Patent Publication Number: US-7707979-B2

Title: Valvetrain switchable lever arm for internal combustion engine using collapsing pivot element at center pivot

Description:
FIELD OF THE INVENTION 
   The invention relates to a switchable valvetrain for an internal combustion engine, having a row of rocker arms which extend in the longitudinal direction of a cylinder head, which rocker arms on the one hand intrinsically have, on an underside at one end, an at least indirect run-on face for at least one cam, and at the other end, a valve rest; and that run on the other hand via a recess on their upper side on a head of a bearing journal, with at least a subset of the bearing journals being axially moveably arranged in a corresponding bore of an above-situated carrier or of an insert part which is connected to the carrier, with each modular unit [moveable bearing journal/carrier or insert part] being assigned coupling means for selectively coupling the moveable bearing journal at least indirectly to the carrier, so that in the deployed state of the moveable bearing journal, a large valve lift is generated when coupled and a relatively small or zero valve lift is generated when decoupled, and with the respectively moveable bearing journal being acted on out of its bore by means of a lost motion spring. 
   BACKGROUND OF THE INVENTION 
   A valvetrain of said type is known from DE 32 39 941 A1 which is considered generic. A disadvantage of said valvetrain (see FIG. 1) is its extremely complexly designed coupling mechanism. Arranged laterally on the carrier is a bar-like slide which, in the coupled case, engages by means of a conical end face on one end into an annular groove of a bearing journal. 
   Said complex mechanism demands an unnecessarily large installation space in the cylinder head. It can be seen that the laterally engaging slide, with its surrounding construction, projects laterally beyond one end of the rocker arm. It is also clear that, as a result of the mere single-sided coupling, increased component loading in the coupled case can occur on the one hand, and the bearing journal has an increased tendency to tilt in the coupled case on the other hand. There are also only very few standard parts (previously used valvetrain parts) which can be resorted to. 
   OBJECT OF THE INVENTION 
   It is therefore the object of the invention to create a switchable valvetrain of the above-specified type, in which the stated disadvantages are eliminated. 
   ACHIEVEMENT OF THE OBJECT 
   According to the invention, said object is achieved in that an annular groove is arranged in the bore of the carrier or insert part, the at least axially upper annular face of which annular groove runs orthogonally with respect to the axial line of the bore of the carrier or insert part, with the bearing journal having at least one radially-running or secant-shaped recess which intersects its outer casing and in which, in the decoupled case, is seated at least one piston as a coupling means, which coupling means, proceeding from its radially outer face end, is of stepped design with a flattening situated above, and which coupling means, for the coupled case, can be displaced with its flattening in sections under the upper annular face of the annular groove of the bore of the carrier or insert part. 
   A valvetrain is therefore provided in which said disadvantages are eliminated. The integration of the coupling means into the journal saves radial installation space in the carrier/insert part. Hydraulic medium for the displacement of the coupling means (piston) (preferably hydraulically radially inward) can be very easily supplied out of the carrier/insert part. The annular groove for the coupling is very simple to form in production terms, with the contact pressure being kept low in the coupled case on account of the flattenings proposed in the claims. In addition, it is possible to dispense with a device for preventing the bearing journal from rotating with respect to its surrounding part. 
   Two pistons, situated diametrically opposite in a simple-to-produce through bore (if appropriate, two blind bores can also be considered) in the bearing journal should preferably be provided as a coupling means, so that a tendency of the bearing journal to tilt in the coupled case is prevented and the contact pressure is kept low. This arrangement also has the advantage that, should an insufficient “deployment” of one of the pistons occur after a triggered coupling command, at least the other piston provides support. 
   It is clear that, for example in the case of multi-valve technology, not every bearing journal need be designed so as to be switchable in the carrier. 
   The pistons can be displaced out particularly far radially in the coupling direction if their outer face end which faces toward the annular groove has a radii profile which correlates with that of the annular groove. A particularly good supporting surface is thereby formed. 
   Edge wear in the coupling region is avoided by means of corresponding bevels/roundings at the face-end-side “at the top” on the piston, and at the contact edge of the annular groove. 
   In general, a displacement of the coupling means in one direction by means of hydraulic medium and in the other direction likewise by means of hydraulic medium or by means of pressure spring force is conceivable and provided. A variety of possible combinations of adjustment means which are known per se are available to a person skilled in the art at this point. 
   It is alternatively possible, instead of the annular groove, for a bore or the like to also be provided for engaging the piston. Here, however, the bearing journal must preferably be prevented from rotating. 
   It is particularly preferable if the carrier is embodied as a continuous rail for at least one row or a partial section of one row of the rocker arms which extend in the longitudinal direction of the cylinder head. Said carrier can therefore, as is also proposed, be stored, delivered to the engine manufacturer and installed there, in a fully pre-assembled state with rocker arms suspended on the bearing journal. 
   The scope of protection of the invention also relates to a valvetrain having a carrier which, in a unipartite fashion, is assigned a plurality of rows of rocker arms which run in the longitudinal direction of the cylinder head. But alternatively, the carrier can also be assigned only to individual rocker arms or groups of rocker arms. 
   Clamp-like elements such as sheet metal or wire clamps, as are known per se, are suitable as connecting means of the rocker arm to the heads of the bearing journals. If appropriate, a jointed connection or the like is also conceivable. 
   In one physical embodiment, it is proposed to provide the valvetrain with hydraulic play compensation. For this purpose, it is proposed to provide the bearing journal with the play compensating device, so that said bearing journal is virtually in two parts and composed of a pressure piston with the head which is held in a guide bore of a housing as a further constituent part of the bearing journal. Complex mechanical play setting measures can therefore be dispensed with, but are indeed also conceivable. 
   It is conceivable and provided to couple the piston not directly to the annular groove in the carrier, but rather to provide a separate insert part for this purpose. The coupling mechanism with the bearing journal, play compensation, piston and insert part can therefore be placed into a receptacle of the carrier in a pre-assembled state. An outer casing of the insert part is held fixedly in the receptacle of the carrier. 
   The lost motion spring which is required for the decoupled case is, according to a further expansion of the invention, embodied as at least one coil or spiral pressure spring, and should act at one end against a face end of the bearing journal, and at the other end against a base of the bore of the carrier. The base of the bore of the carrier can be connected in a unipartite fashion to the carrier, with it however also being provided to apply a separate plug, a holding cap etc. in said region. 

   DESCRIPTION OF THE DRAWING 
   Illustrated is a switchable valvetrain  1  for an internal combustion engine. Said switchable valvetrain  1  is composed of an “overhead” carrier  11  for a row of rocker arms  2  which extend in the longitudinal direction of a cylinder head. The rocker arm  2  illustrated here has, on its underside  3  at one end, a run-on face  4  (rolling-bearing-mounted roller) for a cam  30 , and at the other end a valve rest  5  for at least one gas exchange valve  29 . 
   Between the ends, on an upper side  6 , the respective rocker arm  2  has a spherical-cap-shaped recess  7 . A head  8  of a bearing journal  9  runs in said recess  7 . The head  8  is a constituent part of a pressure piston  26  of a hydraulic play compensating device  25 . The bearing journal  9 , which therefore has the play compensating device  25 , runs with its outer casing  14  in a downwardly open bore  10  of the carrier  11 /insert part  11   a . Said bearing journal  9  is held in a telescopically moveable mariner relative to said bore  10 . As can also be seen, the bore  10  of the carrier  11 /insert part  11   a  has an annular groove  13   a . At least the upper annular face  15  of said annular groove  13   a  runs perpendicularly with respect to the axial line of the bearing journal  9 . 
   Running orthogonally with respect to the longitudinal direction of the carrier  11  (a cross section is shown) in the bearing journal  9  is a recess  16 , which is formed as a through bore  23 , with two pistons situated diametrically opposite as coupling means  12 . Said pistons  12  are shown in their state in which they are engaged into the annular groove  13   a  (coupled state). Said pistons  12  have, proceeding from their radially outer face end  17 , one flattening  18  each on their upper side, which flattening  18 , in the coupled case, lies under the upper annular face  15  of the annular groove  13   a . The coupling state disclosed can for example be produced by the force of a spring means  19 , such as at least one coil pressure spring, which acts between the inner face ends  20  of the pistons  12  (cam base circle phase). A return displacement into the decoupled position is carried out by means of a hydraulic medium which is supplied to an outer face end  17  of the respective piston  12  from the carrier  11 /insert part  11   a . The outer face ends  17  of the pistons  12  can additionally be designed so as to follow the curvature of the annular groove  13   a.    
   In addition, it is disclosed in the drawing that a lost motion spring  13  is integrated within the bore  10  of the carrier  11 /insert part  11   a . Said lost motion spring  13  is seated at one end against a face end  27 , which faces away from the rocker arm  2  of the bearing journal  9 , and acts at the other end against a base  28  of the bore  10 . A cover-like element  24  is applied here as a base  28 . 
   In order to avoid edge wear, it is proposed to bevel an edge region  21  of the upper annular face  15  of the annular groove  13   a , and likewise an edge region  22  of the flattening  18  of the respective radially outer face end  17  of the piston  12 . 
   It is also provided to retain the respective rocker arm  2  pivotably on the head  8  of the bearing journal  9  by means of a connecting means  23   a  such as a thin-walled holding clamp which is formed in the region of the recess  7  of said rocker arm  2 . The entire modular unit (carrier  11  with insert parts  11   a , bearing journal  9 , rocker arms  2  suspended on the latter . . . ) can be stored, delivered to the engine manufacturer and installed there, in a pre-assembled state. The assembly expenditure at the engine manufacturer is therefore drastically reduced. 
   LIST OF REFERENCE SYMBOLS 
   
       
         1 ) Valvetrain 
         2 ) Rocker arm 
         3 ) Underside 
         4 ) Run-on face 
         5 ) Valve rest 
         6 ) Upper side 
         7 ) Recess 
         8 ) Head 
         9 ) Bearing journal 
         10 ) Bore 
         11 ) Carrier 
         11   a ) Insert part 
         12 ) Coupling means, piston 
         13 ) Lost motion spring 
         13   a ) Annular groove 
         14 ) Outer casing 
         15 ) Upper annular face 
         16 ) Recess 
         17 ) Outer face end 
         18 ) Flattening 
         19 ) Spring means 
         20 ) Inner face end 
         21 ) Edge region, annular groove 
         22 ) Edge region, flattening 
         23 ) Through bore 
         23   a ) Connecting means 
         24 ) Plug/element 
         25 ) Play compensating device 
         26 ) Pressure piston 
         27 ) Face end 
         28 ) Base 
         29 ) Gas exchange valve 
         30 ) Cam