VALVE ASSEMBLY FOR AN INJECTION VALVE AND FUEL INJECTION VALVE

Abstract

 A valve assembly (3) comprising a valve body (4) with a cavity (9) having a fluid inlet portion (5) and a fluid outlet portion (7), a valve needle (11) and an armature (23) is disclosed. The armature (23) has a plurality of flow holes (36) extending in an axial direction from an upper side (33) of the armature (23) to a lower side (35), the flow holes (36) permitting fuel to pass through the armature (23) . Inlets (37) of the flow holes (36) are at a distance R₁ from the central longitudinal axis L, wherein R₁ is larger than the radius r_P of a central opening (28) in an element of the valve assembly (3) adjacent to the upper side (33) of the armature (23) . Outlets (39) of the flow holes (36) are at a distance R₂ from the central longitudinal axis L, wherein R₂ is smaller than the radius r_H of a disc-shaped element (40) arranged in an axial region of the valve needle (11) adjacent to the lower side of the armature (23) . A fuel injection valve (1) comprising the valve assembly is also disclosed.

Description

[0001] The present invention relates to a valve assembly for a fluid injection valve and to a fluid injection valve, e.g. a fuel injection valve of a vehicle. It particularly relates to solenoid injection valves.

[0002] Such injection valves must be able to dose fluids even in the case of high fuel pressure. One design to ensure this is the "free-lift" design, which is disclosed e.g. in document EP 2985445 A1. According to this design, the armature of the electro-magnetic actuator unit travels about a "pre-stroke gap" or "free-lift gap" before it engages the needle to open the injector. Thus, kinetic energy is accumulated before the actual opening.

[0003] Injection valves of the "free lift"-design as well as those where the armature is fixed to the needle usually have a chrome plating on surfaces of the armature contacting the pole piece to improve wear resistance. However, the chrome plating is costly and should be avoided for environmental reasons.

[0004] There are alternative designs of injection valves, which eliminate contact between the armature and the pole piece. These "contactless designs" or "no hard stop"-designs make use of a high-stiffness spring to stop the armature during opening transient before it hits the pole piece. However, the high-stiffness spring requires installation space and can be costly.

[0005] It is an object of the present invention to provide a valve assembly for an injection valve and an injection valve that overcome the above-mentioned difficulties and provide a stable performance with a high maximum pressure.

[0006] This object is achieved by means of the valve assembly according to claim 1 and the injection valve according to claim 8. Advantageous embodiment and developments are objects of the dependent claims.

[0007] According to a first aspect of the invention, a valve assembly for an injection valve is provided, comprising a valve body with a central longitudinal axis comprising a cavity with a fluid inlet portion and a fluid outlet portion. Furthermore, the valve assembly comprises a valve needle axially movable in the cavity, the valve needle preventing a fluid flow through the fluid outlet portion in the closing position and releasing the fluid flow through the fluid outlet portion in further positions.

[0008] Furthermore, the valve assembly comprises an armature of an electromagnetic actuator unit being designed to actuate the valve needle. In an expedient embodiment, the armature is arranged in the cavity and axially displaceable relative to the valve body in reciprocating fashion. Preferably, the armature is also axially displaceable relative to the armature in reciprocating fashion. For actuating the valve needle, the armature may expediently be engageable in a form-fit connection with an armature retainer of the valve needle so that the armature is operable to take the valve needle with it, in particular when travelling axially towards a pole piece of the electromagnetic actuator unit, i.e. in direction towards the fluid inlet portion in case of an inward opening valve. An inward opening valve is a valve which is designed such that the valve needle is movable away from the closing position in axial direction from the fluid outlet portion towards the fluid inlet portion for opening the valve. The armature has a plurality of flow holes extending in an axial direction from an upper side of the armature facing towards the fluid inlet portion to a lower side facing towards the fluid outlet portion, the flow holes permitting fuel to pass through the armature.

[0009] Inlets of the flow holes on the upper side of the armature are at a distance R₁ from the central longitudinal axis L, wherein R₁ is larger than the radius r_P of a central opening in an element of the valve assembly adjacent to the upper side of the armature. Furthermore, outlets of the flow holes on the lower side of the armature are arranged at a distance R₂ from the central longitudinal axis L, wherein R₂ is smaller than the radius r_H of a disk-shaped element arranged in an axial region of the valve needle adjacent to the lower side of armature.

[0010] Hence, the following relations apply for the flow holes:



wherein the distances R₁ and R₂ are the distances of the point of the inlet and outlet closest to the longitudinal axis L, in other words: the distances R₁ and R₂ are the distances of an innermost rim of the inlet and outlet, respectively. If radius of the central opening varies along the axis L, r_P denotes the radius directly adjacent to the upper side of the armature.

[0011] According to this aspect of the invention, the inlets of the flow holes on the upper side of the armature have a radial overlap with the element of the valve assembly adjacent to the upper side of the armature. This element is usually the pole piece of the valve assembly and would in a traditional design of the injector be in contact with the upper side of the armature in a fully open position of the valve.

[0012] According to the invention, the inlets of the flow holes are arranged in the region of the upper side of the armature that would in the traditional design be in contact with the elements of the valve assembly adjacent to the other side of the armature, for example the pole piece. This has the effect, that due to the hydraulic force, which the fuel exerts on the upper side of the armature, there is a residual gap between the upper side of the armature and the elements of the valve assembly adjacent to the armature, for example the pole piece. This residual gap stays open because of the hydraulic force acting on the upper side of the armature.

[0013] In fact, the armature is suspended in the maximum opening position by an equilibrium of forces in a stable position. In the maximum opening position, a magnetic force acting in a direction away from the fluid outlet portion is balanced by the sum of the hydraulic force and a spring force exerted by the calibration spring, both acting in a direction towards the fluid outlet portion.

[0014] Consequently, there is no hard stop for the armature in the maximum opening position. Hence, there is no need for a plating of the surfaces to improve wear resistance.

[0015] Furthermore, the outlets of the flow holes on the lower side of the armature have a radial overlap with a disk-shaped element arranged adjacent to the lower side of the armature. Expediently, the disk-shaped element may be positionally fix relative to the valve body or relative to the valve needle.

[0016] This disk-shaped element may also be called a "hydro-disc" and may, in some embodiments, be fixed to the valve needle or may be formed in one piece with the valve needle. In an expedient embodiment, the disk-shaped element and the armature retainer of the valve needle are positioned on opposite axial sides of the armature. In this case, the armature retainer and the disk-shaped element may expediently limit the axial play of the armature relative to the valve needle in both axial directions, in particular the armature retainer in direction towards the fluid inlet portion and the disk-shaped element in direction towards the fluid outlet portion.

[0017] The radial overlap between the outlets and the disk-shaped element means that in a fully closed position of the valve the outlets are covered at least partially by the disk-shaped element. This has the effect, that fluid may be squeezed through the closing gap between the outlets and the disk-shaped element, thereby dissipating energy of the armature and dampening the armature movement.

[0018] Hence, the valve assembly has the advantage, that movement of the armature is dampened at the end of the opening phase as well as at the end of the closing phase of the valve. Because most of the energy of the armature is dissipated before the armature makes contact with the disk-shaped elements at the end of the closing phase, uncontrolled reopening of the needle should be prevented.

[0019] This is achieved solely by a design of the parts which uses the effect of the hydraulic force without the requirement of additional parts.

[0020] According to an embodiment of the invention, the following applies:

wherein d is the diameter of the flow holes.

[0021] In particular, r_H may be r_H > R₂ + 0.7 d, in particular r_H > R₂ + 0.9 d or even r_H > R₂ + d. If r_H is equal to the sum of R₂ and d, the outlets are fully covered by the disc-shaped element in a fully closed position.

[0022] According to an embodiment of the invention, a radial gap is arranged between an outer circumferential surface of the armature and an inner circumferential surface of the valve body, the radial gap establishing a fluid leakage path from the upper side of the armature to the lower side.

[0023] A "fluid leakage path" is understood in the present context to be a fluid path which is in particular dimensioned so that its contribution to the fluid flow is insignificant. In particular, the valve assembly comprises at least one main fluid path in parallel to the above described fluid leakage path. The hydraulic diameter of the main fluid path is preferably at least 10 times as large, for example at least 20 times as large as the hydraulic diameter of the fluid leakage path. The radial gap establishing the fluid leakage path may be just as large as is required due to manufacturing tolerances of the armature and the valve body. Alternatively, the hydraulic diameter of the fuel leakage path might be slightly larger than is required by manufacturing tolerances.

[0024] The radial gap between the armature and the valve body can support the dampening function, if it limits the amount of fluid passing outside the armature. Consequently, the hydraulic diameter of the fluid leakage path is chosen to be small enough to support the dampening effect in particular at the end of the closing phase. According to an aspect of the invention, a fuel injection valve is provided comprising the above-described valve assembly. The fuel injection valve has the advantages described above in connection with the valve assembly and is in particular suitable for being employed as a gasoline direct injection injector.

[0025] Further advantages, advantageous embodiments and developments of the invention will become apparent from the exemplary embodiments which are described below in association with the schematic figures.

Figure 1

shows a section of an injection valve according to a first embodiment of the invention and

Figure 2

shows details of the injection valve according to figure 1.

[0026] Figures 1 and 2 show an injection valve 1 that is in particular suitable for dosing fuel to an internal combustion engine. The injection valve 1 comprises in particular a valve assembly 3. The valve assembly 3 comprises a valve body 4 with a central longitudinal axis L. A housing 6 is partially arranged around the valve body 4.

[0027] 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.

[0028] In a closing position of the valve needle 11, the sealing ball 13 sealingly rests on a seat plate 17 having at least one 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, a fluid flow through the at least one injection nozzle is prevented. The injection nozzle may be, for example, an injection hole. However, it may also be of some other type suitable for dosing fluid.

[0029] The valve assembly 3 is provided with an electro-magnetic actuator unit 19. The electro-magnetic actuator unit 19 comprises a solenoid 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 form an electromagnetic circuit. The actuator unit 19 further comprises a pole piece 25.

[0030] The armature 23 is axially movable in the cavity 9 and fixed to the valve needle 11 by form fit. The needle 11 is guided by a central axial opening 26 in the armature 23. The armature 23 is axially movable relative to the needle 11, i.e. it may slide on the needle 11.

[0031] An armature retainer 25 is fixed to one end of the valve needle 11. An armature spring 27 is arranged between the retainer 25 and an upper side 33 of the armature 23. Adjacent to a lower side 35 of the armature 23, a hydro-disc 40 is fixed to the valve needle 11, an upper side 41 of the hydro-disc 40 being in contact with the lower side 35 of the armature 23 in a fully closed and in a fully open position of the valve 1.

[0032] The armature 23 comprises a number of flow holes 36, which provide a fluid path from the upper side 33 to the lower side 35. The flow holes 36 may be vertical or inclined. The flow holes 36 have a diameter d which is constant in the embodiment shown in figures 1 and 2, but which might vary in other embodiments. The flow holes 36 have an inlet 37 at the upper side 33 of the armature 23 and an outlet 39 at the lower side 35. A distance R₁ between the inlet 37 and the central longitudinal axis L is larger than a radius r_P of a central opening 28 of the pole piece 29.

[0033] A distance R₂ between the outlet 39 of the flow holes 36 and the central longitudinal axis L is smaller than a radius r_H of the hydro-disc 40. Hence, in the fully closed and in the fully open position of the valve, when the upper side 41 of the hydro-disc 40 is in contact with the lower side 35 of the armature 23, the outlets 39 of the flow holes 36 are covered by the hydro-disc 40.

[0034] Between an outer circumferential surface 47 of the armature 23 and an inner circumferential surface 49 of the body 4, there is a radial gap 45. The radial gap 45 establishes a fluid leakage path from the upper side 33 of the armature 23 to the lower side 35. Only a very small amount of fuel is able to pass through the radial gap 45. The main fluid path is through the flow holes 36 in the armature 23.

[0035] Figures 1 and 2 show the injection valve 1 in a fully closed position. To open the valve 1, the solenoid 21 is energized and the armature 23 experiences a magnetic force and slides upwards towards the pole piece 29, moving in axial direction away from the fluid outlet portion 7, thereby compressing the calibration spring 18.

[0036] The embodiment shown in figures 1 and 2 employs a "free-lift" concept. Only after having traveled a free-lift gap and after having taken up kinetic energy, the armature 23 takes the valve needle 11 with it via the retainer 25. Consequently, the valve needle 11 moves in axial direction out of the closing position of the valve 1.

[0037] Fuel starts to flow along the upper side 33 of the armature 23 and through the flow holes 36 and on into the cavity 9 below the armature 23, which is possible because a gap has opened between the hydro-disc 40 and the armature 23. The sealing ball 13 is lifted from the seat plate 17 and the at least one injection nozzle is unblocked.

[0038] While the armature 23 approaches the lower side 31 of the pole piece 29, the gap 43 between the upper side 33 of the armature 23 and the lower side 31 of the pole piece 29 is reduced. Hence, fuel is squeezed out of the gap 43. This process takes up energy. Hence, kinetic energy of the armature 23 is dissipated as the armature 23 approaches the pole piece 29.

[0039] The armature 23 stops moving upwards before contact with the pole piece 29 is made. Thus, in the maximum opening position of the valve 1, in which the needle 11 has travelled furthest upwards away from the fluid outlet portion 7, a residual gap 43 is formed between the upper side 33 of the armature 23 and the lower side 31 of the pole piece 29. The residual gap 43 stays open because of the hydraulic force the fuel exerts on the upper side 33 of the armature 23. Consequently, there is no hard stop for the armature 23 in the maximum opening position.

[0040] Similarly, energy is dissipated when the hydro-disc 40 approaches the armature 23 shortly before a maximum opening position of the valve 1 is reached or when the armature 23 approaches the hydro-disc 40 shortly before a closing position of the valve 1 is reached. In both cases, fuel is squeezed through a decreasing gap between the lower side 35 of the armature 23 and the upper side 41 of the hydro-disc 40 and dissipates energy.

[0041] In the embodiment shown in figures 1 and 2, the radius r_H of the hydro-disc 40 is larger than the sum of R₂ and d. Therefore, the outlets 39 of the flow holes 36 are covered completely by the hydro-disc 40 when the hydro-disc 40 makes contact with the armature 23.

[0042] In alternative embodiments not shown in the figures, the radius r_H of the hydro-disc 40 is smaller than the sum of R₂ and d, but still larger than R₂. Hence, the outlets 39 of the flow holes 36 are covered partially by the hydro-disc 40 when the hydro-disc 40 makes contact with the armature 23. According to these embodiments, the dampening effect is slightly reduced.

[0043] However, the dampening effect depends furthermore on the hydraulic area of the fuel leakage path through the radial gap 45. Therefore, dimensions of the valve assembly 1 may be chosen by taking into account several factors, in particular fuel pressure, the force exerted by the calibration spring 18, the width of the radial gap 45 and the relation between r_H and R₂.

[0044] When the solenoid 21 is de-energized, the calibration spring 18 is able to force the valve needle 11 to move in axial direction into its closing position. By dissipating energy of the armature 23 during the downward movement by way of the closing gap between the hydro-disc 40 and the armature 23, undesired re-opening of the needle 11 is prevented.

Claims

1. Valve assembly (3) for an injection valve (1), comprising

- a valve body (4) with a central longitudinal axis (L) 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 further positions;

- an armature (23) of an electro-magnetic actuator unit (19) being designed to actuate the valve needle (11), the armature (23) having a plurality of flow holes (36) extending in an axial direction from an upper side (33) of the armature (23) facing towards the fluid inlet portion (5) to a lower side (35) facing the fluid outlet portion (7), the flow holes (36) permitting fuel to pass through the armature (23), wherein inlets (37) of the flow holes (36) on the upper side (33) of the armature (23) are at a distance R₁ from the central longitudinal axis L, wherein R₁ is larger than the radius r_P of a central opening (28) in an element of the valve assembly (3) adjacent to the upper side (33) of the armature (23) and wherein outlets (39) of the flow holes (36) on the lower side (35) of the armature (23) are at a distance R₂ from the central longitudinal axis L, wherein R₂ is smaller than the radius r_H of a disc-shaped element (40) arranged in an axial region of the valve needle (11) adjacent to the lower side of the armature (23).

2. Valve assembly (3) according to claim 1,
wherein the disk-shaped element (40) is fixed to the valve needle (11) or in one piece with the valve needle (11) and the valve needle (11) comprises an armature retainer (25), the disk-shaped element (40) and the armature retainer (25) being positioned on opposite axial sides of the armature (23) and limiting an axial play of the armature (23) relative to the valve needle (11) in both axial directions.

3. Valve assembly (3) according to one of the preceding claims, wherein the element of the valve assembly (3) adjacent to the upper side (31) of the armature (23) is a pole piece (29) of the actuator unit (19).

4. Valve assembly (3) according to one of the preceding claims, wherein the following applies:

wherein d is the diameter of the flow holes (36).

5. Valve assembly (3) according to one of the preceding claims, wherein the following applies:

wherein d is the diameter of the flow holes (36).

6. Valve assembly (3) according to one of the preceding claims, wherein the following applies:

wherein d is the diameter of the flow holes (36).

7. Valve assembly (3) according to one of the preceding claims, wherein the following applies:

wherein d is the diameter of the flow holes (36).

8. Valve assembly (3) according to one of the preceding claims, wherein a radial gap (45) is arranged between an outer circumferential surface (47) of the armature (23) and an inner circumferential surface (49) of the valve body (4), the radial gap (45) establishing a fluid leakage path from the upper side (31) of the armature (23) to the lower side (35) .

9. Fuel injection valve (1), comprising a valve assembly (3) according to one of the preceding claims.

Drawing