Abstract:
A fuel injection valve ( 100 ) for internal combustion engines, having a housing ( 10 ) in which a nozzle body ( 11 ) is at least indirectly axially clamped against a holding body ( 15 ) by means of a clamping nut ( 18 ), wherein the clamping nut ( 18 ) radially surrounds the nozzle body ( 11 ), and wherein a threaded connection ( 20 ) between the holding body ( 15 ) and the clamping nut ( 18 ) is formed between the clamping nut ( 18 ) and the holding body ( 15 ) in a region which is axially spaced apart from the nozzle body ( 11 ). The threaded connection ( 20 ) comprises at least two toothing regions ( 21, 22 ) which have different threaded dimensions and are arranged axially one behind the other in the longitudinal direction of the housing ( 10 ).

Description:
BACKGROUND OF THE INVENTION 
     The invention relates to a fuel injection valve for internal combustion engines. 
     A fuel injection valve of this type is known from DE 10 2008 001 330 A1 by the applicant. Said fuel injection valve comprises essentially, on the side facing the combustion chamber of the internal combustion engine, a nozzle body which is accommodated in a housing and in which a nozzle needle is guided in such a way that it can move up and down. The nozzle needle is at least indirectly axially clamped, together with the nozzle body by means of a clamping nut, against a holding body arranged in the housing. The clamping nut has an inner thread as part of a threaded connection, which inner thread interacts with a corresponding external thread on the holding body and also forms, in particular, a seal of the housing for fuel which is arranged in the region of the nozzle body and which is under relatively high pressure; a pressure of more than 1500 bar is meant here; during operation of the fuel injection valve. 
     The trend in fuel injection technology is for increasingly high fuel injection pressures in order to achieve better efficiency levels and/or a lower consumption. As a result, increasingly stringent requirements are made for the seal of the housing, in the present case in particular in the region of the threaded connection. 
     SUMMARY OF THE INVENTION 
     Taking the illustrated prior art as a starting point, the invention is based on the object of developing a fuel injection valve for internal combustion engines in such a way that the threaded connection thereof connects the clamping nut to the holding nut and forms a seal of the housing toward the outside, in such a way that said seal is particularly tight, in particular in the case of relatively high fuel pressures. 
     This object is achieved in a fuel injection valve for internal combustion engines wherein the threaded connection ( 20 ) comprises at least two toothing regions ( 21 ,  22 ) which have different threaded dimensions and are arranged axially one behind the other in the longitudinal direction of the housing. The invention is based here on the idea of developing the threaded connection in such a way that there are at least two toothing regions which have different threaded dimensions and adjoin one another axially one behind the other in the longitudinal direction of the housing. This makes it possible to optimize the respective toothing regions with respect to their specific properties and/or functions. In particular this permits, for example, a first toothing region to be embodied in an optimum way in terms of its seal, while a second toothing region is optimized in terms of the relatively simple mounting of the clamping nut. 
     In a structurally preferred embodiment it is proposed that a thread-free intermediate section is formed between the two toothing regions. This thread-free intermediate section permits, in particular, the two toothing regions on the clamping nut and respectively on the holding body to be implemented relatively easily in terms of fabrication technology. 
     An embodiment in which the threaded dimensions of the two toothing regions differ in the thread diameters and the number of teeth, and in that the lead of the toothing regions are equal, is particularly preferred. Embodying the threaded dimensions in such a different way both provides the desired seal while at the same time permitting easy mounting of the clamping nut on the holding body. 
     In a particularly preferred structural embodiment it is proposed that the axial length of the thread-free intermediate region corresponds to the axial length of a first toothing region on the clamping nut, which toothing region is arranged on the side of the clamping nut facing the holding body. Such an embodiment always permits the clamping nut to be guided and/or to engage on the holding body in the axial direction when the clamping nut is screwed onto the holding body. 
     In order to achieve the desired improved seal of the threaded connection, it is proposed that the second toothing region has, on the side of the clamping nut facing the nozzle body, the smaller thread diameter and twice the number of teeth compared to the first toothing region. As a result, according to a further refinement of the invention, it is made particularly easily possible for the wall thickness of the clamping nut to be larger in the second toothing region than in the first toothing region. In this context, the increased wall thickness of the clamping nut can particularly well absorb the pressure stresses which occur, and widening of the clamping nut compared to the prior art owing to the hydraulic pressure is reduced, which improves the seal of the second toothing region. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Further advantages, features and details of the invention emerge from the following description of preferred exemplary embodiments and on the basis of the drawing, in which: 
         FIG. 1  shows a detail of a fuel injection valve according to the invention for internal combustion engines in a partial longitudinal section, and 
         FIGS. 2 to 4  show the detail X according to  FIG. 1  in the screwing region of a clamping nut with a holding body during various phases of the screwing of the clamping nut to the holding body, in a respectively enlarged view. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  shows an illustrated detail of a fuel injection valve  100  according to the invention such as serves for injecting fuel into a combustion chamber of an internal combustion engine (not illustrated), in particular an auto-ignition internal combustion engine. In particular, the fuel injection valve  100  is a component of what is referred to as a common rail injection system in which each cylinder of the internal combustion engine is assigned a separate fuel injection valve  100  which is supplied with fuel by a common rail. In this context, the injection pressure of the fuel injection valve  100  preferably comprises more than 1500 bar. 
     The fuel injection valve  100  has a housing  10 , of which only certain areas are illustrated and in which, inter alia, an injection valve element (not illustrated), in particular in the form of a nozzle needle, is arranged in such a way that it can move up and down. Arranged within the housing  10  is a nozzle body  11  which simultaneously forms the end of the fuel injection valve  100  facing the combustion chamber of the internal combustion engine. The nozzle body  11  has, on its outer circumference, a step  12 . In the illustration in  FIG. 1  above the nozzle body  11 , a throttle plate  13  is arranged, and on the side of the throttle plate  13  facing away from the nozzle body  11  a valve plate  14  is arranged. On the side of the valve plate  14  lying opposite the throttle plate  13 , there is an adjoining holding body  15  of the housing  10 , against which holding body  15  the nozzle body  11 , throttle plate  13  and the valve plate  14  are axially clamped. The axial clamping of the aforementioned components of the fuel injection valve  100  is carried out by means of a clamping nut  18  which has, on its inner wall at its end facing the nozzle body  11 , a diameter step  19  which bears flush against the step  12  of the nozzle body  11 . 
     With respect to the rest of the design of a fuel injection valve  100  and the method of functioning thereof, reference is made to DE 10 2008 001 330 A1 by the applicant, which document is to be considered in this respect to be a component of this application. 
     In the region of the detail X in  FIG. 1 , a threaded connection  20  is formed between the holding body  15  and the clamping nut  18 . The threaded connection  20  has a first toothing region  21  on the side facing away from the nozzle body  11 , and a second toothing region  22  on the side facing the nozzle body  11 . In each case, as can be seen, in particular, from  FIG. 3 , a toothing-free intermediate region  23  is provided between the first toothing region  21  and the second toothing region  22 , both on the nozzle body  11  and on the holding body  15 . The intermediate region  23  is formed in the region of the holding body  15  as a cylindrical section  17  with an external diameter which is the same all the way through. In contrast, in the region of the clamping nut  18 , two sections  24 ,  25  are formed in the vicinity of the intermediate region  23 , which sections  24 ,  25  are each of cylindrical design, wherein the section  24  facing the first toothing region  21  has a larger internal diameter than the section  25  facing the second toothing region  22 . The two sections  24 ,  25  are preferably embodied with approximately the same length, for example each with approximately 2 mm. 
     While the first toothing region  21  in the region of the clamping nut  18  is arranged at the end of the clamping nut  18  facing away from the nozzle body  11 , the second toothing region  22  is located in the region of the holding body  15 , on the side facing the valve plate  14  near to the lower end face  26  of the holding body  15 . 
     The first toothing region  21 , which is embodied as an external thread on the holding body  15 , has a thread with the dimensions M17×0.75 mm, while the second toothing region  22  on the holding body  15  is embodied as an external thread with the dimensions of M16×0.75 mm. Furthermore, the first toothing region  21 , which is embodied as an internal thread, on the clamping nut  18  has half the number of teeth of the second toothing region  22  on the clamping nut  18 . 
     As is apparent, in particular, from  FIG. 3 , due to the different dimensioning of the threads of the two thread sections  21 ,  22  with a continuously cylindrical external contour of the clamping nut  18  in the region of the threaded connection  20  in the vicinity of the second toothing region  22  of the clamping nut  18  from the tooth base of the toothing a wall thickness A of the clamping nut  18  is formed which is larger than the wall thickness a of the clamping nut  18  in the region of the first toothing region  21 . As is also apparent from  FIG. 1 , the length L 1  of the first toothing region  21  on the clamping nut  18  is preferably of the same length as the length L ZB  of the thread-free intermediate region  23 . 
       FIGS. 2 to 4  illustrate different phases of the assembly process of the clamping nut  18  on the holding body  15 .  FIG. 2  illustrates the state in which the first toothing region  21  of the clamping nut  18  is located in the vicinity of the second toothing region  22  of the holding body  15 . In this context, it is apparent, in particular, that since the number of teeth in the first toothing region  21  on the clamping nut  18  is halved, a gap  27  is respectively formed between the teeth of the second toothing region  22  of the holding body  15 . 
       FIG. 3  illustrates the state in which the first toothing region  21  of the clamping nut  18  moves in the region of the first toothing region  21  of the holding body  15 . The significant feature here is that at the start of the engagement of the thread turn of the first toothing region  21  of the clamping nut  18  in the first toothing region of the holding body  15 , the exit of the turn of the first toothing region  21  of the clamping nut  18  is still in bearing contact with the second toothing region  22  of the holding body  15 . As a result, the first toothing region  21  of the clamping nut  18  is always in engagement with one of the two toothing regions  21 ,  22  of the holding body  15 , with the result that the clamping nut  18  is prevented from slipping through or dropping through during the process of mounting on the holding body  15 . 
     The combination of  FIGS. 1 and 4  illustrates the final state of the mounting of the clamping nut  18  on the holding body  15 , in which the diameter stage  19  of the clamping nut  18  is in bearing contact with the step  12  of the nozzle body  11 , and therefore axially clamps the nozzle body  11  against the holding body  15  via the valve plate  14  and the holding body  15 . 
     The threaded connection  20  which is described in this fashion on the fuel injection valve  100  can be modified in a variety of ways without departing from the inventive idea.