Abstract:
Crankshaft main bearing failure in variable compression ratio engines having eccentric main bearing supports is prevented by supporting the bearings in a crankshaft cradle ( 16 ) having a high stiffness and a high natural frequency. The crankshaft cradle ( 16 ) is rotatable mounted in the engine on a first axis, and the crankshaft ( 8 ) is mounted in the crankshaft cradle ( 16 ) on a second axis off-set from the first axis, the first axis and the second axis defining a first plane. The crankshaft cradle comprises a primary eccentric member ( 24 ) and a plurality of smaller bearing caps ( 26 ) separated by a parting line. The crankshaft cradle comprises accentric members ( 24 ) that support the bearing element ( 64 ), and structural webbing ( 72 ) that rigidly holds the eccentric members ( 24 ) in alignment with one another at all times.

Description:
PROVISIONAL APPLICATION REFERENCE 
     This application relates to U.S. Provisional Application No. 60/164,774, having a filing date of Nov. 12, 1999. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates to a method and apparatus for adjusting the compression ratio of internal combustion engines, and more specifically to a method and apparatus for adjusting the position of the crankshaft with eccentric crankshaft main bearing supports. 
     Designs for engines having eccentric crankshaft main bearing supports have been known for some time. In these engines the eccentric main bearings are rotated to adjust the axis of rotation of the crankshaft. Significant forces bear down on the eccentric main bearing supports during operation of the engine, causing the eccentric main bearing supports to twist out of alignment. Poor alignment of the eccentric main bearing supports is a problem for these engines because even small amounts of main bearing misalignment can cause rapid main bearing failure. Another problem with engines having eccentric main bearing supports is that of a low natural frequency of vibration. Operation of these engines at or near the natural frequency of the eccentric main bearing supports can destroy the engine. The low natural frequency of these engines is a problem because the engines cannot be operated at speeds necessary for use of the engine in passenger cars, trucks, and other applications. 
     Engines having only one cylinder and two main bearings can tolerate much greater twisting of the main bearing supports, because the crankshaft is free to self align within the two bearings. Single cylinder engines, however, are not employed in the major automobile markets. An objective of the present invention is to provide an eccentric main bearing support for engines having more than one cylinder that provides a long main bearing life, a high natural frequency, and a low manufacturing cost. Another objective of the present invention is to provide an eccentric main bearing support that does not significantly alter overall engine size and mass. Further objectives of the present invention are to provide a compact eccentric main bearing support that permits balancing of primary cranktrain forces and use of a conventional connecting rod having a length no more than two and one quarter times the stroke of the engine. 
     European patent EP 345-366-A issued to Buffoli Dec. 13, 1989 shows a variable compression ratio engine having a lower main bearing support 30 and an upper main bearing support 41 fastened together with screws 49. The force applied to the main bearing supports causing them to twist is proportional to the cross sectional area of the power cylinder bore and the power cylinder pressure. Main bearing support 30 includes five lower hemispherical disc segments joined by lower webbing. FIG. 1 of EP 345-366-A shows the webbing to have a small cross sectional area relative to the cross sectional area of the power cylinder bore. FIG. 1 also shows that the cross sectional area of the lower webbing is about 3.8% of the projected area of the eccentric member assembly, where the area of the eccentric member is projected on a plane perpendicular to the axis of rotation of the crankshaft. The lower webbing also has a short length, and spans a small arcuate length about the pivot axis of the main bearing support, about 63 degrees. The webbing with its small area and short length fails to provide rigid support of the main bearings. Furthermore, the part has a low natural frequency due to its lack of rigidity. The length and area of the webbing can only be extended downward a small amount without causing mechanical interference with the connecting rod. 
     Similarly, main bearing support 41 includes five upper hemispherical disc segments joined by upper webbing. FIG. 1 also shows the upper webbing to have a small cross sectional area relative to the size of the cross sectional area of the power cylinder bore. The upper webbing has a short length, and spans a small arcuate length about the pivot axis of the main bearing support. The length and area of the upper webbing cannot be significantly increased upward without causing mechanical interference with the connecting rod. The small cross sectional area of the upper and lower webbing and the small arcuate length of the upper and lower webbing is incapable of maintaining precise alignment of the main bearings, and consequently the main bearings of the engine shown in EP 345-366-A would fail. Furthermore, the main bearing supports have a natural frequency too low for the engine to be commercially viable. The natural frequency is exceptionally low because the webbing shown does not provide a rigid structure and the eccentric discs are massive relative to the size of the webbing. Additionally, because the upper and lower bearing main supports are tightly fastened together with screws, the mass of the upper bearing support is likely to even further lower the natural frequency of the lower main bearing support, and the mass of the lower bearing support is likely to even further lower the natural frequency of the upper bearing support. The outer diameter of the main bearing supports could be increased and the webbing made thicker to increase rigidity, however, the increased mass of the disc segments would adversely effect the natural frequency of the main bearing segments. 
     Accordingly, and objective of the present invention is to provide, in multi-cylinder engines having eccentricly supported crankshaft main bearings, rigid support and rigid alignment of the crankshaft main bearings at all times to provide a long main bearing life. A further objective of the present invention is to provide a high natural frequency for the eccentric supports to permit operation of the engine over the range of speeds required for commercial use of the engine. 
     SUMMARY OF THE INVENTION 
     In the present invention, a crankshaft cradle, made up of a large primary eccentric member and small main bearing caps, is employed to rigidly hold the crankshaft main bearings in alignment. The parting line between the primary eccentric member and the main bearing caps is oriented approximately vertically, or approximately parallel with the power cylinder line of action. Additionally, the bearing cap fasteners are located horizontally above (closer to the piston) and below the crankshaft, and the bearing cap bridge thickness minimized in order to locate the crankshaft main bearings in close proximity to the crankshaft cradle outer diameter. According to the present invention, the primary eccentric member is made up of eccentric disc segments rigidly joined by webbing, the arcuate span of the webbing about the eccentric disc segments being greater than 120 degrees, and preferably greater than 150 degrees. The large arcuate span of the webbing is made possible by the large size of the primary eccentric member relative to the main bearing caps, by the vertical orientation of the parting line, and by placement of the crankshaft main bearings in close proximity to the crankshaft cradle outer diameter. According to the preferred embodiment of the present invention, the cross sectional area of the webbing within the 120 degree arcuate span is greater than 35 percent of the cross sectional area of the cradle within the same 120 degree arcuate span. Concurrently the diameter of the primary eccentric member is preferably less than 2.5 times the diameter of the power cylinder and less than 4 times the working diameter of the crankshaft main bearing to provide a high natural frequency. Preferably, at mid span between the eccentric discs the cross sectional area of the webbing is greater than 40 percent of the cross sectional area of the power cylinder. The large contiguous area of the webbing provides a high rigidity and a high stiffness for the primary eccentric member, and precise alignment of the main bearings at all times, which in turn provides a long bearing life, and the small diameter of the eccentric discs provides a light weight and a high natural frequency, permitting operation of the engine over the full speed range required for commercial use of the engine. 
     The webbing is deeply scalloped towards the eccentric discs to provide further support, to further minimize twisting of the primary eccentric member under firing engine loads and to further increase the natural frequency of the crankshaft cradle. Preferably at one forth span between the eccentric disc segments the cross sectional area of the webbing is at least 20 percent greater than the cross sectional area of the webbing at mid span between the eccentric discs. Preferably the primary eccentric member is a single cast piece, and the webbing is contiguous and has no large holes. Additionally, in the preferred embodiment of the present invention the overall mass of the bearing caps is less than 25 percent of the mass of the primary eccentric member, and consequently the bearing caps cause only a small reduction in natural frequency. According to the preferred embodiment of the present invention, the crankshaft cradle has a natural frequency greater than 100 Hz. 
    
    
     BRIEF DESCRIPTION OF THE FIGURES 
     FIG. 1 shows a sectional elevation view of the variable compression ratio mechanism according to the present invention taken along cut lines B—B shown in FIG.  2 . 
     FIG. 2 shows a bottom view of the variable compression ratio engine according to the present invention along cut lines A—A shown in FIG. 1, with the connecting rod and pistons removed to show the crankshaft. 
     FIG. 3 shows a top view of a portion of the crankshaft cradle shown in FIGS. 1 and 2. 
     FIG. 4 shows the cross sectional webbing area of the crankshaft cradle shown in FIGS. 1,  2  and  3 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 shows a portion of a variable compression ratio mechanism  1  in a variable compression ratio engine  2  according to the present invention. Engine  2  has a piston  4 , a connecting rod  6 , a crankshaft  8  having an axis of rotation  10 , a power cylinder  12  having a cross sectional area  13  in an engine block  14 , a crankshaft cradle  16  having a pivot axis  18 , an optional power take-off shaft or balance shaft  20 , and an optional bedplate or cradle bearing cap  22 . Connecting rod  6  connects piston  4  to crankshaft  8  for reciprocating motion of piston  4  in cylinder  12 . Cradle  16  includes a primary eccentric member  24  and a plurality of main bearing caps  26  and a plurality of fasteners  28  for removably fastening bearing caps  26  to primary eccentric member  24  for rotatably supporting crankshaft  8  in crankshaft cradle  16 . Engine  2  further includes a control shaft  30  mounted in engine block  14  having one or more off-set journals  32 , one or more one or more control pins  34  mounted in cradle  16  and one or more control arms  36  connecting control shaft  30  and control pin  34 , control arm  36  being rotatably mounted on off-set journal  32 . Rotation of control shaft  30  pivots off-set journal  32  causing control arm  36  to move causing cradle  16  to pivot about pivot axis  18  causing crankshaft axis of rotation  10  to move causing the compression ratio of engine  2  to change. 
     FIG. 2 shows a bottom view of engine  2  according to the present invention along cut lines A—A shown in FIG. 1, with pistons  4  and connecting rods  6  removed to show crankshaft  8 . In the embodiment shown, crankshaft  8  and balance shaft  20  include gears  38 . In the preferred embodiment of the present invention gears  38  transfer power from crankshaft  8  to power take-off shaft  20 , and power take-off shaft  20  transfers power out of engine  2 . Gears  38  may have helical teeth or straight cut teeth, and gears  38  may include a single helical gear pair or a double helical gear pair (shown) for neutralizing axial thrust loads caused by the helix angle of the gear teeth. Power take-off shaft  20  may include balance webs  40  for balancing primary (shown) or secondary engine forces. Crankshaft  8  includes crank balance webs  42 . 
     Crankshaft  8  is preferably mounted in journal main bearings  44 . Oil is fed to journal bearings  44  through an oil galley  46  and oil feeds  48  located in cradle  16 . Preferably, oil is fed to oil galley  46  in cradle  16  through oil fitting  50 , oil fitting  50  preferably being located on pivot axis  18 . Oil fitting  50  includes an oil feed line  52  in fluid communication with oil galley  46 , oil feeds  48  and journal bearings  44 . Preferably oil feeds  48  are located between fasteners  28  to provide a rigid mid section of primary eccentric member  24 . 
     Crankshaft  8  may include a first flywheel  54 , and power take-off shaft  20  may include a second flywheel  56  having a rotational direction opposite that of the first flywheel  54  to provide reduced engine vibration according to the principles disclosed in U.S. Pat. No. 3,402,707 issued to Paul Heron on Sep. 24, 1968. In the preferred embodiment of the present invention, power take-off shaft  20  includes a first end  58  located in close proximity to gears  38 , and a second end  60 , where power take-off from the engine  2  is through first end  58  of power take-off shaft  20 , thereby providing low torsional loads through the length of power take-off shaft  20 , and a larger direct force and a smaller alternating force on gears  38 . Second flywheel  56  is located on the first end  58  of power take-off shaft  20 , and first flywheel  54  is located on the far end of crankshaft  8 . Flywheel  56  may span across crankshaft rotational axis  10  (shown), and flywheel  54  may span across the rotational axis of power take-off shaft  20  (shown) to provide a minimum spacing between crankshaft  8  and power take-off shaft  20 , in order to provide optimum engine balancing and a small engine size. A valve gear sprocket or chain  62  (shown), belt, gear or other type of drive is preferably located on the second end  60  of power take-off shaft  20  for driving the valvetrain and/or other engine accessories, it being understood that more than one drive may be located on power take-off shaft  20 . Preferably chain  62  is located adjacent to flywheel  54 , and between flywheel  54  and flywheel  56 , to provide a compact engine size. 
     Referring now to all of the figures, according to the preferred embodiment of the present invention engine  2  has a variable compression ratio mechanism  1 , a plurality of cylinders  12 , it being understood that engine  2  may alternatively have only one cylinder, a piston  4  mounted for reciprocating movement in each of cylinders  12 , crankshaft  8  has an axis of rotation  10 , and connecting rod  6  connects each piston  4  to crankshaft  8 . Referring now to FIGS. 1,  2 , and  3 , connecting rod  6  has a connecting rod crankshaft bearing  64  having a mid span  66 , mid span  66  being shown in FIGS. 2 and 3. Cradle  16  supports crankshaft  8  for rotation of crankshaft  8  about axis of rotation  10 , and cradle  16  is mounted in engine  2  for pivoting relative to engine  2  about pivot axis  18 , pivot axis  18  being substantially parallel to and spaced from crankshaft rotational axis  10 . An actuator  68  (shown in FIG. 2) is mounted on one end of control shaft  30  for varying the position of cradle  16  about pivot axis  18  for varying the position of crankshaft axis of rotation  10 , it being understood that a rotary actuator (shown), a hydraulic cylinder type actuator, or another functional type of actuator may be employed to adjust the rotational position of cradle  16  about pivot axis  18 . Cradle  16  includes primary eccentric member  24  and a plurality of bearing caps  26  and a plurality of bearing cap fasteners  28  for removably fastening each bearing cap  26  to primary eccentric member  24 . According to the present invention, primary eccentric member  24  comprises a plurality of disc segments  70  and webbing  72 , disc segments  70  being rigidly jointed together by webbing  72 . Preferably, primary eccentric member  24  comprising eccentric discs  70  and webbing  72  is a single cast piece. Crankshaft axis of rotation  10  and pivot axis  18  define a first plane  74 , and each bearing cap  26  has a primary contact surface  76  for contact with primary eccentric member  24 , primary contact surface  76  being within ±30 degrees of perpendicular to first plane  74 , and fasteners  28  are within ±30 degrees of parallel to first plane  74  for providing space on the far side of the cradle from bearing caps  26  for a large and contiguous webbing  72 . Primary contact surface  76  is generally perpendicular to the clamping force line of action of fasteners  28 , and may be a single flat surface (shown), a serrated or fractured surface where the surface texture of the serration or fracture provides alignment and prevents slip between the bearing caps  26  and primary eccentric member  24 , and in such cases primary contact surface  76  may be approximated as a generally flat surface where the minor surface irregularities are ignored. Dowels, stepped joints, fitted bolts, and other functional means may be employed to prevent slip between primary eccentric member  24  and bearing caps  26  such as configurations shown in Bearings, a Tribology Handbook, Edited by M. J. Neale, Reed Educational and Professional Publishing Ltd., 1998, page 61. Crankshaft  8  is mounted in main bearings  44 , main bearings  44  have a working diameter  78  (shown in FIG. 4) and a main bearing mid span  80  (shown in FIGS.  2  and  3 ), and bearing caps  26  have a bridge thickness  82 , the bridge thickness  82  of at least one bearing cap being less than 70 percent of the thickness of at least one crankshaft bearing working diameter  78 , and preferably less than half the thickness of at least one crankshaft bearing working diameter  78 , for location of crankshaft  8  adjacent to the outer diameter of the cradle for providing space for a large web on the far side of the cradle from the bearing caps. Main bearing mid span  80  is located at the center of the radial load bearing portion of the bearing along the axial length of the bearing. Bridge thickness  82  is measured with main bearing  44  removed, and is the shortest distance measured on first plane  74  across bearing cap  26 . For engines with a variable bridge thickness as measured at various axial locations of main bearing  44 , bridge thickness  82  is the average bridge thickness being in radial load bearing contact with main bearing  44 . 
     Each bearing cap  26  has an upper contact face length or upper centering distance  75  and a lower contact face length or lower centering distance  77  (shown in FIG.  4 ), each centering distance spanning from main bearing  44  to cradle bearings  122  along the plane of primary contact surface  76 . Pivot axis  18  and bearing working diameter (e.g., the crankshaft bearing surface)  78  may be separated by a fitting distance  79  to provide access for oil feed line  52 . Preferably, the lower centering distance  77  is at least 1.5 times longer than fitting distance  79 . Preferably lower centering distance  77  is at least twice as long as bridge thickness  82  to position the crankshaft near the outer diameter of the crankshaft cradle. 
     Webbing  72  has a first thick section  84  (shown in FIG. 4) located within a 120 degree arcuate span  88  about pivot axis  18  and located on a second plane  85  perpendicular to pivot axis  18 , perpendicular to first plane  74  and passing through the mid span  66  of connecting rod crankshaft bearing  64 , first thick section  84  having an outer perimeter  86 . First thick section  84  is preferably a single cast piece. The arcuate span of webbing  72  being greater than 120 degrees about the pivot axis in the preferred embodiment of the present invention, and preferably greater than 150 degrees. 120 degree arcuate span  88  has an arcuate area  90  located within outer perimeter  86  and within 120 degree arcuate span  88 . First thick section  84  has a first thick section cross sectional area  92 , the cross sectional area of first thick section  92  being greater than 25 percent of arcuate area  90 , and preferably greater than 35 percent of arcuate area  90 , in order to provide crankshaft cradle  16  with a high stiffness and a high natural frequency of vibration. For engines according to the present invention having webbing  72  that spans more than 120 degrees about pivot axis  18 , 120 degree arcuate span  88  falls within the arcuate span of webbing  72 . For engines according to the present invention having webbing  72  that spans less than 120 degrees about pivot axis  18 , 120 degree arcuate span  88  is centered about webbing  72 . Preferably webbing  72  has an arcuate span about pivot axis  18  of at least 120 degrees on second plane  85  and perpendicular to first plane  74 , for providing a rigid cradle having a high natural frequency. 
     Preferably, primary eccentric member  24  has a first overall mass, and the removable bearing caps  26  have a second overall mass, the second overall mass being less than 25 percent of the first overall mass, in order to provide a high natural frequency. According to the preferred embodiment of the present invention, cradle  16  has a natural frequency greater than 100 hertz, however, cradle  16  may have a lower natural frequency in some embodiments of the present invention. 
     Referring to FIGS. 1 and 4, webbing  72  may include one or more holes  94  for reducing the weight of cradle  16  or for draining engine oil away from the spinning crankshaft or for another purpose. Preferably webbing  72  has no single hole  94  spanning more than 60 degrees within said 120 degree arcuate span  88 . Webbing  72  further comprises holes  95  in primary eccentric member  24  for fasteners  28 , where between adjacent discs segments  70  webbing  72  is located on both sides of each hole  95  for providing additional structure (e.g., webbing is located above and below each hole  95  as shown in FIG.  1 ). Preferably main bearing cap  26  includes tapped holes  97  for retaining fasteners  28 , and fasteners  28  are screws having an accessible head in primary eccentric member  24  for assembly, in order to provide a bearing cap having a maximum thickness and a maximum strength and stiffness. Alternatively, fasteners  28  may be bolts having an approximately oval head  99 , oval heads  99  being seated in main bearing cap  26 . 
     Referring now to FIGS. 2,  3 , and  4 , webbing  72  includes scalloping  96  between eccentric discs  70  for increasing the rigidity and the natural frequency of primary eccentric member  24 . FIG. 2 shows a sectional view of scalloping  96  on first plane  74 . The profile of scalloping  96  is indicated by a dashed line in FIG.  3 . FIG. 3 shows a top view of a portion of the cradle  16  shown in FIG. 2, and FIG. 2 shows a bottom sectional view of cradle  16 . Referring to FIG. 3, line  98  is intended to indicate the profile of scalloping at the top of eccentric member  24  closest to piston  4 . Scalloping profile  98  is indicated by a dashed line in FIG.  4 . Similarly, line  100  in FIG. 3 is intended to indicate the profile of scalloping at the bottom of eccentric member  24 . Scalloping profile  100  is indicated by a dashed line in FIG.  4 . Referring now to FIGS. 3 and 4, due to scalloping, the sectional area of webbing  72  is greater near eccentric discs  70 , and smaller towards mid span  66 . According to the present invention, scalloping increases the rigidity and increases the natural frequency of primary eccentric member  24  and cradle  16 . As previously described, webbing  72  has a first thick section  84  having a first thick section cross sectional area  92  located on a second plane  85 . Primary eccentric member  24  has a second thick section  102  having a second thick section cross sectional area  104  located on a third plane  106  located parallel to second plane  85 , perpendicular to pivot axis  18  and perpendicular to first plane  74  and located within arcuate span  88 . Second plane  85  and main bearing mid span  80  being separated by a first distance  108 , second plane  85  and third plain  106  being separated by a second distance  110 , second distance  110  being half as long as first distance  108 . Preferably, according to the present invention, second thick section cross sectional area  104  is at least 10 percent greater than first thick section cross sectional area  92  for providing a rigid cradle  16  and a high natural frequency. 
     Primary eccentric member  24  has a third thick section  112  having a third thick section cross sectional area  114  located on a forth plane  116  located parallel to second plane  85 , perpendicular to pivot axis  18  and perpendicular to first plane  74 , and located within arcuate span  88 . Second plane  85  and forth plane  116  being separated by a third distance  120 , third distance  120  being 60 percent as long as long as first distance  108 . Preferably, according to the present invention, third thick section cross sectional area  114  is at least 15 percent greater than first thick section cross sectional area  92  for providing a rigid cradle  16  and a high natural frequency. 
     Referring now to FIG. 1, preferably each bearing cap  26  is fastened to primary eccentric member  24  by at least two first fasteners  28 , the first fastener and the second fastener being located approximately perpendicular to primary contact surface  76 , and the first fastener is located on the far side of crankshaft main bearing  44  from the second fastener. 
     Referring now to FIG. 4, cradle  16  is supported by one or more cradle bearings  122  having a cradle bearing diameter  124  for pivotally supporting cradle  16  about pivot axis  18 . Cradle bearing diameter  124  is preferably no more than 4 times crankshaft bearing working diameter  78  in order to provide a cradle having a low mass, a low polar moment of inertia, and a high natural frequency. Cradle  16  may have cradle bearings diameters  124  of various diameters, and may have crankshaft bearing working diameters  78  of various diameters, in some embodiments of the present inventions. Cradle bearing diameter  124  is the average bearing diameter of the bearings supporting cradle  16 , and crankshaft bearing working diameter  78  is the average bearing diameter of the bearings supporting crankshaft  8  in embodiments having dissimilar bearing diameters, where average diameter is determined by weighting the bearings for their axial length (e.g., the sum of each bearing diameter times its load bearing axial length in the numerator, and the sum of the axial load bearing lengths of the bearings in the denominator). Optimally bridge thickness  82  is no more than half the thickness of at least one crankshaft bearing working diameter  78  in order to provide a cradle having a low mass, a low polar moment of inertia, and a high natural frequency. 
     Accordingly, the present invention provides, in multi-cylinder engines having eccentricly supported crankshaft main bearings, rigid support and rigid alignment of the crankshaft main bearings at all times for provide a long main bearing life. The present invention provides a high natural frequency for the eccentric supports permitting operation of the engine over the range of speeds required for commercial use of the engine. Additionally, the present invention can be manufactured at a low cost. Those skilled in the art will recognize that the invention can be practiced with modifications within the spirit and scope of the claims. For example, the present invention may be employed in compressors, pumps, and expanders, and also in single cylinder as well as multi-cylinder machines.