The present disclosure relates to a method for manufacturing a magnetic coil for a magnetic actuator, particularly for an injector. The disclosure further relates to a magnetic coil for a magnetic actuator and to an injector, particularly a fuel injector nozzle for a combustion engine, comprising such a magnetic actuator.
A common fuel injector nozzle is for instance known from EP 0 132 623 A2. The injector nozzle is provided with a magnetic actuator comprising an induction coil which is encapsulated and arranged in a fashion fixed to a housing.
Injectors for the fuel supply for combustion engines are generally known. Injectors of that kind are also referred to as injector nozzles. Modern injectors are provided with mechatronical actors, for instance with magnetic actuators, so as to control the opening and closing of the nozzles in a high-precision fashion. Modern injection systems for diesel engines are configured for maximum injection pressures of several hundred bars up to more than 1000 bar or even up to 2500 bar.
Injectors comprising so-called piezo-actuators are known. Nevertheless, also injectors comprising magnetic actuators are widely used. Injectors of that kind are commonly provided with a magnetic coil which cooperates with a movable armature for controlling the injector.
Actuators for injector nozzles must be manufactured in a high-precision fashion so as to be able to provide a respectively desired injection volume in a repeatedly accurate manner. Accordingly, there are frequently very tight tolerance specifications for the production. Further, it must be noted that the utilized components of the injector have to be considerably fuel-resistant or propellant-resistant so as to be resistant to the fuel which flows through the injector. The fuel may for instance involve diesel fuel, gasoline fuel, ethanol, light oil, heavy oil, kerosene or mixtures thereof.
The frequency at which the actuators of the injectors are controlled typically corresponds to the speed of rotation of the combustion engine. However, there are also injectors known that enable a plurality of injections event in a single combustion cycle. This may involve a further increased load to the injector and to the actuator thereof. Further, injectors are regularly fixedly attached to a cylinder head or a similar housing component of the combustion engine. This involves that the injector and the components provided therein are exposed to heavy vibration exposures, temperature variations and similar environmental impacts. Accordingly, there is a general need to design injectors in a robust fashion so as to ensure a specified minimum lifespan (for instance defined by operating cycles and such like).
For injectors that utilize magnetic actuators, it is a common measure to at least sectionally overmold and/or pot a coil winding of the magnetic coil of the actuator. In this way, the sensitive coil winding may be protected against environmental influences. Generally, such a magnetic coil comprises a coil body made from plastic material which supports a copper winding. For instance, the coil carrier that is provided with the coil winding is arranged in a magnet pot which defines a yoke of the magnetic actuator. By sealing, potting or overmolding the coil carrier that is received at or in the magnet pot, the coil winding is at least sectionally overmolded and/or potted with a (temporarily) fluid filler material.
The armature of such a magnetic actuator which cooperates with the magnet pot and the coil winding is frequently arranged as a plate armature and/or in a similar fashion. A lifting distance of the armature is frequently in a range of a few hundredths of a millimeter up to about 0.1 mm. As a result, even deviations in the range of a few micrometers at the seating surface and/or the abutment surface of the armature have a great influence on the function of the injector. A design goal may therefore involve to avoid, as much as possible, deviations of the armature stroke that is defined by the design.
It has been observed that the required potting and/or the required overmolding of the coil winding may in this respect have a negative impact. Generally, the overmolding and/or potting of the coil winding is performed in connection with the magnet pot, that is, in a state when the coil carrier that is provided with the coil winding is already arranged at the magnet pot in the desired final position. This involves that a molding form and/or potting form for such a procedure has to cooperate with the magnet pot in a high-precision fashion so as to ensure a sufficient sealing. If this is not the case, excess molding material (flash material) may be formed which involves events wherein the filler material (molding compound or potting compound) enters regions which actually shall not be entered for design and/or functional reasons. Even though there exist established solutions for avoiding such excess molding material, these solutions always involve increased production efforts. For instance, the tool which is used for overmolding or potting may be manufactured at an increased accuracy, and the magnet pot which cooperates with the tool may be also provided with an increased precision in a portion thereof that is arranged for contacting such a tool. However, this involves an increased production effort and also an increased wear on the side of the tool.
By contrast, in cases where no complete sealing of the magnet pot by the injection molding or potting tool may be ensured, excess molding material (flash material) may be present. Hence, in these cases, an increased scrap/waste or functional deficiencies have to be expected. Excess molding material may be generally referred to as residual flash.
In view of this, it is a first object of the present disclosure to provide a method for manufacturing a magnetic coil for a magnetic actuator which results in an improved quality of the potting and/or molding.
It is a further object to provide a method for manufacturing a magnetic coil for a magnetic actuator which involves an improved reproducibility and process reliability.
It is a further object to provide a method for manufacturing a magnetic coil for a magnetic actuator which prevents excess flash molding material to a great extent or even entirely.
More particularly, it is a further object to provide a method for manufacturing a magnetic coil for a magnetic actuator, wherein residual flash of the filler material at functional surfaces, particularly at contact surfaces or seating surfaces for the armature may be avoided to a considerable extent.
It is a further object to provide a method for manufacturing a magnetic coil for a magnetic actuator that is arranged to utilize robust tools/molds for the potting or overmolding which may achieve a great service life and/or lifespan.
It is a further object to provide a method for manufacturing a magnetic coil for a magnetic actuator that enables a reduction of efforts for quality management and a reduction of scrap production.
It is a further object to provide a method for manufacturing a magnetic coil for a magnetic actuator that enables the production of injectors which provide an increased operation performance and which are arranged to be controlled in a highly-accurate fashion.
It is a further object to present exemplary arrangements of magnetic coils and of injectors that are provided with respective magnetic coils that may profit from exemplary embodiments and aspects of the manufacturing method.