Fuel injector and injection system

Abstract

A fuel injector for an internal combustion engine comprises an elongated body (1), a nozzle (2) at the end of the body (1) opening into a combustion chamber (3), the nozzle (2) having a wall through which a plurality of holes (7) pass through which the fuel enters the combustion chamber (3), the injector having a direct-acting opening device comprising a shutter (5) designed to bear against a seat (6) carried by the nozzle (2), and an actuator for raising or pressing the shutter (5) against the seat (6) as required. The wall is dome-shaped (22) having an axis of symmetry, the holes (7) opening from the wall into the combustion chamber (3), the surface of the wall forming an angle of less than 20° with respect to the axis of symmetry. Fuel supply system with such an injector. Figure for the abstract: Fig. 4

Description

Title of the invention: Fuel injector and injection system technical field

[0001] The invention relates to an injector for the direct injection of fuel into a combustion chamber of an internal combustion engine. It relates to a fuel supply system comprising such an injector. Previous technique

[0002] Fuel supply systems in modern gasoline-powered internal combustion engines, particularly those for the automotive market, use direct gasoline injection, in which fuel injectors are used to inject fuel directly into the engine's combustion chambers. In such direct injection systems, fuel from the tank 8 is supplied by a low-pressure fuel pump integrated into the tank. This low-pressure pump is generally electric and supplies a high-pressure pump 9.

[0003] This technique has led to the development of specific injectors, such as the one shown in document GB2582013A. Figure 1 represents an injector of this type, reproduced from that document, integrated into a fuel supply system diagram. The body 1 of the injector is generally elongated and has at its end a nozzle 102 for injecting fuel into a combustion chamber 3. An actuator 4, comprising a solenoid 4.1 and an armature 4.2, is located in an upper housing. The actuator 4 acts with pressure springs to move a needle-shaped obturator 5 up and down in the injector, thereby controlling the gasoline injection. The distal part of the obturator 5 cooperates with a seat 106 carried by the nozzle 102 to form a valve. The distal tip of the obturator can be formed with a curved distal surface and therefore the tip 50 of the needle can generally be ball-shaped.The tip of the needle 50 engages and disengages from the upper surface of the valve seat 106 as it moves up and down to block the flow of fuel or to allow the flow of fuel to flow into a combustion chamber 3 via holes 107 which pass through the nozzle 102, as is well known.

[0004] In the case of direct gasoline injection into the cylinder, the injection is carried out at a phase close to bottom dead center. The holes are thus oriented towards the center of the combustion chamber 3 with a hole orientation between 0 and 60° relative to the axis of the injector.

[0005] Such injectors could also be useful in engines using diesel or kerosene, that is, for compression-ignition engines, such as diesel engines. However, in such engines, injection occurs when the piston is close to top dead center. The shape of the combustion chamber is therefore very different, and the injector must be adapted accordingly. Description of the invention

[0006] It is therefore an objective to propose an injector adapted for direct injection in a compression-ignition engine.

[0007] With these objectives in mind, the invention relates to a fuel injector for a heat engine intended to be arranged in a passage opening into a combustion chamber, said injector comprising an elongated body, a nozzle at the end of the body, the nozzle comprising a wall through which a plurality of holes are passed, through which the fuel is intended to enter the combustion chamber, the injector comprising a direct-acting opening device comprising a movable shutter between a closed position bearing against a seat carried by the nozzle and an open position in which the shutter is lifted from the seat and allows fuel injection through the holes, an actuator for bringing the shutter to the open position on command, characterized in that the wall has the shape of a dome having an axis of symmetry, the holes opening from the wall into the combustion chamber,the surface of the wall forming an angle of less than 20° with respect to the axis of symmetry.

[0008] By equipping the injector nozzle with a dome-shaped wall, the injector can be fitted with holes oriented almost perpendicularly to the injector axis. Indeed, the holes are made approximately perpendicular to the surface they open into, due to manufacturing constraints, particularly to minimize the wetting of this surface during liquid injection. The holes are generally made by electrical discharge machining (EDM), and the tool entering the hole during its creation would be deflected if the wall were very inclined.

[0009] According to other characteristics: • The number of holes is between 5 and 10. • The diameter of the holes is between 70 and 250 pm, and preferably between 100 and 200 pm. • The holes have an axis oriented at an angle between 75 and 90° to the axis of symmetry. Thus, the fuel is injected into a free volume and there is no risk of the fuel reaching a wall of the combustion chamber. • The wall thickness is between 0.4 and 0.9 mm, preferably between 0.6 and 0.8 mm. This thickness has been found to be a good compromise between wall strength and the nozzle's ability to diffuse the fuel. • The injector has a frustoconical annular surface connected to an outer face of the dome. The shape thus given to the end of the injector makes it easier to create holes by creating space for a tool to approach the dome. • A contact area between the obturator and the seat has a diameter between 1 and 2 mm, preferably between 1.2 and 1.5 mm. • The obturator includes a needle at the end of which is fixed a ball intended to come into contact with the seat. • The holes open inside the dome with a diameter between 0.4 and 0.6 mm. • The actuator includes a solenoid and an armature mechanically coupled to the shutter. • The frame acts on a proximal shoulder defined by an annular collar of the obturator, a spring recalling the obturator organ in the closed position, said spring resting on a distal shoulder of the annular collar.

[0010] The invention also relates to a fuel injection system for a heat engine comprising a fuel tank, a high-pressure pump receiving fuel from the tank and supplying fuel under high pressure to at least one injector as described above.

[0011] According to a particular feature, the pump is designed to supply fuel under a pressure of up to 250 bar, or up to 350 bar, or up to 500 bar, or even up to 700 bar.

[0012] The invention also relates to a compression-ignition internal combustion engine comprising the present fuel injection system.

[0013] It will be appreciated that the present invention, thanks to the modified design of the dome / bag, allows the conversion of a gasoline-type injector to allow the injection of diesel or kerosene fuel (i.e., for compression ignition) at pressures of several hundred bar. Compared to conventional diesel injectors, the proposed solution is efficient, much simpler to manufacture (direct control of the obturator / needle instead of hydraulically controlled structures with a control valve), and therefore less expensive.

[0014] The fuel injection system according to the invention finds a particular application for so-called 'off-road' vehicles and subject to standards different from automobiles. Brief description of the figures

[0015] The invention will be better understood and other features and advantages will become apparent upon reading the following description, the description referring to the accompanying drawings, among which:

[0016] - [Fig. 1] is a schematic view of a fuel supply system according to earlier art. - [Fig.2] is a perspective view of an injector nozzle according to an embodiment of the invention; - [Fig.3] is a side view of the nozzle of [Fig.2]; - [Fig.4] is a cross-sectional view of the nozzle along line IV-IV of [Fig.3]. Detailed description

[0017] The present invention will now be described with reference to [Fig. 1] of the prior art. Indeed, the injector of the invention differs principally from the injector of [Fig. 1] by the design of the nozzle 2 shown in Figures 2 to 4. Thus, the invention relates to an injector of the type of [Fig. 1] equipped with a nozzle 2 as illustrated in Figs. 2 to 4, and an injection system incorporating such an injector.

[0018] A fuel injection system for an internal combustion engine comprises, as shown in [Fig.1], a fuel tank 8, a high-pressure pump 9 receiving fuel from the tank 8 and supplying fuel under high pressure to at least one injector mounted on the cylinder head of the engine so as to inject fuel into a combustion chamber 3. Typically the injector is arranged in a passage / bore made in the cylinder head and opening into the combustion chamber 3.

[0019] The present invention has been particularly designed for a compression-ignition engine operating with diesel or kerosene, and the fuel tank 8 therefore contains, for example, diesel or kerosene.

[0020] The pump 9 is designed to supply fuel under a nominal pressure of the order of 500 bar, for example.

[0021] The fuel injector extends along an axis A from a proximal end P (through which the fuel arrives) to a distal end D. The injector comprises an elongated, generally symmetrical, cylindrical body 1, defining a fuel passage flowing from the proximal end P to the distal end D. A nozzle 2 is arranged at the distal end of the body 1 and is configured to inject / discharge the fuel into the combustion chamber 3. This nozzle 2 is shown in detail in Figures 2 to 4 and is described in detail below.

[0022] The injector further comprises a direct-acting opening device including a shutter 5 intended to bear against a seat 106 carried by the nozzle 2. The shutter 5 cooperates with an actuator, which are briefly described below, as they are conventional.

[0023] The obturator 5 is needle-shaped, the distal part of the needle being ball-shaped 50, shown in dashed lines in [Fig. 4]. The opening device allows the obturator 5 to be lifted from its seat 106 on command, to open the injector.

[0024] Typically, the obturator 5 is held, by default, in the closed position against the seat by a spring 17 bearing on a distal shoulder 19.1 of the obturator 5 defined by an annular collar 19. The injector is therefore closed by default.

[0025] The actuator 4, arranged in the proximal region, allows the obturator to be brought 5 in the open position on command. The actuator 4 includes a solenoid 4.1 capable of generating a magnetic field that acts on a magnetic armature 4.2 cooperating with the obturator 5. A pole piece 21 allows the magnetic field to be formed. The armature 4.1 has an annular shape and surrounds the obturator needle 5 with a functional clearance allowing it to slide. It is positioned distally to the collar 19, opposite a proximal shoulder 19.2 of the latter. The armature 4.2 is thus mechanically coupled to the obturator 5 in the axial opening direction. The solenoid actuator thus directly controls the obturator. Alternatively, the armature could be fixed to the obturator.

[0026] The nozzle 2 comprises a tubular part 20 which is connected with the end of the body 1 and which extends into a frustoconical annular surface 21. The nozzle 2 further comprises a wall having the shape of a dome 22 having an axis of symmetry A and connected to the frustoconical annular surface 21.

[0027] The nozzle 2 is typically press-fitted via the tubular part 20, and preferably completed by a continuous annular weld to improve sealing.

[0028] The dome-shaped wall 22 delimits a cavity 23, also called a bag, and is traversed by a plurality of holes 7 connecting the cavity 23 to the combustion chamber 3.

[0029] As can be seen from [Fig. 4], the seat 106 forms an annular surface that surrounds the cavity 23, upstream of it. Thus, when the tip 50 of the needle rests on the seat 106, the valve is closed, and the flow of fuel towards the cavity 23 is prevented.

[0030] At the level of the opening of the holes 7, the outer surface 220 of the wall 22 forms an angle of less than 20° with respect to the axis of symmetry, for example between 10 and 20°, in particular 15°.

[0031] The number of holes 7 is 8 in this example.

[0032] The diameter of the holes 7 is between 70 and 250 pm, and is 70 pm in this example.

[0033] The holes 7 are distributed in a substantially symmetrical manner around the axis of symmetry of the dome 22 and have an axis oriented at an angle α between 75 and 90° with respect to the axis of symmetry.

[0034] The thickness of the wall 22, in the section crossed by the holes 7, is between 0.4 and 0.9 mm, and is 0.6 mm in this example.

[0035] The contact area between the shutter 5 and the seat 106 has a diameter between 1 and 2 mm, and is 1.3 mm in this example.

[0036] It should also be noted that the holes 7 are cylindrical (i.e., with a substantially constant diameter) throughout the entire wall thickness or may be slightly conical (the diameter of hole 7 on the inlet side – i.e., the bag) being larger than the diameter on the outlet side – i.e., at the opening in the wall 220 – throughout the entire wall penetration. In the case of a conical hole, the variation in diameter between the inlet and outlet does not exceed 30%.

[0037] There is therefore no counter-hole on the side of surface 220, as is often the case on gasoline injectors.

[0038] In addition, the holes 7 are advantageously so-called long holes, with a length (L) of hole to diameter ratio of between 5 and 10.

[0039] During operation, fuel from the tank 8 is sent to the high-pressure pump 9, then to the injector. The fuel passes through the body of the injector 1, along the needle 5 to the valve. The tip of the needle 50 is held in the closed position by the spring 7 and the fuel pressure. To inject fuel, the solenoid 4.1 of the actuator 4 generates a magnetic field that moves the armature proximally, which in turn moves the needle 5, lifting it from the seat to the open position. The fuel then passes around the tip 50 in the cavity 23, and exits the injector through the holes 7. When the actuator 4 is no longer powered, the spring 17 of the direct-acting opening device returns the tip 50 of the needle to contact the seat 106 and closes the fuel passage.

Claims

Demands

1. A fuel injector for an internal combustion engine intended to be arranged in a passage opening into a combustion chamber (3), said injector comprising an elongated body (1), a nozzle (2) at the end of the body (1), the nozzle (2) having a wall through which a plurality of holes (7) pass through which the fuel is intended to enter the combustion chamber (3), the injector comprising a direct-acting opening device having a shutter (5) movable between a closed position bearing against a seat (6) carried by the nozzle (2) and an open position in which the shutter is lifted from the seat and allows fuel injection through the holes (7), an actuator (4) for bringing the shutter (5) to the open position on command, characterized in that the wall has the shape of a dome (22) having an axis of symmetry, the holes (7) opening from the wall towards the combustion chamber (3),the surface of the wall forming an angle of less than 20° with respect to the axis of symmetry.

2. Injector according to claim 1, wherein the number of holes (7) is between 5 and 10.

3. Injector according to claim 1 or 2, wherein the diameter of the holes (7) is between 70 and 250 pm, and preferably between 100 and 200 pm.

4. Injector according to any one of the preceding claims, wherein the holes (7) have an axis oriented at an angle between 75 and 90° with respect to the axis of symmetry.

5. Injector according to any one of the preceding claims, wherein the wall thickness is between 0.4 and 0.9 mm, preferably between 0.6 and 0.8 mm.

6. Injector according to any one of the preceding claims, characterized in that it comprises a frustoconical annular surface (21) connected to an outer face of the dome (22).

7. Injector according to any one of the preceding claims, wherein a contact area between the obturator (5) and the seat (6) has a diameter of between 1 and 2 mm, preferably between 1.3 and 1.5 mm.

8. Injector according to any one of the preceding claims, wherein the holes (7) open into the inside of the dome (22) on a diameter of between 0.4 and 0.6 mm.

9. Injector according to any one of the preceding claims, wherein the obturator (5) has a needle at the end of which is fixed a ball intended to come into contact with the seat (6).

10. Injector according to any one of the preceding claims, wherein the actuator comprises a solenoid (4.1) and an armature (4.2) mechanically coupled to the obturator (5), and preferably the armature acts on a proximal shoulder defined by an annular collar of the obturator, a spring (17) returning the obturator to the closed position bearing on a distal shoulder of the annular collar.

11. Fuel injection system for an internal combustion engine comprising a fuel tank (8), a high-pressure pump (9) receiving fuel from the tank (8) and supplying fuel under high pressure to at least one injector, characterized in that the injector is of the type according to one of the preceding claims.

12. System according to claim 11, wherein the pump (9) is designed to supply fuel under a pressure of up to 250 bar, or up to 350 bar, or up to 500 bar, or even up to 700 bar.

13. Internal combustion engine with compression ignition comprising a fuel injection system according to claim 11 or 12.

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