Patent Publication Number: US-10787973-B2

Title: Variable compression ratio engine

Description:
INTRODUCTION 
     The present disclosure relates to an internal combustion engine having the ability to operate with the advantages of the Atkinson cycle and also provide the ability to vary the compression ratio of the engine. 
     Internal combustion engines operating on an Atkinson cycle are known. An engine operating on an Atkinson cycle has a compression stroke length that is less than the expansion stroke length, during both high load and high engine speed conditions and low load and low engine speed conditions. This provides fuel economy benefits. 
     In addition to the operating on an Atkinson cycle, it is advantageous to be able to change the compression ratio of an internal combustion engine. While the ability to do this exists, technologies allowing this can add cost and weight to a vehicle and increase packaging requirements for the engine. 
     Thus, while current technologies achieve their intended purpose, there is a need for a new and improved internal combustion engine that provides the benefits of operating on an Atkinson cycle and provides the ability to selectively vary the compression ratio of the engine. 
     SUMMARY 
     According to several aspects of the present disclosure, an internal combustion engine comprises an engine block defining a cylinder bore, a piston slideably supported within the cylinder bore, a crankshaft rotatably supported by the engine block and rotatable about a crank axis, a control shaft rotatably supported by the engine block and rotatable about a control axis, wherein the control axis is parallel to and distal from the crank axis, a link rod rotatably connected to the crankshaft and rotatable relative to the crankshaft about an axis that is parallel to and distal from the crank axis, a lower connecting rod having a first end rotatably connected to the link rod, and a second end rotatably connected to the control shaft and rotatable relative to the control shaft about an axis that is parallel to and distal from the control axis, an upper connecting rod having a first end rotatably connected to the link rod, and a second end rotatably connected to the piston; and a phasing device supported by the engine block between and interconnecting the crankshaft and the control shaft and rotates the control shaft at a rotational speed relative to the rotational speed of the crankshaft and can selectively vary the ratio of the rotational speed of the control shaft to the rotational speed of the crankshaft. 
     According to several aspects of the present disclosure, an internal combustion engine includes an engine block defining a cylinder bore, a piston slideably supported within the cylinder bore, wherein the piston slides reciprocally within the cylinder bore throughout an engine cycle, including a piston compression stroke having a compression stroke length and a piston expansion stroke having an expansion stroke length. A crankshaft is rotatably supported by the engine block and rotatable about a crank axis, and a control shaft is rotatably supported by the engine block and rotatable about a control axis. The control axis is parallel to and distal from the crank axis. A link rod is rotatably connected to the crankshaft and rotatable relative to the crankshaft about an axis that is parallel to and distal from the crank axis. A lower connecting rod has a first end rotatably connected to the link rod, and a second end rotatably connected to the control shaft. The lower connecting rod is rotatable relative to the control shaft about an axis that is parallel to and distal from the control axis. An upper connecting rod has a first end rotatably connected to the link rod, and a second end rotatably connected to the piston. A phasing device is supported by the engine block between and interconnecting the crankshaft and the control shaft and selectively changes the rotational speed of the control shaft relative to the crankshaft, thereby changing the compression stroke length of the piston compression stroke. 
     In another aspect of the present disclosure, internal combustion engine further comprises a drive gear co-axially mounted on the crankshaft and a driven gear co-axially mounted on the control shaft, and the phasing device includes an idler shaft rotatable about a phase axis, a gearbox mounted co-axially on the idler shaft, a crank gear supported on the gearbox co-axial to the idler shaft, and a control shaft gear mounted co-axially on the idler shaft distal from the crank gear, wherein the drive gear engages the crank gear and transfers rotation of the crank shaft to the idler shaft, and the driven gear engages the control shaft gear and transfers rotation of the idler shaft to the control shaft. 
     In another aspect of the present disclosure, the phasing device includes an electric motor connected to the idler shaft and adapted to rotate the idler shaft. 
     In another aspect of the present disclosure, the gear box is adapted to allow the rotational speed of the idler shaft relative to the rotational speed of the crank gear to change when the idler shaft is being rotated by the electric motor. 
     In another aspect of the present disclosure, the electric motor is adapted to induce rotation of the idler shaft in a first direction, wherein the rotational speed of the idler shaft is increased relative to the rotational speed of the crank gear, or a second direction, wherein the rotational speed of the idler shaft is decreased relative to the rotational speed of the crank gear. 
     In another aspect of the present disclosure, crank gear, the gear box, the idler shaft and the control shaft gear rotate unitarily unless the idler shaft is rotated by the electric motor. 
     In another aspect of the present disclosure, a gear ratio between the drive gear and the crank gear is 2:1, and a gear ratio between the control shaft gear and the driven gear is 1:1, and wherein, when there is no input from the electric motor the control shaft rotates at one half the rotational speed of the crankshaft. 
     In another aspect of the present disclosure, a gear ratio between the drive gear and the crank gear is 2:1, a gear ratio between the control shaft gear and the driven gear is 1:1, and the gear ratio of the gearbox is 1:1, and wherein, without input from the electric motor the control shaft rotates at one half the rotational speed of the crankshaft. 
     In another aspect of the present disclosure, a gear ratio between the drive gear and the crank gear is 1:1, a gear ratio between the control shaft gear and the driven gear is 1:1, and the gear ratio of the gearbox is 2:1, and wherein, without input from the electric motor the control shaft rotates at one half the rotational speed of the crankshaft. 
     Further areas of applicability will become apparent from the description provided herein. It should be understood that the description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The drawings described herein are for illustration purposes only and are not intended to limit the scope of the present disclosure in any way. 
         FIG. 1  is a perspective view of an internal combustion engine according to an exemplary embodiment, with the engine block shown partially broken away; 
         FIG. 2  is a sectional view taken from  FIG. 1  along line  2 - 2 ; 
         FIG. 3  is a phasing device for an internal combustion engine according to an exemplary embodiment; and 
         FIG. 4  is graphical representation of an engine cycle for an internal combustion engine according to an exemplary embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     The following description is merely exemplary in nature and is not intended to limit the present disclosure, application, or uses. 
     Referring to  FIGS. 1 and 2 , an internal combustion engine according to an exemplary embodiment of the present disclosure is shown generally at  10 . The internal combustion engine  10  includes an engine block  12 . The engine block  12  defines at least one cylinder bore  14  formed therein. A piston  16  is slideably supported within the cylinder bore  14 . While  FIG. 1  shows an internal combustion engine  10  with four cylinder bores  14  and four pistons  16 , it should be appreciated that the engine block  12  may be configured to include different multiples of cylinder bores  14 . For example, the engine block  12  may be configured as a V-style engine having 2, 4, 6, 8, or 10 cylinder bores  14 , or as an inline style engine having one or more cylinder bores  14 . It should be appreciated that the engine block  12  may be configured in a manner other than the exemplary V-style or inline style engines noted above, and may include any number of cylinder bores  14  other than the exemplary numbers described herein. The piston  16  slides back and forth reciprocally within the cylinder bore  14  throughout an engine cycle  18 , including a piston compression stroke  20  having a compression stroke length  22  and a piston expansion stroke  24  having an expansion stroke length  26 . 
     A crankshaft  28  is rotatably supported by the engine block  12  and rotates about a crankshaft axis  30 . The crankshaft  28  includes a drive gear  32  co-axially mounted thereon. A control shaft  34  is rotatably supported by the engine block  12  and rotates about a control shaft axis  36  that is parallel to and distal from the crank axis  30 . The control shaft  34  includes a driven gear  38  co-axially mounted thereon. A link rod  40  is rotatably supported on the crankshaft  28  and rotatable relative to the crankshaft  28  about a link rod axis  42  that is parallel to and distal from the crankshaft axis  30 . A lower connecting rod  44  has a first end  46  that is rotatably connected to the link rod  40 , and a second end  48  that is rotatably connected to the control shaft  34 . The lower connecting rod  44  is rotatable relative to the control shaft  34  about a lower connecting rod axis  50  that is parallel to and distal from the control shaft axis  36 . An upper connecting rod  52  has a first end  54  rotatably connected to the link rod  40 , and a second end  56  rotatably connected to the piston  16 . 
     A phasing device  58  is supported by the engine block  12  between and interconnecting the crankshaft  28  and the control shaft  34 . The phasing device  58  is adapted to selectively change the rotational speed of the control shaft  34  relative to the crankshaft  28  and changes the clearance volume within the cylinder bore  14  above the piston  16 . 
     Referring to  FIG. 3 , the phasing device  58  include an idler shaft  60  rotatable about an idler axis  62  that is parallel to and spaced from both the crankshaft axis  30  and the control shaft axis  36 . An electric motor  64  is connected to the idler shaft  60  and selectively rotates the idler shaft  60  about the idler axis  62 . A gearbox  66  is mounted co-axially on the idler shaft  60 . A crank gear  68  is supported on the gearbox  66  co-axial to the idler shaft  60 . A control shaft gear  70  is mounted co-axially on the idler shaft  60  distal from the crank gear  68 . 
     The drive gear  32  is fixedly mounted onto the crankshaft  28  and rotates along with the crankshaft  28 . The drive gear  32  engages the crank gear  68  and transfers rotation of the crank shaft  28  to the idler shaft  60 . The driven gear  38  is fixedly mounted onto the control shaft  34  and the control shaft gear  70  is fixedly mounted onto the idler shaft  60 . When the crankshaft  28  rotates, rotational motion is transferred from the crankshaft  28  through the drive gear  32 , crank gear  68  and gearbox  66  to rotate the idler shaft  60 . When the idler shaft  60  rotates, rotational motion is transferred from the idler shaft  60  through the control shaft gear  70  and driven gear  38  to rotate the control shaft  34 . In this way, the control shaft  34  rotates in relation to the crankshaft  28 . 
     The gear box  66  is adapted to allow the rotational speed of the idler shaft  60  relative to the rotational speed of the crank gear  68  to change when the electric motor  64  acts on the idler shaft  60 . It should be understood that the gear box  66  may be any high ratio device adapted to interconnect the crank gear  68  and the idler shaft  60 . For example, the gearbox could be a harmonic drive, a planetary gearset, or roller reducer. These examples are exemplary in nature and are not intended to limit the scope of this disclosure. 
     The electric motor  64  can induce rotation of the idler shaft  60  in a first, or clockwise direction or in a second, counterclockwise direction. The idler shaft  60  rotates at a given rotational speed due to input from the crank gear  68 . If the electric motor  64  acts to rotate the idler shaft  60  in the same direction that the idler shaft  60  is already rotating, the additional rotational input from the electric motor  64  will cause the idler gear  60  to speed up. Alternatively, if the electric motor  64  acts to rotate the idler shaft  60  in the opposite direction, the force of the electric motor  64  will work against the rotation of the idler shaft  60  and cause the idler shaft  60  to slow down. Thus, the electric motor  64  can selectively cause the rotational speed of the idler shaft  60 , and consequently, the rotational speed of the control shaft  34  to speed up or slow down relative to the rotational speed of the crankshaft  28 . 
     The link rod  40  is rotatably supported on the crankshaft  28  and rotatable relative to the crankshaft  28  about the link rod axis  42 . The eccentric connection between the link rod  40  and the crankshaft  28  causes the link rod  40  to move as the crankshaft  28  rotates. The first end  46  of the lower connecting rod  44  is rotatably connected to the link rod  40 , and the second end  48  is rotatably connected to the control shaft  34 . The lower connecting rod  44  is rotatable relative to the control shaft  34  about the lower connecting rod axis  42 . Due to the eccentric connection of the second end  48  of the lower connecting rod  48  and the control shaft  34 , rotation of the control shaft  34  about the control shaft axis  36  causes the lower connecting rod  44  to act upon the link rod  40  and affects the pattern or path of the link rod  40 . 
     The motion of the link rod  40  due to the rotation of the crankshaft  28  and input from rotation of the control shaft  34  controls the reciprocating motion of the piston  16  within the cylinder bore  14 . Referring to  FIG. 4 , an engine cycle  18  of an internal combustion engine  10  is graphically represented. The position of the piston  16  is generally shown along a vertical axis  72 , and the stage or time duration of the cycle is generally shown along a horizontal axis  74 . A top dead center position  76  is the position of the piston  16  at the end of an exhaust stroke  78  and at a beginning of an intake stroke  80 .  FIG. 4  is a graphical representation of a complete cycle of the piston  16 . The top dead center position  76  of the piston  16  at the end of the exhaust stroke  78  and the beginning of the intake stroke  80  occurs at both the far left and far right ends of the engine cycle  18 . 
     Beginning at the top dead center position  76  of the piston  16  at the far left side of the engine cycle  18 , the piston  16  moves downward within the cylinder bore  14  and begins the intake stroke  80 . During the intake stroke, an intake valve in the cylinder head is opened to allow fuel and combustion air to enter the cylinder bore  14 . The end of the intake stroke  80  occurs at point  82 . During the intake stroke  80 , the distance the piston  16  travels between the top dead center position  76  and the end of the intake stoke  82  is an intake stroke length  84 . At the end of the intake stroke  82 , the intake valve closes and the piston  16  changed direction and begins moving upward within the cylinder bore  14 , beginning the piston compression stroke  20 . The piston compression stroke  20  ends at point  86 . The distance the piston  16  travels during the compression stroke  20  is the compression stroke length  22 . 
     At the end of the piston compression stroke  20 , the fuel air mixture is ignited and the piston  16  begins moving downward and begins the piston expansion stroke  24 . During the piston expansion stroke  24  the ignited fuel air mixture rapidly expands and forces the piston  16  downward within the cylinder bore  14 . The end of the piston expansion stroke  24  occurs at point  88 . The expansion stroke length  26  is the distance the piston  16  travels within the cylinder bore  14  during the piston expansion stroke  24 . Near the end  88  of the piston expansion stroke  24 , an exhaust valve is opened in the cylinder head and the piston  16  begins moving upward in the cylinder bore  14  to force the combusted gases to exhaust through the exhaust valve. This begins the exhaust stroke  78 . The end of the exhaust stroke occurs at the top dead center position  76  of the piston  16 , shown at the far right of the engine cycle  18 . The distance the piston  16  travels within the cylinder bore  16  during the exhaust stroke  78  is the exhaust stroke length  90 . 
     In a steady state condition, the rotational speed of the control shaft  34  relative to the rotational speed of the crankshaft  28  is constant and the position of the second end  48  of the lower connecting rod  44  is always at the same position relative to any given point in the engine cycle  18 . The electric motor  64  of the phasing device  58  can be used to temporarily speed up or slow down the rotational speed of the control shaft  34  relative to the rotational speed of the crank shaft  28 . Afterward, electric motor  64  is turned off, the rotational speed of the control shaft  34  relative to the rotational speed of the crankshaft  28  is once again constant again. However, after temporarily varying the rotation speed of the control shaft relative to the rotational speed of the crankshaft, the position of the second end  48  of the lower connecting rod  44  is rotationally shifted, or “phased”. This means that the rotational position of the second end  48  of the connecting rod  44  about the control shaft axis  36  relative to the position of the crankshaft  28  at any given point during the engine cycle  18  after being phased is different than the rotational position of the second end  48  of the connecting rod  44  about the control shaft axis  36  relative to the position of the crankshaft  28  at that same point during the engine cycle  18  prior to being phased. 
     The compression stroke length  22  is less than the expansion stroke length  26 . By changing the position of the lower connecting rod  44 , the movement or path that the link rod  40  follows is altered, which changes the compression stroke length  22 , but more importantly, changes the clearance volume within the cylinder bore  14  above the piston  16 . By changing the compression stroke length  22  of the piston  16 , the compression ratio of the internal combustion engine is changed. By changing the clearance volume, the compression ratio of the internal combustion engine  10  that occurs during the compression stroke  20  is reduced. A small change in the clearance volume results in a large change in compression ratio. Accordingly, by controlling the position of the lower connecting rod  44 , the compression ratio of the internal combustion engine  10  may be controlled and changed between a high compression ratio during certain engine operating conditions, and a low compression ratio during other engine operating conditions. The internal combustion engine  10  described herein provides a variable compression ratio engine that enables the use of an Atkinson cycle, in which the compression stroke length  22  is less than the expansion stroke length  26 , in both high load and high engine speed conditions and low load and low engine speed conditions, to achieve the fuel economy benefits that may be realized from the Atkinson cycle for all operating conditions of the internal combustion engine  10 . 
     The optimal ratio between the rotational speed of the crankshaft  28  and the rotational speed of the control shaft  34  during a steady state condition may not be 1:1. In an exemplary embodiment, the gear box  66  allows no relative rotation between the idler shaft  60  and the crank gear  68  unless there is input from the electric motor  64 . The crank gear  68 , the gear box  66 , the idler shaft  60  and the control shaft gear  70  rotate unitarily unless the electric motor  64  intercedes and causes the idler shaft  60  to speed up or slow down relative to the crank gear  68 . The gear ratio between the drive gear  32  and the crank gear is 2:1, and the gear ratio between the control shaft gear  70  and the driven gear  38  is 1:1. In the absence of input from the electric motor  64 , the control shaft  34  rotates at one half the rotational speed of the crankshaft  28 . 
     In another exemplary embodiment, the gear box  66  allows no relative rotation between the idler shaft  60  and the crank gear  68  unless there is input from the electric motor  64 . The crank gear  68 , the gear box  66 , and the idler shaft  60  do not rotate unitarily, but the gear ratio of the gear box  66  is 1:1, unless the electric motor  64  intercedes and causes the idler shaft  60  to speed up or slow down relative to the crank gear  68 . The gear ratio between the drive gear  32  and the crank gear is 2:1, and the gear ratio between the control shaft gear  70  and the driven gear  38  is 1:1. In the absence of input from the electric motor  64 , the control shaft  34  rotates at one half the rotational speed of the crankshaft  28 . 
     In another exemplary embodiment, the gear box  66  has a gear ratio of 2:1, unless there is input from the electric motor  64 . The gear ratio between the drive gear  32  and the crank gear  68  is 1:1, and the gear ratio between the control shaft gear  70  and the driven gear  38  is 1:1. In the absence of input from the electric motor  64 , the control shaft  34  rotates at one half the rotational speed of the crankshaft  28 . 
     The description of the present disclosure is merely exemplary in nature and variations that do not depart from the gist of the present disclosure are intended to be within the scope of the present disclosure. Such variations are not to be regarded as a departure from the spirit and scope of the present disclosure.