Abstract:
A high-pressure fuel pump includes an outlet valve, a valve ball, a valve spring that acts on the valve ball in a closing direction, and a stop body for the valve ball. The stop body has a stop section that limits the opening stroke of the valve ball, and the valve spring is supported by the stop body. The stop body has a cut-out section that at least partially accommodates the valve spring and that has a radial inner periphery which forms a guide for the valve spring.

Description:
This application is a 35 U.S.C. §371 National Stage Application of PCT/EP2014/062806, filed on Jun. 18, 2014, which claims the benefit of priority to Serial No. DE 10 2013 215 275.2, filed on Aug. 2, 2013 in Germany, the disclosures of which are incorporated herein by reference in their entirety. 
     BACKGROUND 
     The disclosure concerns a high-pressure fuel pump. 
     High-pressure fuel pumps, in particular piston pumps for a fuel system for an internal combustion engine, are known from the market. Frequently, such high-pressure fuel pumps comprise an inlet valve and an outlet valve which can open and close depending on a control command and/or depending on a fuel pressure. The outlet valve allows a pressurized fuel accumulator (rail) to close against a delivery chamber of the high-pressure fuel pump during a suction stroke. When however the fuel pressure in the delivery chamber exceeds a counter-force caused by the pressure in the fuel accumulator plus a closing spring force, the outlet valve can open. 
     SUMMARY 
     The problem on which the disclosure is based is solved by a high-pressure fuel pump as described herein. Advantageous refinements are given in the subclaims. Features important to the disclosure are also contained in the description which follows and in the drawings, wherein the features may be important for the disclosure both alone and in different combinations, without this being explicitly mentioned. 
     The disclosure concerns a high-pressure fuel pump having an outlet valve, a valve ball, a valve spring acting on the valve ball in the closing direction, and a stop body for the valve ball with a stop portion which limits the opening stroke of the valve ball, wherein the valve spring rests on the stop body. The stop body has a recess in which the valve spring is received at least in regions, and the radially inner limiting surface of which forms a guide for the valve spring. By means of the recess, the valve spring can be guided comparatively precisely, whereby the outlet valve can be constructed smaller. Thus the high-pressure fuel pump can be made particularly versatile in design. The disclosure has the advantage that an outlet valve of a high-pressure fuel pump has a comparatively low hydraulic adhesion of a valve element to a sealing seat, since this can be formed linear. Accordingly, the noise during an opening process of the outlet valve can be reduced. 
     In one embodiment of the high-pressure fuel pump, an edge of the recess facing the valve ball in the stop body forms an annular stop portion. This allows a defined limitation for the opening travel (stroke) of the valve element, whereby the function of the outlet valve can be improved. In particular, as a result of the stroke limitation, a closing time of the outlet valve can be kept comparatively short and relatively constant. This allows a reduction in so-called “back flow losses” during an incipient suction phase of the high-pressure fuel pump, wherein a fuel already compressed to high pressure can flow back from the high-pressure accumulator (rail) to the delivery chamber of the high-pressure fuel pump. A delivery level of the high-pressure fuel pump can thus be increased. Preferably, the stop portion is designed at least approximately conical. In this way, the valve ball can be held definedly in an opened state of the outlet valve. 
     The outlet valve becomes cheaper if the valve ball comprises a comparatively economic steel material. A comparatively costly valve ball made of a ceramic material is therefore not necessary for the outlet valve according to the disclosure. 
     In a further embodiment of the high-pressure fuel pump, the recess has a simple cylindrical cross-section. In this way, production of the outlet valve can be simplified and made cheaper. In a further embodiment of the high-pressure fuel pump, the valve spring is configured as a pressure-loaded coil spring and has different diameters in an axial direction, and in particular is waisted. In this way, the construction space of the valve spring or coil spring can be reduced and the function of the outlet valve improved, in particular a non-linear spring characteristic can be achieved. 
     In a preferred embodiment, the outlet valve of the high-pressure fuel pump has a valve body on which a sealing seat is formed and which has a guide collar in which the valve ball is guided radially, wherein the guide collar has a first plurality of recesses which are arranged distributed—preferably evenly—in the peripheral direction and form first flow channels, and wherein the stop body, radially outside the recess, has a second plurality of recesses which are arranged distributed —preferably evenly—in the peripheral direction and form second flow channels, wherein the cross-section areas of the second flow channels are selected such that, independently of the radial orientation of the stop body, at least one second flow channel at least partly overlaps with a first flow channel. This describes a particularly suitable embodiment of the high-pressure fuel pump according to the disclosure. In particular, the mounting of the valve body, valve ball, coil spring and stop body may be particularly simple. In this way, production of the high-pressure fuel pump may be made cheaper. Elements of the outlet valve may be mounted independently of a radial angle of the elements to each other, and installation is therefore simplified. 
     In addition, it may be provided that the first plurality and the second plurality are different. In this way, above all with an even distribution of recesses, effectively a radial “interference” is created between the first and second flow channels, whereby a total resulting hydraulic opening cross-section is substantially independent of a radial angle between the guide collar and the stop body. This improves the function of the outlet valve and simplifies the installation, since the elements need not be aligned in the peripheral direction. 
     In a further embodiment it is proposed that the stop body is formed as a punched part and/or deep-drawn part. In this way, the outlet valve and hence the high-pressure fuel pump according to the disclosure become cheaper. 
     In a further embodiment, the stop body and/or the valve body are arranged by force fit—in particular by pressing—in a housing of the outlet valve. In this way, installation of the outlet valve becomes simpler and its production therefore cheaper. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Exemplary embodiments of the disclosure are described in more detail with reference to the drawings. The drawings show: 
         FIG. 1  a diagram of a high-pressure fuel pump of a fuel system for an internal combustion engine of a motor vehicle in a simplified axial section view; 
         FIG. 2  an outlet valve of the high-pressure fuel pump of  FIG. 1  in an axial section view; and 
         FIG. 3  a perspective view of elements of the outlet valve of  FIG. 2  arranged spaced axially in the installation sequence (partly exploded depiction) in front of an opening on a housing of the high-pressure fuel pump. 
     
    
    
     DETAILED DESCRIPTION 
     Values and elements of equivalent function, even in different embodiments, carry the same reference numerals in all figures. 
       FIG. 1  shows a simplified diagram of a high-pressure fuel pump  10  in an axial section view. The high-pressure fuel pump  10  is an element of a fuel system (not shown) of an internal combustion engine (not shown) of a motor vehicle. The high-pressure fuel pump  10  has a housing  12 , in the portion of which on the left in the drawing are arranged an electromagnet  14  with a magnetic coil  16 , an armature  18  and an armature spring  20 . 
     Furthermore, the high-pressure fuel pump  10  comprises an inlet  24  with an inlet valve  26  connected to a low-pressure line  22 , and an outlet  30  with an outlet valve  32  connected to a high-pressure line  28 . A high-pressure accumulator (rail) connected to the high-pressure line  28  is not shown. In open state, the outlet valve  32  is hydraulically connected to a delivery chamber  36  via an opening  34 . The outlet valve  32  comprises a valve ball  38  and a valve spring  40 , and is depicted only highly diagrammatically in  FIG. 1 . The outlet valve  32  is shown again and described in detail further below with reference to  FIGS. 2 and 3 . 
     The inlet valve  26  comprises a valve spring  42  and a valve body  44 . The valve body  44  can be moved by a valve needle  46 , displaceable horizontally in the drawing, which is coupled to the armature  18 . When the electromagnet  14  is powered, the valve needle  46  moves to the left in  FIG. 2 , and the inlet valve  26  can be closed by the force of the valve spring  42 . 
     If the electromagnet  14  is not powered, the inlet valve  26  can be forced open by the force of the armature spring  20 . A piston  48 , moveable vertically in the drawing, is arranged in the delivery chamber  36 . The piston  48  can be moved by means of a roller  50  of a cam  52 —elliptical in the present case—in a cylinder  54 . The cylinder  54  is formed in a portion of the housing  12 . The inlet valve  26  is hydraulically connected to the delivery chamber  36  via an opening  56 . 
     In operation, the high-pressure fuel pump  10  delivers fuel from the inlet  24  to the outlet  30 , wherein the outlet valve  32  opens or closes according to a respective pressure difference between the delivery chamber  36  and the outlet  30  or the high-pressure line  28 . On full delivery, a respective pressure difference between the inlet  24  and the delivery chamber  36  acts on the inlet valve  26 ; on part delivery however, the valve needle  46  or the electromagnet  14  also act thereon. 
       FIG. 2  shows an axial section view of the outlet valve  32  which is arranged in the housing  12  of the high-pressure fuel pump  10 . The outlet valve  32  is designed substantially rotationally symmetrical or radially symmetrical, and in the present case comprises four elements: a valve body  58  (on the left in the drawing), a stop body  60  (on the right in the drawing), the valve ball  38  arranged axially centrally between the valve body  58  and the stop body  60 , and the valve spring  40  designed as a coil spring. 
     The valve spring  40  acts on the valve ball  38  in the closing direction and is received in a recess  62  of the stop body  60 . The valve spring  40  here rests on a base (on the right in the drawing but without reference numeral) of the stop body  60 . A radially inner limiting face of the recess  62  forms a guide for the valve spring  40 . The recess  62  has a simple cylindrical cross-section. The base has an axially central opening  64  which has a smaller diameter than the valve spring  40 . In the embodiment of the outlet valve  32  shown in  FIG. 2 , the valve spring  40  has (ever) varying diameters in the axial direction and is designed waisted in the present case. 
     An edge of the recess  62  facing the valve ball  38  in the stop body  60  forms an annular stop portion  66  for the valve ball  38 . An annular, linear sealing seat  68  is formed on the valve body  58 . On the right of the sealing seat  68  in the drawing, the valve body  58  has a guide collar  70  in which the valve ball  38  is guided radially. The guide collar  70  has a first plurality of recesses  72  which are arranged evenly distributed in the peripheral direction and form first flow channels  74 . The guide collar  70  is designed radially symmetrically in an axial region of the first flow channels  74 , corresponding to the first plurality of recesses  72 . 
     Radially on its outside i.e. outside the recess  62 , the stop body  60  has a second plurality of recesses  76  which are arranged evenly distributed in the peripheral direction and form second flow channels  78 . In an axial region of the second flow channels  78 , the stop body  60  is designed radially symmetrical, corresponding to the second plurality of recesses  76 . In the present case, the first plurality and the second plurality are different and amount to three and five respectively, see  FIG. 3  below. 
     In  FIG. 2 , the valve body  58  and the stop body  60  are arranged or shown axially spaced by a small dimension (without reference). In one embodiment (not shown) of the outlet valve  32 , the valve body  58  and stop body  60  are arranged axially adjacent without spacing. Preferably, the stop body  60  and/or the valve body  58  are arranged by force fit in the housing  12 , in that a radially outer face of the stop body  60  or valve body  58  is for example pressed against a radially inner wall portion of the housing  12 . It is understood that to arrange the stop body  60  and/or valve body  58  in the housing  12 , techniques other than pressing are possible according to the disclosure. 
     In the present case, the valve ball  38  is made of a steel material. The stop body  60  is produced by means of punching and deep-drawing. In total, the outlet valve  32  is dimensioned or configured such that in open state of the outlet valve  32 , a resulting hydraulic cross-section area is sufficiently large to deliver a necessary fuel quantity with a comparatively low hydraulic flow resistance. 
     When, in operation of the high-pressure fuel pump  10 , a fuel pressure in the delivery chamber  36  or in a region of the opening  34  is smaller than a fuel pressure in a region of the recess  62  plus the force of the valve spring  40 , the valve ball  38  is pressed against the sealing seat  68 , to the left in the drawing. The outlet valve  32  is thus closed. 
     When however the fuel pressure in the region of the opening  34  is greater than the fuel pressure in the region of the recess  62  plus the force of the valve spring  40 , the valve ball  38  can lift away from the sealing seat  68 , to the right in the drawing. The outlet valve  32  is thus opened. 
     Insofar as the fuel pressure in the region of the opening  34  is sufficiently large, the valve ball  38  can be pressed fully to the right in the drawing, up to the stop portion  66 . This gives a “travel limitation” for the valve ball  38 . A circle  80  shown in dotted lines indicates the position of the valve ball  38  in this extreme case. It is evident that the valve body  58  and the stop body  60  allow a radial guidance of the valve ball  38 , see also  FIG. 3  below. 
     An arrow  82  illustrates the resulting flow of fuel when the outlet valve  32  is opened. The flow takes place from left to right in the drawing, through the opening  34 , then past the valve ball  38 , then through the first flow channels  74  into the valve body  58 , then through the second flow channels  78  into the stop body  60 , then into the high-pressure line  28  and through to the high-pressure accumulator (not shown). 
       FIG. 3  shows a perspective view of the high-pressure fuel pump  10  and housing  12  together with the elements of the outlet valve  32  described in  FIG. 2 . These elements are shown axially spaced, in the installation sequence, in a right-hand region in the drawing along a line  84 , in front of an arrangement of openings (without reference) of the housing  12 . 
     It is evident that the valve body  58  is designed radially symmetrical in a region of the guide collar  70 , and in the present case comprises three first flow channels  74 , wherein for reasons of clarity only one is marked with a reference numeral. The stop body  60  is also designed radially symmetrical in the region of the recesses  76 , and in the present case comprises five second flow channels  78 , wherein for reasons of clarity again only one carries a reference numeral. 
     Firstly, the cross-section areas of the second flow channels  78  are selected such that, independently of the radial orientation of the stop body  60  relative to the valve body  58 , at least one of the second flow channels  78  at least partly overlaps one of the first flow channels  74 . Secondly, because the first plurality and the second plurality are different, effectively a “radial interference” is created between the three first and the five second flow channels  74  and  78 . This gives a resulting total hydraulic opening cross-section of the outlet valve  32  which is substantially independent of any arbitrary radial mounting angle between the guide collar  70  and the stop body  60 .