Abstract:
A nozzle module for an injection valve has a nozzle body with a nozzle body opening extending in the direction of a longitudinal axis, and which can be hydraulically coupled to a fluid feed; a nozzle needle which is movable axially in the nozzle body opening and which in a closed position prevents a flow of fluid through at least one injection opening and otherwise releases the fluid flow; and an induction-heated heating element disposed between the nozzle body and the nozzle needle. The heating element is at least partially spaced a distance away from the nozzle body and from the nozzle needle, and during operation of the injection valve the fluid can flow against a side of the heating element facing the nozzle body and a side of the heating element facing the nozzle needle.

Description:
BACKGROUND OF THE INVENTION 
     Field of the Invention 
     Ever more stringent statutory requirements relating to the permissible emission of harmful substances from internal combustion engines employed in motor vehicles make it necessary to adopt various measures by means of which the harmful emissions can be reduced. One approach here is to cut the harmful emissions generated by the internal combustion engine. The formation of soot depends greatly on the preparation of the air/fuel mixture in the particular cylinder of the internal combustion engine. 
     US 2001/0040187 A1 discloses a method for heating fuel, in which an injector is provided with an internal heating device and an associated valve needle. Fuel for the injector is provided, fuel is directed and heated by means of at least one flow distribution element. 
     U.S. Pat. No. 5,758,826 discloses an internal heating device for a fuel injector, with a field with plates made of a material with a positive temperature coefficient (PTC), which is arranged in the form of a square pipe around a valve element and is surrounded by a heat-insulated sleeve. 
     DE 100 45 753 A1 discloses a method for operating a self-igniting internal combustion engine, where at least one combustion chamber of the internal combustion engine is fed with fuel from at least one injection valve. Before injection, the fuel is heated in the at least one combustion chamber. 
     DE 198 35 864 A1 discloses a device for heating fluid substances. This comprises a container or a corresponding pipe provided for accommodation or direction of the substance to be heated and a heatable heat transfer element, which is arranged in the container or as the case may be pipe, and preferably comprises steel wool, metal chips or expanded metal. 
     DE 22 10 250 discloses a fuel injection device, in particular for externally ignited internal combustion engines with heating of the fuel by means of an electrical heating element taking place directly ahead of the injection location, controllable through the engine temperatures influencing the mixture formation. 
     BRIEF SUMMARY OF THE INVENTION 
     The object of the invention is to create a nozzle module and an injection valve which enable reliable and precise operation. 
     The object is achieved by the features of the independent claims. Advantageous embodiments of the invention are indicated in the subclaims. 
     According to a first aspect, the invention is characterized by a nozzle module for an injection valve, with a nozzle body, which has a nozzle body recess extending in the direction of a longitudinal axis, which can be coupled hydraulically with a fluid feed, a nozzle needle arranged in an axially movable manner in the nozzle body recess, which in a closed position prevents a fluid flow through at least one injection opening and otherwise releases the fluid flow, and a heating element which can be heated by induction, and which is arranged between the nozzle body and the nozzle needle, where the heating element is at least partially embodied spaced at a distance from the nozzle body and the nozzle needle, and where during operation of the injection valve fluid can flow against a side of the heating element facing the nozzle body and a side of the heating element facing the nozzle needle, and the heating element is embodied as a path folded in zigzag form between the nozzle body and the nozzle needle, which takes the form of a hollow cylinder extending in an axial direction. 
     This has the advantage that an extensive heat transfer area between heating element and fluid is enabled at the same time as a minimal average distance between heating element and fluid. Good heat transfer between the heating element and the fluid is thus achieved. A large heat transfer area between heating element and fluid is realized by means of the embodiment of the heating element as a path folded in zigzag form. 
     In an advantageous embodiment of the invention, the heating element has a porous material. A very large area of the heating element relative to the fluid and thus a very large heat transfer area between heating element and fluid can thus be embodied. 
     In a further advantageous embodiment of the invention, the heating element abuts the nozzle body, and is fixed relative to the nozzle body at least in a radial direction to the longitudinal axis. Simple fixing of the heating element in a radial direction can thus be realized. 
     In a further particularly advantageous embodiment of the invention, the heating element is embodied as a sintered body, with voids, which are arranged and embodied such that the heating element can be flowed through by the fluid in an axial direction. This has the advantage that a very large heat transfer area between the heating element and the fluid is possible. It is thus possible to realize small external dimensions of the heating element. 
     In a further advantageous embodiment of the invention, the heating element is of a material which has a Curie temperature between 100° C. and 200° C. An inherently safe embodiment of the heating element is thus possible through limitation of the temperature of the heating element and thus of the fluid flowing through this. External regulation of the heating element can thus be dispensed with. 
     In a further particularly advantageous embodiment of the invention, the heating element is of a material with a Curie temperature of around 120° C. The Curie temperature of the heating element is thus in the area of a typical evaporation temperature of a fluid embodied as the fuel, with at the same time more inherently safe embodiment of the heating element. If the fluid is in particular ethanol, which at a pressure of 5 to 6 bar has an evaporation temperature of 120° C., this can safely evaporate. 
     In a further advantageous embodiment of the invention, the heating element is made of titanium oxide. Titanium oxide has a Curie temperature of 120° C. It is therefore possible to limit the temperature of the heating element and thus the temperature of the fluid flowing through it to a temperature of 120° C. 
     According to a second aspect, the invention is characterized by a nozzle module for an injection valve, with a nozzle body, which has a nozzle body recess extending in the direction of a longitudinal axis, which can be coupled hydraulically with a fluid feed, a nozzle needle arranged in an axially movable manner in the nozzle body recess, which in a closed position prevents a fluid flow through at least one injection opening and otherwise releases the fluid flow, and a heating element which can be heated inductively, and which is arranged between the nozzle body and the nozzle needle, where the heating element is of a porous material, and during operation of the injection valve can be flowed through by the fluid in an axial direction. 
     The advantageous embodiments of the second aspect of the invention correspond to those of the first aspect of the invention. 
     The advantage of a nozzle module of this kind consists in that a very large heat transfer area between the heating element and fluid is possible. Small external dimensions of the heating element can thus be realized. 
     According to a third aspect, the invention is characterized by an injection valve with an actuator and a nozzle module, where the actuator and the nozzle module are connected with each other. 
     Exemplary embodiments of the invention are explained in greater detail as follows on the basis of the schematic drawings, wherein: 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
         FIG. 1  shows a longitudinal section through an injection valve with a nozzle module, 
         FIG. 2  shows a detailed view of a first embodiment of the nozzle module as a cross-section along the line II-II′ of  FIG. 1 , 
         FIG. 3  shows a further detailed view of the first embodiment of the nozzle module as a three-dimensional view, 
         FIG. 4  shows a detailed view of a second embodiment of the nozzle module as a cross-section. 
     
    
    
     Elements of the same construction or function are identified with the same reference numbers across all the figures. 
     DESCRIPTION OF THE INVENTION 
     An injection valve  62  ( FIG. 1 ), which is provided in particular to inject fuel into an internal combustion engine, comprises a fluid inlet pipe  2 , an actuator  40  and a nozzle module  60 . 
     The nozzle module  60  has a nozzle body  4  with a longitudinal axis L and a nozzle body recess  8 . The nozzle body  4  can be embodied in one piece or in a number of parts. A one-piece or multipart nozzle needle  10  is arranged in the nozzle body recess  8 . A heating element  42  is further arranged in the nozzle body recess  8  between the nozzle body  4  and the nozzle needle  10 , which can be heated magnetically and inductively. Part of an injector body  12  is additionally arranged in the nozzle body recess  8 . 
     The injection valve  62  is connected to a pressure circuit of a fluid which is not shown, via the fluid inlet pipe  2 . In the fluid inlet pipe  2  is a recess  16 , which extends as far as a recess  18  of the injector body  12 . A spring  14  is arranged in the recess  16  of the fluid inlet pipe  2  and/or the recess  18  of the injector body  12 . The spring  14  is supported on the one hand preferably on a disk  20 , which is mechanically connected with the injector body  12 . The injector body  12  is in turn permanently mechanically linked with the nozzle needle  10 , so that the spring  14  is mechanically linked with the needle  10 . A pipe sleeve  22  is arranged in the recess  16  of the fluid inlet pipe  2 , forming a further seating for the spring  14 . 
     The pipe sleeve  22  is positioned such that the spring  14  is pretensioned in such a way that the nozzle needle  10  assumes a closed position on a seat body  26  which is assigned to it, and in which it prevents the fluid flow through an injection opening  24 . Instead of one injection opening  24 , multiple injection openings can also be embodied in the seat body  26 . The injection opening  24  is preferably an injection orifice. 
     The seat body  26  can be embodied as one piece with the nozzle body  4 , however the seat body  26  and nozzle body  4  can be embodied as separate parts. The nozzle module  60  furthermore has a distance plate  28  for guidance of the nozzle needle  10  and a swirl disk  30  for distribution of the fluid. 
     A coil unit  32  is arranged around part of the nozzle body  4 , which interacts with the heating element  42  which can be heated inductively, and the function of which is explained further below. 
     The actuator  40  of the injection valve  62  is preferably an electromagnetic unit with a coil  36  arranged in an actuator housing  34 . The actuator housing  34  is preferably formed from plastic. An electric voltage can be applied to the actuator  40  via a connection socket  38 . Parts of the nozzle body  4 , the injector body  12  and the fluid inlet pipe  2  form an electromagnetic circuit. The actuator  40  can alternatively also be a solid state actuator, in particular a piezoelectric actuator. 
       FIGS. 2 and 3  show, respectively, a cross-section and a three-dimensional view of part of the nozzle module  62 . The heating element  42  arranged between the nozzle body  4  and the nozzle needle  10 , which can be heated inductively, is embodied as a path, which is folded in zigzag form between the nozzle body  4  and the nozzle needle  10 . In this way a hollow cylinder extending in an axial direction is embodied. At least one side  44  of the heating element  42  facing the nozzle body  4  is spaced at a distance from an internal wall  50  of the nozzle body  4 . At least one side  46  of the heating element  42  facing the nozzle needle  10  is spaced at a distance from an external wall  48  of the nozzle needle  10 . The heating element  42  additionally has wall sections  47 , which abut the internal wall  50  of the nozzle body  4 . They are preferably arranged such that they are evenly distributed over the circumference of the internal wall of the nozzle body  4 . The heating element  42  is thus fixed relative to the nozzle body  4  in a radial direction to the longitudinal axis L in a particularly simple manner. 
     As a result of the zigzag-form folding of the heating element  42 , a large heat transfer area is available between the heating element  42  which can be heated by induction, and the fluid located in the nozzle body recess  8 . Furthermore, the average distance between the heating element  42  and the fluid in the nozzle body recess  8  is small. A small thermal resistance and a small thermal time constant can thus be attained. In conjunction with a relatively long dwell time on the fuel at the sides  44 ,  46  of the heating element  42 , a favorable value for the dynamic heat transfer is then achievable. 
       FIG. 4  shows a cross section through the nozzle module  60  analogous to the cross section in  FIG. 2 . Between the nozzle body  4  and the nozzle needle  10  a heating element  142  is arranged in the nozzle body recess  8 , which has a porous material and is preferably embodied as a sintered body. The heating element  142  is preferably spaced at a distance from the nozzle needle  10 , in order to be able to guarantee friction-free movement of the nozzle needle  10  in the nozzle body recess  8 . The heating element  142 , which is embodied as a sintered body has a multiplicity of interconnected studs  152  and voids  154 . 
     The voids  154  are arranged between the studs  152 . Some of the voids  154  form the areas of the heating element  142  lying opposite the nozzle body  4  or the nozzle needle  10 . The voids  154  are embodied in such a way that the heating element  142  can be flowed through by the fluid in an axial direction. The sides  44  of the voids  154  of the heating element  42  lying opposite the nozzle body  4  are spaced at a distance from the internal wall  50  of the nozzle body  4 . Accordingly, the sides  46  of the voids  154  lying opposite the nozzle needle  10  are at a distance from the external wall  48  of the nozzle needle  10 . 
     By means of the multiplicity of studs  152 , a very large heat transfer area can be achieved between the heating element  142  and the fluid in the nozzle body recess  8 . At the same time, a very small average distance between the fluid and the studs  152  is achieved. A very low thermal resistance and a very small thermal time constant can thereby be attained. Consequently, the relationship between the dwell time of the fluid and the thermal time constant can reach such a high value that the desired fluid temperature in concrete applications is largely independent of the fluid mass flow rate. Alternatively, as a result of the relationship of dwell time to thermal time constant achieved, the heating element  142  can also be embodied to be sufficiently small that it can be used in a restricted structural space and costs thereby saved. 
     In an alternative embodiment the heating element  142  which can be heated by induction can be embodied in such a way that in the direction of the nozzle needle  10  the heating element  142  has a completely continuous internal wall and/or in the direction of the nozzle body  12  has a completely continuous external wall. The expression completely continuous here means that the internal wall or external wall respectively are not penetrated by voids  154 . 
     The method of functioning of the injection valve is represented below: 
     In the closed position, the nozzle needle  10  is pressed against the injection opening  24  by means of the spring  14 , and a flow of fluid through the injection opening  24  prevented. 
     In an open position, the nozzle needle  10  is spaced at a distance from the seat body  26 , and fluid can travel from the recess  16  of the fluid inlet pipe  2  via the recess  18  of the injector body  12  and the nozzle body recess  8  to the injection opening  24 , by means of which a flow of fluid through the injection opening  24  is enabled. 
     If the temperature of the fluid is not sufficiently high, then by means of a coil unit  32  a magnetic field can be established, which brings about inductive heating in the heating element  42 ,  142 . The heating element  42 ,  142  is heated until the material of the heating element  42 ,  142  loses its magnetic properties upon its Curie temperature being exceeded. A further induction in the heating element  42 ,  142  and consequential further heating to a level above the Curie temperature of the material of which the heating element  42 ,  142  consists is thereby prevented. 
     If further fluid flows through or around the heating element  42 ,  142  which can be heated by induction, and the temperature of the heating element  42 ,  142  which can be heated by induction consequently again falls below the Curie temperature of the material of which the heating element  42 ,  142  consists, then by means of the magnetic field of the coil unit  32 , an induction can once again set in the heating element  42 ,  142  and a consequent renewed heating of the heating element  42 ,  142  can take place. An inherently safe embodiment of the heating elements  42 ,  142  is thus enabled by means of a limitation of the temperature of the heating element  142 ,  42  to its Curie temperature and a consequent limitation of the temperature of the fluid flowing through the heating element  42 ,  142 . External regulation of the heating element  42 ,  142  with an associated temperature sensor and control loop can thereby be dispensed with. 
     If the heating element  42 ,  142  has a material with a Curie temperature between 100 and 200° C., then the fluid can be inherently safely heated to a temperature between 100 and 200° C. In the event that the fluid is a fuel for an internal combustion engine, then by means of the suitable choice of material for the heating element  42 ,  142  a sufficiently high evaporation temperature of the fuel can be achieved, without the fear of excessively powerful heating of the fuel arising. 
     If the heating element  42 ,  142  comprises a material with a Curie temperature of approximately 120° C., then ethanol can be employed as the fluid for an internal combustion engine. At a working pressure of 5 to 6 bar, ethanol has an evaporation temperature of 120° C. Through the use of a material with a Curie temperature of approximately 120° C. for the heating element  42 ,  142 , it is thus possible to achieve reliable evaporation of ethanol without compromising safety. 
     If the heating element  42 ,  142  comprises titanium oxide, which has a Curie temperature of approximately 120° C., then the temperature of the fluid flowing through the heating element  42 ,  142  can be limited to 120° C. in a simple manner. The use of titanium oxide on the one hand brings about inherent thermal safety of the heating elements  42 ,  142  for the fluid, and on the other ensures that reliable evaporation of a fluid such as ethanol can be achieved.