Injector and fuel injection system

Abstract

A fuel injector for a heat engine comprises an elongated body (1), a nozzle (2) at the end of the body (1) intended to open into a combustion chamber (3), the nozzle (2) comprising a wall crossed by a plurality of holes (7) through which the fuel is intended to enter the combustion chamber (3), the injector comprising a directly controlled opening device comprising a shutter (5) intended to bear against a seat (6) carried by the nozzle (2), an actuator making it possible to lift or press the shutter (5) against the seat (6) on command. 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. 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 direct injection of fuel into a combustion chamber of an internal combustion engine. It relates to a fuel supply system comprising such an injector. Prior art

[0002] Fuel delivery 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 combustion chambers of the engine. 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 powers a high-pressure pump 9.

[0003] This technique has led to the development of specific injectors, such as that shown by document GB2582013A. [Fig.l] shows an injector of this type, reproduced from this document, integrated into a fuel supply system diagram. The body 1 of the injector is of generally elongated shape and carries at its end a nozzle 102 allowing the injection of 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 shutter 5 up and down in the injector, and thus control the injection of gasoline. The distal part of the shutter 5 cooperates with a seat 106 carried by the nozzle 102 to form a valve. The distal tip of the obturator may be formed with a curved distal surface and thus the tip 50 of the needle may be generally ball-shaped.The tip of the needle 50 engages and disengages 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 injection of gasoline into the cylinder, the injection is carried out in a phase close to the bottom dead center. The holes are thus oriented towards the center of the combustion chamber 3 with an orientation of the holes between 0 and 60° relative to the axis of the injector.

[0005] Such injectors could also be useful in engines using diesel or kerosene, i.e. for compression ignition engines, such as Diesel engines. However, in such engines, injection takes place 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. Statement of the invention

[0006] It is therefore an objective to propose an injector suitable for direct injection into a compression ignition engine.

[0007] With these objectives in view, 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 crossed by a plurality of holes through which the fuel is intended to enter the combustion chamber, the injector comprising a directly controlled opening device comprising a shutter movable between a closed position resting against a seat carried by the nozzle and an open position in which the shutter is lifted from the seat and allows the injection of fuel through the holes, an actuator making it possible to bring the shutter into 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 towards the combustion chamber,the surface of the wall forming an angle less than 20° with respect to the axis of symmetry.

[0008] By providing the injector nozzle with a dome-shaped wall, the injector can be provided with holes oriented almost perpendicular to the axis of the injector. In fact, the holes are made substantially perpendicular to the surface from which they open, due to manufacturing constraints, in particular to minimize the phenomenon of wetting of this surface during injection of the liquid. The holes are generally made by electroerosion, and the tool which enters the hole being made 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° relative 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 distribute fuel. • The injector has a truncated annular surface connected to an outer face of the dome. The shape thus given to the end of the injector makes it easier to make holes by clearing the space for a tool to approach the dome. • A contact area between the shutter and the seat has a diameter between 1 and 2 mm, preferably between 1.2 and 1.5 mm. • The shutter has 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 comprises a solenoid and an armature mechanically coupled to the shutter. • The armature acts on a proximal shoulder defined by an annular collar of the shutter, a spring returning the shutter member to 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 the fuel from the tank and supplying the fuel under high pressure to at least one injector as described above.

[0011] According to a particular characteristic, the pump is designed to supply the 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 thermal 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 in order to allow the injection of diesel or kerosene type fuel (therefore for compression ignition) at pressures of a few hundred bars. Compared to conventional diesel injectors, the proposed solution is efficient, much simpler to manufacture (direct control of the shutter / needle instead of hydraulically controlled structures with 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 subject to standards different from those of automobiles. Brief description of the figures

[0015] The invention will be better understood and other features and advantages will appear on reading the description which follows, the description making reference to the appended drawings among which:

[0016] - [Fig.l] is a schematic view of a fuel supply system according to prior art. - [Fig.2] is a perspective view of an injector nozzle according to one embodiment of the invention; - [Fig.3] is a side view of the nozzle of [Fig.2]; - [Fig.4] is a 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 is mainly distinguished 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 a heat engine comprises, as shown in [Fig.l], a fuel tank 8, a high pressure pump 9 receiving the fuel from the tank 8 and supplying the fuel under high pressure to at least one injector mounted on the cylinder head of the engine so as to inject the 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 the fuel at a nominal pressure of the order of 500 bars, 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 a body 1 of elongated, generally symmetrical and cylindrical shape, 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. The present nozzle 2 is shown in detail in Figures 2 to 4 and is described in detail below.

[0022] The injector also comprises a directly controlled opening device comprising a shutter 5 intended to come to bear against a seat 106 carried by the nozzle 2. The shutter 5 cooperates with an actuator, which are described briefly below, as they are conventional.

[0023] The shutter 5 has the shape of a needle, the distal part of the needle being in the shape of a ball 50, shown in dotted lines in [Fig. 4]. The opening device makes it possible to lift the shutter 5 from its seat 106 on command, to open the injector.

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

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

[0026] The nozzle 2 comprises a tubular part 20 which is connected to the end of the body 1 and which is extended by 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 force-fitted, via the tubular part 20, and preferably completed by a continuous annular weld to improve the seal.

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

[0029] As understood from [Fig.4], the seat 106 forms an annular surface which surrounds the cavity 23, upstream of the latter. Thus when the tip 50 of the needle rests on the seat 106 the valve is closed, the flow of fuel towards the cavity 23 is prevented.

[0030] At the outlet of the holes 7, the outer surface 220 of the wall 22 forms an angle of less than 20° relative 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 of between 75 and 90° relative 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 of between 1 and 2 mm, and is 1.3 mm in this example.

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

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

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

[0039] In operation, the fuel from the tank 8 is sent to the high-pressure pump 9, then to the injector. The fuel passes into 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. In order to carry out a fuel injection, the solenoid 4.1 of the actuator 4 generates a magnetic field which moves the armature in the proximal direction, the latter driving with it the needle 5 which rises from the seat to take an open position. The fuel then passes around the tip 50 in the cavity 23, then leaves the injector through the holes 7. When the actuator 4 is no longer powered, the spring 17 of the direct-controlled opening device brings the tip 50 of the needle back into contact with the seat 106 and closes the fuel passage.

Claims

Claims

1. Fuel injector for a heat engine intended to be arranged in a passage opening into a combustion chamber (3), said injector comprising a body (1) of elongated shape, a nozzle (2) at the end of the body (1), the nozzle (2) comprising a wall crossed by a plurality of holes (7) through which the fuel is intended to enter the combustion chamber (3), the injector comprising a directly controlled opening device comprising a shutter (5) movable between a closed position resting against a seat (6) carried by the nozzle (2) and an open position in which the shutter is lifted from the seat and allows the injection of fuel through the holes (7), an actuator (4) making it possible to bring the shutter (5) into 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 out of the wall towards the combustion chamber (3),the surface of the wall forming an angle less than 20° with respect to the axis of symmetry.,

2. An 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 one of the preceding claims, in which the holes (7) have an axis oriented at an angle of between 75 and 90° relative to the axis of symmetry.

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

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

7. Injector according to one of the preceding claims, in which a contact zone between the shutter (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 one of the preceding claims, in which the holes (7) open inside the dome (22) with a diameter of between 0.4 and 0.6 mm.

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

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

11. Fuel injection system for a heat engine comprising a fuel tank (8), a high pressure pump (9) receiving the fuel from the tank (8) and supplying the 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 adapted to supply the 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. A compression-ignition heat engine comprising a fuel injection system according to claim 11 or 12.

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