Abstract:
A spring retaining sleeve includes a cylinder press-fit connection surface which has a press-fit diameter and a press-fit length. To enable cost-effective production of a stable press-fit assembly, at least one end of the cylinder press-fit connection surface, an optimized insertion chamfer for long press-fit assemblies is provided with a ratio of press-fit diameter to press-fit length of greater than thirty five percent.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a 35 USC 371 application of PCT/EP2009/052684 filed on Mar. 6, 2009. 
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The invention relates to a spring retaining sleeve having a cylinder press-fit connection surface, which has a press-fit diameter and a press-fitting length. 
     The spring retaining sleeve is part of a high-pressure fuel valve in a high-pressure fuel pump, with a receiving bore for the high-pressure fuel valve. In the receiving bore, a valve closing body of the high-pressure fuel valve is received movably back and forth counter to the prestressing force of a valve spring. The valve spring is fastened between the valve closing body and the spring retaining sleeve that is press-fitted into the receiving bore. 
     OBJECT AND SUMMARY OF THE INVENTION 
     The object of the invention is to create a spring retaining sleeve which makes economical production of a stable press-fit assembly possible. 
     In a spring retaining sleeve having a cylinder press-fit connection surface, which has a press-fit diameter and press-fitting length, the object is attained in that on at least one end of the cylinder press-fit connection face, an optimized insertion chamfer is provided, for long press-fit assemblies having a ratio of press-fit diameter to press-fitting length that is greater than 35 percent. The cylinder press-fit connection surface essentially has the shape of a rectilinear circular-cylindrical jacket, which is press-fitted with an oversize into the likewise circular-cylindrical jacket-like receiving chamber for the spring retaining sleeve. Because of the optimized insertion chamfer, a relatively long, elastic press-fit assembly which makes it possible to absorb major flow forces, is created in a simple way. In the context of the invention it was discovered that especially with long press-fit assemblies, unavoidable coaxiality errors between the insertion diameter and the press-fit diameter have an especially adverse effect. If the cylinder press-fit connection surface is not constant, jittering effects and finally seizing marks can occur during the press-fitting operation. Complicated minimization of the coaxiality errors can be dispensed with as a result of the optimized insertion chamfer. 
     One preferred exemplary embodiment of the spring retaining sleeve is characterized in that the insertion chamfer has an angle which is in a range from 18 to 22 degrees. In the context of the present invention it was discovered that in relatively long press-fit assemblies, in comparison to the insertion chamfer angle of 5 degrees, for instance, the indicated angle or range makes a pronounced reduction of unwanted jittering and seizing effects during a press-fitting operation possible. 
     A further preferred exemplary embodiment of the spring retaining sleeve is characterized in that the insertion chamfer has an angle that amounts to 20 degrees plus or minus degrees. This insertion chamfer angle has proved to be especially advantageous in the context of the present invention. 
     In a spring retaining sleeve having a cylinder press-fit connection surface, which has a press-fit diameter and a press-fitting length, in particular a spring retaining sleeve as described above, the above-stated object is also attained in that the cylinder press-fit connection surface has at least one lubrication groove. The cylinder press-fit connection surface essentially has the shape of a rectilinear circular-cylindrical jacket, which is press-fitted with an oversize and to the likewise circular-cylindrical jacket-like receiving chamber for the spring retaining sleeve. By means of the lubrication groove, a uniform supply of lubricant as the spring retaining sleeve is press-fitted in can be ensured. The lubrication groove creates a lubricant reservoir, which dispenses lubricant during the press-fitting operation and thereby provides for virtually constant friction. 
     A further preferred exemplary embodiment of the spring retaining sleeve is characterized in that the lubrication groove extends in the circumferential direction. The lubrication groove is preferably an encompassing annular groove. 
     A further preferred exemplary embodiment of the spring retaining sleeve is characterized in that the lubrication groove, in cross section, has the shape of a circular arc. This shape has proved to be especially advantageous in the context of the present invention. 
     A further preferred exemplary embodiment of the spring retaining sleeve is characterized in that the lubrication groove is disposed in the center of the cylinder press-fit connection surface. It is also possible for a plurality of lubrication grooves to be disposed centrally or symmetrically offset from one another. 
     Further advantages, characteristics, and details of the invention will become apparent from the ensuing description, in which various exemplary embodiments are described in detail in conjunction with the drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a cylinder head of a high-pressure fuel pump in section; 
         FIG. 2  shows an enlarged detail II of  FIG. 1 ; 
         FIG. 3  shows a spring retaining sleeve having an insertion chamfer of 5 degrees; 
         FIG. 4  shows the spring retaining sleeve of  FIG. 3  showing the influence of a coaxiality error; 
         FIG. 5  shows two enlarged details of  FIGS. 3 and 4 ; 
         FIG. 6  shows an illustration similar to  FIG. 5 , with an insertion chamfer angle of approximately 20 degrees; 
         FIG. 7  shows an illustration of the effect of a different press-fit face distribution; 
         FIG. 8  shows a spring retaining sleeve in a further exemplary embodiment, with a lubrication groove; and 
         FIG. 9  shows a section taken along the line IX-IX in  FIG. 8 . 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In  FIG. 1 , a cylinder head  2  of a high-pressure fuel pump  1  is shown in section. The cylinder head  2  includes a cylinder bore  4 , in which a high-pressure piston  5  is received movably back and forth. The high-pressure piston  5 , on one end, has a piston base  6 , which is driven, for example by a drive cam of a drive shaft (not shown). 
     In the cylinder bore  4 , the other end of the high-pressure piston  5  defines a high-pressure chamber  8 , which is filled with fuel via a suction valve  9 . The fuel is subjected to high pressure in the high-pressure chamber  8  by the high-pressure piston  5  and is delivered via a high-pressure valve  10 , for instance to a fuel injection system of an internal combustion engine. The high-pressure valve  10  is disposed in a receiving bore  14  in the cylinder head  2 . The receiving bore  14  communicates with the high-pressure chamber  8  via a high-pressure conduit  12 . 
     In  FIG. 2 , the detail II of  FIG. 1  having the high-pressure valve  10  is shown on a larger scale. In the enlarged view, it can be seen that a valve closing body  16  is guided, movably back and forth, in the receiving bore  14 . The valve closing body  16  serves to keep a valve seat closed or to open it intentionally, so as to carry away fuel, subjected to high pressure, from the high-pressure chamber  8  via the high-pressure valve  10 . For that purpose, the closing body  16  is movable back and forth along a longitudinal axis  18 , counter to the prestressing force of a valve spring  20 . 
     The valve spring  20  is braced on and guided in a spring retaining sleeve  22 . The spring retaining sleeve  22  includes a base body  24  with a central through hole  25  and is press-fitted into the receiving bore  14  in the cylinder head  2 . 
     In  FIGS. 3 and 4 , the spring retaining sleeve  22  is shown with a cylinder press-fit connection surface  31 , which essentially has the shape of a rectilinear circular-cylindrical jacket. One insertion chamfer  32 ,  33  is provided on each of the ends of the cylinder press-fit connection surface  31 . The press-fit diameter is indicated by a dimensioning line  34 . The press-fitting length of the cylinder press-fit connection surface  31  is indicated by a further dimensioning line  35 . 
     An insertion chamfer angle of the insertion chamfer  33  is marked  36 . The insertion chamfer angle  36  has a size of 5 degrees plus or minus 1 degree in  FIGS. 3 and 4 . The insertion diameter is indicated by a further dimensioning line  37 . In the exemplary embodiment shown in  FIG. 3 , the coaxiality error is equal to zero. In  FIG. 4 , the effect of a coaxiality error of 0.025 is illustrated by a line  38 . 
     In  FIG. 5 , the influence of the coaxiality error is shown, for an insertion chamfer angle  36  of 5 degrees plus or minus 1 degree. In  FIG. 6 , in comparison, the influence of the coaxiality error is shown for an insertion chamfer angle  36  of 20 degrees plus or minus two degrees. 
     In  FIG. 7 , the spring retaining sleeve  22  is shown on being press-fitted into the receiving bore  14 . The press-fitting direction is indicated by an arrow  39 . Further arrows  40  and  41  indicate forces which result because of an existing coaxiality error  43  of 0.025. The different magnitudes of the forces  40  and  41  are due to a different press-fitting face distribution that is the result of the coaxiality error  43 . Because of the different distribution of the press-fitting forces, tilting and torques can occur during the press-fitting operation. 
     By means of the choice according to the invention of an insertion chamfer angle  36  of 18 to 22 degrees, and in particular of approximately 20 degrees, it can be ensured in simple way that the press-fitted spring retaining sleeve, which is also known as a spring holder, maintains its position and does not slip during its entire service life. As a result, a necessary flow rate can be ensured during operation of the high-pressure valve. 
     The prestressing of the valve spring and thus the opening pressure of the high-pressure valve are set by means of the geometry of the spring holder or spring retaining sleeve. So that the spring retaining sleeve will not change its position over its entire service life, the press-fit assembly must be sufficiently certainly capable of absorbing the incident flow forces, which increase with an increasing flow rate; these flow forces can be greater than 2000 Newtons during the valve opening and valve closing operations. 
     The forces of the press-fit assembly to be absorbed can be increased, for example by the length of the press-fit assembly and by the press-fit diameter and a resultant press-fit oversize of the partners in the press-fit. If the press-fit assemblies are too long, uniformly supplying lubricant, in particular oil, to the entire press-fitting length during the press-fitting operation can prove difficult. 
     Within the context of the present invention, a percentage of 35 percent was found as a limit value for the ratio of press-fit diameter to press-fitting length. In other words, for a press-fitting length of 9 mm, the limit diameter is approximately 5.85 mm. At 60 percent, the limit diameter is 3.6 mm. If the limit diameter is exceeded, there is the danger of variously distributed and locally increased coefficients of friction. The result can be jittering effects and in the final analysis unwanted seizing during the press-fitting operation. 
     Moreover, in the relatively long press-fit assemblies discussed above, an unwanted influence of coaxiality errors occurs to an increased extent. Because of the unavoidable coaxiality errors, not only the aforementioned jittering effects and seizing effects during the press-fitting operation, but also an undesirably high mechanical load on an assembly device used for the press-fitting occur. Beyond a certain press-fitting oversize, the weaker partner in the press-fit moreover becomes plastically deformed. A purely elastic press-fit assembly, by comparison, has the advantage that elongation effects, which can occur for example with temperature differences, can be partly compensated for. 
     In  FIGS. 8 and 9 , a spring retaining sleeve  52  with a base body  54  is shown in various views. The base body  54  includes a central through hole  55 . The base body  54  furthermore includes a cylinder press-fit connection surface  61 , which on each of its ends has a respective insertion chamfer  62 ,  63 . The press-fit diameter is indicated by a dimensioning line  64 . The press-fitting length of the press-fit connection surface  31  is indicated by a further dimensioning line  65 . 
     In the exemplary embodimentshown in  FIGS. 8 and 9 , a lubrication groove  70 , which is embodied as an encompassing annular groove, is provided in the center of the cylinder press-fit connection surface  61 . The annular groove has a cross section that has the shape of a circular arc. As the spring retaining sleeve  52  is being press-fitted, the lubrication groove  70  represents a lubricant reservoir, in particular an oil reservoir, which dispenses lubricant during the press-fitting operation. As a result, a virtually constant friction during the press-fitting can be ensured. 
     The foregoing relates to the preferred exemplary embodiments 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.