The present disclosure relates to a fuel injection valve for injecting fuel directly or indirectly into an internal combustion engine of a vehicle.
Fuel injection valves typically have a valve body of stainless steel comprising a cavity with a fluid inlet portion and a fluid outlet portion and a valve needle axially movable in the cavity. The valve needle is actuated by an electromagnetic actuator unit which has an armature connected to the valve needle and movable in the cavity.
The electromagnetic actuator unit further comprises a coil which can be energized to move the armature. Pole pieces made of a material of high magnetic permeability serve to direct the magnetic field. Other metal parts of the injection valve can influence the magnetic field likewise and have an impact on the performance of the injection valve.
It is an object of the present invention to provide a fuel injection valve with a better magnetic performance. In particular, magnetic losses shall be minimised.
This object is achieved by means of a fuel injection valve having the features of claim 1.
Advantageous embodiments and developments of the fuel injection valve are specified in the dependent claims, the following description and the drawings.
According to an aspect of the invention, a fuel injection valve is provided comprising a valve body with a central longitudinal axis. The valve body comprises a cavity with a fluid inlet portion and a fluid outlet portion. In particular, the cavity is defined by an interior surface of the hollow valve body. The fuel injection valve further comprises a valve needle axially movable in the cavity, i.e. the valve needle is received in the cavity and axially movable with respect to the valve body. The valve needle prevents a fluid flow through the fluid outlet portion in a closing position and releases the fluid flow through the fluid outlet portion in further positions.
The fuel injection valve further comprises an electromagnetic actuator unit being operable to actuate the valve needle.
A metal housing is partially arranged around the valve body and the electromagnetic actuator unit. The metal housing is at least partially laminated.
The housing may expediently represent a magnetic yoke for guiding magnetic flux of the electromagnetic actuator unit. In particular, the electromagnetic actuator unit comprises an armature which is fixed to the needle or coupled to the needle by a form-fit and/or force-fit connection to cause the needle to move axially in the cavity in response to a magnetic field generated when the coil is energized. The housing may expediently be operable to guide the magnetic field towards the armature.
By the housing being at least partially laminated it is understood that at least a part of the housing is made of multiple layers of metal.
Typically, the housing is arranged around the valve body to receive the actuator unit, in particular the coil and part of its power supply. The housing is made of a metal, e.g. stainless steel, for example by a turning manufacturing technology.
The fuel injection valve according to the present invention has the advantage, that due to the laminated design of the housing eddy currents are minimized. Thus, magnetic losses can be reduced and the overall magnetic performance of the injector can be improved.
In one embodiment, the housing may be overmoulded, preferably to be permanently connected to the valve body. Additionally or alternatively, a press-fit connection may be established between the housing and the valve body for permanently connecting the housing to the valve body.
Preferably, the housing is comprised by an integrally formed power group module of the fuel injection valve. The power group module may expediently comprise the housing, the coil and a plastic part - the plastic part being in particular produced by overmolding the housing and the coil. That the power group module is "integrally formed" means in particular that it cannot be nondestructively disassembled. The plastic part preferably comprises an electrical connector for connecting the coil to an electronic control unit. The power group module may be permanently connected to the valve body by means of the overmolded plastic part fixing the module to the valve body and/or by a press-fit connection with the valve body, e.g. between the housing and the valve body.
According to an embodiment, a laminated part of the housing comprises a plurality of single layers which extend perpendicular to the radial direction with respect to the central longitudinal axis L of the injection valve. In other words, the single layers follow one another in radial direction.
This has the advantage that the orientation of the layers effectively helps to reduce eddy currents, which tend to occur in radial direction in the housing.
According to an embodiment, the housing is at least partially formed by a wrapped metal sheet. By this it is understood that at least a part of the housing is formed by a metal sheet which is wound around an axis. In particular, a metal sheet can be wound around the central longitudinal axis L of the valve body.
This has the advantage, that eddy currents, which typically occur in radial direction, cannot propagate but would have to travel along the turns of the wrapped housing increasing the total length of travel. Thus, magnetic losses due to eddy currents can be minimized.
Furthermore, a housing formed by a wrapped metal sheet can be manufactured easily and at low cost.
The housing may consist entirely of metal. This may be advantageous for assembling the housing, including e.g. producing of welded and/or soldered connections. Alternatively, the single layers are metal layers which alternate with insulating layers. In another development, the wrapped metal sheet is laminated with an insulating layer. For example, the metal layers or the metal sheet, respectively, are/is coated with an insulating film. In this way a particular high resistance between the metal layers or the turns of the wrapped metal sheet is achievable and the eddy currents may be particularly small.
According to an embodiment of the invention, the metal sheet has a thickness of 0.05 mm to 0.2 mm, the limits being included. Such a sheet may be wound in 5 to 40 turns, the limits being included, to build up a housing of the required thickness which may be in the order of 1.6 mm.
According to an embodiment, the housing comprises a mantle part extending around the valve body and surrounding the electromagnetic actuator unit, the mantle part being laminated. The mantle part can also be denoted as a peripheral part. The housing further comprises a washer part forming the base of the housing and extending radially from the valve body. The washer part may be in the shape of a disc having a main plane of extension which is perpendicular to the longitudinal axis. One axial end of the mantle part may expediently adjoin the washer part.
According to this embodiment, the housing has at least two separate parts which may be joined for example by laser welding. One part of the housing, the mantle part, can be easily manufactured in the laminated design, for example by wrapping a metal sheet.
The second part, the washer part, would be more difficult to manufacture in a laminated fashion. However, this part typically has a lower contribution to the magnetic performance of the valve. Therefore, the washer part may be massive and may be produced by a process like stamping.
This embodiment has the advantage, that the housing can be manufactured easily and at low cost.
According to an embodiment of the invention, at least the laminated part of the housing is made of ferritic or martensitic stainless steel. These materials are suited for the use in an injection valve and are magnetic.
Further advantages, advantageous embodiments and developments of the valve assembly for an injection valve, the fluid injection valve and the engine will become apparent from the exemplary embodiments which are described below in association with the schematic figures.
A valve needle 11 is arranged axially movable in the cavity 9. The valve needle 11 prevents a fluid flow through the fluid outlet portion 7 in a closing position. To achieve this, the needle 11 has a ball 13 welded to its lower end which interacts with a valve seat (not shown in detail) of the valve body 4.
The injection valve 1 further comprises an electromagnetic actuator unit 20 to actuate the valve needle 11. The actuator unit 20 comprises an armature 21 which may be fixed to the needle 11 or coupled to the needle 11 in some other way to cause the needle 11 to move axially in the cavity 9 in response to a magnetic field. The actuator unit 20 further comprises a coil 23 which may be energized to induce a magnetic field. The magnetic field acts on the armature 21 to cause it to travel upwards and take the needle 11 with it against the force of the calibration spring 25. Thus, the ball 13 leaves the valve seat and fuel is released through the fluid outlet portion 7.
When the magnetic field ceases, the valve needle 11 is moved downwards by the force of the calibration spring 25 and the fluid outlet portion 7 is closed again.
The injection valve 1 further comprises a pole piece 27 which serves to direct the magnetic field. Other magnetic components of the injection valve 1 contribute to directing the magnetic field, too. A metal housing 29 is arranged around the valve body 4 enclosing the coil 23 and being fixed to the valve assembly 3 by means of a plastic housing 31.
The metal housing 29, the coil 23 and the plastic housing 31 are, thus, comprised by an integrally formed power group module of the fuel injection valve.
The housing 29 is made of stainless steel, in particular ferritic or martensitic stainless steel, and is therefore magnetic. Thus, the housing 29 contributes to the magnetic performance of the injection valve 1. More Specifially, the housing 29 is operable to guide magnetic flux generetad by the coil 23 in operation in axial direction along the coil 23 on the side of the coil facing away from the valve body 4 and in radial direction towards the armature 21. Therefore, the housing 29 axially overlaps the pole piece 27, the coil 23 and the armatuare 21.
The housing 29 is at least partially formed of laminated metal, that is multiple layers of metal. In particular, the layers extend perpendicular to the radial direction with respect to the central longitudinal axis L, thereby reducing the occurrence of eddy currents.
The first part of the housing 29 is the mantle part 33 which is laminated and consists of multiple layers 37 of metal. The mantle part 33 has the shape of a hollow cylinder extending coaxially with the coil 23 and the valve body 4 around the central longitudinal axis L. In this way, a good axial guidance of the magnetic flux is enabled in the mantle part 33, while eddy currents in the mantle part 33 may be particularly small.
The layers 37 may be formed by a single metal sheet which is wrapped around the central longitudinal axis L in a number of turns. However, the layers 37 may also be formed by a number of cylindrical metal parts of different diameters. In the embodiment shown in
The second part of the housing 29 is the washer part 35 which forms a base of the housing 29 and extends radially from the valve body 4. The washer part 35 has an inner surface 39 which contacts the valve body 4 when the injection valve 1 is assembled. On an upper side 41 of the washer part 35, the mantle part 33 is arranged. The washer part 35 is not laminated, but massive and can be manufactured by stamping. In this way, it advantageously enables a good guidance of the magnetic flux in radial direction towards the armature 21. Therefore, the washer part 35 may expediently axially overlap the armature 21.
The washer part 35 and the mantle part 33 are joined together by laser welding before the injection valve 1 is assembled.
This list of references cited by the applicant is for the reader's convenience only. It does not form part of the European patent document. Even though great care has been taken in compiling the references, errors or omissions cannot be excluded and the EPO disclaims all liability in this regard.