Abstract:
A device for changing a compression ratio of a cylinder unit of a reciprocating piston combustion engine is provided. An eccentric bushing is rotatably arranged in a receiving bore hole of a bearing eye of a connecting rod (“conrod”). The conrod bearing eye is formed by a conrod upper part and a conrod lower part, and which surrounds a crankpin of a crankshaft. In addition, the eccentric bushing is rotatably guided in the receiving bore hole and can be locked preferably in two positions which are offset from one another by approximately 180° in the circumferential direction of the eccentric bushing. In order to achieve a targeted rotation of the eccentric bushing in the bore hole of the conrod bearing eye between the locking positions, a freewheel is arranged between an outer casing surface of the eccentric bushing and the receiving bore hole of the conrod bearing eye.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is the U.S. National Phase of PCT Appln. No. PCT/DE2015/200371 filed Jun. 16, 2015, which claims priority to DE Patent Application No. 10 2014 216 533.4 filed Aug. 20, 2014, the disclosures of which are incorporated in their entirety by reference herein. 
     
    
     TECHNICAL FIELD 
       [0002]    This disclosure relates to a device for changing a compression ratio of a cylinder unit of a reciprocating piston combustion engine, comprising an eccentric bushing which is rotatably arranged in a receiving bore hole of a bearing eye of a connecting rod (or “conrod”), said conrod bearing eye being formed by a conrod upper part and a conrod lower part, and which surrounds a crankpin of a crankshaft, whereby the eccentric bushing that is rotatably guided in the receiving bore hole is preferably lockable in two positions which are offset from one another by preferably approximately 180° in the circumferential direction of the eccentric bushing. 
       BACKGROUND 
       [0003]    The compression ratio of a reciprocating piston combustion engine E is used to describe the ratio of the volume of the entire cylinder chamber to the volume of the compression chamber. Through an increase in the compression ratio, the efficiency of the reciprocating piston combustion engine may be increased and the fuel consumption my thus be reduced overall. With reciprocating piston combustion engine with external ignition, their knocking tendency however increases with the increase of the compression ratio in full-load operation. The knocking is an uncontrolled self-ignition of the air-fuel mixture. On the other hand, the compression ratio during partial-load operation, during which the filling is lower, could be increased for the improvement of the respective partial-load efficiency, without the previously mentioned knocking occurring. The result is thus that it is expedient to operate the reciprocating piston combustion engine in partial-load operation with a relatively high compression ratio and in full-load operation with a compression ratio reduced towards it. 
         [0004]    A change of the compression ratio is also particularly advantageous for loaded reciprocating piston combustion engines with external ignition as a lower compression ratio is stipulated with them in view of the load, whereby the compression must be increased to improve the thermodynamic efficiency in unfavorable areas of a respective engine map. There is furthermore the possibility to generally change the compression ratio depending on more operating parameters of the reciprocating piston combustion engine, for example like with running conditions of the motor vehicles, operating points of the internal combustion engine, signals of a knock sensor, emission values, etc. 
         [0005]    Devices are known from the state of the art, among other things, which perform an adjustment in distance between a crankpin, a crankshaft, and a piston pin. It thereby pertains to different devices, namely to such that perform a change in position of the conrod as opposed to the crankshaft. 
         [0006]    A device for changing a compression ratio of a reciprocating piston combustion engine in the type described in the generic claim of patent claim  1  is known from the DE 197 03 948 A1. According to that, a conrod device in the area of its conrod bearing eye assumes an eccentric bushing. It is guided to an inside wall of the conrod bearing eye with its cylindrical outer circumferential surface and is supposed to be formed as a plain bearing. On its inside circumferential surface that is eccentrically offset to the outer circumferential surface, the bushing is guided sliding on a crankpin of a crankshaft of the reciprocating piston combustion engine. A rotation of the bushing in the bore of the conrod bearing eye shall be automatic. This movement of the eccentric bushing shall be triggered by outside forces resulting from the rotation of the crankshaft, respectively the conrod movement. The eccentric bushing is furthermore provided with flanges on its ends which overlap the conrod bearing eye and have locking recesses offset by 180° in peripheral direction. A locking member intended on the conrod is activated through a cam segment in such a way that it optionally engages in the one or the other locking recess after a respective twist of the bushing. 
         [0007]    A device for changing the compression ratio of a reciprocating piston combustion engine is furthermore known from DE 10 2008 032 665 A1, in which an eccentric bushing is also supposed to be arranged on the respective crankpin of the crankshaft. This eccentric bushing has flanges on tis ends that are provided with external teeth. Through these, and through gears that are arranged in the webs of the crankshaft, and which are arranged to the external teeth at the drive and the output side, a mechanical drive system is created whereby adjusting shafts are arranged between the gears that run coaxially to the crankshaft. The gears shall thereby be driven via free runs from the adjusting shafts. 
       SUMMARY 
       [0008]    It is the task of the present disclosure to effect a specific torsion of the eccentric bushing in the bore of the conrod bearing eye between the locking positions. 
         [0009]    Advantageous embodiments are portrayed in the patent claims depending on it, which in their own right, or used in different combinations, may represent an aspect of the invention together. 
         [0010]    According to that, a free wheel is arranged between an outer casing surface of the eccentric bushing and the location hole. This free wheel prevents that the eccentric bushing is offset in short turning motions in opposite directions of rotation due to the inertia forces or gas forces as well as the moments created by the rotating crankpin. A change of rotation can result in the area of the top or bottom dead center of the working piston connected with the conrod, as moments work on the eccentric bushing, which can assume both positive and negative values. The consequence of this is that the respective eccentric bushing is not rotated into its other position serving the change of the compression ratio of the position serving the cylinder unit. This ultimately results in that some of the cylinder units are operated with a high and some with a low compression ratio. These disadvantages can be eliminated according to the disclosure by locating the free wheel between the eccentric bushing and the conrod bearing eye to allow one specific rotation in one direction of rotation. 
         [0011]    On the other hand, according to DE 197 03 948 A1, the eccentric bushing is arranged directly in the location hole of the conrod bearing eye. There is therefore no specific rotation of the bushing in one direction of rotation. Free wheels are however intended in the arrangement according to DE 10 2008 032 665 A1, but these are located between the individual actuating shafts and the driven gear wheels. 
         [0012]    In another embodiment of the invention, the free wheel is supposed to be formed as a roller free wheel. The respective clamping rollers are formed cylindrically and work together with clamping ramps that are intended on the outer casing surface of the eccentric bushing. Provided that the barrier effect is sufficient, balls can also be intended instead of the cylindrical clamping rollers. Alternatively to the use of a roller free wheel, there is also the possibility to intend for a clamping body freewheel, in which both the inside locking surface and the outer locking surface would be formed cylindrically. The outer casing surface of the eccentric bushing therefore does not need to be provided with clamping ramps like with the roller free wheel. 
         [0013]    When using a roller free wheel it is furthermore suggested that its clamping rollers are guided in a cage and that the eccentric bushing and the cage consist of two half shells. With a half-shell-like formation of the two parts of the cage, these can be provided dovetail-like on the one hand and with slots on the other hand on its two ends each. In an assembled condition of the cage, the dovetail-like end pieces of the one half shell reach into the respective opening of the other half-shell so that the half shells are guided to one another. The cage can also be formed in one part and can thereby only be slit in one area so that it can be bent upwards for the assembly on the eccentric bushing. It thereby may have a bending point and a cage lock. 
         [0014]    It is also suggested that roller bearings or plain bearings are formed on both sides, above which the eccentric bushing is stored across from the receiving bore hole. The eccentric bushing shall thereby be guided in the unlocked direction of rotation in the receiving bore hole so smoothly that the respective adjustment can take place without any special means during the operation of the reciprocating piston combustion engine. 
         [0015]    In another embodiment of the invention, provision is made for that the eccentric bushing is provided with boards running radially towards the outside, which are guided in a sliding fashion on both axially directed front surfaces of the conrod upper part and the conrod lower part. On these boards that have the shape of circular ring-shaped flanges, lock openings can be formed that are offset by 180° to each other on the circumference of the eccentric bushing. A locking element is thereby arranged movable in a pilot hole running in parallel to the receiving bore hole of the conrod bearing housing, which may optionally be slid into one of the lock openings. This locking is usually done in the two positions of the eccentric bushing for a low and a high compression ratio. 
         [0016]    Alternatively to the previously listed embodiment of the freewheel as a roller freewheel or a clamping body free wheel, it is furthermore intended to form it as a wrap-spring freewheel, whereby one end of at least one wrap spring is coupled to the conrod bearing eye. This end of the wrap spring can be fixated in the parting plane between the conrod upper part and the conrod lower part. The other end of the wrap spring is slid onto the eccentric. It is thereby important that the screw-shaped aligned wrap spring can be installed above the crankpin or the offset of the crankshaft. This is done by that the cross section of the wrap spring is chosen in such a way that the rectangular tape in the direction to be bent open is executer weaker and can thus be brought across the crankpin. Once the first wind has been slid over the crankpin, the remaining wrap spring can be wound up on the crankpin. In comparison with a positive-locking, respectively force-locking freewheel, the wrap spring has the advantage that the wrap spring can assume a clearly higher overload. 
         [0017]    Finally it is intended that the wrap-spring freewheel is arranged in a ring-shaped inclusion that usually extends within the conrod upper part and the conrod lower part and that has a rectangular cross section. Alternatively to that, there is also the possibility to intend for a respectively formed inclusion in the eccentric bushing. The eccentric bushing can also be formed in connection with this wrap-spring freewheel so that it can be set by means of axially, therefore locking means that are moved in parallel to the crankpin or radially to it in two positions offset from each other by 180° across from the conrod bearing eye. 
         [0018]    This disclosure is not restricted to the listed combination of features of the claims. There are furthermore more possibilities to combine individual features with each other, especially when they are the result from the patent claims, from the following description of the execution examples or from the figures directly. The reference of the patent claims to the figures shall not restrict the scope of protection of the patent claims due to the use of reference signs in any case either. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0019]    For a further explanation of embodiments of the invention, the drawing is referred to representing several different execution examples in a simplified manner. The following is shown: 
           [0020]      FIG. 1  as a perspective representation, a partial view of a crankshaft with a conrod arranged on a crankpin recording a working piston, which is cut in the area of its conrod lower part, 
           [0021]      FIG. 2  a partial view of the conrod with a partial section through a crankpin and a cam disc, 
           [0022]      FIG. 3  a perspective representation of an eccentric bushing that includes a roller freewheel on an outer casing surface, 
           [0023]      FIG. 4  an eccentric bushing with a roller freewheel, 
           [0024]      FIG. 5  a roller freewheel that has roller bearings arranged to it on both sides, 
           [0025]      FIG. 6  a perspective representation of the eccentric bushing provided with the roller freewheel, 
           [0026]      FIG. 7  a perspective representation of a cage intended for the roller freewheel, 
           [0027]      FIG. 7A  a perspective representation of another version of a cage intended for the roller freewheel, 
           [0028]      FIG. 7B  an enlarged section VII b in  FIG. 7A , 
           [0029]      FIG. 7C  an enlarged section VII c in  FIG. 7A , 
           [0030]      FIG. 8  as perspective representation, a conrod cut sideways, whereby a wrap-spring freewheel is arranged between a conrod eye and an eccentric bushing, 
           [0031]      FIG. 9  an enlarged representation of the conrod bearing eye of the conrod represented in  FIG. 7   
           [0032]      FIG. 10  a perspective representation to explain the assembly of a wrap-spring on a crankpin of a crankshaft, 
           [0033]      FIG. 11  a wrap-spring freewheel made from two wrap-springs wrapped inside each other, and 
           [0034]      FIG. 12  in a longitudinal section, a partial view of an eccentric bushing that is provided with a double winded wrap-spring freewheel, equipped with roller bearings on its two sides. 
       
    
    
     DETAILED DESCRIPTION 
       [0035]    A crankshaft of a reciprocating piston combustion engine is designated  1  in  FIG. 1 , of which only one partial section is represented consisting of four crank webs  2 ,  3 ,  4 , and  5 . The crank webs  2  and  5  are thereby provided with counterweights  6  for mass balance and insofar differ from the crank webs  3  and  4 . A crankpin  7  is furthermore formed between the crank webs  2  and  3  for the inclusion of a connecting rod (“conrod”) not explained in detail, while the crank webs  3  and  4  run on both sides of a main bearing pin  8 , above which the crankshaft  1  is stored in a crankcase of the reciprocating piston combustion engine not explained in detail. Finally, a crankpin is intended again between the two crank webs  4  and  5 , which is however not visible in this representation as a conrod is arranged on it. Due to the offset of the crankshaft  1 , this non-visible crankpin assumes a different position compared to the crankpin  7 . 
         [0036]    This conrod  9  consists of a conrod upper part  10  and a conrod lower part  11  that are connected with each other by screws  12 . The conrod upper part  10  includes a working piston  13  on its end facing away from the conrod lower part  11 , which is attached to the conrod upper part by means of a piston pin  14  with a piston pin bearing not explained in detail as well as a conrod eye. A parting plane  15  between the conrod upper part  10  and the conrod bottom part  11  runs through a conrod bearing eye that is also not visible in the perspective representation of  FIG. 1 , as already stated, as the conrod  9  is installed on the respective crankpin of the crankshaft  1 . 
         [0037]    An eccentric bushing  16  is arranged in this conrod bearing eye  16  that has boards  17  and  18  running outwards. The eccentric bushing  16  is guided on the face through the boards  17  and  18  both on the conrod upper part  10  and the conrod bottom part  11 . It can be seen from the partial section through the conrod bottom part  11  according to  FIG. 1  that a cylindrical locking element  19  is arranged moveable axially, therefore in parallel to the longitudinal axis of the crankshaft  1  in it. This locking element  19  has a radial running cylindrical carrier  20 , which engages in a carrier groove  21  of a cam disc  22  at times, meaning in the area of a bottom dead center of the working piston  13 . This cam disc  22  arranged in an oil sump of the reciprocating piston combustion engine is arranged moveably in longitudinal direction of the crankshaft  1  and is moved accordingly by means of adjusting means not described in more detail. It can thus move the locking element  19  in the direction of one of the two boards  17  or  18  through its carrier groove  21  recording the carrier  20 . The carrier groove  21  and be widened in the inlet area for the carrier  20  and can taper off continuously to the discharge area to offset possible tolerances. 
         [0038]    There is a locking bore in each of the boards that the locking element  19  can be moved into.  FIG. 1  has the locking element  19  with its respective end in a locking hole  23  of the board  17 . The respective position of this locking hole  23  of board  17  to a locking bore intended in board  18  will still be addressed in connection with the following  FIGS. 3, 4, and 6 . 
         [0039]    A section of the conrod  9  is represented in  FIG. 2  in the area of a conrod bearing eye  24 , which is formed by a half-shell formation of the end section of the conrod upper part  10  and the entire conrod lower part  11 . The conrod upper part  10  and the conrod lower part  11  are fixated to each other with screws  12  and jointly form a location hole  25 . The eccentric bushing  16  is arranged in this location hole  25 , which is thus guided rotational in the location hole  25 . The eccentric bushing  16  also consists of two half shells  16   a  and  16   b , whereby the two boards  17  and  18  of the eccentric bushing  16  are thus also arranged to these half shells accordingly, and which are executed by means of circular ring sections described with  17   a ,  17   b  as well as  18   a  and  18   b . But only the board  17  is visible in  FIG. 2  so that also only half of the circular ring section  17   a  is shown. 
         [0040]    For clarification of the arrangement, the conrod bearing eye  24  is represented as a half-section in  FIG. 2  so that the locking element  19  with the carrier is visible in its arrangement in the conrod lower part  11 . The locking element  19  has a snap contour that works together with a spring-loaded locking pin  27 . The arrangement of the cam disc and its interaction with the carrier is also shown in  FIG. 2 . 
         [0041]    As is furthermore shown in  FIG. 3 , a freewheel  29  is arranged on an outer casing surface  28  of the eccentric bushing  16  that is formed as a roller freewheel in this case. For this purpose, the outer casing surface  28  of the eccentric bushing  16  is provided with clamping ramps that run outwards in a radially angular manner, and which are not displayed in detail in  FIG. 3 . This representation furthermore shows that the eccentric bushing  16  is provided with sliding surfaces  31  and  32  on axial sections of its outer casing surface  28  to form a plain bearing. The two boards  17  and  18  that together with the hollow cylindrical section of the eccentric bushing  16  are halved into partial sections  17   a  and  17   b  as well as  18   a  and  18   b  have locking holes  23  and  33  that are offset to each other by 180°. Clamping rollers  30   a  of the roller freewheel are guided rotationally in a cage  34 . The embodiment according to  FIG. 3  furthermore has a carrier  20   a  formed with a rectangular cross section. The cam disc  22  in this case is provided with a carrier groove that is formed relatively wide in the inlet area for the carrier  20   a  and which continuously tapers off to the outlet area so that tolerances can be offset. 
         [0042]    The eccentric bushing  16 , as already explained in connection with  FIG. 2 , will be arranged in the location hole  25  of the conrod bearing eye  24 , whereby the boards  17  and  18  are guided sliding on the front faces of the conrod bearing eye  24 . The eccentric bushing  16  is also guided through the sliding surfaces  31  and  32  as well as the roller free wheel  30  in the location hole  25 . The roller freewheel ensures that a rotation of the eccentric bushing  16  across from the conrod bearing eye  24  is only possible in one direction of rotation, while the roller freewheel  30  blocks the rotary motion in the other direction of rotation. 
         [0043]    The arrangement of the roller freewheel  30  comprising the cage  34  on the outer casing surface  28  of the eccentric bushing  16  is shown once more in  FIG. 4 . The eccentric bushing  16  is thereby shown in a position, in which the locking hole is visible. 
         [0044]    An alternative embodiment of a cage  42  is represented in  FIG. 5 , which is formed in a middle area for the inclusion of clamping rollers  30   a  of the roller freewheel  30  and which has pockets  43  for the inclusion of cylindrical rolling elements next to this area. A roller bearing is thus created on both sides of the roller freewheel. 
         [0045]    With regard to the formation of the eccentric bushing,  FIG. 6  is referred to, which shoes it in a different perspective, in which a locking hole  23  of the board  17  is visible. The eccentric bushing  16  can be formed as a plain bearing  36  on its inner casing surface  35 ; above which the conrod  9  is arranged on the respective crankpin of the crankshaft  1 . 
         [0046]      FIG. 7  shows the cage  34  that comprises the cage halves  34   a  and  34   b  and which is intended for the inclusion of the clamping rollers  30   a  of the roller freewheel. The cage ends are thereby guided together through cage locks  37  and  38 . Each of these cage locks  37  or  38  consists of an end piece  39  formed as a dovetail and an end piece  41  comprising a slot  40 . The cage halves  34   a  and  34   b  can thus perform radial compensation movements to one other. 
         [0047]    Another embodiment of the cage  34  is represented in  FIG. 7A  in connection with the  FIGS. 7B and 7C . This cage  34  is formed as one piece and has a bending point  34   c  and a cage lock  34   d.    
         [0048]    According to another embodiment, per  FIG. 8 , a conrod  45  shall consist of a conrod upper part  46  and a conrod bottom part  47 , whereby a piston pin bearing  48  is formed on one end of the conrod upper part  46 . The conrod  45  further comprises a conrod bearing eye  49 , in whose receiving bore hole an eccentric bushing is rotatably mounted. Both the conrod upper part  46  and the conrod lower part  47  are provided with a recess  52  comprising a rectangular cross section, which consequently encompasses the eccentric bushing  51  on an outer casing surface  53 . 
         [0049]    As can be seen from  FIG. 8  in connection with  FIG. 9 , a wrap-spring freewheel  54  is arranged within this recess, which thus wraps the eccentric bushing  51  on its outer casing surface  53 . The respective wrap spring  55  is thereby fixated on the conrod bearing eye  49  on its one end. A respective wrap-spring freewheel  54  enables a rotation of the eccentric bushing  51  in one direction of rotation across from the conrod bearing eye  49  and prevents a rotation in the other direction of rotation. The eccentric bushing  51  is formed hollow cylindrical overall in this case, therefore without ribs. 
         [0050]    A pilot hole  56  is intended in the conrod lower part  47 , in which a sliding guideway  57  is arranged. The sliding guideway  57  has end sections  58  and  59 , in which it is provided with a recess or a reduced diameter. Actuating pins  60  and  61  are furthermore provided for in the bottom part of the piston, which run radially to the sliding guideway  57 . These actuating pins  60  and  61  work together with tie pins  62  and  63 , which are arranged in radial lock holes  64  and  65  of the eccentric bushing  51 . The lock holes  65  and  65  that are located on circumferential tracks of the eccentric bushing  51 , which are offset to each other axially, are thereby preferably formed as bored holes, in which the tie pins are supported through springs  66 ,  67 . The sliding guideway  57  thereby also comprises a carrier, which is activated through a cam disc that is movable in axial direction in the same way as is portrayed in  FIG. 1 . 
         [0051]    When the sliding guideway  57  assumes a position, in which the respective actuating pin  60  or  61  is located in one of the end sections  58  or  59 , the respective tie pin  62  or  63  can exit the lock hole  64  or  65  and can consequently lock the eccentric bushing  51  across from the conrod bearing eye  49 . According to  FIG. 9 , this is the case for the tie pin  62  exiting from the lock hole  64 . 
         [0052]    The additional  FIG. 10  shows a shaft stub, by means of which the assembly of a wrap-spring  69  on a crankpin is supposed to be shown. An end of the wrap spring is thereby guided around the shaft stub and is then continuously wrapped around the shaft stub  68 . As the eccentric bushing  51  consists of half shells  51   a  and  51   b  in accordance with  FIGS. 8 and 9 , and they don&#39;t have a rib, these half shells  51   a  and  51   b  can subsequently be inserted between the wrap spring  69  and the respective crankpin. 
         [0053]    According to  FIG. 11  provision is made for that the wrap-spring freewheel  54  has another wrap spring beside the already named wrap spring  69 , and that these two wrap springs  69  and  70  are wound up inside each other in spiral form. 
         [0054]    According to  FIG. 12 , the eccentric bushing  51  is provided with a double-wound wrap-spring freewheel  54 , beside which roller bearings  71  and  72  are intended on each side. Plain bearings may also be provided for instead of the two rolling bearings. 
       LIST OF REFERENCE SIGNS 
       [0000]    
       
           1  Crankshaft 
           2  Crank web 
           3  Crank web 
           4  Crank web 
           5  Crank web 
           6  Counterweight 
           7  Crankpin 
           8  Main bearing pin 
           9  Conrod 
           10  Conrod upper part 
           11  Conrod lower part 
           12  Screw 
           13  Working piston 
           14  Piston pin 
           15  Parting plane 
           16  Eccentric bushing 
           16   a  Half shell of  16   
           16   b  Half shell of  16   
           17  Board 
           17   a  Section of  17   
           17   b  Section of  17   
           18  Board 
           18   a  Section of  18   
           18   b  Section of  18   
           19  Locking element 
           20  Carrier 
           21  Carrier groove 
           22  Cam disc 
           23  Locking holes 
           24  Conrod bearing eye 
           25  Location hole 
           26  Snap contour 
           27  Locking pin 
           28  Outer casing surface of  16   
           29  Freewheel 
           30  Roller freewheel 
           30   a  Clamping rollers of  30   
           31  Sliding surface 
           32  Sliding surface 
           33  Locking hole 
           34  Cage 
           34   a  Half shell of  34   
           34   b  Half shell of  34   
           34   c  Bending point of  34   
           34   d  Cage lock 
           35  Inner casing surface 
           36  Plain bearings 
           37  Cage lock 
           38  Cage lock 
           39  Dovetail-like end piece of  34   a  and  34   b    
           40  Slot 
           41  End piece of  34   a  and  34   b    
           42  Cage 
           43  Pockets 
           44  Cylindrical rolling elements 
           45  Conrod 
           46  Conrod upper part 
       
     
         [0112]      47  Conrod lower part 
         [0113]      48  Piston bin bearings
     49  Conrod bearing eye     50  Receiving bore hole     51  Eccentric bushing     52  Recess     53  Outer casing surface     54  Wrap-spring freewheel     55  Wrap-spring     56  Pilot hole     57  Sliding guideway     58  End section     59  End section     60  Actuating pin     61  Actuating pin     62  Tie pin     63  Tie pin     64  Lock hole     65  Lock hole     66  Spring     67  Spring     68  Shaft stub     69  Wrap spring     70  Wrap spring     71  Roller bearing     72  Roller bearing