at distance between them, for an even fuel distribution in the air. The microinjector pairs 14 are positioned circumferentially along the external surface of the induction manifold 2 and fed by the branch 10a and metering device 13. The fuel feed hydraulic circuit 10 also comprises further branches 10b, 10c, 1 Od, 1 Oe, each one of them fitted with a metering device 13 and a respective duct 27, not shown here for simplicity's sake, which puts it in communication with the relevant induction duct 7, and microinjectors 14, similar to the ones located in the induction manifold, which are placed tangentially and circumferentially on each induction duct 7.

An electronic control system 16 is provided, well known as such, but fitted with electric connections 7a, 17b, 17c, 17d e 17e to the microinjectors 14 on the induction manifold 2 and induction ducts 7, while an electric connection 18 receives a signal regarding the throttle valve 5 position.

A basic schematics of the microinjector 14 according to the present invention is represented in Figure 2. Said microinjector 14 is a device similar to ink-jet print heads, called 'bubble-jets'. It consists, in fact, of a silicon substrate 19 about 500 μm thick, coated with a photopolymeric layer 20, wherein a window is obtained to form a pressure chamber 21. A coating layer 22 delimits a micronozzle 23 with a diameter of a few tens of μm. The silicon substrate 19 inside the pressure chamber 21 is coated with a thin film heater 24. The fuel is conveyed to the pressure chamber 21 , where it is quickly heated by the thin film heater at a temperature apt to convert some fuel in vapour, indicatively 200°C, causing a plurality of small gas bubbles to form on the thin film heater surface 24, which coalesce rapidly to a bubble 25 shown in Figure 2, said bubble expelling a drop 26 out of the micronozzle 23.

The electric pulse to the thin film heater 24 is short, in the order of a few microseconds, but it is accompanied by a high power density, which can be evaluated in hundreds of m W/m . The kinetic energy of the drop 26 outside the micronozzle 23 is very small, just a few μJ. Therefore, a high frequency operation in the order of thousands Hz can be obtained, with flow rates in the order of cm³/min each microinjector 14. Since drops 26 have a smaller size than 50 μm, a far better fuel atomization can be obtained with microinjectors 14 with respect to other known electroinjectors. The fuel injection system in internal-combustion engines 1 represented in Figure 1 operates as follows: the fuel is fed to the fuel feed circuit 10 through the fuel pump 11. The metering device 13 is used to feed the microinjectors 14 and supply the fuel volume required at the same pressure as for the induction duct 2. Microinjectors 14, whose thin film heater 24 is driven by the electronic system 16, will then spray the fuel in the induction manifold 2, if pertaining to the branch 10a, or in the relevant induction ducts 7, if pertaining to branches 10b, 10c, lOd, lOe, respectively. Thus, the atomized fuel is projected in the air flow either through the induction manifold 2 or induction ducts 7, forming the air-fuel mixture required for engine feeding.

The electronic system 16 receives information about the position of the throttle valve 5 through the connection 18, so as to conveniently drive the spraying frequency of microinjectors 14 and eventually the number of active microinjectors 14, ensuring an optimal feed for each rotation speed with reference to consumption and observance of antipollution Standards.

The metering device 13 is represented in Figure 3, receiving at its input the branch 10a of the fuel feed hydraulic circuit 10 and feeding the fuel to the microinjectors 14 through an outlet duct 28. The air duct inlet 27 located in the upper portion of the metering device 13 puts the metering device 13 in communication with the induction manifold 2. A float 29 with a needle shutter 30 in its upper portion is located inside the metering device 13. The fuel fed by the fuel pump 1 1 enters the metering device 13 through the branch 10a and flows out through the outlet duct 28 to the microinjectors 14. When the fuel level inside the metering device 13 is such to cause the needle shutter 30 on the float 29 to close the branch 10a, then the fuel feed will stop. The fuel feeds the microinjectors 14 by gravity until the fuel level will decrease letting the needle shutter 30 release the branch 10a. The function of the air duct 27 is to cause a pressure reaction of the induction manifold 2 in the upper portion of the metering device 13, not reached by the fuel. In fact, the pressure inside the induction manifold 2 changes depending on the number of engine revolutions and open-close time intervals of the induction valve. A constant differential pressure between air and fuel is always required in order to obtain correct operation of the microinjectors 14. As a result of returning the induction manifold pressure 2 inside the metering device 13, the fuel pressure in the microinjector 14 will be followed by the pressure evolutions in the induction manifold 2. Obviously, in order to achieve an optimal pressure control in the metering device 13, the duct 27 has to pick up the pressure of the induction manifold 2 near the microinjectors 14. The same function is performed by the ducts 27 in correspondence with the induction ducts 7. A block diagram of the electronic system operation 16 is represented in Figure 4. Said electronic system 16 receives information from a revs and phase sensor of the motor 31 , from a knock sensor 32, from a throttle position sensor 33 through the connection 18 described above, from a water temperature sensor 34 and an oxygen sensor 35. When processing such information both the fuel pump 11, ignition system 36 and microinjectors 14 are driven by the electronic system 16.

Through the electronic system 16 the fuel injection system in internal-combustion engines 1 is able to control a plurality of microinjectors 14 operating on their injection frequency, on the number of active microinjectors 14 and on the displacement of active microinjectors 14. Thus, fuel supply can be suited to each engine operating situation, in particular through the availability of the microinjectors 14 being displaced on both the induction manifold 2 and induction ducts 7, so as to achieve the advantages of both the Single Point and Multi Point injection systems by one same injection system. For instance, only the microinjectors 14 in correspondence with the induction manifold can be activated as long as just a fraction of the engine maximum power is requested, whereas the microinjectors 14 in correspondence with the induction ducts 7 can be activated when the engine full power is requested. The fuel injection system for internal-combustion engines according to the present invention is based on the use of microjet injectors, similar to microjet ink-injectors for ink-jet print heads, since said microjet injectors, against lower flow rates in comparison with known electroinjectors, offer a reduced size and weight, a high operation frequency and a high fuel atomising capacity. Moreover, they are featured by their operation as fuel injectors, performing a local pumping and metering function at the outlet of the air conveying ducts, i.e. the fuel pump 1 1 applies a first pressure, which is by far lower than the pressure used in the known systems, namely about 1 bar against 4 to 6 bar, inasmuch as said first pressure will only operate to let the fuel flow in the fuel feed hydraulic circuit 10. Microinjectors 14 receive the fuel at this first pressure and apply a pressure through the thin film heater 24, which is apt to let the micronozzle 23 eject a drop 26 of desired size and speed.

An injection system 40 is represented in Figure 5, which is an implementation to the injection system 1 shown in Figure 1. Such an injection system 40 is suitable for two-stroke engines using oil-gasoline mixture for their feeding. Therefore, it provides an oil tank 41 with an oil duct 42 maintained under pressure by a proper oil pump 43. Oil will flow through a metering device 44 alike the metering device 13 to some microinjectors 45 arranged on the induction manifold 2, in the same way as to microinjectors 14. Said microinjectors 45 are controlled by the electronic system 16 through a connection 47. The remaining portion of the injection system 40, i.e. the portion related to gasoline injection, is quite similar to the one of the injection system 1 represented in Figure 1, including, in particular, the microinjectors 14 arranged on the induction manifold 2.

The oil contained in the oil tank 41 is pre-diluted in the gasoline to reduce viscosity. Therefore, through the injection system 40 a suitable oil-fuel mixture for two-stroke engines can be directly achieved in the induction duct 2. A microinjector 14 assembled on the induction manifold 2 in association with a turbulator device 50 is represented in Figure 6. Said turbulator device 50 comprises substantially two elements 51 with a parallelepipedal shape in parallel with the micronozzles 23. Said elements 51 are provided with through-channels 52 of a proper profile. Elements 51 are arranged on the window 15 to have some external apertures 53 of the channels 52 outside the induction manifold 2, whereas some internal apertures 54 of the channels 52 are to be found inside the induction manifold 2, in particular substantially in correspondence with the micronozzles 23. The turbulator device 50 puts the induction manifold 2 in communication with the environment outside through the channels 52. Since, substantially, there is always a vacuum inside the induction manifold 2 compared to the environment outside, air will flow through the channels 52 from the external aperture 53 to the internal aperture 54. Due to the channels profile, vortexes and a resulting turbulence will form in correspondence with the micronozzles 23. Such a turbulence has the function of further atomizing the fuel drops in cooperation with the microinjector 14. Therefore, adoption of the turbulator device 50 will further favour fuel atomization; otherwise, if the size of fuel drops is maintained constant, the micronozzle diameter 23 should be increased for a greater flow rate.

According to the above description the features of the present invention will be clear as also its advantages are clear.

Advantageously, the fuel injection device for internal-combustion engines according to the present invention allows fuel atomization in the air to a greater extent than with known injection devices, thus increasing engine performance. More advantageously, due to their small dimensions and plate shape microjet injectors in the manifold and induction ducts are arranged tangentially to the air flow. This will favour fuel mixture in the air. Moreover, the fuel injection device for internal-combustion engines according to the present invention has advantageously a frequency behaviour particularly suitable for air-fuel mixture fine control. Adopting microinjectors without moving parts, i.e. deprived of inertia, allows more sudden and monitorable frequency changes as well as higher operating frequency values with respect to present devices. Their small overall dimensions and plate shape allow a more free positioning inside the air conveying ducts.

Moreover, the fuel injection device for internal-combustion engines according to the present invention allows advantageously its operation at a lower pressure in the fuel feed circuit extending from the tank to the microinjectors. The pressure required for the fuel pump is about 1 bar, so that a simple low-cost membrane pump directly fed by the motor can be used or in the instance of a favourable arrangement of the hydraulic circuit the use of a pump may be avoided and hydrostatic pressure used instead. Additionally, a low pressure entails obvious advantages in terms of design for the fuel feed hydraulic circuit, such as preventing implementation of an inertial switch for locking gasoline feed in the event of impact, since there is no longer a pressure as high as 4-6 bars to throw gasoline out of likely interrupted ducts, independently from engine operation.

It is obvious that many changes are possible for the man skilled in the art to the fuel injection device for internal-combustion engines and/or 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 one described and be replaced with technical equivalent elements. Each microjet injector may be fitted with a plurality of micronozzles. Microjet injectors may not only be 'bubble-jet' injectors, but also piezoelectric microjet injectors, i.e. using the expansion of a piezoelectric actuator instead of a fuel steam bubble. Said piezoelectric microjet injectors may for instance be more suitable for oil injection as well as for gas injection. Also the use of various microjet injectors is possible, always classified as microjet injectors for ink-jet printers, provided they have substantially no mechanical moving parts in their pressure application means to the fuel in a microchamber, i.e. an irrelevant inertia allowing high operation frequency.

The various microjet injectors may have different injection functions. Besides the instance described above of oil injection for two-stroke engine mixtures, specific microjet injectors can be used under particular operating conditions of the engine for injecting fuel additives in the induction manifold. Said microjet injectors may be controlled by the electronic system actuating them as a function of their performance and/or antipollution optimization. Microjet injectors can be arranged in a different way from the above illustration. In particular, microjet injectors can be in correspondence with the induction manifold only, reproducing SPI systems; or in correspondence with the induction ducts only near the cylinders, reproducing MPI systems. Moreover, microjet injectors in correspondence with the induction manifold may be positioned downstream the throttle housing and upstream the air plenum. Microject injectors are preferably arranged circumferentially, either on several parallel circumferences or along a helical path. Microjet injectors arranged on parallel adjacent circumferences may be staggered them to ensure covering of a larger number of air threads flowing in the induction ducts.

The nozzles of one same microjet injector may be arranged on parallel rows along the plate dimensions or also diagonally, so as to have their arrangement intersecting a larger number of air threads and improving the mixture. The channels of the turbulator device can be protected by a filtering sleeve to prevent dust penetration and deadening air flows noisiness.

Claims

1. A fuel injection device for internal-combustion engines, which fuel injection device is apt for injecting the fuel reaching a first pressure from a tank in a gaseous phase including air, which is conveyed through air feed ducts to the combustions chambers, characterized in that it comprises means for spraying liquid microjets (14;45), associated to the air feed ducts (2;7), said means for spraying liquid microjets (14;45) comprising at least a pressure microchamber (21) for receiving the fuel, a micronozzle (23) and means for applying a second pressure (24) to the fuel contained in the pressure microchamber (21).

2. A fuel injection device for internal-combustion engines, according to claim 1, characterized in that said means for spraying liquid microjets (14;45) are arranged in correspondence with openings (15) obtained on the external surface of the air feed ducts (2,

7).

3. A fuel injection device for internal-combustion engines, according to claim 2, characterized in that said means for spraying liquid microjets (14;45) are associated to fuel metering devices (13; 44).

4. A fuel injection device for internal-combustion engines, according to claim 3, characterized in that said fuel metering devices (13;34) are provided with means (27;46) for feeding back pressure in the ducts (2,7) to said fuel metering devices (13;34).

5. A fuel injection device for internal-combustion engines, according to claim 4, characterized in that said means (27;46) for feeding back pressure in the ducts (2,7) to said fuel metering devices (13;34) comprise a main duct putting a fuel metering device (13;44) in communication with its respective duct (2,7).

6. A fuel injection device for internal-combustion engines, according to claim 1 , characterized in that said means for spraying liquid microjets (14;45) are injectors used as ink- jet injectors in ink-jet printer heads, and the means for applying a second pressure (24) to the fuel contained in the pressure microchamber (21) comprise a heater.

7. N fuel injection device for internal-combustion engines, according to claim 1, characterized in that said means for spraying liquid microjets (14;45) are injectors used as ink-jet injectors in ink-jet printer heads, and the means for applying a second pressure (24) to the fuel contained in the pressure microchamber (21) comprise a piezoelectric actuator.

8. A fuel injection device for internal-combustion engines, according to claim 2, characterized in that said air feed ducts (2, 7) comprise the air induction manifold (2).

9. A fuel injection device for internal-combustion engines, according to claim 2, characterized in that said air feed ducts (2, 7) comprise the air induction ducts (7).

10. N fuel injection device for internal-combustion engines, according to claim 3 characterized in that it provides a fuel feed circuit (10), which is apt to feed the fuel from a tank to the metering device (13) and that said fuel feed circuit (10) comprises a fuel pump (11) operating at a lower pressure than the pressure exerted on the fuel at the injection point.

11. A fuel injection method for internal -combustion engines, which method provides for fuel atomization through injection means in a gaseous phase comprising air, characterized in means for spraying liquid microjets (14;45) used as ink-jet injectors in ink -jet printer heads are utilized as injection means.

12. A fuel injection method for internal-combustion engines, according to claim 11 , characterized in that said means for spraying liquid microjets (14;45) are more than one.

13. A fuel injection method for internal-combustion engines, according to claim 12, characterized in that said means for spraying liquid microjets (14;45) atomize the fuel inside the induction manifold (2).

14. A fuel injection method for internal-combustion engines, according to claim 12, characterized in that said means for spraying liquid microjets (14;45) atomize the fuel inside the induction ducts (7) near the cylinders.

15. A fuel injection method for internal-combustion engines, according to claim 13, characterized in that said means for spraying liquid microjets (14;45) atomize the fuel also inside the induction ducts (7) near the cylinders.

16. A fuel injection method for internal-combustion engines, which provides for fuel atomization through injection means in a gaseous phase comprising air, characterized in that said injection means (14;45) apply a pressure at the outlet (15) in the air ducts (2, 7).

17. A fuel injection device for internal-combustion engines, according to claim 2, characterized in that fuel consists of a gasoline and oil mixture and that said means for spraying liquid microjets (14;45) are provided at least in two sets, the first of said sets (14) injecting gasoline, the second of said sets (45) injecting oil.

18. A fuel injection device for internal-combustion engines, according to claim 2, characterized in that at least one of the means for spraying liquid microjets (14;45) is apt for injecting fuel additives.

19. A fuel injection device for internal-combustion engines, according to claim 2, characterized in that said means for spraying liquid microjets (14;45) have no relative moving parts.

20. A fuel injection device for internal-combustion engines, according to claim 2, characterized in that said means for spraying liquid microjets (14;45) are associated to means for creating a turbulence in the fluids (50), which operate on said liquid microjets with the purpose of favouring their atomization.

21. The use of liquid jet injectors, substantially as used for ink-jet printer heads, for fuel injection for internal-combustion engines in a gaseous phase comprising air, which is conveyed through air feed ducts to the combustion chambers of said internal-combustion engines.