EP3875747A1

EP3875747A1 - Valve assembly for an injection valve and injection valve

Info

Publication number: EP3875747A1
Application number: EP20161453.4A
Authority: EP
Inventors: Stefano Filippi; Valerio Polidori; Mauro Grandi
Original assignee: Vitesco Technologies GmbH
Current assignee: Vitesco Technologies GmbH
Priority date: 2020-03-06
Filing date: 2020-03-06
Publication date: 2021-09-08

Abstract

Valve assembly (2) for an injection valve (1) for pre-combustion injections, comprising- a valve body (4) with a longitudinal axis L, the valve body (4) comprising a cavity (9) with a fluid inlet portion (5) and a fluid outlet portion (7),- a valve needle (11) axially moveable in the cavity (9), the valve needle (11) preventing a fluid flow through the fluid outlet portion (7) in a closing position and releasing the fluid flow through the fluid outlet portion (7) in at least one opening position,- an electro-magnetic actuator unit (19) being designed to actuate the valve needle (11), the electro-magnetic actuator unit (19) comprising- an armature (23) axially movable in the cavity (9) and joined to the valve needle (11), the armature (23) having an upper side (27) facing towards the fluid inlet portion (5) and a lower side (29) facing towards the fluid outlet portion (7) and a circumferential side wall (31) facing towards the valve body (4);- a pole piece (25), towards which the armature (23) is movable into the at least one opening position;wherein- the armature (23) divides the cavity (9) into an upper part (33) adjacent to the upper side (27) of the armature (23) and a lower part (35) adjacent to the lower side (29) of the armature (23) and the only fluid path between the upper part (33) and the lower part (35) is provided by a gap (37) between the side wall (31) of the armature (23) and the valve body (4), a width b of the gap (37) being smaller or equal to 5 µm, and- the fluid outlet portion (7) comprises an opening (39) with a diameter d of less than 80 µm.

Description

The present invention relates to a valve assembly for an injection valve and to an injection valve, e.g. a fuel injection valve of a vehicle. It particularly relates to solenoid injection valves for pre-combustion injections.
The stringent legislation regarding particulate matter in combination with the requirement to decrease CO₂ emissions leads the automotive industries to consider new strategies for torque production. One of the areas of strong development are hybrid vehicles as a mix of a traditional internal combustion engine and an electrical engine. In some applications, a pre-combustion in a special chamber is considered. This chamber has diverging paths for the flame front to ignite the combustion in the main chamber of the internal combustion engine at lean mixture. This architecture is under development with preliminary very encouraging results in terms of CO₂-reduction.
An injector suitable for pre-combustion injections needs to work well at a limited pressure, for example at about 100 to 200 bar. Furthermore, the amount of fuel injected and the intended spray formation differ from standard injectors. While standard injectors working at pressures of about 350 to 500 bar typically have a minimum dynamic flow of 1 mg per stroke, for a pre-combustion injection a flow of only 0,1 to 0,3 mg per stroke is required.
Furthermore, standard injectors optimised to work at higher pressure are likely to experience micro-bounces and reopening events if used for pre-combustion injections, which might lead to considerable additional injections.
It is an object of the present invention to provide a valve assembly for an injection valve suitable for pre-combustion injections that overcomes the above-mentioned difficulties and which provides a stable performance under the special conditions of pre-combustion injections.
This object is achieved by means of the valve assembly according to the independent claim.
Advantageous embodiments and developments are objects of the dependent claims.
According to an aspect of the invention, a valve assembly for an injection valve for pre-combustion injections is provided. The valve assembly comprises a valve body with a longitudinal axis L, the valve body comprising a cavity with a fluid inlet portion and a fluid outlet portion. The valve assembly further comprises a valve needle axially movable in the cavity, the valve needle preventing a fluid flow through the fluid outlet portion in a closing position and releasing the fluid flow through the fluid outlet portion in at least one opening position.
The valve assembly further comprises an electromagnetic actuator unit designed to actuate the valve needle. The electromagnetic actuator unit comprises an armature axially movable in the cavity and joined to the valve needle. The armature has an upper side facing towards the fluid inlet portion and a lower side facing towards the fluid outlet portion. The essentially cylindrical armature furthermore has a circumferential sidewall facing towards the valve body. The electromagnetic actuator unit further comprises a pole piece, towards which the armature is movable into the at least one opening position.
The armature divides the cavity into an upper part adjacent to the upper side of the armature and a lower part adjacent to the lower side of the armature. The only fluid path between the upper part and the lower part is provided by a gap between the sidewall of the armature and the valve body. A width of the gap is smaller than or equal to 5 µm. The fluid outlet portion comprises an opening with a diameter d of less than 80 µm.
The opening is in particular a single opening. If there is more than one opening provided at the fluid outlet portion, the diameter d indicates the sum of the diameters of these openings.
The valve assembly according to the invention has the advantage, that it is suitable to provide a fuel spray with limited penetration and a limited injection quantity as required for pre-combustion. This is achieved by the ballistic motion of the armature in combination with the nozzle design as follows:
The initial pressure in the lower part of the cavity in combination with the geometry of the opening itself controls the flow out of the opening. The small diameter d of the opening results in a limited penetration of the spray and a limited quantity of injected fuel.
When the valve is actuated and the armature moves upwards towards the pole piece, moving the valve needle away from the fluid outlet portion, the pressure in the lower part of the cavity drops. Since the only fuel path between the upper part and the lower part of the cavity is the relatively small gap between the sidewall of the armature and the valve body, fuel cannot pass from the upper part to the lower part fast enough to compensate the pressure drop. This results in a pressure difference between the upper part and the lower part, the relatively low pressure in the lower part resulting in a small quantity of fuel injected and a small penetration of the spray, the relatively large pressure in the upper part resulting in a deceleration of the armature due to hydraulic damping.
At closing event, the large pressure in the upper part of the cavity exerts a force on the armature to prevent a re-opening of the valve, which might result in undesirable further injections.
As a result, the valve assembly is particularly well suited for pre-combustion injectors.
According to an embodiment of the invention, the width b of the gap between the sidewall of the armature and the valve body is 1 ≤ b ≤ 3 µm.
According to an embodiment, to the diameter d of the opening 50 ≤ d ≤ 70 µm applies.
It has been found, that with a gap of this width and/or an opening with this diameter, the sought spray characteristic and quantity of injected fuel may be achieved.
According to an embodiment of the invention, the opening is tilted with respect to the longitudinal axis L of the valve body. By the opening being tilted it is understood that a longitudinal axis I of the opening is not parallel to the longitudinal axis L of the valve body. In particular, the opening may, on an inner side of the valve body, be in a central position, while on the outside of the valve body, it is in a position somewhat peripheral. In this case, the longitudinal axis I of the opening and the longitudinal axis L of the valve body intersect at an angle, where the opening is positioned on the inner side of the valve body.
This has the advantage, that the spray penetration is reduced and the spray geometry is advantageous for pre-combustion injections.
A maximum lift of the valve needle is preferably less than 30 µm, for example 20 µm, which is about half the lift of a standard injector.
According to an aspect of the invention, an injection valve for pre-combustion injections is provided with the described valve assembly. The injection valve is particularly well suited for pre-combustion injections due to the spray geometry and the low spray penetration.
Further advantages, advantageous embodiments and developments of the valve assembly for an injection valve and the fluid injection valve will become apparent from the exemplary embodiments which are described below in association with schematic figures.

Figure 1: shows a cross sectional view of an injection valve with a valve assembly according to one embodiment of the invention;
Figure 2: shows a cross-sectional detailed view of a part of the injection valve according to figure 1 and
Figure 3: shows a cross-sectional detailed view of a further part of the injection valve according to figure 1.

Figure 1 shows an injection valve 1 that is in particular suitable for dosing fuel into an internal combustion engine in a pre-combustion injection. The injection valve 1 comprises in particular a valve assembly 2. The valve assembly 2 comprises a valve body 4 with a central longitudinal axis L. A housing 6 is partially arranged around the valve body 4.
The valve body 4 comprises a cavity 9. The cavity 9 has a fluid outlet portion 7. The fluid outlet portion 7 communicates with a fluid inlet portion 5 which is provided in the valve body 4. The fluid inlet portion 5 and the fluid outlet portion 7 are in particular positioned at opposite axial ends of the valve body 4. The cavity 9 takes in a valve needle 11. The valve needle 11 comprises a needle shaft 15 and a sealing ball 13 welded to the tip of the needle shaft 15.
In a closing position of the valve needle 11 it sealingly rests on a seat plate 17 having a single opening functioning as an injection nozzle. A preloaded calibration spring 18 exerts a force on the needle 11 towards a closing position. The fluid outlet portion 7 is arranged near the seat plate 17. In the closing position of the valve needle 11 a fluid flow through the opening is prevented.
The valve assembly 2 is provided with an electro-magnetic actuator unit 19. The electro-magnetic actuator unit 19 comprises a coil 21, which is preferably arranged inside the housing 6. Furthermore, the electro-magnetic actuator unit 19 comprises an armature 23. The housing 6, parts of the valve body 4 and the armature 23 are forming an electromagnetic circuit. The actuator unit 19 further comprises a pole piece 25.
The armature 23 is axially movable in the cavity 9. The armature 23 is, in this embodiment, fixed to the valve needle 11 and is axially movable relative to the valve body 4.
The armature 23, which is shown in more detail in figure 2, has an essentially cylindrical shape with an upper side 27, a lower side 29 and the circumferential sidewall 31. A gap 37 is arranged between the sidewall 31 of the armature 23 and the valve body 4. The gap 37 has a width b of not more than 5 µm. The gap 37 provides the only fuel path between the upper part 33 and the lower part 35 of the cavity 9.
The armature 23 divides the cavity 9 in an upper part 33 and a lower part 35. The upper part 33 of the cavity 9 extends from the fluid inlet portion 5 to the upper side 27 of the armature 23. The lower part 35 of the cavity 9 extends from the lower side 29 of the armature 23 to the fluid outlet portion 7.
Figure 3 shows a detail of figure 1 in the region of the fluid outlet portion 7. In figure 3, the injection nozzle is shown as a single opening 39 with a longitudinal axis I and a diameter d. The opening 39 extends from an inner side 41 of the seat plate 17 to an outer side 43. The longitudinal axis I of the opening 39 and the longitudinal axis L of the valve body 4 intersect where the opening 39 is positioned on the inner side 41 of the seat plate 17. Hence, the opening 39 extends from the centre of the seat plate 17 outwards.
When the injection valve 1 is operated and the coil 21 is energised, the armature 23 experiences a force upwards towards the pole piece 25. While moving upwards, the armature 23 takes the needle 11 with it and lifts the sealing ball 13 off the seat plate 17, unblocking the opening 39.
While the armature 23 is moving upwards, the pressure of the fuel in the lower part 35 of the cavity 9 decreases and the pressure in the upper part 33 of the cavity 9 increases or remains the same. The difference in pressure cannot be balanced quickly because the only fluid path between the upper part 33 and the lower part 35 is the relatively small gap 37 between the sidewall 31 of the armature 23 and the valve body 4. Hence, a pressure drop between the upper part 33 and the lower part 35 of the cavity 9 is established.
The pressure drop has several effects. Firstly, the decreasing pressure in the lower part 35 limits the quantity of fuel injected. Furthermore, the pressure drop results in a dampening of the upwards motion of the armature 23.
Furthermore, when the coil 21 is denergised, the armature 23 starts moving downwards, taking the needle 11 with it. Once again, the motion of the armature 23 is dampened and the pressure difference between the lower part 35 of the cavity 9 and the upper part 33 of the cavity 9 prevents reopening events of the needle 11.
When the valve 1 has closed after an injection, a re-filling of the lower part 35 of the cavity 9 takes place through the gap 37. The width b of the gap 37 is optimised considering the maximum frequency of operation.

Claims

Valve assembly (2) for an injection valve (1) for pre-combustion injections, comprising
- a valve body (4) with a longitudinal axis L, the valve body (4) comprising a cavity (9) with a fluid inlet portion (5) and a fluid outlet portion (7),

- a valve needle (11) axially moveable in the cavity (9), the valve needle (11) preventing a fluid flow through the fluid outlet portion (7) in a closing position and releasing the fluid flow through the fluid outlet portion (7) in at least one opening position,

- an electro-magnetic actuator unit (19) being designed to actuate the valve needle (11), the electro-magnetic actuator unit (19) comprising

- an armature (23) axially movable in the cavity (9) and joined to the valve needle (11), the armature (23) having an upper side (27) facing towards the fluid inlet portion (5) and a lower side (29) facing towards the fluid outlet portion (7) and a circumferential side wall (31) facing towards the valve body (4);

- a pole piece (25), towards which the armature (23) is movable into the at least one opening position;
wherein
- the armature (23) divides the cavity (9) into an upper part (33) adjacent to the upper side (27) of the armature (23) and a lower part (35) adjacent to the lower side (29) of the armature (23) and the only fluid path between the upper part (33) and the lower part (35) is provided by a gap (37) between the side wall (31) of the armature (23) and the valve body (4), a width b of the gap (37) being smaller or equal to 5 µm, and

- the fluid outlet portion (7) comprises an opening (39) with a diameter d of less than 80 µm.
Valve assembly (2) according to claim 1,
wherein the width b of the gap (37) between the side wall (31) of the armature (23) and the valve body (4) is 1 ≤ b ≤ 3 µm.
Valve assembly (2) according to claim 1 or 2,
wherein to the diameter d of the opening (39) 50 ≤ d ≤ 70 µm applies.
Valve assembly (2) according to any of the preceding claims,
wherein the opening (39) is tilted with respect to a longitudinal axis L of the valve body (4).
Valve assembly (2) according to any of the preceding claims,
wherein the maximum lift of the valve needle (11) is less than 30 µm.
Injection valve (1) for pre-combustion injections with a valve assembly (2) according to one of the preceding claims.