WO2019101499A1

WO2019101499A1 - Fuel injector

Info

Publication number: WO2019101499A1
Application number: PCT/EP2018/080117
Authority: WO
Inventors: Philippe Legrand; Nicolas CEZON
Original assignee: Delphi Technologies Ip Limited; Delphi France Sas
Priority date: 2017-11-23
Filing date: 2018-11-05
Publication date: 2019-05-31
Also published as: FR3073903A1; FR3073903B1

Abstract

A fuel injector (20) for an internal combustion engine, the injector (20) extending along a main axis (X) and comprising (32), - a needle (26) that is able to move axially in the body (22) between a closed position and an open position of the injection nozzle (32), - an electromagnetic actuator (24) comprising a stationary annular coil (34), a stationary pole piece (36) and an armature (38) that is able to move in the body (22) provided with an axial hole inside which the needle (26) is slidingly guided, characterised in that the injector (20) also comprises an armature spring (30) attached under the armature (38) and to the needle (26).

Description

Fuel Injector TECHNICAL FIELD

The present invention relates to a fuel injector and in particular a fuel injector for a direct injection of gasoline into the combustion chamber of an internal combustion engine. BACKGROUND OF THE INVENTION

Direct injection gasoline engines require fuel injectors to operate under extreme conditions of temperature and pressure. In addition, the fuel injector must open and close very quickly to provide multi-pulse injection cycles necessary for energy efficiency and low emissions.

The current direct injection fuel injectors use either inward opening valves (nozzle or multi-hole type) in conjunction with actuation of the solenoid or outward opening valves using the piezoelectric actuation. The outward opening piezoelectric injector has shown the greatest potential to reduce fuel consumption, but the cost of the driver's piezoelectric actuator is prohibitive for high volume applications.

The piezoelectric actuator can provide a high opening force to overcome the needle return spring necessary to maintain the valve closed and the high hydraulic forces generated during high pressure operation of the injector. The piezoelectric actuator also provides a quick opening of the valve and can realize a variable valve. However, piezoelectric fuel injectors are very expensive to produce compared to solenoid operated injectors and require complex and expensive control systems for the operation of the piezoelectric actuator.

In contrast, solenoid actuated fuel injectors as described in EP 1783356 are much cheaper to produce.

However, known solenoid-operated fuel injectors can not provide the same level of performance as devices powered by piezoelectric devices, mainly because of the opening force lower achievable by solenoid electromagnetic actuators and the slower increase in strength over time.

Known solenoid operated fuel injectors utilize a rebar spring to return it to its home position, i.e., closing the injector. The reinforcement spring is a return spring which is arranged above a frame. However, the position of the reinforcement spring is not optimized because it reduces the air gap between the armature and the pole piece and thus reduces the magnetic force available to attract the armature.

As described in FIG. 1 of an existing injector, the injector 1 comprises an electromagnetic actuator 2, a body 3, a needle 4 comprising a ball 5 secured to a reinforcing spring 6. The electromagnetic actuator 2 comprises a fixed coil 7, a pole piece 8 and an armature 9. The armature spring 6 is arranged above the armature 9. The armature spring 6 is fixed firstly in a recess 10 of the piece 8 and on the other hand in an annular groove 11 of an active face 12 of the armature. The active face 12 is oriented facing the pole piece 8. The operating method of the injector 1, not shown, comprises:

a rest stage in which the actuator 2 is unpowered, the assembly consisting of the needle 4 and the ball 5 is in contact with the seat and the injector 1 is closed. There is no fuel injection.

a preopening step in which the actuator 2 is energized, the pole piece 8 attracts the armature 9 and the armature spring 6 is compressed. The armature 9 drives the needle 4 and the ball 5 upwards, the needle 4 and the ball 5 being away from the seat and the injector 1 is open. There is fuel injection.

an opening step in which the actuator 2 is energized, the armature 9 continues to move towards the pole piece 8, the armature spring 6 continues to be compressed.

a closing step in which the actuator 2 is unpowered, the assembly consisting of the needle 4 and the ball 5 is in contact with the seat and the injector 1 is closed. There is no fuel injection.

The object of the present invention is to provide a solution that will alleviate the problem mentioned above. SUMMARY OF THE INVENTION

The present invention aims to remedy the disadvantages mentioned above by proposing a simple and economical solution.

For this purpose, the invention provides a fuel injector of an internal combustion engine which extends along a main and longitudinal axis.

The injector comprises an axially movable needle in the body between a closed position and an open position of the injection nozzle, an electromagnetic actuator comprising an annular fixed coil, a fixed pole piece and a movable armature in the body provided with a axial hole within which the needle (26) is slidably guided. The injector further comprises a reinforcing spring fixed on the one hand under the armature and on the other hand to the needle.

In addition the length of the spring of the armature does not vary during the opening phase of the needle between the open position and the closed position of the injection nozzle. The frame comprises an active face facing the pole piece and opposite to a lower face. The spring of the armature is arranged between the needle and the underside of the frame. The pole piece is a cylinder provided with a central axial bore of constant section.

The method of operation of a injector according to the injector described above comprises:

a resting step in which the needle is in the closed position and the reinforcing spring has a LO length at rest,

a pre-opening step in which the needle remains in the closed position, the armature is attracted by the pole piece and the reinforcing spring elongates to have a length L1,

an opening step in which the armature still continues its movement towards the pole piece and drives the needle towards the open position, the reinforcement spring remaining at the length L1.

In addition, said method further comprises:

a closing step in which the needle in the open position moves towards the closed position and drives the armature, the armature spring remains at the length L1, a post-closure step in which the needle is in the closed position and the armature moves pulled by the armature spring, the armature spring compresses from the length L1 to the length L0.

BRIEF DESCRIPTION OF THE DRAWINGS

Other features, objects and advantages of the invention will appear on reading the detailed description which follows, and with reference to the accompanying drawings, given by way of non-limiting example and in which:

Figure 1 is a sectional view of an injector of the prior art.

Figure 2 is a sectional view of an injector with the armature spring according to a first embodiment of the invention.

Figure 3 is a sectional view of the armature spring of the first embodiment of the invention.

Figure 4 is a sectional view of the injector according to the invention during the four operating phases of the injector and the armature spring.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The invention is now described with reference to the figures and for the sake of clarity and conciseness of the description a top-down orientation in the sense of FIG. 1 will be used without any limiting intention as to the extent of the protection, particularly with regard to the different installations of an injector in a vehicle. Words such as "up, down, below, above, vertical, up, down ..." will be used without limiting intent.

As shown in FIG. 2, the invention relates to a fuel injector 20 for an internal combustion engine, here the injector 20 is a gasoline injector although the invention can be fully transposed to a diesel injector or any other fuel . The description will detail the elements of the invention and will remain more succinct and general as to the elements

surrounding.

According to FIGS. 2 and 3, the injector 20 extends along an axis

longitudinal X. The injector 20 is a fuel injector for an internal combustion engine. The injector 20 comprises a tubular injector body 22, an electromagnetic actuator 24, a needle 26 with a ball 28 integral and a armature spring 30.

The injector body 22 comprises an open upper end and a lower end provided with an injection nozzle 32. The body 22

injector extends along the X axis.

The electromagnetic actuator 24 comprises a fixed annular coil 34, a fixed pole piece 36 and an armature 38. The movable armature 38 is provided with an axial hole inside which the needle 26 is guided axially sliding.

The needle 26 is axially movable in the body 22 between a closed position and an open position of the injection nozzle 32. The needle 26 comprises a first end arranged close to the ball 28 and the injection nozzle 32 of the body and a second end arranged close to the pole piece 36, a return spring of the needle 26 and the coil 34. The needle 26 has a diameter D1 and a diameter D2, the diameter D1 between the first end of the needle 26 and a conical shoulder 39 and the diameter D2 included the second end and the conical shoulder 39. The diameter D1 of the needle 26 is less than or equal to the diameter D2 of the needle 26.

The armature spring 30 is fixed on the one hand to the armature 38 and on the other hand to the needle 26. The armature spring 30 is a tension spring with turns contiguous at these ends. The armature spring 30 is a return spring.

According to Figures 2 and 3, a first embodiment is shown. The armature 38 comprises an active face 40 facing the pole piece 36 opposite a lower face 42. The armature spring 30 is arranged on the side of the lower face 42 of the armature. The armature 38 further comprises a circular groove 44 having a first annular face 46 close to the central hole emerging from the armature 38. The first face 46 of the groove 44 of the armature has a diameter D46. The first annular face 46 is provided with a thread arranged to receive turns of the reinforcing spring 30 during assembly. The needle 26 is provided with a thread above the conical shoulder 39 to receive turns of the reinforcing spring 30.

The reinforcing spring 30 has an internal diameter D30 less than the diameters D1 of the needle 26 and the diameter D46 of the first face of the groove. It will also be possible to choose the pitch of the thread of the rod 26 and / or the armature 38 to be slightly less than or greater than the wire diameter of the spring to generate additional frictional force (better hold). The reinforcement spring 30 is fixed. The assembly of the reinforcing spring 30 with the needle 26 and the armature 38 is as follows:

to provide the reinforcement spring 30, the needle 26, the armature 38,

-engaging the needle 26 in the central axial hole of the armature 38 to near the conical shoulder 39,

engage the reinforcement spring 30 around the needle 26 by the first end of the needle 26,

slide the armature spring 30 towards the second end of the needle 26 as far as the first face 46 of the armature groove, the turns of a first end of the armature spring 30 are arranged on the threading of the first face 46 of the groove of the armature as described in the left-hand part of FIG. 3,

-turning the turns of the second end of the reinforcing spring 30 to near the conical shoulder 39, the last turns of the second end of the reinforcing spring 30 being below the conical shoulder 39.

Alternatively the reinforcement spring 30 can be set up by rotation of the armature 38 and the needle 26 relative to the return spring of the needle 26, the engagement being made by screwing. It may be noted that the value of tensile force will be achieved by the more or less important screwing of the reinforcement spring 30 on respectively the reinforcement 38 and the needle 26. The tensile force on the reinforcement spring 30 will be about 5 N.

In a second embodiment not shown, the armature 38 is provided with the first face 46 of the groove with a substantially smooth face. The surface of the needle 26 near the conical shoulder 39 has a smooth surface.

The assembly of the reinforcing spring 30 with the needle 26 and the armature 38 is done by a tight assembly. The assembly is done as follows:

to provide the reinforcement spring 30, the needle 26, the armature 38,

the needle 26 is engaged in the central axial hole of the armature 38 to a distance, for example approximately 2 and 10 mm, from the conical shoulder 39. engage the reinforcement spring 30 around the needle 26 by the first end of the needle 26,

slide the armature spring 30 towards the second end of the needle 26 as far as the first face 46 of the armature groove, the turns of a first end of the armature spring 30 are arranged on the first face 46 of the throat of the frame. The diameter D30 of the reinforcing spring is smaller than the diameters D1 of the needle 26 and D46 of the first face 46 of the groove of the armature, the reinforcing spring 30 can therefore be mounted to tighten and remain fixed on the armature 38 and needle 26,

-To mount the turns of the second end of the armature spring 30 near the conical shoulder 39 so as to have a few turns, of the order of 1 to 4 turns, above the conical shoulder 39.

In an alternative to the second embodiment not shown, the coil arranged at the end of the first end of the reinforcing spring 30 is laser welded to the frame 38 to ensure its maintenance. In addition, to reinforce the retention of the armature spring 30 on the needle 26, the nearest turn arranged above the conical shoulder 39 is laser-welded to the needle 26.

When assembling the reinforcing spring 30, the steps are identical to the first embodiment, to which a soldering step is added:

laser-welding the coil arranged at the end of the first end of the armature spring 30 to the armature 38 and the coil arranged closest to the conical shoulder 39 to the needle 26.

In a third embodiment not shown, the first face 46 of the groove has a substantially flat surface. The conical shoulder 39 of the needle has a smooth surface. The reinforcement spring 30 is a piece of metal fixed on the one hand to the first face 46 of the reinforcement groove 44 and on the other hand to the needle 26.

The assembly of the reinforcing spring 30 with the needle 26 and the armature 38 may be carried out as described above for the previous embodiments, such as adding a thread on the first face 46 of the armature groove or the laser welding or the tight fitting of the armature spring 30. FIG. 3 represents on a left-hand side the mounting of the armature spring 30 on the needle 26, ie the step of engagement of the armature spring 30 on the needle 26. FIG. 3 shows on a straight part the final assembly of the reinforcement spring 30 on the needle 26.

As shown in FIG. 4, the operating method of the injector 20 according to the invention will be presented in this chapter. The operating method of the injector 20 corresponds to the embodiments of the invention described above. The operating method of the injector 20 comprises:

a rest stage A in which the needle 26 is in the closed position and the armature spring 30 has a length L0 at rest,

a preopening step B in which the needle remains in the closed position, the armature 38 is attracted by the pole piece 36 and the armature spring 30 extends to a length L 1,

an opening step C in which the armature 38 still continues its movement towards the pole piece 36 and drives the needle 26 to the open position, the armature spring 30 remaining at the length L1.

a closing step D in which the needle 26 in the open position moves towards the closed position and drives the armature 38, the armature spring 30 remains at the length L 1,

- A post-closure step in which the needle 26 is in the closed position and the armature 38 moves pulled by the armature spring 30, the armature spring 30 is compressed from the length L1 to the length L0. The post-closure step corresponds to the return to rest step A.

LIST OF REFERENCES USED

1 injector

2 actuator

3 bodies

4 needle

5 ball

6 reinforcement spring

7 fixed coil

8 piece fleece

9 frame

10 recess of the polar piece

11 annular groove

12 active face of the frame 20 injector

22 bodies

24 actuator

26 needle

28 ball

30 reinforcement spring

32 injection nozzle

34 reel

36 pole piece

38 frame

39 conical shoulder

40 active face

42 underside

44 reinforcement throat

46 first face of the throat

X axis longitudinal axis

D46 diameter of the first face of the groove D30 inside diameter of the reinforcement spring DI diameter of the needle

D2 diameter of the needle

Claims

A fuel injector (20) for an internal combustion engine, the injector (20) extending along a main axis (X) and comprising:

a needle (26) axially movable in the body (22) between a closed position and an open position of the injection nozzle (32),

an electromagnetic actuator (24) comprising an annular fixed coil (34), a fixed pole piece (36) and an armature (38) movable in the body (22) provided with an axial hole inside which the needle (26) is slidably guided,

characterized in that the injector (20) further comprises an armature spring (30) fixed on the one hand under the armature (38) and on the other hand on the needle (26), the needle 26 being provided threading above the conical shoulder 39 to receive turns of the reinforcing spring 30.

2. Injector (20) according to any one of the preceding claim wherein the length of the spring of the armature (26) does not vary during the opening phase of the needle (26) between the open position and the closed position of the injection nozzle (32).

3. Injector (20) according to any one of claims 1 or 2 wherein the armature (38) comprises an active face (40) facing the pole piece (36) and opposite a lower face (42), the spring the armature (30) being arranged between the needle (26) and the lower face (42) of the armature.

4. Injector (20) according to the preceding claim wherein the pole piece (36) is a cylinder provided with a central axial bore of constant section.

An operating method of an injector (20) according to any one of claims 1 to 4, said method comprising:

a resting step in which the needle (26) is in the closed position and the reinforcing spring (30) has a length L0 at rest, a pre-opening step in which the needle remains in the closed position, the armature (38) is attracted by the pole piece (36) and the armature spring (30) extends to a length L1,

an opening step in which the armature (38) still continues its movement towards the pole piece (36) and drives the needle (26) towards the open position, the reinforcement spring (30) remaining at the length ll.

The method of operation of an injector (20) according to claim 5, said method comprising:

a closing step in which the needle (26) in the open position moves towards the closed position and drives the armature (38), the armature spring (30) remains at the length L1,

a post closure step in which the needle (26) is in the closed position and the armature (38) moves pulled by the armature spring (30), the armature spring (30) is compressed from the length L1 to length L0.