Valve assembly for an injection valve and injection valve

Abstract

 A valve assembly (11) for an injection valve (100) comprises a valve body (14) including a central longitudinal axis (L), wherein the valve body (14) comprises a cavity (18). Furthermore the valve assembly (11) comprises a valve needle (20) axially moveable in the cavity (18) and preventing a fluid flow out of an injection nozzle in a closing position and enabling the fluid flow out of the injection nozzle apart from the closing position. The valve assembly (11) comprises an electro-magnetic actuator unit (36) being designed to actuate the valve needle (20). The electro-magnetic actuator unit comprises a coil (38) and a core, wherein the core comprises at least a pole piece (12). Additionally the actuator unit (36) comprises an armature (22) axially moveable in the cavity (18) between a first position and a second position. In the case the armature (22) is in the first position, the armature (22) and the pole piece (12) abut. In the case the armature (22) is in the second position, there is a given maximum gap between the pole piece (12) and the armature (22). Furthermore the valve assembly (11) comprises a permanent magnet (48) axially extending at least partly along the extension of the maximum gap, wherein the permanent magnet (48) is arranged radially outwards relative to the armature (22).

Description

[0001] The invention relates to a valve assembly for an injection valve and an injection valve. The vale assembly comprises a permanent magnet.

[0002] Increasingly stringent rules concerning the admissibility of noxious emissions from internal combustion engines which are arranged in vehicles render it necessary to take various measures which reduce the emission. One way to reduce these emissions is to improve the combustion process in the internal combustion engine. Injection valves are in wide spread use, in particular for internal combustion engines where they may be arranged in order to dose fluid into an intake manifold of the internal combustion engine or directly into the combustion chamber of a cylinder of the internal combustion engine.

[0003] The object of the invention is to provide a valve assembly and an injection valve which facilitate a reliable and precise function of the injection valve.

[0004] This object is achieved by the features of the independent claims. Advantageous embodiments of the invention are given in the sub-claims.

[0005] According to a first aspect the invention is distinguished by a valve assembly for an injection valve. The valve assembly comprises a valve body including a central longitudinal axis, wherein the valve body comprises a cavity. Furthermore the valve assembly comprises a valve needle axially moveable in the cavity and preventing a fluid flow out of an injection nozzle in a closing position and enabling the fluid flow out of the injection nozzle apart from the closing position. The valve assembly comprises an electro-magnetic actuator unit being designed to actuate the valve needle. The electro-magnetic actuator unit comprises a coil and a core, wherein the core comprises at least a pole piece.

[0006] Additionally the actuator unit comprises an armature axially moveable in the cavity between a first position and a second position. In the case the armature is in the first position, the armature and the pole piece abut. In the case the armature is in the second position, there is a given maximum gap between the pole piece and the armature. Furthermore the valve assembly comprises a permanent magnet axially extending at least partly along the extension of the maximum gap, wherein the permanent magnet is arranged radially outwards relative to the armature.

[0007] This contributes to a better control of the magnetic flux of the coil and the core. A higher magnetic force between the pole piece and the armature may be achieved and therefore a faster control of the actuator unit may be realized. By such a faster and more precise control of the actuator unit it may be possible to operate the injection valve under partial lift conditions or in a ballistic operating mode. In this way an influence of fluid properties and fluid pressure on a fluid flow may be reduced.

[0008] In the case the armature is in the first position it may be possible that the armature and the pole piece abut, in particular in the sense that there may be at least partly a minimal gap. The given maximum gap depends, for instance, on a detailed design of the valve assembly and its elements, e. g. like a calibration spring and/or a damping spring and/or an upper guide.

[0009] For instance the core may be mainly formed by a pole piece which for instance is at least a part of an inlet tube. But there may be additional or other elements guiding and/or amplifying a magnetic field induced by the coil and therefore may be assigned to the core, like a housing and/or a valve body. The armature, the coil and the core of the actuator unit and, for instance, the other elements guiding and/or amplifying the magnetic field induced by the coil form an electro-magnetic circuit. An electrical behaviour of this electro-magnetic circuit can be characterized by an actuator unit voltage.

[0010] To control injection durations and quantity of the injection valve the actuator unit may be activated by a predetermined activation signal during a given activation period. During activation the magnetic field induced by the coil is controlled by the activation signal. In this way the armature is directly controlled by the activation signal during the activation period. After the activation period, when the activation signal has returned to zero or another off state this force coupling is interrupted and there is a transient phase. During the transient phase the armature and other with the armature mechanically coupled components move themselves depending upon their inertia and/or a mechanic condition and/or a hydraulic condition to close the injector. The permanent magnet may effect that during said transient phase an additional magnetic flux generated by a closing movement of the armature is not by-passed by the valve body but the energy is transformed and causes a current in the electro-magnetic circuit. This discharging current impacts a characteristic of the actuator unit voltage during said transient phase. This actuator unit voltage characteristic may advantageously be used to determine a closing time, representing a time when the valve needle effectively reaches the closing position.

[0011] According to a preferred embodiment the permanent magnet axially extends at least along the extension of the maximum gap.

[0012] According to a further preferred embodiment the permanent magnet is magnetized in an axial direction. The actuator unit may advantageously be activated by the activation signal at least during an opening phase, during which the valve needle moves out of its closing position, in that way that a magnetic flux of the coil induced into an inner part of the coil, i. e. in particular into the pole piece and/or armature, and a magnetic flux induced by the permanent magnet in particular into the armature and/or pole piece extend in approximately opposite direction.

[0013] According to a further preferred embodiment the permanent magnet is formed as a circular tube section. This supports an economical manufacturing of the valve assembly.

[0014] According to a further preferred embodiment the permanent magnet is arranged between the valve body and the housing. This also supports an economical manufacturing of the valve assembly.

[0015] According to a further preferred embodiment the permanent magnet is arranged inside the valve body.

[0016] According to a second aspect the invention is distinguished by an injection valve with a valve assembly in accordance with the first aspect.

[0017] Exemplary embodiments of the invention are shown in the following with the aid of schematic drawings. These are as follows:

Figure 1

an embodiment of an injection valve 100,

Figure 2a, 2b, 2c

magnetic flux lines of a permanent magnet 48, magnetic flux lines of the coil 38 and resulting magnetic flux lines inside the injection valve 100.

[0018] Elements of the same design and function that appear in different illustrations are identified by the same reference character.

[0019] An injection valve 100 (figure 1), that is particular suitable for dosing fuel into an internal combustion engine, comprises e. g. a valve assembly 11 and an inlet tube 15.

[0020] The valve assembly 11 comprises a valve body 14 with a central longitudinal axis L and a housing 16. The housing 16 is partially arranged around the valve body 14. Furthermore a cavity 18 is arranged in the valve body 14.

[0021] The cavity 18 takes in a valve needle 20, an armature 22 and in this particular case a damper element, e. g. a damper spring 46. The damper spring 46 forms a soft stop element for the armature 22. In the shown embodiment the armature 22 has an upper guide 24 formed as a circular tube section around the valve needle 20. The upper guide 24 is mechanically coupled with the valve needle 20.

[0022] A calibration spring 28 is arranged in a recess 26 provided in the inlet tube 15.

[0023] The valve needle 20 comprises, for example, a valve needle body and a sealing element. The sealing element is mechanically coupled with the valve needle body. The valve needle body preferably has a cylindrical shape. The sealing element has for example a spherical shape. Alternatively, the sealing element can have a conical shape. In a closing position of the valve needle 20, the sealing element rests on a seat preventing a fluid flow through at least one injection nozzle of the injection valve 100. The injection nozzle may be, for example, an injection hole. However, it may also be of some other type suitable for dosing fluid. The sealing element permits the fluid injection into the combustion chamber in further positions, i. e. when it does not rest on the seat. The further positions represent non-closing positions.

[0024] The valve assembly 11 is provided with an actuator unit 36 which is preferably an electro-magnetic actuator. The actuator unit 36 comprises, for example, an armature 22, a core and a coil 38, which is preferably arranged inside the housing 16 and overmolded. The coil 38 and the core form an electromagnet. In this embodiment the core is mainly formed by a pole piece 12, which is for instance a part of the inlet tube 15. But also the housing 16 and the valve body 14 are affected by a magnetic field induced by the activated coil 38 and therefore may be assigned to the core. There may be other and/or additional elements guiding and/or amplifying the magnetic field induced by the coil 38.

[0025] The armature 22 is axially moveable in the cavity 18 between a first position and a second position. In the case the armature 22 is in the first position a first armature surface area 23 and a pole piece surface area 13 facing each other may abut in particular in the sense that there may be a minimal gap between these surfaces 23, 13. In the case the armature 22 is in the second position, there is a given maximum gap between the pole piece surface area 13 and the first armature surface area 23.

[0026] Furthermore the valve assembly 11 may comprise a permanent magnet 48 extending at least partly along the extension of the maximum gap, wherein the permanent magnet 48 is arranged radially outwards relative to the armature 22.

[0027] It may be in particular advantageous if the permanent magnet 48 of the valve assembly 11 comprises an axially total extension exceeding the extension of the maximum gap in both axial directions, in particular with approximately one-third of the total extension in axial direction towards the inlet tube 15 and with approximately 20% of the total extension in axial direction towards the damper spring 46.

[0028] The permanent magnet 48 may be formed as a circular tube section. The circular tube section may be made in one piece, but it is also possible that the circular tube section is formed by more the one piece.

[0029] The permanent magnet 48 is arranged between the valve body 14 and the housing 16. Alternatively or additionally the permanent magnet 48 may be arranged inside the valve body 14.

[0030] In an arrangement, as shown in figure 1, the permanent magnet 48 is preferably magnetized in an axial direction. Figure 2b exemplarily shows magnetic flux lines of the permanent magnet 48.

[0031] In the case the electro-magnetic actuator unit 36 with the coil 38 is activated by a predefined activation signal during a given activation period, the electromagnet may effect, depending on the activation signal, an electro-magnetic force on the armature 22. The armature 22 may be attracted by the electromagnet and moves in the direction of the longitudinal axis L away from a fluid outlet portion of the cavity 18. The armature 22 pushes on the upper guide 24 which is mechanically coupled with the valve needle 20 and therefore the valve needle 20 moves in axial direction out of the closing position.

[0032] Figure 2a shows magnetic flux lines of the coil 38. The actuator unit 36 may advantageously be activated by the activation signal at least during an opening phase, during which the valve needle 20 moves out of its closing position, in that way the magnetic flux induced by the coil 38 and the magnetic flux induced by the permanent magnet 48 in particular into the armature 22 and/or pole piece 12 extend in approximately opposite direction.

[0033] During said opening phase the permanent magnet flux in the armature 22 and the pole piece 12 is not in phase with the coil flux forcing the coil flux going faster into the armature 22 and pole piece 12 anticipating the opening phase. Since the coil flux is not in the same direction as the permanent magnet flux, the coil flux partially passes into the valve body 14 and a bigger part of the flux enters into the armature 22 and pole piece 12, increasing the maximum force to open and keep open the injector. Figure 2c shows resulting magnetic flux lines inside the injection valve 100 during the opening phase.

[0034] The actuator unit 36 and the other elements guiding and/or amplifying the magnetic field induced by the coil 38 form an electro-magnetic circuit. An electrical behaviour of this electro-magnetic circuit can be characterized by an actuator unit voltage. For instance, the actuator unit voltage can be measured by a voltage sensor. A variation of the armature dynamic, which happens in a moment the valve needle 20 reaches the closing position, can be detected depending on the actuator unit voltage characteristic.

[0035] After the activation period, when the activation signal has returned to zero or another off state the force coupling between the electromagnet and the armature 22 is interrupted and there is a transient phase because some energy is still stored in the electro-magnetic circuit. Depending on a force balance between the force on the armature 22 caused by the electromagnet and the force on the armature 22 caused by the calibration spring 28 the valve needle 20 moves in its closing position. In this case, for instance, the armature 22 moves into the second position. The motion of the armature 22 has an impact on the electrical behaviour of the electro-magnetic circuit and therefore on the actuator unit voltage during the transient phase. Depending on an architecture of the injection valve 100 the armature 22 has a different dynamic behaviour and so a different impact on the actuator unit voltage.

[0036] The permanent magnet flux prevents that the flux generated by the armature movement enters into the valve body 14 and therefore the flux generated by the armature movement is passed into the housing 16.

Claims

1. Valve assembly (11) for an injection valve (100), comprising

- a valve body (14) including a central longitudinal axis (L), wherein the valve body (14) comprises a cavity (18),

- a valve needle (20) axially moveable in the cavity (18) and preventing a fluid flow out of an injection nozzle in a closing position and enabling the fluid flow out of the injection nozzle apart from the closing position,

- an electro-magnetic actuator unit (36) being designed to actuate the valve needle (20), wherein the electro-magnetic actuator unit (36) comprises

- a coil (38),

- a core, wherein the core comprises at least a pole piece (12) and

- an armature (22) axially moveable in the cavity (18) between a first position and a second position, wherein in the case the armature (22) is in the first position, the armature (22) and the pole piece (12) abut, and in the case the armature (22) is in the second position, there is a given maximum gap between the pole piece (12) and the armature (22), and

- a permanent magnet (48) axially extending at least partly along the extension of the maximum gap, wherein the permanent magnet (48) is arranged radially outwards relative to the armature (22).

2. Valve assembly (11) in accordance with claim 1, wherein the permanent magnet (48) axially extends at least along the extension of the maximum gap.

3. Valve assembly (11) in accordance with claim 1 or 2, wherein the permanent magnet (48) is magnetized in an axial direction.

4. Valve assembly (11) in accordance with one of the preceding claims, wherein
the permanent magnet (48) is formed as a circular tube section.

5. Valve assembly (11) in accordance with one of the preceding claims, wherein
the permanent magnet (48) is arranged between the valve body (14) and the housing (16).

6. Valve assembly (11) in accordance with one of the preceding claims, wherein
the permanent magnet (48) is arranged inside the valve body (14) .

7. Injection valve (100) with a valve assembly (11) according to one of the preceding claims.

Drawing