Patent Publication Number: US-6216583-B1

Title: Piston pump for high pressure fuel supply

Description:
The invention relates to a piston pump, in particular a radial piston pump of the roller tappet type for high-pressure fuel delivery in fuel injection systems of internal combustion engines, particularly in a common rail injection system. A drive shaft that has a number of cam-like projections in the circumference direction and with at least one tappet that is disposed radially with regard to the drive shaft. In its radially inner end region, this tappet has a rotatable roller, which is reliably supported against the drive shaft in the region of its projections so that this roller can roll in the circumference direction. 
     It goes without saying that with a piston pump of this kind, preferably a number of radially disposed tappets is provided, which on their end remote from the drive shaft, either rest against a piston that defines a high-pressure side or define the high-pressure side themselves and thus directly perform a displacement or compression function. 
     Particularly in the above-mentioned common rail applications, the piston pump is not used for direct injection into the motor cylinder, but is instead used for delivery into a high-pressure reservoir. For functional and cost-related reasons, the aim is to reduce the number of separate supply units in comparison to conventional injection systems (e.g. series pump, plug-in pump) by virtue of the fact that—as already mentioned at the beginning—the drive shaft of the piston pump has a number of projections in the circumference direction, which consecutively produce a stroke motion in a radial piston or radial tappet during a rotation of the drive shaft (multiple cam system). 
     However, this leads to an increased load on the drive components, in particular of the tappet and the rotatably supported roller. In comparison to single-cam systems, the delivery times of the radial piston or radial tappet are increased while the relief times between the delivery phases are shortened. As a result of this, there is less time available for the formation of a lubricating film or a regeneration of the lubricating film in the region of the bearing of the roller. In piston pumps of the type mentioned above, this leads to increased wear as a result of insufficient lubrication in the region of the bearing of the roller. Because of the long delivery times, the lubricating oil is pressed out of the bearing gap and cannot penetrate back into the bearing location in sufficient quantity during the relatively short relief times. 
     The object of the current invention, therefore, is to reduce the wear in piston pumps of this generic type, without having to reduce the tappet load (piston force, piston or tappet stroke, relative speed of the roller in relation to its bearing). 
     This object is attained by means of a piston pump of the type mentioned above, which is characterized according to the invention by means of a lubricant supply opening that leads from the circumference of the tappet and feeds into the radially inner tappet end region supporting the roller and at least during a part of the stroke, communicates with a lubricant supply line of the housing, which line feeds into the cylinder chamber. 
     The proposal is therefore made according to the invention to produce a lubrication of the bearing location of the roller by means of the lubricant supply opening embodied in the tappet. According to the invention, the lubricant supply opening, which preferably communicates with a lubricating oil circuit of the motor, feeds either directly into the region of the slide surfaces or into the so-called roller chamber, which is defined by the roller axle and by the end region of the tappet that contains the roller. 
     Since lubricant is introduced by way of the lubricant supply opening either directly into the boss or into the roller chamber of the tappet, there is a sufficient quantity of lubricant available. In the first instance, the lubricant is introduced directly into the region of the surfaces sliding against each other and in the second instance, there is always so much lubricant available in the roller chamber that the lubricant can nevertheless penetrate in a sufficient quantity into the bearing location during the relatively short relief times mentioned at the beginning. 
     The piston pump can be embodied in a particularly simple manner from a technical manufacturing standpoint so that each tappet has a roller with rigidly attached bearing pins, with which the roller is rotatably supported in the end region of the tappet. 
     The roller, however, can also be rotated in relation to a bolt that extends parallel to the rotation axis of the drive shaft and can be supported by this bolt in the end region of the tappet. 
     As already indicated above, it turns out to be particularly advantageous if the lubricant supply opening in the end region of the tappet feeds into at least one tappet boss that is for supporting the bearing pins or the bearing bolt of the roller. It would also be conceivable for the bearing pins or the bolt to be embodied with an annular groove in the boss region, which groove coincides with the lubricant supply opening. 
     It has also turned out to be advantageous if the bolt is fixed in relation to the tappet and has a lubricant conducting device that communicates with or coincides with the lubricant supply opening and leads to the surfaces of the bolt/roller pairing that slide against each other. With a fixed bolt, these slide surfaces are disposed on the inside between the roller and bolt. The lubricant conducting device is thus used to transport the lubricant, which is supplied into the boss or into the roller by way of the lubricant supply opening, to the surfaces of the bolt/roller pairing that slide against each other. If the lubricant supply opening feeds into the boss region, then according to one variant of the invention, the proposal is made that the lubricant conducting device be constituted by a lateral bore in the bolt and another bore in the bolt that extends obliquely in relation to the longitudinal direction of the bolt and feeds into the region of the slide surfaces. The lubricant thus travels via the lubricant supply opening into the lateral bore that extends essentially in the radial direction, into the interior of the bolt, and from there, into the region of the slide surfaces by way of the other bore that extends obliquely to the longitudinal direction of the bolt. 
     The lubricant conducting device, however, in a manner that is simple and therefore advantageous from a technical manufacturing standpoint, could also be constituted by a surface groove that runs in the longitudinal direction of the bolt and extends into the region of the slide surfaces. 
     The surface groove can have an intrinsically arbitrary cross sectional shape; it has turned out to be advantageous if it is embodied as convexly rounded in terms of the cross section in the longitudinal direction of the bolt. Moreover, it has turned out to be advantageous if the surface groove is closed in the longitudinal direction of the bolt, i.e. if it does not feed to the end faces of the bolt, in order to prevent the lubricant from escaping in this undesired direction. 
     The lubricant conducting device could furthermore be constituted by a flattening on the bolt circumference extending in the longitudinal direction of the bolt, which is particularly easy to produce from a technical manufacturing standpoint. 
     It also turns out to be advantageous if a groove extending in the stroke direction is provided in the circumference surface of the tappet and/or in the inner surface of the cylinder. In the reciprocating motion of the tappet, the groove assures that in each stroke position, the lubricant supply opening of the tappet communicates with the lubricant supply line of the housing, which line feeds into the inner surface of the cylinder. 
     In order to be able to control the lubricant flow rate in the system, the proposal is made to provide a throttle device in the lubricant supply line of the housing, i.e. upstream of the tappet in the supply direction. This achieves freedom with regard to the dimensioning and efficiency of the lubricant supply. 
     In another embodiment of the invention, the bolt and/or the roller are comprised of ceramic material and therefore excel in comparison to metallic slide pairings with regard to their capacity for temperature loading and wear. 
     In a quite particularly advantageous modification of the invention, the bolt has a structured circumference surface that preferably has groove-shaped recesses that extend along the bolt in an intrinsically arbitrary form, or lubricating pockets can be provided. By means of this surface structuring, on the one hand, a lubricant transport into the gap between the bearing pin and the boss or between the roller and the particular fixed bolt is produced by means of the particular capillary action of the structure, and on the other hand, a storage of the lubricating oil is produced in the loaded zone (lubricating pocket action). Preferable dimensions of the surface structures can be inferred from advantages set forth herein. 
     It has also turned out to be advantageous if an intermediary bush is provided between the bolt and the roller since this reduces the relative speed of the sliding partners and consequently reduces the energy conversion in the mixed friction or solids friction that occurs. 
     Other features, details, and advantages of the invention can be inferred from the accompanying claims and from the graphic representation and subsequent description of preferred embodiments of the invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows a partial sectional view through a piston pump according to the invention; 
     FIG. 2 shows a sectional view with a detail depiction along the line II—II in FIG. 1; 
     FIG. 2 a  is an enlarged view of the insert  2 ; 
     FIGS. 3 and 3 a  show two different sectional views of a tappet according to FIG. 1; 
     FIGS. 4 and 4 a  show a sectional view and a side view, respectively, of a tappet that is embodied according to the invention, with a lubricant supply opening; 
     FIGS. 5-5 g  show two additional sectional views of another embodiment of a tappet according to the invention, as well as different views of different embodiments of a bolt for the tappet roller; 
     FIGS. 6 and 6 a  show different a sectional views of the tappet according to FIG. 4, with a rotation prevention means of the bolt; 
     FIGS. 7 and 7 a  show two different sectional views of a tappet with a lubricating oil supply directly into the roller chamber; 
     FIGS. 8,  8   a ,  8   b  and  8   c  show various surface structures of tappet bolts, and 
     FIGS. 9 and 9 a  show two different sectional views of a tappet with an additional intermediary bush between the bolt and roller. 
    
    
     DETAILED DESCRIPTION 
     FIGS. 1 and 2 show a piston pump with a pump housing  2  in which a drive shaft  4  as well as a number of roller tappet compression units  6  are disposed in the radial direction or in a star shape in relation to one another. The drive shaft  4  has three cam-like projections  8  in the circumference direction, whose radially outermost points are respectively offset from one another by 120° in the circumference direction and each constitute the apex of an even curvature. Furthermore, a corresponding cam-like formation  10  of the drive shaft  4  is provided in a plane that extends parallel to the plane of the figures; this formation, however, is rotated by 60° in relation to the first one and cooperates with another roller tappet compressor unit  6 ′ (FIG.  2 ). 
     The roller tappet compressor unit  6  includes a tappet  12  that is provided so that it can execute a reciprocating motion in the radial direction  14  in a cylinder chamber  16  of the pump housing  2 . A roller  20  is rotatably supported on the end section  18  of the tappet oriented toward the drive shaft  4 . To this end, the end section  18  constitutes a bolt seat  22  (FIG. 3) in which bosses  24  are provided in order to receive a bolt  26  for rotatably supporting the roller  20 . The roller  20  rolls in the circumference direction against the cam-like projections  8  of the drive shaft  4  and thus produces a reciprocating motion of the tappet  12 . 
     On its end remote from the drive shaft  4 , the tappet  12  is prestressed inward in the radial direction  14  toward the drive shaft  4  by means of a spring  28 . The spring  28  is supported on the tappet end against a spring plate  30 , which is pressed with its outer region  32  against the tappet  12 . In the inner region  34 , a central opening  36  is provided, through which a piston  38  is guided. The piston  38  is supported on the tappet end against a central projection  40  of the tappet  12  and protrudes with its opposite free end  42  into a high-pressure side cylinder chamber  44 , which is constituted by a flange-shaped section  46  of the pump housing  2 . With the reciprocating motion of the tappet  12 , the piston  38  in the high-pressure side cylinder chamber  44  is set into a reciprocating motion in the compression direction or in the suction direction. 
     The high-pressure side cylinder chamber  44  communicates in a manner not shown with an intake line and a high-pressure line that leads to a common rail reservoir. The end section  18  on the drive axle end and the bolt seat  22  of the tappet  12  form a roller chamber  50  above the longitudinal axis  48  of the bolt. By way of a ventilation opening  52 , this roller chamber  50  communicates with the end of the tappet  12  remote from the drive shaft, which end supports the spring  28 , in order not to hinder the reciprocal motion of the tappet  12  by means of compression/vacuum production. 
     Furthermore, a lubricant supply conduit  54  is provided in the pump housing  2  and cooperates with a lubricant supply of a vehicle motor. A branch line  56  not shown in FIG. 1 with a throttle device  55  (FIG. 2 a ) leads away from the lubricant supply conduit  54  and feeds into the inner cylindrical surface of the cylinder chamber  16 . A groove  58  (FIG. 3) that extends in the stroke direction is provided at the corresponding location in the outer circumference surface  56  of the tappet  12 . A lubricant supply opening  60  extends from this groove  58  into the tappet and feeds into the region of the boss  24 , i.e. into the region of the bearing location of the bolt  26 . 
     FIG. 4 shows another embodiment of a tappet  70 , with a roller  72  that is supported by way of a bolt  74  in the bosses  76  of the bolt seat  78  of the tappet  70 . A lubricant supply opening  82  is in turn provided, which leads from the outer circumference surface  80  of the tappet  70 , and this lubricant supply opening is embodied in the form of a straight bore that feeds into the apex of the boss  76 . The bolt  74  is embodied as a fixed bolt and is oriented in the bosses  76  so that a bore  84  provided in the radial direction of the bolt  74  communicates with the mouth of the lubricant supply opening  82  in the boss  76 . The radial bore  84  in the bolt  74  extends approximately to the center of the bolt. From there, another bore  86  extends obliquely to the bolt axis and feeds into the bolt circumference surface  88  in the region of the surfaces of the bolt  74  and roller  72  that slide against each other. In this manner, lubricant can be brought into the region of the surfaces of the bolt  74  and roller  72  that travel against each other, by way of the lubricant supply opening  82  in the tappet and the lateral bore  84 , as well as the other bore  86  that adjoins it. The bores  84  and  86  thus constitute a lubricant conducting device  89 . As can be seen from the depiction on the right in FIG. 4 a , in contrast to FIGS. 1,  3 , no groove extending in the stroke direction is provided on the circumference surface  80  of the tappet. A groove of this kind, however, could be provided in the inner cylinder surface in order to assure a connection to the lubricant circuit over the entire stroke in a particularly advantageous manner. 
     FIGS. 5 and 5 a  show a tappet  90  with a roller  92  and a fixed bolt  94 . The tappet  90  in turn has a longitudinal groove  96  extending in the stroke direction on its outer circumference surface  98 , from which a lubricant supply opening  100  leads, which feeds into the region of the boss  102 . The bolt  94  has a lubricant conducting device  104  in the form of a groove  106  that is disposed in the circumference surface of the bolt  108  and extends in the longitudinal direction of the bolt. By way of the lubricant conducting device  104 , the lubricant supplied via the lubricant supply opening  100  into the boss region is brought in the axial direction (arrow  110 ) into the region of the surfaces of the roller  92  and bolt  94  that slide against each other. The longitudinal groove  106  is closed in the axial direction of the bolt and is embodied as convexly rounded in cross section (see detail X). In FIGS. 5 d  and  5   e , another alternative embodiment in the form of a bolt  94 ′ is depicted, which in lieu of the longitudinal groove  106  has a flattening  108 , which is also depicted in the detail Y. 
     FIGS. 6 and 6 a  show a tappet  110 , that corresponds to the one in FIG.  5  and is provided with a rotation prevention means  112  of the bolt  114  in relation to the boss  116 . The rotation prevention means  112  is constituted by a pin  118  that is inserted through the tappet  110  radial to the longitudinal direction of the bolt. 
     FIGS. 7 and 7 a  show another embodiment according to which a tappet  120  is embodied with lubricant supply openings  124  feeding into the roller chamber  122 . The lubrication thus takes place here by way of the roller chamber  122 . This embodiment turns out to be advantageous in connection with a loose bolt. By means of this, at least an increased supply of lubricating oil is achieved with a machining and assembly expenditure that is relatively low from a technical manufacturing standpoint. 
     In FIGS. 8-8 c , a bolt  130  is shown with a groove-shaped structure  134  that extends helically on its outer circumference surface  132 . Other surface structures  136  (FIG. 8 a ) (waffle pattern) and  138  (FIG. 8 b ) in the form of separate lubricant pockets are represented in FIG.  8 . Furthermore, a cross section of a V-shaped groove profile  140  (FIG.  c ) is shown, which preferably has a depth of 40 μm and a width of 70 μm in the vicinity of the circumference surface. It should be emphasized that even with a structure like  136 , additional lubricant pockets can be provided in order to produce a combined effect. 
     Finally, FIGS. 9 and 9 a  show a tappet in which an intermediary bush  158  that travels in relation to the bolt  156  and the roller  154  is provided between the roller  154  and the bolt  156  in order to reduce the relative speed of the friction partners. 
     The foregoing relates to a 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.