Patent Publication Number: US-9429048-B2

Title: Support element for a valve train of an internal combustion engine, and method for production of support element

Description:
INCORPORATION BY REFERENCE 
     The following documents are incorporated herein by reference as if fully set forth: German Patent Application No. 102014208811.9, filed May 9, 2014. 
     BACKGROUND 
     The invention relates to a hydraulic support element for, among other things, the lash compensation of a valve train of an internal combustion engine. 
     From DE 103 30 510 A1, a support element for a switchable cam follower of a valve train of an internal combustion engine is known that has, in a housing, two separate flow paths for a hydraulic medium. The first flow path is used for supplying a hydraulic lash compensation device, while the second flow path is used to supply the hydraulic medium to coupling agents in a supported, switchable cam follower. A non-return valve with the hydraulic lash compensation device is formed with a ball that closes a hole in a base of a work piston in the closed position of the non-return valve. A valve spring presses the ball axially with a defined mechanical biasing force against the open end of the hole in the piston base, wherein the valve spring is supported between the ball and a pot-shaped cap. A radially outward directed flange of the cap contacts a bottom side axial recess of the work piston with a defined force, wherein a compression spring for generating the necessary contact pressure force is supported between the flange of the cap and a base surface of a cylindrical space of the housing of the support element. Although this support element has many advantages, it is nevertheless considered disadvantageous that the non-return valve requires, in addition to the ball and the bottom side hole in the base of the work piston, also two additional components in the form of the valve spring and the pot-shaped cap. 
     SUMMARY 
     The invention is therefore based on the objective of providing a universally usable support element without caps and valve springs for the lash compensation of a valve train of an internal combustion engine, which also has a prolonged service life with simultaneously reduced manufacturing costs. In addition, the invention is also based on the objective of providing a method for producing such a support element. 
     The invention is based on the knowledge that the failure rate, the installation costs, and also the testing costs, especially for tightly toleranced, complex assemblies, can be generally reduced by decreasing the number of individual parts. 
     The invention therefore relates to a hydraulic support element for, among other things, the lash compensation of a valve train of an internal combustion engine, with a hollow cylindrical housing that can be installed with its outer lateral surface in a receptacle hole of a cylinder head of the internal combustion engine and that holds, in its radial inward axial hole, a piston that can be displaced coaxial to a longitudinal center axis, wherein the piston is comprised of an essentially hollow cylindrical pressure part and a pot-shaped work part connecting to this pressure part, wherein at least one axially end-side head of the pressure part projects past a housing edge and is used as a support for a cam follower, wherein an inner space of the pressure part and also an inner space of the work part form a storage space for a hydraulic medium, wherein a high-pressure space for the hydraulic medium is defined by a base of the pot-shaped work part and also by the hole of the housing, wherein the storage space and also the high-pressure space are connected to each other hydraulically by a non-return valve with a ball for guaranteeing automatic lash compensation of the valve train, wherein the piston is supported with the base of the pot-shaped work part by a compression spring on a housing base, and a retaining ring that limits an axial travel of the piston is arranged between the pressure part of the piston and the housing. 
     To meet the stated objectives, for this support element it is provided that the ball is held in the base of the work part in an axially oriented ball guide so that it can be displaced axially and so that the ball guide has a first ball seat on the storage space side and a second ball seat on the high pressure space side, and that the two ball seats are formed integrally with the base of the work part of the piston. 
     Through this construction of the support element, a valve spring and a retaining cap that must otherwise be provided for the valve spring and the ball can be eliminated without replacement, which significantly decreases the number of parts and along with this, decreases the manufacturing costs and the failure rate of the support element. In particular, the comparatively expensive use of sophisticated valve springs necessary in conventional constructions can be eliminated, which also leads to a considerable reduction in the testing costs within the scope of quality assurance. The ball guidance is preferably constructed as a cylindrical hole. 
     According to one advantageous refinement of this support element it is provided that the first ball seat closes completely hydraulically for a ball contacting this ball seat. In this way, the high pressure space is closed hermetically tightly relative to the storage space when the ball is in contact, so that the practically incompressible hydraulic medium ideally completely filling the high pressure space acts like a rigid or mechanically fixed connection in the longitudinal direction for an axially downward motion of the piston in the direction of the housing base. 
     According to another advantageous refinement of this support element it is provided that the second ball seat remains at least partially open for a ball contacting this ball seat. In this way it is guaranteed that the hydraulic medium can flow into the high pressure space from the storage space while overcoming a relatively low flow resistance and the piston can travel out of the housing of the support element at least up to a height limited by the travel limit and/or the cam follower or a rocker arm. 
     In another construction it can be provided that the second ball seat has at least one radially inward directed projection or is formed by this projection or projections. This arrangement prevents the ball from falling out of the ball guide in the work part of the piston. The projection or projections can have, for example, the shape of a sinusoidal half wave or a semicircle. Between the projection and the hole edge and/or each of the projections, a flow space for the hydraulic medium is formed. Advantageously, three projections are constructed to form the second ball seat. 
     In addition, for this support element it can be provided that the axial material thickness of the base of the work part of the piston is equal to or greater than the diameter of the ball of the non-return valve. This guarantees a reliable seat for the ball within the ball guide. In addition, an integral formation of the ball seats on the base of the work part of the piston can be produced without problems in terms of production through suitable shaping processes. 
     The objective with respect to the method is met by a method with the following steps:
         a) Production of a pot-shaped work part of a piston of the hydraulic support element, which has, in its base, an axially oriented ball guide that has a cylindrical section and an end-side narrowing section adjacent to this cylindrical section, wherein the narrowing section has a smaller diameter than a ball to be inserted into the ball guide and forms a first ball seat on the storage space side,   b) Insertion of the ball into the ball guide of the work part of the piston,   c) Shaping of the base of the work part of the piston on its bottom side on the high pressure space side in the area of the ball guide for forming at least one radially inward pointing projection for forming a second ball seat on the high pressure space side, wherein the ball is held captively in the ball guide in interaction with the storage space side first ball seat but can move in the axial direction, and   d) Axial insertion of the piston into a housing of the support element.       

     This arrangement provides a production of the support element that is more economical in terms of production, because, in contrast to the previously known solutions, all of the production steps are not performed in isolation only on the work part of the piston, but instead can be completed on the entire ball-piston work part assembly beginning with the usually obligatory heat treatment. The method allows the creation of a work part that has only two parts by means of a cap-less and valve spring-less design of the support element. 
     According to one advantageous refinement of the method it is provided that the shaping in method step c) is formed by impact extrusion of the work part of the piston that is not hardened at least in some area or of the work part of the piston that is completely not hardened. Due to the work part of the piston that is not completely hardened in all areas, the shaping process of the work part is made considerably easier, wherein, however, under some circumstances, a final heat treatment is required for hardening the work part and/or the ball. In this configuration, the shaping takes place in the area of the second, high pressure space side ball seat of the work piston for forming the radial projections, so that the work piston is not completely hardened at least in this zone. A projection of the hollow cylindrical ball guide forming the first, storage space side ball seat can be formed, under some circumstances, simultaneously, in advance, or afterwards, for example, by a shaping process, wherein the work part of the piston is at least not completely hardened in this area. 
     According to another embodiment of the method, the shaping can be performed in the method step b) by orbital forming or by radial point forming of the work part of the piston hardened at least in some areas. In this way, the necessary shaping can be completed on the already hardened work part of the piston, so that usual additional treatment steps for hardening can be eliminated, but the shaping process has a more complicated form. 
     Corresponding to another embodiment of the method it can be provided that, before the method step a) or after the method step d), at least the ball, the work part, and/or a pressure part of the piston are subjected to a heat treatment for their hardening at least in some areas. 
     This arrangement enables a flexible configuration of the sequence for the method according to the invention. 
     For the complete assembly of the support element it can be provided that at least one compression spring acting on the work part of the piston, the shaped work part of the piston with the ball held therein, the pressure part of the piston, and also a retaining ring are inserted into a hole of the housing of the support element and secured axially by means of the retaining ring. In this way, only relatively large and easy to handle components or one assembly in the form of the work part and ball must be integrated for completing the support element. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For further explanation of the invention, a drawing accompanies the description. Shown in the drawings are: 
         FIG. 1  a longitudinal section through a support element formed according to the invention, 
         FIG. 2  a top view on the high pressure space side of the work part of the piston of the support element with radially inward pointing projections, and 
         FIG. 3  to  FIG. 5  schematic representations of the sequence for producing a high pressure space side ball seat on the work part of the piston. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The support element  10  according to  FIG. 1  has an essentially pot-shaped housing  12  with a housing base  14 . The support element  10  can be inserted with the outer lateral surface  16  of the housing  12  in a mount of a not-shown cylinder head of an internal combustion engine. In a cylindrical hole  18  of the housing  12 , a piston  24  composed axially from a pot-shaped work part  20  and an essentially cylindrical pressure part  22  is held so that it can be displaced along a longitudinal center axis  26 . 
     The work part  20  of the piston  24  has an essentially flat base  28  and a hollow cylindrical wall  30 , whose outer lateral surface  32  contacts an inner surface  34  of the cylindrical hole  18  in an essentially pressure-tight manner. An end face  38  of the wall  30  of the work part  20  contacts an end face  36  of the pressure part  22 . The end of the pressure part  22  pointing away from the end face  36  of the pressure part  22  is formed as a dome-shaped head  40  that is used as a support for a not-shown switchable cam follower of a valve train of the internal combustion engine. The supply of the cam follower with a hydraulic medium takes place via a coaxial cylindrical hole  42  formed centrally to the longitudinal center axis  26  of the support element  10  in the head  40 . 
     The work part  20  that is open in the area of its end face  38  and the pressure part  22  of the piston  24  that is similarly open in the area of its end face  36  each forms approximately cylindrical inner spaces  44 ,  46  that together define a storage space  48  for the hydraulic medium. The hydraulic medium is preferably a lubricating oil that is otherwise necessary for lubricating the internal combustion engine and can be diverted with low expense from lubricating oil galleries or lubricating oil holes of a cylinder head of the internal combustion engine. 
     The feeding of the hydraulic medium into the storage space  48  is performed via a radial hole  50  in the housing  12  of the support element  10  and an opening  52  in the pressure part  22  of the piston  24 . For this purpose, the radial hole  50  is in hydraulic connection with not-shown lubricating oil holes in the cylinder head of the internal combustion engine, so that, the normal lubricating oil pressure of the internal combustion engine is established in the storage space  48 . To make the circulation of the hydraulic medium easier, an annular gap  49  is provided between the pressure part  22  of the piston  20  and the housing  12  of the support element  10 . 
     At least the dome-shaped head  40  projects, in each operating state of the support element  10 , past a housing edge  54  of the housing  12 , wherein a retaining ring  56  in the area of an annular groove  58  of the pressure part  22  of the piston  24  and/or the cam follower contacting the dome-shaped head  40  with a positive-fit connection form an axial travel limit for the piston  24 . 
     The base  28  of the pot-shaped work part  20  of the piston  24  defines, together with the housing base  14  and the axial hole  18  of the housing  12 , a high pressure space  60  for the hydraulic medium, in which this space is at a significantly higher pressure than in the storage space  48 . Between a high pressure space side annular groove  62  in the base  28  of the work part  20  and the housing base  14  there is a compression spring  64  that is arranged coaxially and by which the piston  24  is biased in a mechanically spring-like way relative to the cam follower and/or the retaining ring  56 . 
     The high pressure space  60  is separated hydraulically from the storage space  48  by means of a non-return valve  66 , so that the previously explained structural configuration of the support element  10  corresponds, in this respect, to the known embodiments of so-called “hydraulic tappets” for the lash compensation of valve trains in internal combustion engines and a detailed explanation of the lash compensation function of the support element  10  along the longitudinal center axis  26  can be eliminated at this point. 
     The valve spring-less and cap-less non-return valve  66  has a ball  68  that is held along the longitudinal center axis  26  in a hollow cylindrical ball guide  70  between a first ball seat  72  on the storage space side or facing the storage space  48  and a second ball seat  74  on the high pressure space side or facing the high pressure space  60  so that it can be displaced in the axial direction. 
     For the ball  68  contacting the first ball seat  72 , the non-return valve  66  is closed hermetically tight, so that the incompressible hydraulic medium enclosed in the high pressure space  60  acts like a mechanically rigid connection relative to any downward motion of the piston  24  in the direction of the housing base  14 . In contrast, in the event of an opposite, upward motion of the piston  24 , the ball  68  is lifted from the first ball seat  72  by the hydraulic medium flowing into the high pressure space  60  and pressed against the second ball seat  74 . The second ball seat  74  remains at least partially open also when the ball  68  is in contact and thus allows a passage of the hydraulic medium, so that the upward motion of the piston  24  acts against only a relatively low flow resistance and pumps up, so to speak, the support element  10 . Here, the piston  24  of the support element  10  is pushed out slightly from the housing  12  along the longitudinal center axis  26 , wherein the desired dynamic lash compensation takes place with respect to the cam follower of the internal combustion engine contacting the head  40 . 
     To prevent the ball  68  from falling out of the non-return valve  66  or from the base  28  of the work part  20  of the piston  24 , the second ball seat  74  has four small, radially inward directed projections  76 ,  78 ,  90 ,  92 , of which only two projections  76 ,  78  are visible in  FIG. 1 . According to the invention, the two ball seats  72 ,  74  are formed integrally with or on the base  28  of the work part  20  of the piston  24 , so that the non-return valve  66  requires, for its proper function, neither a valve spring nor a cap for securing the position of the ball  68 . 
     To enable the integral formation of the non-return valve  66  in the course of a simple shaping process of the work part  20  of the piston  24 , the axial material thickness  80  of the base  28  of the work part  20  is slightly smaller, equal to, or greater than a diameter  82  of the ball  68 . The diameter  82  of the ball  68  is approximately smaller than the diameter  102  of the ball guide  70  shown in  FIG. 4  in the base  28  of the work part  20 . The first ball seat  72  is formed in the area of the storage space side top side  84  and the second ball seat  74  is formed in the area of the high pressure space side bottom side  86  of the base  28  integrally on the work part  20  of the piston  24 . The top side  84  of the base  28  is directed toward the storage space  48  and the bottom side  86  is directed toward the high pressure space  60 . A so-called axial ball travel  108  that cannot be seen in  FIG. 1  is defined by the maximum axial path along the longitudinal center axis  26  that the ball  68  can travel between the two ball seats  72 ,  74 , that is, until it contacts one of the ball seats  72 ,  74 . This ball travel  108  that can be seen in  FIG. 5  is, at most, a few tenths of a millimeter. 
     The valve spring-less and retaining cap-less non-return valve  66  of the support element  10  leads, in comparison to known support elements, to increased advance travel losses in the valve train of the internal combustion engine due to the structure, that is, to a slight axial sinking of the hydraulic support element  10 , when a force acts in the axial direction from above on the head  40  of the pressure part  22 , as is the case in the valve train, for example, immediately at the beginning of the cam follower travel. This increased advance travel loss can be explained in that the non-return valve  66  closes only when the hydraulic medium out of the high pressure space  60  begins to flow into the storage space  48  and here more and more takes along the ball  68  of the non-return valve  66 . This advance travel loss therefore must be taken into account by a corresponding opening curve of the ball travel in the non-return valve  66 . For this purpose, in known valve trains, a smallest possible and precisely reproducible ball travel should be given. In contrast, in variable valve trains that use, for example, a sliding cam system with corresponding radial tolerances of the camshaft, a larger ball travel can be advantageous in order to better compensate for the reference circle impact of the camshaft. 
     Additionally or alternatively, the ball travel can also be influenced by a variation of the surface geometry of the two ball seats  72 ,  74 . This consequently enables a universal use of the support element  10  in a plurality of different types of valve trains of internal combustion engines. 
       FIG. 2  shows a top view of the high pressure space side bottom side  86  of the work part  20  of the piston  24  with the already mentioned radial projections. In the bottom side  86  of the base  28  of the work part  20  of the piston  24 , the annular groove  62  is formed for securing the radial position of the compression spring not shown here. The high pressure space side, second ball seat  74  has the four radially inward pointing projections  76 ,  78 ,  90 ,  92  for the axial securing of the position of the ball  68  in connection with the first, here covered ball seat  72 . The projections  76 ,  78 ,  90 ,  92  are each formed integrally on the work part  20  of the piston  24  and spaced equally from each other and grouped circumferentially around the second ball seat  74  or around the ball guide  70  constructed as a hole. 
     Deviating from the four projections  76 ,  78 ,  90 ,  92  that are shown here only as an example and are positioned offset by 90° relative to each other around the longitudinal center axis  26 , three or more than four projections could also be formed in the area of the second ball seat  74 . The projections  76 ,  78 ,  90 ,  92  preferably have the shape of a sinusoidal half wave or a semicircle, but could also be formed with a different geometry. The projections  76 ,  78 ,  90 ,  92  prevent the ball  68  from falling out of the cylindrical ball guide  70 . In addition, the four projections  76 ,  78 ,  90 ,  92  guarantee a defined flow of hydraulic medium when the ball  68  contacts these projections. 
       FIGS. 3 to 5 , which will be referenced together in the description below, each show a schematic representation of the sequence of the production method according to the invention. The work part  20  of the piston  24  has the annular groove  62 , a section-wise spherical radial narrowing section  100  forming the first ball seat  72  in the cylindrical ball guide  70  and the cylindrical inner space  44  as one part of the whole storage space  48 . 
     As  FIG. 3  shows, in a first method step first the ball  68  is inserted along the longitudinal center axis  26  into the ball guide  70  of the preassembled work part  20  of the piston  24 , wherein the first ball seat  72  prevents the ball  68  from falling out due to the radial narrowing section  100 , or is used as a stop for the ball  68 . The first ball seat  72  is preferably formed integrally with the work part previously in the course of a production method, for example, impact extrusion or die-casting, that is suitable for producing the work part  20 . 
     In the position shown in  FIG. 4 , the ball  68  is inserted completely into the ball guide  70 , so that the shaping process for producing at least the high pressure space side, second ball seat  74  can begin. The diameter  82  of the ball  68  is advantageously slightly smaller than a diameter  102  of the cylindrical ball guide  70 , which produces a radial play and a slightly axial displacement of the ball  68  between the ball seats  72 ,  74 . 
     In a subsequent method step, starting from  FIG. 4 , the shaping of the work part  20  of the piston  24  takes place in the area of the bottom side  86  of the base  28  of the work part  20 , until the radial projections, of which only two projections  76 ,  78  are visible in  FIG. 5 , are completely shaped and the ball  68  is secured in its axial position between the two ball seats  72 ,  74 . The shaping is performed here as a function of the local hardness degree of the work part  20  of the piston  24 , for example, in the direction of the two arrows  104 ,  106 , for example, by impact extrusion shaping, orbital forming, radial point forming, or other suitable shaping methods. 
     As  FIG. 5  shows, the shaping process of the work part  20  of the piston  24  is then completed and the second ball seat  74  with its projections, here only the radial projections  76 ,  78  are visible, is completely shaped, wherein, under some circumstances, at least the shaped areas, in particular, the radial projections and/or the ball  68 , must be subjected to a final hardening process. In  FIG. 5 , the maximum axial ball travel  108  of the ball  68  can also be seen, namely the distance between the second position of the ball  68  shown in  FIG. 5  with a solid line, in which this contacts the second ball seat  74 , and the first position of the ball  68  symbolized with a dashed line in which this formed a tightly sealing contact on the first ball seat  72 . 
     In a final method step not shown in the figures, the final installation of the support element shown in  FIG. 1  is performed. This can happen, for example, by inserting the compression spring  64 , the shaped work part  20  with the ball  68  held therein of the pressure part  22  of the piston  24 , and also the retaining ring  56  for securing the position of the entire arrangement in the hole  18  of the housing  12  of the support element  10 . 
     A deviation from the sequence of method steps listed here only as an example for the final installation of the support element can be advantageous for further optimizing the production process, if necessary. 
     By eliminating the valve spring and the retaining cap needed for securing the position of the ball and valve spring typical in known constructions, the production costs of the support element can be considerably reduced. Furthermore, an incorrect installation of the sophisticated valve spring is eliminated because this part is not used, which also eliminates the high testing costs that are otherwise needed for ensuring problem-free installation of the valve spring. Likewise, a displacement of the valve spring for larger ball strokes is prevented, which otherwise could easily lead to faulty functioning of the support element and along with this to serious problems in the valve train of the internal combustion engine. 
     The described construction of the non-return valve  66  can be used in single-flow or double-flow hydraulic support elements. In addition, the construction of the non-return valve  66  can also be used in other hydraulic support elements, for example, those not used for lash compensation for a valve train of an internal combustion engine. 
     REFERENCE SYMBOLS 
     
         
         
           
               10  Hydraulic support element 
               12  Housing 
               14  Housing base 
               16  Outer lateral surface of the housing 
               18  Axial hole in the housing 
               20  Work part of the piston 
               22  Pressure part of the piston 
               24  Piston 
               26  Longitudinal center axis 
               28  Base of the piston 
               30  Walls of the piston 
               32  Outer lateral surface of the walls of the work part of the piston 
               34  Inner surface of the axial hole in the housing 
               36  End face of the wall of the work part of the piston 
               38  End face of the pressure part 
               40  Dome-shaped head 
               42  Hole in the head 
               44  Inner space in the work part 
               46  Inner space in the pressure part 
               48  Storage space, formed by inner spaces  44 ,  46   
               49  Annular gap 
               50  Radial hole in the housing 
               52  Opening in the pressure part of the piston 
               54  Housing edge 
               56  Retaining ring 
               58  Annular groove in the pressure part of the piston 
               60  High-pressure space 
               62  Annular groove in the base of the work part 
               64  Compression spring 
               66  Non-return valve 
               68  Ball 
               70  Ball guide 
               72  First ball seat on the storage space side 
               74  Second ball seat on the high-pressure space side 
               76  First projection on the second ball seat 
               78  Second projection on the second ball seat 
               80  Material thickness of the base of the work part of the piston 
               82  Diameter of the ball 
               84  Top side of the base of the work part 
               86  Bottom side of the base of the work part 
               90  Third projection on the second ball seat 
               92  Fourth projection on the second ball seat 
               100  Narrowing section on the first ball seat 
               102  Diameter of the ball guide 
               104  Arrow 
               106  Arrow 
               108  Ball stroke