Abstract:
The invention relates to a check valve with a spherical valve element whose service life and operating reliability is considerably increased in relation to conventional check valves. The improved check valve is used in an injector for a fuel injection system of an internal combustion engine, having a hydraulic pressure booster.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a 35 USC 371 application of PCT/EP 2008/050016 filed on Jan. 2, 2008. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to a check valve and to an injector. 
     2. Description of the Prior Art 
     Such check valves are well known from the prior art. These check valves typically have a valve housing, in which a bore is made, and a valve seat is embodied in the bore. These check valves furthermore have a spherical valve member, which is disposed in the bore, and a stroke stop element for the valve member is provided, on which the valve member comes to rest when the check valve is open. 
     These check valves are suitable for many applications, but particularly in use in injectors with a hydraulic pressure booster, of the kind used in modern fuel injection systems for internal combustion engines, applications exist in which the conventional check valves have proven insufficiently durable. In conventional check valves, the lateral deflection of the valve member in the open position of the check valve has the effect that not until the valve member meets the valve seat is the valve member centered again by the valve seat. This leads to a relative motion between the valve member and the valve seat. This relative motion causes wear and shortens the service life of the valve seat and valve member considerably. 
     ADVANTAGES AND SUMMARY OF THE INVENTION 
     The check valve of the invention has the advantage that the valve member in the open state is centered in the indentation in the stroke stop element, and as a result, the valve member of the check valve of the invention strikes the valve seat precisely centrally when the check valve closes again, so that no significant wear between the valve seat and the valve member can be found. Moreover, in this exemplary embodiment, a valve spring can be dispensed with, which reduces the production costs and space required for the check valve of the invention considerably. Because of the reduced masses, this check valve responds especially fast. Because of the at least indirect axial fixation of the stroke stop element by means of a welded connection, no additional component is required for this, and as a result the production costs and space required for the check valve of the invention are likewise reduced. 
     In order to move the fuel past or through the valve member and the stroke stop element when the valve member is open, at least one transverse bore is provided in the stroke stop element, and the transverse bore connects an annular gap between the stroke stop element and the bore with a longitudinal bore in the stroke stop element. The longitudinal bore is preferably embodied as a throttle bore toward the indentation, and the transition from the indentation to the throttle bore is embodied with sharp edges, in order upon opening of the check valve to damp the motion of the valve member before it strikes the stroke stop element. The transition from the throttle bore to the region of the longitudinal bore remote from the indentation, by comparison, is embodied in streamlined fashion, to enable a rapid lifting of the valve member from the stroke stop element upon closure of the check valve. 
     The check valve of the invention can be used especially advantageously in an injector with a hydraulic pressure booster for an internal combustion engine. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Further advantages will become apparent in the description of the preferred embodiment below in conjunction with the accompanying drawing, in which: 
         FIG. 1  is a longitudinal section through one exemplary embodiment of a check valve of the invention; and 
         FIG. 2  is an injector of the invention with a hydraulic pressure booster and a check valve of the invention. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     In  FIG. 1 , a component, which may for instance be a pressure booster piston of a hydraulic pressure booster, is identified by reference numeral  1 . In this component  1 , there is a check valve, described in further detail hereinafter, and the component  1  forms a valve housing for the check valve. In the valve housing  1 , a stepped bore  3  is provided. A valve seat  5  is embodied between two portions of the bore  3  that have different diameters. 
     An at least approximately spherical valve member  7  is disposed in the bore  3 . The valve member  7  cooperates with the valve seat  5  in the valve housing  1  and closes the check valve as soon as the valve member  7  rests on the valve seat  5 . Adjoining the valve seat  5 , the bore  3  has a portion  3   a  with a diameter that is somewhat greater than the diameter of the valve member  7 . Toward the end of the valve housing  1 , the bore  3  is open and has a portion  3   b  with a greater diameter compared to the portion  3   a . Because of the change in diameter from the portion  3   a  to the portion  3   b,  an annular shoulder  10  facing away from the valve seat  5  is formed in the bore  3 . 
     For limiting the opening stroke of the valve member  7 , a stroke stop element  12  is inserted into the bore  3 , from an open end of the valve housing  1 . The stroke stop element  12  has a stepped diameter and has a portion  12   a , disposed in the portion  3   a  of the bore  3 , whose diameter is somewhat smaller than the diameter of the portion  3   a  of the bore  3 , so that there is an annular gap  14  between the portion  12   a  of the stroke stop element  12  and the portion  3   a  of the bore  3 . The stroke stop element  12  furthermore has a portion  12   b , disposed in the portion  3   b  of the bore  3 , with a greater diameter compared to the portion  12   a . The diameter of the portion  12   b  of the stroke stop element  12  is only slightly less than the diameter of the portion  3   b  of the bore  3 . As a result of the change in diameter of the stroke stop element  12 , an annular shoulder  13  facing toward the valve seat  5  is formed on the stroke stop element. 
     On the side of the stroke stop element  12  toward the valve member  7 , a funnel-shaped indentation  16  is made, which is embodied for instance as approximately frustoconical or domelike. The diameter of the indentation  16  is less than the diameter of the valve member  7 , so that the valve member  7  can dip partway into the indentation  16 . The indentation  16  is disposed at least approximately coaxially to the longitudinal axis  4  of the bore  3 , and the valve member  7  is disposed at least coaxially in the bore  3  and is movable in the direction of the longitudinal axis  4 . 
     A continuous longitudinal bore  20  with a multiply graduated diameter is made in the stroke stop element  12  and discharges on one end into the indentation  16  and on the other at the open end of the bore  3  on the stroke stop element  12 . In its region extending toward the indentation  16 , the longitudinal bore  20  has a small diameter and thus forms a throttle bore  20   a . An orifice  20   b  of the longitudinal bore  20  into the indentation  16  has a substantially greater diameter than the throttle bore  20   a . The transition from the orifice  20   b  into the throttle bore  20   a  is abrupt and is embodied with sharp edges, so that the flow, beginning at the indentation  16 , into the throttle bore  20   a  is severely hindered. The throttle bore  20   a  is adjoined, on its side remote from the indentation  16 , by a further region  20   c  of the longitudinal bore  20 , which has a greater diameter than the throttle bore  20   a . The transition from the region  20   c  of the longitudinal bore  20  to the throttle bore  20   a  is embodied in streamlined fashion; for instance, as shown in  FIG. 1 , an approximately conical or rounded transition is provided. At least one transverse bore  22  is made in the portion  12   a  of the stroke stop element  12 , and through this transverse bore, the region  20   c  of the longitudinal bore  20  is in communication with the annular gap  14 . Preferably, a plurality of transverse bores  22 , distributed over the circumference, are provided in the stroke stop element  12 . 
     The stroke stop element  12  is preferably made from hardened steel, to assure low wear, since when the check valve opens, the valve member  7  strikes the stroke stop element  12 . The valve member  7  is likewise preferably made from hardened steel; conventional balls for ball bearings, which are available as standard parts, can for instance be used as the valve member  7 . By means of the funnel-shaped indentation  16 , the valve member  7  is centered in its reciprocal motion, and as a result it is attained that upon its closing motion, the valve member  7  strikes the valve seat  5  at least approximately centrally, so that the wear to the valve seat  5  can be kept low as well. 
     In the open state of the check valve, the orifice  20   b  of the longitudinal bore  20  in the indentation  16  in the stroke stop element  12  is closed by the valve member  7 . An outflow of fluid is made possible by the annular gap  14 , the at least one transverse bore  22 , and the longitudinal bore  20  in the stroke stop element  12 . Because of the sharp-edged transition from the orifice  20   b  of the longitudinal bore  20  in the indentation  16  into the throttle bore  20   a,  the positive displacement of fluid from the indentation  16  into the longitudinal bore  20  is made more difficult, and there is increased flow resistance there. Upon opening of the check valve, the valve member  7  enters into the indentation  16  and positively displaces fluid from it into the longitudinal bore  20 . Because of the increased flow resistance, the motion of the valve member  7  is damped, so that its impact on the stroke stop element  12  is less powerful. Upon closure of the check valve, fast lifting of the valve member  7  from the stroke stop element  12  is assured, since the inflow of fluid from the longitudinal bore  20  into the indentation  16  is made possible by the streamlined transition from the region  20   c  to the throttle bore  20   a.    
     Upon installation of the check valve in the valve housing  1 , the valve member  7  is first introduced into the bore  3 . Next, the stroke stop element  12  is inserted from the open side of the valve housing  1  into the bore  3 , in the direction of the longitudinal axis  4 , until the annular shoulder  13  of the stroke stop element  12  comes into contact with the annular shoulder  10  of the valve housing  1 . The maximum stroke of the valve member  7  that the valve member can execute between its contact with the valve seat  5  and with the stroke stop element  12  is fixed by the axial position of the stroke stop element  12 . 
     The stroke stop element  12  is fixed at least indirectly in the axial direction in the bore  3  of the valve housing  1  by means of a welded connection. Preferably, the stroke stop element  12  itself is joined by material engagement on its circumference to the valve housing  1  by means of a welded connection  26  in the bore  3 , as shown in the upper half of  FIG. 1 . The check valve is disposed near the open end of the valve housing  1 . Alternatively, it can also be provided that after the insertion of the stroke stop element  12  into the bore  3 , as shown in the lower half of  FIG. 1 , a welded ring  28  is inserted, by which the stroke stop element  12  is fixed in the axial direction and which is joined by material engagement to the valve housing  1  by means of a welded connection  30 . 
     In  FIG. 2 , an example of the use of the check valve of the invention is shown schematically. An injector is identified in its entirety by reference numeral  55 . The injector  55  is supplied with fuel at high pressure from a common rail  57  via a high-pressure line (not identified by reference numeral). A hydraulic pressure booster  59  is provided in the injector  55 . The hydraulic pressure booster  59  includes a booster piston  61 , which divides a low-pressure chamber  63  from a high-pressure chamber  65 . In the booster piston  61 , there is a longitudinal bore  3 . In the bore  3 , there is a check valve  67 , shown in stylized fashion, which prevents fuel from being able to flow out of the high-pressure chamber  65  into the low-pressure chamber  63 . This check valve  67  is a check valve in accordance with the exemplary embodiment of  FIG. 1  described above. 
     The high-pressure chamber  65  communicates hydraulically with a drum  69  in which a nozzle needle  71  is disposed. Via a first magnet valve  73 , which is embodied as a 3/2-way valve and which controls the hydraulic pressure booster  59 , and a second magnet valve  75 , which controls the pressure in the drum  69 , the nozzle needle  71  is opened and closed. 
     The booster piston  61  is preferably made from a roller bearing steel having a carbon content of approximately 1%. The booster piston  61  is guided with very little play and has a wear protection layer on its outer surface. The heat input into the booster piston  61  in the production of the welded connection  26 ,  30  for fixation of the stroke stop element  12  in the bore  3  of the booster piston  61  must therefore be kept as slight as possible. As a result, the guidance play of the booster piston  61  and damage to the wear protection layer of the booster piston  61  from thermal factors in welding and/or thermal warping is minimized, and subsequent overly slight guidance play of the booster piston  61  and accordingly increased wear is avoided. 
     The foregoing relates to the preferred exemplary embodiment of the invention, it being understood that other variants and embodiments thereof are possible within the spirit and scope of the invention, the latter being defined by the appended claims.