GB2569588A - Direct acting fuel injector - Google Patents

Abstract

An electromagnetic actuator and a fuel injector are disclosed. The actuator 16 comprises a magnetic outer body 17, housing an annular solenoid 20 that surrounds a central pole 22. A movable magnetic armature 24 is slidably guided along an axis X and defines an air gap G1 with the core 22. The moving core 24 has means 44 to shunt the magnetic flux M to force it to follow a magnetic flow path P and so prevent magnetic leaks. The magnetic barrier 44 may be integral to a skirt portion 32, formed by: a groove in the internal or external surface, a non-magnetic tubular welded to the base 30 of the armature, or a demagnetized zone. The actuator limits counter forces and prevents delay of injection without the need for extract cost and complexity due to extra components such as a non-magnetic stop ring.

Description

DIRECT ACTING FUEL INJECTOR

TECHNICAL FIELD

The present invention relates to a direct acting fuel injector and more particularly to an electromagnetic actuator arranged to control a valve member of said injector.

BACKGROUND OF THE INVENTION

In direct acting fuel injectors an electromagnetic actuator directly controls the displacements of a needle valve member. Said needle lifts off a valve seat toward an open position enabling fuel injection when a magnetic armature magnetically attracted toward a pole piece pulls the needle. Furthermore, a nonmagnetic steel-made stop ring is arranged on a shoulder face internal to the injector body in order to maximise the magnetic attracting forces. Said ring drives the magnetic flux and reduces the magnetic leaks between the armature and the injector body, said leaks generating undesired counter forces resulting in a delay of injector opening and adding part to part variation. The non-magnetic stop ring is an additional component requiring additional process step during the injector build thereby adding complexity and cost and increasing part to part variations due to stack-up and geometrical imprecision.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to resolve the above mentioned problems in providing and electromagnetic actuator suitable to be arranged in a fuel injector of a fuel equipment of an internal combustion engine. Said actuator comprises the fixed coaxial and concentric arrangement of a magnetic outer tubular body housing an annular solenoid itself surrounding a central pole piece and, a mobile magnetic armature slidably guided along a longitudinal axis and defining an air-gap with said pole piece. When energising the solenoid a magnetic flux attracting the armature toward the pole piece in an active position closing said air-gap is generated. Said magnetic flux loops around the solenoid in a magnetic path comprising the body, the pole piece and said armature. The actuator is further provided with a magnetic shunt forcing said flux to follow said magnetic path preventing magnetic leaks, said magnetic shunt being integral to the armature.

The armature may have a cup-like shape with a disc-like base radially extending to a circular edge wherefrom a tubular skirt axially extends toward a distal end. Said skirt forms a wall having a cylindrical outer face coaxial to an inner face partially defining an inner void and wherein, said magnetic shunt is integral to the skirt forming a boundary preventing, at least partially, the flux to get in the skirt.

In an embodiment, the shunt is a groove provided in the outer face of the skirt, said groove locally restricting the thickness of skirt.

In another embodiment, the shunt is a groove provided in the inner face of the skirt.

In yet another embodiment said shunt comprises non-magnetic tubular welded to the base.

In yet another embodiment, said shunt defines a demagnetised zone of the skirt extending from said distal end, said zone defining a non-magnetic ring.

The invention further extends to a fuel injector suitable to spray fuel in a cylinder of an internal combustion engine, said injector comprising an electromagnetic actuator as described above.

Said fuel injector may further comprise a longitudinally guided valve member cooperating with said magnetic armature so that in use, when the armature moves toward the pole piece closing said air-gap it pulls the valve member into an open position enabling fuel spray through injection holes.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is now described by way of example with reference to the accompanying drawings in which:

Figure 1 is an axial section of a fuel injector actuator as per a first embodiment of the invention.

Figure 2 is a magnified view of a first embodiment of the magnetic armature of the actuator of figure 1.

Figure 3 is similar to figure 2 showing a second embodiment of the invention.

Figure 4 is similar to figure 3 showing a third embodiment of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

A gasoline injector 10 adapted to be arranged in a fueling equipment of an internal combustion engine extends along a longitudinal axis X and it comprises an actuator assembly 12 and a nozzle assembly 14, wherein an electromagnetic actuator 16 cooperates with a needle valve member 18 which controls the opening and the closing of injection holes through which fuel is sprayed in a cylinder of the engine.

More precisely in reference to figure 1, in the actuator assembly 12 said electromagnetic actuator 16 comprises a mobile magnetic armature 24 cooperating with a fixed coaxial and concentric arrangement of an outer tubular actuator body 17 housing an annular solenoid 20, itself surrounding a central pole piece 22.

The nozzle assembly 14 has a hollow body 26 defining an inner space in which said needle valve member 18 is guided along said longitudinal axis X, the needle extending from a head portion 28, visible on figure 1, to a tip end, not shown, cooperating with a valve seat to control said injection holes.

The armature 24 has a cup-like shape, shown upside-down on the figure, with a thick disc-like base 30 radially extending to an outer edge wherefrom a skirt 32 axially X extends from said base 30 toward a distant annular end 34. Said skirt 32 forms a cylindrical wall surrounding a void V under the base 30, the base 30 and the skirt 32 sharing a common outer cylindrical face 36 defining with an inner face of the nozzle body 26 means for slidably guiding the armature 24.

The armature 24 is further provided with a magnetic shunt 44 arranged by the junction of the base 30 and the skirt 32, said shunt 44 magnetically isolating the skirt 32 from the base 30. Several embodiments of said shunt 44 are detailed afterward. In use, said armature 24 moves between a rest position P0, shown on the figure, where the distant end 34 of the skirt abuts a shoulder 46 of the nozzle body 26 opening at the opposite end an air-gap G1 between the armature base 30 and the pole piece 22 and, an active position Pl where the armature 24 is closer to the pole piece, the skirt distant end 34 being lifted from said shoulder 46 and said air-gap G1 being closed.

Furthermore, the disc base 30 is provided with a central hole 40 through which the needle head 28 is slidably guided and upwardly extends in a bore 42 axially X provided in the pole piece 22, and, the needle 18 downwardly extends toward said tip end not shown. In the upper face 38 of the armature, said central hole 40 opens in a recess 48 and, the needle head 28 is provided with a collar 50 defining a spring seat, said collar 50 being in said recess 48, a small clearance G2 being defined between the under face of the collar and the bottom face of the recess, said small clearance G2 being smaller than the air-gap G1.

The actuator assembly 12 further comprises a coaxial arrangement of a needle spring 52 and an armature spring 54 both surrounding the needle head, the needle spring 52 being arranged in the pole piece central bore 42 wherein it is compressed between said needle head collar 50 and a shoulder provided in said bore 42 and, the armature spring 54 outwardly surrounding the needle spring 52 and being compressed between a bottom face 56 of the armature recess 48 and a shoulder 58 arranged in said pole piece central bore. The needle spring 52 downwardly pushes the needle 18 toward a closed position CP to close the injection holes and, the armature spring 54 downwardly pushes the armature 24 toward the rest position P0.

In use, in a first phase, as shown on figure 1, the solenoid 20 is not energised. The needle spring 52 and the armature spring 54 respectively push the needle 18 toward the closed position CP and the armature 24 toward the rest position P0. The end 34 of the skirt abuts the shoulder 46 of the nozzle body 26, the air-gap G1 and the clearance G2 are maximised.

In a second phase, the solenoid 20 is energised and it generates a magnetic flux M that loops in a magnetic path P comprising the actuator body 17, the pole piece 22 and the magnetic armature 24. As it is known, under the influence of said magnetic flux M, the armature 24 is attracted toward the pole piece 22 and it lifts off the rest position P0 toward the active position Pl.

At beginning, the armature 24 upwardly moves and closes the clearance G2. The armature spring 54 compresses, the needle 18 remaining in said closed position CP.

Subsequently, the bottom face 56 of the recess comes in contact against the collar 50 closing the clearance G2. The armature 24 pursues its upward displacement and upwardly drives the needle 18 that lifts off the closed position CP toward the open position OP, the needle spring 52 further compressing.

The magnetic force attracting the armature depends on the magnetic flux going from the armature to the pole piece through the air-gap G1. To maximise said magnetic force it is key to direct the magnetic flux entering the armature 24 toward the air-gap G1 and to prevent downward magnetic leaks through the skirt 32 and the nozzle body 26. Indeed said leaks generate between the skirt end 34 and the body shoulder 46 parasitic forces tending to maintain the armature in the rest position P0.

The magnetic shunt 44 creates a barrier that channels the flux M to the base 30 and reduces said leaks through the skirt 32.

In a first embodiment of the invention shown in figures 1 and 2, the magnetic shunt 44 is an annular groove 60 dug in the outer cylindrical face 36 of skirt, said groove 60 restricting the material thickness of the skirt. In this embodiment the base 30 and the skirt 32 are made of the same material and have the same mechanical and magnetic properties, the groove 30 making the passage of the magnetic flux more difficult thus forcing the flux M toward in the base 30. For instance, tests have been successfully performed within an armature made in stainless steel, the skirt 32 having a wall thickness of 0.5 mm and the groove 60 having a width of about 1mm.

In an alternative not shown, said groove may be dug in the inner face of the skirt.

In a second embodiment of the invention shown on figure 3, the shunt 44 is a tubular member 62 welded to the base 30, said tubular member 62 forming the skirt 32 of the armature and being made of a non-magnetic material.

In an alternative not shown, said tubular member 62 is made of nonmagnetic material and is fixed using another known process adapted to said material.

In this second embodiment, the sequence of manufacturing steps comprises the step of welding, or other fixation means, of the tubular member 62 onto the base 30 followed by the step of machining the outer face 36 of the armature, this being done, for instance, by grinding or turning.

In a third embodiment of the invention shown on figure 4, the armature 24 is integrally made of a single magnetic material and, the end zone 64 of the skirt 32 is afterward demagnetized, creating said magnetic shunt 44. The at least partial alteration of the magnetic properties is done thanks to a local heat treatment of the skirt 32 or any other process that influence the magnetic properties locally

Another known method is the alloying of the skirt with nickel to increase the proportion of austenite in the martensitic structure

All said invention embodiments enable to have an integral armature 24 wherein the flux M circulating is driven to pass through the base 30 and not through the skirt 32.

LIST OF REFERENCES

X longitudinal axis

G1 air-gap

G2 clearance

P0 rest position of the armature

Pl active position of the armature

CP closed position of the needle

OP open position of the needle

V void

M magnetic flux

P magnetic path injector actuator assembly nozzle assembly electromagnetic actuator actuator body needle valve member solenoid pole piece magnetic armature nozzle body needle head base of the armature skirt of the needle distant end of the skirt outer face of the armature upper face of the armature central hole bore in the pole piece magnetic shunt shoulder recess collar - spring seat needle spring armature spring bottom face of the recess shoulder groove - magnetic shunt (1st embodiment) tubular member - magnetic shunt (2nd embodiment) demagnetised zone of the skirt (3rd embodiment)

Claims (8)

1. Electromagnetic actuator (16) suitable to be arranged in a fuel injector (10) of a fuel equipment of an internal combustion engine, said actuator (16) comprising the fixed coaxial and concentric arrangement of a magnetic outer tubular body (17) housing an annular solenoid (20) itself surrounding a central pole piece (22) and, a mobile magnetic armature (24) slidably guided along a longitudinal axis (X) and defining an air-gap (Gl) with said pole piece (22) so that when energising the solenoid (20) a magnetic flux (M) attracting the armature (24) toward the pole piece (22) in an active position (Pl) closing said air-gap (Gl) is generated, said magnetic flux (M) looping around the solenoid (20) in a magnetic path (P) comprising the body (17), the pole piece (22) and said armature (24) and wherein, the actuator (16) is further provided with a magnetic shunt (44) forcing said flux (M) to follow said magnetic path (P) preventing magnetic leaks said magnetic shunt (44) being integral to the armature (24).

2. Electromagnetic actuator (16) as claimed in the preceding claim wherein the armature (24) has a cup-like shape with a disc-like base (30) radially extending to a circular edge wherefrom a tubular skirt (32) axially (X) extends toward a distal end (34), said skirt (32) forming a wall having a cylindrical outer face (36) coaxial to an inner face partially defining an inner void (V) and wherein, said magnetic shunt (44) is integral to the skirt (32) forming a boundary preventing, at least partially, the flux (M) to get in the skirt (32).

3. Electromagnetic actuator (16) as claimed in claim 2 wherein said shunt (44) is a groove (60) provided in the outer face of the skirt, said groove (60) locally restricting the thickness of skirt (32).

4. Electromagnetic actuator (16) as claimed in claim 2 wherein said shunt (44) is a groove provided in the inner face of the skirt.

5. Electromagnetic (16) actuator as claimed in claim 2 wherein said shunt (44) comprises non-magnetic tubular welded to the base (32).

6. Electromagnetic actuator (16) as claimed in claim 2 wherein said shunt (44) defines a demagnetised zone of the skirt (32) extending from said distal end (34), said zone (64) defining a non-magnetic ring.

7. Fuel injector (10) suitable to spray fuel in a cylinder of an internal combustion engine, said injector comprising an electromagnetic actuator (16) as claimed in any one of the preceding claims.

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8. Fuel injector (10) as claimed in claim 7 further comprising a longitudinally guided valve member (18) cooperating with said magnetic armature (24) so that in use, when the armature moves toward the pole piece (22) closing said air-gap (Gl) it pulls the valve member (18) into an open position (OP) enabling fuel spray through injection holes.