Patent Publication Number: US-6210129-B1

Title: High-pressure pump for a fuel injection device of an internal combustion engine

Description:
The invention relates to a pump, in particular a high-pressure pump for a fuel injection device of an internal combustion engine; 
     PRIOR ART 
     DE 44 19 927 A1 has disclosed a high-pressure pump for fuel embodied as a piston pump, and a piston/cylinder unit, which contains a work chamber, disposed in the pump housing of this high-pressure pump, and a pump shaft for driving the piston/cylinder unit is supported in this pump housing. The pump shaft is supported in its center and, on its cantilevered drive-side end, supports a cam which is used to act on the piston/cylinder unit. In order to drive the pump shaft, a drive gear is fastened to its end protruding from the pump housing. 
     The support of the pump shaft in the pump housing results in a relatively large structural length of the pump, which consequently has a relatively large space requirement. In addition, a relatively costly drive connection from a motor shaft to the drive gear is required, which likewise requires a certain amount of installation space in the engine compartment. Furthermore, large bearing loads are produced, which lead to an increased wear and to a reduced service life since the effective bearing length is relatively small compared to the length of the drive-side end of the pump shaft protruding from the bearing. 
     DE 42 17 910 A1 has disclosed a hydraulic pump driven by an internal combustion engine, which is disposed in a cavity in a cylinder head wall. An end of a cam shaft, on which a cam is non-rotatably disposed, which drives a piston of a pump element, extends into this cavity through an opening in the cylinder head wall. After the insertion of the pump element and the attachment of the cam to the cam shaft end, the cavity in the cylinder head wall is closed by means of a cap. 
     This known pump, which is used as a lubricant pump, does indeed have a relatively short structural length, but cannot be produced independently of the internal combustion engine. Furthermore, the function of this known pump and of its individual pump elements can only be tested after installation into the cylinder head wall of the engine. 
     ADVANTAGES OF THE INVENTION 
     The pump according to the invention, has the advantage over the prior art that through the non-rotatable support of the pump shaft on a shaft of the drive motor, no bearings are needed for the pump shaft in the pump housing so that a shortened structural length of the pump is produced. Moreover, the elimination of the bearing of the pump shaft in the pump housing results in an increased service life. 
     Furthermore, the pump according to the invention can be manufactured as a separate subassembly and can be tested as to its function independently of the internal combustion engine. In transport and storage, in order to prevent uncontrolled movements of the movable pump elements and therefore to prevent damage and problems in the subsequent installation, in a preferred exemplary embodiment of the invention, a transport securing device is provided for the pump shaft, which preferably has two securing means spaced apart from each other. 
     It is particularly advantageous if the passage of the pump shaft out of the pump housing is sealed since the pump interior is thus protected from impurities during storage, transport, and installation. 
     In order to be able to compensate for a radial play in the bearing of the shaft of the internal combustion engine without influencing the tightness of the pump, in an advantageous embodiment of the invention, the provision is made that the passage of the pump shaft out of the pump housing is sealed by means of an axial shaft seal in which two smooth faces are pressed tightly against each other. As a result, a perfect seal can be assured, even with an eccentric motion of the sealing faces in relation to each other. 
     A particularly non-problematic installation of the pump is produced if the pump shaft has a drive-side bearing pin which can be slid into a corresponding axial bore in the shaft of the internal combustion engine. This embodiment also permits the particularly simple connection of an auxiliary drive, which is necessary for a test operation of the pump for testing purposes. 
     Advantageous improvements and updates of the piston pump disclosed are possible by means of the measures taken hereinafter. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Exemplary embodiments of the invention are shown in a simplified form in the drawings and will be explained in more detail in the subsequent description. 
     FIG. 1 shows a section through a pump according to a first exemplary embodiment of the invention, 
     FIG. 2 a  shows a section through the drive-side end of a shaft of an internal combustion engine for use with a pump according to the invention. 
     FIG. 2 b  shows a side view, rotated by 90°, of the end of the shaft according to FIG. 2 a,    
     FIG. 3 shows a side view of a pump shaft for the pump according to FIG. 1, 
     FIG. 4 shows a side view of a pump shaft for a pump according to a second exemplary embodiment of the invention, and 
     FIG. 5 shows a section through a pump according to the second exemplary embodiment of the invention. 
    
    
     Parts that correspond to one another are provided with the same reference numerals in the different Figs. of the drawings. 
     DESCRIPTION OF THE EXEMPLARY EMBODIMENTS 
     As shown in FIG. 1, a pump according to the invention includes a pump housing  10  with one or more containing regions  11  each for a pump element  12 , and a containing region  13  in which a pump shaft  14  is disposed with its drive-side end formed as a cam  31 . The containing region  13  for the drive-side end of the pump shaft  14 , together with sections of the containing region(s)  11  oriented toward it, constitutes an inlet region  15  for a medium to be supplied at a relatively low pressure, in particular for fuel at precompression. By way of an inlet line, not shown, the inlet region  15  is connected to a low-pressure inlet connection, not shown, on the pump housing  10 . 
     As a working element, the pump element  12  includes a piston  16 , which is guided so that it can move in a piston guide  17 . The piston guide  17  is inserted into a securing part  18 , which holds the pump element  12  in the containing region  11  of the pump housing  10 . On the outer circumference of the securing part  18 , in the region of its inner end  9 , a seal  19  is provided, which seals the inlet region  15  in relation to a supply region  20 , in which the medium to be supplied is pumped with relatively high pressure, in particular with high pressure, and this supply region encompasses the securing part  18  in the region of outlet bores  21  provided in the securing part  18 . By way of a line, not shown, the supply region  20  is connected to a high-pressure outlet connection, not shown, on the pump housing  10 . The supply region  20  is sealed in relation to the outside by means of a seal  22  between the securing part  18  and the inner housing wall that encloses the containing region  11  for the pump element  12 . 
     The piston  16  has an axial inlet conduit  23 , which opens out at the end of the piston  16  disposed in the piston guide  17  and is connected to the inlet region  15  by way of a laterally extending inlet bore  24  in the end of the piston  16  protruding from the piston guide  17 . At the mouth of the axial inlet conduit  23 , the piston  16  has an inlet valve  25  and thus defines a work chamber  26  in the piston guide  17  and this chamber can be closed in relation to a high-pressure outlet region  28  by an outlet valve  27 . The high-pressure outlet region  28  is connected to the supply region  20  by way of the outlet bores  21 . 
     The inlet valve  25  is embodied so that it opens during the intake stroke of the piston  16 , i.e. when the piston is moving out of the piston guide  17 , so that during the intake stroke, medium to be supplied can flow from the inlet region  15 , through the inlet bore  24 , the inlet conduit  23 , and the open inlet valve  25 , into the work chamber  26 . During the supply stroke, i.e. when the piston  16  is moving into the piston guide  17 , the inlet valve  25  closes so that the medium enclosed in the work chamber  26  is put under pressure. As soon as the pressure in the work chamber  26  achieves a high pressure predetermined by the outlet valve  27 , this valve opens and the high-pressure medium to be supplied can be pumped through the open outlet valve  27 , the high-pressure outlet region  28 , the outlet bores  21 , and into the supply region  20 , from which it flows through the line, not shown, to the high-pressure outlet connection on the pump housing  10 . 
     A slide shoe  29  is connected to the free end of the piston  16  protruding from the piston guide  17 , and with it, the piston  16  is supported by way of a stroke ring  30  that is rotatably supported on a cam  31  of the pump shaft  14 , which cam is used as a crank element, so that the piston  16  can be driven by the pump shaft  14 . In order to hold the piston  16  in contact with the stroke ring  30  by way of the slide shoe  29  during the intake stroke of the piston  16 , a spring  32  is provided, which is supported with its one end against the slide shoe  29  and with its other end against the securing part  18 . 
     As can be seen particularly well in FIG. 3, the pump shaft  14  has a sealing collar  33 , which on the end remote from the cam  31 , is adjoined by a bearing pin  34  that has a reduced diameter in relation to the sealing collar  33 . On the shoulder  35  formed between the bearing pin  34  and the sealing collar  33 , catch lugs  36  are provided that are disposed diametrically opposite each other with regard to the pump shaft axis A. Between the sealing collar  33  and the cam  31 , a circumferential securing piece  37  is provided, whose outer diameter is greater than that of the sealing collar  33 . An auxiliary pin  38  is connected to the free end face of the cam  31  and is aligned coaxial to the bearing pin  34 . 
     As shown in FIG. 1, the pump shaft  14  is inserted into the pump housing  10  so that its auxiliary pin  38  travels with radial play in an auxiliary bore  39  in an inner housing wall  10   a  provided in the pump housing  10 , while the sealing collar  33  rests in the region of a through opening  40  of the pump housing  10 , which opening is encompassed by a centering collar  41  extending axially with regard to the pump shaft axis A. In this connection, the centering collar  41  and the auxiliary bore  39  are aligned coaxially to each other. 
     A radial shaft seal  43  is inserted in a sealed fashion into the through opening  40  and its inner diameter is greater than the outer diameter of the sealing collar  33 . A support face  42  is provided on the inner diameter of the radial shaft seal  43 . To seal the inlet region  15  or the containing region  13  for the cam  31  of the pump shaft  14 , there is a sealing lip  44  in the radial shaft seal  43  whose inner diameter is smaller than the outer diameter of the sealing collar  33 . Consequently, the sealing lip  44  is deformed by the sealing collar  33  and rests against it in a sealed fashion. In lieu of the sealing lip  44 , a grooved ring or the like can also be used, for example. 
     In the storage and transport of the pump, i.e. of the independent subassembly comprised of the pump housing  10 , pump element  12 , pump shaft  14 , and radial shaft seal  43 , the pump shaft  14  is pressed by the spring(s)  32  and held with its sealing collar  33  against the support face  42  provided on the radial shaft seal  43  and is held with the auxiliary pin  38  against the inner wall of the auxiliary bore  39 . The sealing lip  44  of the radial shaft seal  43  can only be deformed by half the diameter difference between the inner diameter of the support face  42  and the outer diameter of the sealing collar  33 . This diameter difference is laid out so that a constant deformation of the sealing lip  44  is prevented. The inner diameter of the sealing lip  44  is suitably chosen so that the sealing lip  44  seals the interior of the pump against dust and dirt, even when it is deformed in the manner described during transport and storage. The radial shaft seal  43  is formed and the sealing lip  44  is incorporated so that the pump shaft  14  comes to rest against the support face  42  before the sealing lip  44  can be damaged by crushing. 
     The sealing collar  33  and the support face  42  of the radial shaft seal  43 , together with the auxiliary pin  38  and the auxiliary bore  39 , thereby constitute a transport securing device for the pump shaft  14  in the pump housing  14 , which holds the pump shaft  14  essentially in its later operating position in the pump housing  10  when the pump is not attached to the motor housing  45 ′. In this connection, it is advantageous that the support face  42 , which constitutes a first securing means, and the auxiliary bore  39 , which constitutes a second securing means, are spaced axially apart from each other so that the pump shaft  14  cannot tilt in the pump housing  10 . In this way, the piston(s)  16  can in particular be prevented from being pulled too far out of the associated piston guide(s)  17 , which can result in problems upon installation of the pump, particularly in damage to the pistons  16  when sliding back in. 
     In lieu of the auxiliary bore  39 , an auxiliary pin or the like can also be provided as a second securing means on the inner wall of the pump housing  10 . In this instance, a corresponding auxiliary bore or the like would then have to be disposed in or on the cam  31 . 
     In addition, during transport and storage, the securing piece  37  on the pump shaft  14 , together with the radial shaft seal  43 , is used to secure the pump shaft against falling out. 
     In order to mount the pump—i.e. the independent subassembly comprised of the pump housing  10 , pump element  12 , pump shaft  14 , and radial shaft seal  43 —to a wall  45  of an internal combustion engine and thereby to bring the pump shaft  14  into engagement with a driven shaft  46  which is supported in a bore  47   a  of the internal combustion engine, e.g. with a cam shaft, first the bearing pin  34  of the pump shaft  14  is slid into an axial bearing bore  47 , in particular embodied as a fitted bore, in the shaft  46  and then, the centering collar  41  is slid into a receiving bore  48  coaxial to the shaft  46  of the internal combustion engine. In the course of this, the catch lugs  36  on the shoulder  35  of the pump shaft  14  enter into a groove  49  on the end face of the shaft  46 , which groove acts as a catch recess and is provided in an end-face collar  50 , as particularly shown in FIGS. 2 a  and  2   b . The pump shaft  14  is consequently supported radially by means of the insertion of the bearing pin  34  of the pump shaft  14  into the bearing bore  47  of the shaft  46  and is supported in the shaft  46  of the internal combustion engine fixed against relative rotation by means of the interlocking of the catch lug  36  with the groove  49 . 
     The radial support of the pump shaft  14  against the shaft  46  of the internal combustion engine can also be produced in the reverse manner, with a bearing pin on the shaft  46  and a bearing bore in the pump shaft  14 . It is furthermore possible to respectively provide both the shaft  46  of the internal combustion engine and the pump shaft  14  with a bearing bore and to use a bearing pin that is inserted into both bearing bores in order to support the pump shaft  14  against the shaft  46  of the internal combustion engine. Parts that protrude well beyond the pump housing  10  or the motor housing  45 ′ and can be easily damaged particularly during transport can therefore be avoided, particularly on both the as yet unmounted pump and the internal combustion engine. 
     The axial support of the pump shaft  14  can be carried out in almost any arbitrary manner since only very low bearing forces have to be absorbed here. For example, the pump shaft  14  with the auxiliary pin  38  can be supported against the bottom of the auxiliary bore  39  or can be supported with the end face of the cam  31  directly against an opposing inner wall of the pump housing  10  or can be supported against this wall by way of the stroke ring  30 . In the other axial direction, the axial support of the pump shaft  14  can be carried out for example by the support of the catch lugs  36  against the shaft  46  of the internal combustion engine or by the support of the securing piece  37  against the support ring  44 . 
     In the receiving bore  48 , a leakage chamber is formed for medium to be supplied, in particular fuel, leaking from the inlet region  15  through the radial shaft seal  43  and this chamber is sealed in relation to the outer environment by means of a sealing ring  52  employed on the outer circumference face of the centering collar  41  and is sealed in relation to the shaft  46  and therefore in relation to lubrication oil from its shaft bearing by means of a lip seal  51 . This leakage chamber is evacuated, for example by way of a bore  48 ′ in the pump housing  10 , which can be connected in a manner not shown in detail to an intake tube of the internal combustion engine if the medium to be supplied is fuel. In lieu of the bore  48 ′ in the pump housing  10 , a bore  48 ″ can also be provided in the motor housing  45 ′, as shown in FIG.  5 . 
     By means of a continual evacuation of the leakage chamber, the lip seal  51 , which is designed to produce a seal in relation to lubrication oil, is protected from damaging effects of the medium to be supplied, in particular fuel. This permits the service life of the lip seal  51  to be extended. 
     Since the receiving bore  48  in the wall  45  of the internal combustion engine is aligned coaxial to the driven shaft  46  and since the centering collar  41  is likewise aligned coaxial or concentric to the auxiliary bore  39 , the pump shaft  14 —which is supported with its bearing pin  34  in the bearing bore  47  of the shaft  46 , which bore is embodied as a fitted bore—is also aligned with its auxiliary pin  38  coaxial to the auxiliary bore  39  and with its support collar  33  coaxial to the radial shaft seal  43 . Since furthermore, the outer diameter of the auxiliary pin  38  is smaller than the inner diameter of the auxiliary bore  39  and since the outer diameter of the sealing collar  33  is smaller than the diameter of the support face  42  on the radial shaft seal  43 , during operation, i.e. when the pump shaft  14  is driven by the internal combustion engine by way of the shaft  46 —preferably the camshaft, the pump shaft  14  runs freely in the pump housing  10  without a separate radial support in it and without touching anywhere. 
     The subassembly comprised of the pump housing  10 , pump element  12 , pump shaft  14 , and radial shaft seal  43 , which is connected to the wall  45  of the motor housing  45 ′ of the internal combustion engine, can be fastened to the wall  45  of the engine, for example, by means of screws  53  only one of which is shown. 
     In lieu of the described pump shaft  14  with the catch lugs  36 , a pump shaft  14 ′ can also be used which in the bearing pin  34  adjacent to the sealing collar  33 , has a lateral bore  54  into which a catch pin  55  is inserted, as shown in FIG. 5 in connection with a second exemplary embodiment of the invention, and this catch pin  55  extends beyond the outer circumference of the bearing pin  34  to the point that it can be brought into catching contact with the grooves  49  on the shaft  46  of the internal combustion engine. 
     As FIG. 5 shows, the second exemplary embodiment of the pump according to the invention includes a pump housing  10  in which one or a number of pump elements  12  and a pump shaft  14 ′ are disposed. The design and the disposition of the pump element  12  corresponds to the design described in conjunction with FIG.  1 . The pump shaft  14 ′ differs from the pump shaft described in conjunction with FIGS. 1 and 3 only by means of the differing embodiment of the catch means for the rotationally fixed support against the shaft  46  of the internal combustion engine. In lieu of the radial shaft seal  43  provided in the pump according to FIG. 1, however, an axial shaft seal  56  is provided in the pump shown in FIG. 5 in order to seal off the inlet region  15  in relation to the receiving bore  48  in the wall  45  of the internal combustion engine. 
     The axial shaft seal  56  includes a catch  57  press-fitted onto the sealing collar  33  and, adjacent to the securing piece  37 , a spring  58  and a pressing ring  59  are inserted into this catch on the side of the spring  58  remote from the securing piece  37 . In addition, a sealing ring  60  is disposed between the pressing ring  59  and the sealing collar  33  and seals the pressing ring  59  in relation to the sealing collar  33  so that the pressing ring  59  can move in the axial direction for the purpose of tolerance compensation. 
     A slide ring  62  is inserted into an axial extension  61  of the centering collar  41  and supports a sealing ring  63  on its outer circumference. A disk  64 , which is fastened to the extension  61  of the centering collar  41 , for example by means of crimping, holds the slide ring  62  together with the sealing ring  63  in the containing region of the extension  61  of the centering collar  41 . 
     In the assembly of the pump according to FIG. 5, first the catch  57 , the spring  58 , the sealing ring  60 , and the pressing ring  59  are mounted in this order on the sealing collar  33  of the pump shaft  14 ′. Then the catch pin  55  is inserted into the lateral bore  54 . Since the length of the catch pin  55  is greater than the outer diameter of the sealing collar  33  or is greater than the inner diameter of the pressing ring  59 , the catch pin  55  secures the parts of the axial shaft seal  56  disposed on the pump shaft  14 ′ against the sealing collar  33  and is consequently used to secure them against falling out, in particular for the pressing ring  59  as long as it is not yet resting against the slide ring  62 . 
     As soon as the pump shaft  14 ′ is inserted into the pump housing  10  and the parts of the axial shaft seal  56  secured in the axial extension  61  of the centering collar  41  are mounted, the pressing ring  59  is pressed by the spring  58  with its end face  65  remote from the spring  58 , which end constitutes a radial sealing face disposed crosswise to the pump shaft axis A, against an end face on the slide ring  62 , which represents a slide face  66  that is used as a sealing face. The force of the spring  58 , which is disposed between the pressing ring  59  and the securing piece  37 , is supported against the pump housing  10  by way of the securing piece  37 , the cam  31 , and the auxiliary pin  38 . 
     In this connection, the axial shaft seal  56  functions as a first securing means of the transport securing device while the disk  64  that holds the slide ring  62  in the extension  61  of the centering collar  41  is used to secure it against falling out during transport and storage of the pump. 
     In order to supply a low-friction axial slide bearing for the pump shaft  14 ′ during operation of the pump, a disk  67  is inserted into the auxiliary bore  39 , which supports the auxiliary pin  38  in the axial direction and is preferably made of a low-friction material, in particular of a slide bearing material. 
     The use of the above-described axial shaft seal  56  in the pump according to the invention has the advantage that a possible radial play of the shaft  46  of the internal combustion engine, which leads to an eccentric rotation of the pump shaft axis A and therefore to an eccentric rotation of the pressing ring  59 , has no influence on the sealing of the pump since the sealing surfaces resting against each other are smooth and are disposed perpendicular to the desired course of the pump shaft axis A. A tilting of the pressing ring  59  in relation to the sealing collar  33  due to the radial play of the shaft  46  of the internal combustion engine is compensated for in this connection by means of the spring  58  and the sealing ring  60 . 
     The pump according to the invention, which has been described by way of example in conjunction with radial piston pumps with one pump element  12  or a number of pump elements  12 , preferably three disposed in a star pattern, can also be embodied as an axial piston pump. Furthermore, it is also possible to embody the pump according to the invention, in which the pump shaft  14 ,  14 ′ is inserted in a sealed fashion into the pump housing  10  without a separate bearing in this housing and can be supported in a drive shaft radially and in such a way that it is fixed against relative rotation, as an internal gear pump or the like. In a particularly advantageous manner, the invention can be used in all pump types in which one or a number of working elements are intended to be driven by way of a cam of a pump shaft. 
     In particular, the pump according to the invention has the advantage that it can be manufactured as a separate subassembly, independently of other parts and can be tested as a completely preassembled, already sealed subassembly directly at the manufacturer. As a result, the pump operation in particular, i.e. both the functioning of the individual pump elements  12  and their cooperation with the pump shaft  14 ,  14 ′ as well as the tightness, can also be fully tested. A further advantage is comprised in that with the subsequent installation in the final position of use, i.e. on an internal combustion engine, no installation dirt can penetrate into the pump. Furthermore, the elimination of the bearing of the pump shaft  14 ,  14 ′ in the pump housing  10  extends the service life of the pump. 
     The transport securing device provided in the pump according to the invention significantly facilitates the subsequent installation of the pump on the motor housing  45 ′ since the pump shaft  14 ,  14 ′ and therefore also the bearing pin  34  are secured essentially in the operating position provided. 
     In a particularly reliable manner, the use of an axial shaft seal furthermore permits a sealing of the pump independent of tolerances of the shaft  46  of the internal combustion engine, in particular independent of its radial play. 
     Dimensionally stable, fuel resistant materials that are matched to each other in the best way with regard to friction and wear can be used as materials for the pressing ring  59  and the slide ring  62 . The spring  58  provides for a uniform and constant surface pressure, which is largely independent of measurement tolerances and wear, between the surfaces of the pressing ring  59  and the slide ring  62  sliding against each other, i.e. between the end face  65  and the slide face  66 . 
     In the exemplary embodiment shown in FIG. 1, the support face  42  is provided indirectly against the pump housing  10  by way of the radial shaft seal  43 . However, it is also possible, for example, to match the outer diameter of the securing piece  37  to the diameter of the through opening  40  so that before the mounting of the pump housing  10  onto the motor housing  45 ′, the pump shaft  14  or  14 ′ can be supported at the through opening  40  by way of the circumferential securing piece  37 . In this variant, the through opening  40  is used as a support face  42 ′ provided directly on the pump housing  10  (FIG.  5 ). The support face  42  or  42 ′ is therefore respectively connected at least indirectly to the pump housing  10 . 
     There is a diametrical difference, i.e. a radial distance, between the support face  42  or  42 ′ and the region of the pump shaft  14  or  14 ′, which rests against the support face  42 ,  42 ′ before the mounting of the pump housing  10  onto the motor housing  45 ′, wherein the distance is dimensioned so that as soon as the pump is mounted onto the motor housing  45 ′, the pump shaft  14 ,  14 ′ cannot touch the support face  42  or  42 ′, independent of possibly occurring radial runout of the shaft  46 . 
     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.