Patent Publication Number: US-6668768-B2

Title: Variable compression ratio engine

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to a variable compression connecting rod for use with an internal combustion engine. 
     2. Background Art 
     A “compression ratio” of an internal combustion engine is defined as the ratio of the volume in a cylinder above a piston when the piston is at bottom-dead-center (BDC) to the volume in the cylinder above the piston when the piston is at top-dead-center(TDC). The higher the compression ratio, the more the air and fuel molecules are mixed and compressed, thereby resulting in increased efficiency of the engine. This in turn results in improved fuel economy and a higher ratio of output energy versus input energy of the engine. 
     In conventional internal combustion engines, however, the compression ratio is fixed and cannot be changed to yield optimal performance. Accordingly, variable compression ratio (VCR) internal combustion engines have been developed to vary the clearance volume of a cylinder in order to achieve improved fuel economy and increased engine power performance. Such VCR engines are designed to have a higher compression ratio during low load conditions, and a lower compression ratio during high load conditions. Known techniques include using “sub-chambers” and “sub-pistons” to vary the volume of a cylinder (see, for example, U.S. Pat. Nos. 4,246,873 and 4,286,552), varying the actual dimensions of all or a portion of a piston attached to a fixed length connecting rod (see U.S. Pat. No. 5,865,092), and varying the actual length of a connecting rod (see U.S. Pat. No. 5,724,863). 
     Other techniques include the use of eccentric rings or bushings either at the lower “large” end of a connecting rod or the upper “small” end of the connecting rod for varying the effective length of the connecting rod or height of a reciprocating piston. U.S. Pat. Nos. 5,417,185, 5,562,068 and 5,960,750 and Japanese Publication JP-03092552 disclose devices that include eccentric rings. These eccentric ring devices, however, are undesirable in that each eccentric ring must be rotated 180 degrees before one of the desired operating modes or positions is engaged. As a result, locking of the eccentric ring in a proper position may not occur within an optimum period of time, thereby leaving the effective length of the device and consequently the compression ratio of an associated cylinder in an undesired intermediate state. 
     SUMMARY OF THE INVENTION 
     The invention addresses the shortcomings of the prior art by providing a connecting rod assembly that may be transitioned quickly and reliably between two or more compression modes without requiring rotation of an eccentric ring member about a crankpin or wrist pin. 
     The connecting rod assembly of the invention is configured to vary a compression ratio of an internal combustion engine having a crankshaft and a piston. The assembly includes a first portion adapted to be connected to the crankshaft and having a cylindrical aperture. The assembly further includes a second portion adapted to be connected to the piston and movable with respect to the first portion. In addition, the assembly includes a locking element having a cylindrical portion that is disposed at least partially in the cylindrical aperture. The locking element is movable between an unlocked position and a locked position for locking the second portion at a first position relative to the first portion, wherein the first position corresponds to a first compression ratio of the engine. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a diagram of a variable compression ratio system according to the invention including a variable compression ratio internal combustion engine, a fluid supply system and an engine controller in communication with the engine and the fluid supply system; 
     FIG. 2 is a diagram of the system of FIG. 1 showing multiple connecting rod assemblies of the engine; 
     FIG. 3 is a perspective view of one connecting rod assembly shown in an unextended position, wherein the connecting rod assembly includes a bearing retainer and a body portion that is axially moveable with respect to the bearing retainer; 
     FIG. 4 is a perspective view of the connecting rod assembly shown in an extended position; 
     FIG. 5 is a cross-sectional view of the connecting rod assembly in the unextended position showing first and second locking mechanisms disposed between the bearing retainer and the body portion; 
     FIG. 6 is a cross-sectional view of the connecting rod assembly in the extended position; 
     FIG. 7 is a partially exploded view of the bearing retainer and the locking mechanisms; and 
     FIG. 8 is a perspective view of a locking element of the locking mechanisms. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S) 
     FIGS. 1 and 2 show diagrams of a variable compression ratio system  10  according to the invention for use with a vehicle (not shown). The system  10  includes a variable compression ratio internal combustion engine  12 , a fluid supply system  14  and an electronic control unit, such as engine controller  16 , in electrical communication with the engine  12  and fluid supply system  14 . While the engine  12 , fluid supply system  14  and engine controller  16  are shown as separate components, the fluid supply system  14  and engine controller  16  may each be considered part of the engine  12 . 
     The engine  12  shown in FIG. 1, by way of example and not limitation, is a gasoline, four-stroke, port fuel injection, internal combustion engine. Alternatively, the engine  12  may be any internal combustion engine, such as a direct fuel injection engine or a diesel engine. The engine  12  includes an air intake manifold  18 , an exhaust manifold  20  and a plurality of cylinders  22  (only one shown) connected to the manifolds  18  and  20 . Each of the cylinders  22  is fed fuel by one or more fuel injectors  24  and is supplied with an ignition spark by a spark plug  26 . Furthermore, each cylinder  22  has a combustion chamber  28  for receiving a reciprocating piston  30 . Each piston  30  is coupled to a connecting rod assembly  32  with a wrist pin  33 , and each connecting rod assembly  32  is coupled to a crankpin  34  of a crankshaft  36 . 
     Each connecting rod assembly  32  is in fluid communication with the fluid supply system  14 , and is operative to vary the compression ratio of the engine  12  as explained below in greater detail. “Compression ratio” for a particular cylinder  22  is defined as the ratio of the volume in combustion chamber  28  above the piston  30  when the piston  30  is at bottom-dead-center (BDC) to the volume in the combustion chamber  28  above the piston  30  when the piston  30  is at top-dead-center (TDC). Although each connecting rod assembly  32  is described below as providing first and second or high and low compression ratios, each connecting rod assembly  32  may be configured to provide one or more intermediate compression ratios for the engine  12 . 
     Referring to FIG. 2, the fluid supply system  14  includes first and second fluid supply devices, such as low and high pressure pumps  38  and  39 , respectively, that supply pressurized oil to the engine  12 . Each pump  38  and  39  may draw oil from a reservoir (not shown), which collects oil that drains from the engine  12 . Furthermore, each pump  38  and  39  is in fluid communication with first and second passage arrangements  40  and  42 , respectively. The first passage arrangement  40  includes a first valve  44 , and the second passage arrangement  42  includes a second valve  46 . 
     When both valves  44  and  46  are closed, the low pressure pump  38  may operate to provide oil at a first pressure to the engine  12  for lubrication purposes. Such oil may be provided, for example, through one or both passage arrangements  40  and  42  to main bearings  48 , and/or through third passage arrangement  50  to the cylinder head (not shown) of the engine  12 . 
     When one of the valves  44  or  46  is open, the high pressure pump  39  and/or an accumulator  51 , which stores high pressure oil, may provide oil at a second pressure greater than the first pressure to one of the passage arrangements  40  or  42 . This oil is then provided to the connecting rod assemblies  32  so as to cause a change in the effective length of the connecting rod assemblies  32 , and thereby vary the compression ratio of the engine  12 , as explained below in greater detail. 
     The fluid supply system  14  may further include check valves  52  for isolating the low pressure pump  38  from high pressure oil. The check valves  52  may be disposed in connector passage  53  that extends between the passage arrangements  40  and  42 . 
     The fluid supply system  14  and connecting rod assemblies  32  may be operated to effect a change in the compression ratio of the engine  12  in accordance with one or more operating parameters, such as engine load and speed. Referring to FIG. 1, such parameters may be measured by appropriate sensors, such as crankshaft speed sensor  54 , mass air flow (MAF) sensor  56  and pedal position sensor  58 , which are electronically coupled to the engine controller  16 . Referring to FIG. 2, the engine  12  may also include one or more position sensors  59  for sensing position of the connecting rod assemblies  32 . 
     Returning to FIG. 1, the engine controller  16  includes a central processing unit (CPU)  60 , input/output ports  62 , read-only memory (ROM)  64  or any suitable electronic storage medium containing processor-executable instructions and calibration values, random-access memory (RAM)  66 , and a data bus  68  of any suitable configuration. The engine controller  16  receives signals from a variety of sensors, such as sensors  54 ,  56 ,  58  and  59 , and controls operation of the fluid supply system  14 , the fuel injectors  24  and the spark plugs  26 . 
     FIGS. 3 through 6 show one connecting rod assembly  32  according to the invention. The connecting rod assembly  32  includes a first portion, such as bearing retainer  69 , that is adapted to be rotatably coupled to crankpin  34 , and a second portion, such as body portion  70 , that is adapted to be rotatably coupled to wrist pin  33 . The bearing retainer  69  and body portion  70  may be manufactured in any suitable manner and may comprise any suitable material or materials, such as hardened steel. 
     The bearing retainer  69  is configured to retain a bearing  71  between the bearing retainer  69  and the crankpin  34 , and includes a bearing retainer axis  72  that is coincident with crankpin axis  73 . The bearing retainer  69  may further include first and second sections  74  and  75 , respectively, that are joined together in any suitable manner, such as with bolts, screws or other suitable fasteners (not shown). In addition, the bearing retainer  69  includes first and second continuous, circumferential grooves or channels  76  and  77  that receive fluid from fluid supply system  14 . 
     The bearing retainer  69  also includes one or more apertures disposed proximate each end of the bearing retainer  69 . Referring to FIG. 7, for example, the first section  74  defines a first end  78  of the bearing retainer  69 , and includes first and second cylindrical apertures or bores  80  and  82 , respectively, disposed proximate the first end  78 . The first section  74  further includes first and second extension apertures  84  and  86 , respectively, extending from the first and second cylindrical bores  80  and  82 , respectively. While each extension aperture  84  and  86  may have any suitable configuration, such as a cylindrical aperture or rectangular aperture, in the embodiment shown in FIG. 7, each extension aperture  84  and  86  is an oblong aperture defined by two generally planar surfaces joined together by arcuate or curved end surfaces. 
     Similarly, the second section  75  defines a second end  88  of the bearing retainer  69 , and includes third and fourth cylindrical apertures or bores  90  and  92 , respectively, disposed proximate the second end  88 . The second section  75  further includes third and fourth extension apertures  94  and  96 , respectively, extending from the third and fourth cylindrical bores  90  and  92 , respectively. The extension apertures  94  and  96  may have any suitable configuration, such as described above with respect to the extension apertures  84  and  86 . 
     Returning to FIGS. 3 and 4, the body portion  70  has a lateral axis  98  that is coincident with wrist pin axis  100 , and a longitudinally extending body portion axis  102 . In addition, the body portion  70  includes first and second sections  103  and  104 , respectively, and each section  103  and  104  defines a generally semicircular aperture for receiving the bearing retainer  69 . The sections  103  and  104  may be joined together in any suitable manner, such as with fasteners  106 , so as to retain the bearing retainer  69  therebetween. 
     Furthermore, the body portion  70  is axially movable with respect to the bearing retainer  69  between a first position, or unextended position shown in FIGS. 3 and 5, and a second position, or extended position shown in FIGS. 4 and 6. In the embodiment shown in FIGS. 3 through 6, for example, the body portion  70  is displaceable by a distance x. When the body portion  70  is in the unextended position, which corresponds to a first or low compression ratio mode of the engine  12 , the effective length l L  of the body portion  70  is equal to the unextended length l u . When the body portion  70  is in the extended position, which corresponds to a second or high compression ratio mode of the engine  12 , the effective length l H  of the body portion  70  is equal to the extended length l u +x. Thus, the body portion  70  is selectively displaceable with respect to the bearing retainer  69  so as to cause a change in the effective length of the body portion  70  and the compression ratio of the engine  12 . 
     The connecting rod assembly  32  also includes first and second locking mechanisms  108  and  110 , respectively, for locking the body portion  70  at the unextended and extended positions. Each locking mechanism  108  and  110  includes one or more locking elements  112  that are each moveable laterally between an unlocked position and a locked position. Referring to FIGS. 5 through 7, for example, each locking mechanism  108  and  110  includes two locking elements  112 , and the locking elements  112  of a particular locking mechanism  108  or  110  are laterally moveable in opposite directions between unlocked and locked positions. When a particular locking element  112  is in the locked position, the locking element  112  extends into a gap formed between the bearing retainer  69  and the body portion  70 . More specifically, when a particular locking element  112  is in the locked position, the locking element  112  overlaps and is engaged with the bearing retainer  69  and the body portion  70  (one locking element  112  of the first locking mechanism  108  is shown in the locked position in FIG.  5  and the unlocked position in FIG. 6, and one locking element  112  of the second locking mechanism  110  is shown in the unlocked position in FIG.  5  and the locked position in FIG.  6 ). 
     Referring to FIGS. 7 and 8, each locking element  112  may be manufactured in any suitable manner and may comprise any suitable material, such as hardened steel. Each locking element  112  includes a cylindrical portion  114  disposed in a respective cylindrical bore  80 ,  82 ,  90  or  92 , and a locking projection  115  extending from the cylindrical portion  114 . Each cylindrical portion  114  is configured to closely mate with a respective cylindrical aperture  80 ,  82 ,  90  or  92  such that fluid leakage around the cylindrical portions  114  may be minimized. Furthermore, each cylindrical portion  114  has first and second ends  116  and  118 , respectively, and a cylindrical aperture  120  extending from the second end  118  toward the first end  116 . Each cylindrical portion  114  also includes first and second fluid passages  122  and  124 , respectively, disposed at the first and second ends  116  and  118 , respectively. 
     Referring to FIGS. 5 through 8, when the locking elements  112  of the first locking mechanism  108  are in the locked positions, each first fluid passage  122  of the first locking mechanism  108  is substantially aligned with a first unlocking fluid passage  125  that extends between a respective cylindrical bore  80  or  82  and the second channel  77 . When the locking elements  112  of the first locking mechanism  108  are in the unlocked positions, each second fluid passage  124  of the first locking mechanism  108  is substantially aligned with a first locking fluid passage  126  that extends between a respective cylindrical bore  80  or  82  and the first channel  76 . 
     Similarly, when the locking elements  112  of the second locking mechanism  110  are in the locked positions, each first fluid passage  122  of the second locking mechanism  110  is substantially aligned with a second unlocking fluid passage  127  that extends between a respective cylindrical bore  90  or  92  and the first channel  76 . When the locking elements  112  of the second locking mechanism  110  are in the unlocked positions, each second fluid passage  124  of the second locking mechanism  110  is substantially aligned with a second locking fluid passage  128  that extends between a respective cylindrical bore  90  or  92  and the second channel  77 . 
     The fluid passages  122  and  124  may have any suitable configuration for receiving fluid from the fluid supply system  14 , as explained below in greater detail. In the embodiment shown in FIGS. 7 and 8, for example, each first fluid passage  122  may include a main portion or channel  129  that extends around a respective locking projection  115 , and one or more connector portions or channels  130  that extend from the main channel  129  to the periphery of the cylindrical portion  114 . Each second fluid passage  124  may include, for example, one or more generally radially extending channels  131  that extend between a respective cylindrical aperture  120  and the periphery of the cylindrical portion  114 . 
     Still referring to FIGS. 7 and 8, each locking projection  115  is extendable through a respective extension aperture  84 ,  86 ,  94  or  96  so as create a compression fit between the bearing retainer  69  and the body portion  70  when the associated locking element  112  is in the locked position. Furthermore, each locking projection  115  is configured to closely mate with a respective extension aperture  84 ,  86 ,  94  or  96  such that the locking projections  115  substantially fill the extension apertures  84 ,  86 ,  94  and  96  when the locking elements  112  are in both the locked and unlocked positions. With such a configuration, fluid leakage from the cylindrical bores  80 ,  82 ,  90  and  92  may be minimized. 
     While each locking projection  115  may have any suitable configuration, such as a cylindrical projection or a rectangular projection, in the embodiment shown in FIGS. 7 and 8, each locking projection  115  includes two generally planar engaging surfaces  132  that are spaced apart from each other and generally parallel with each other. Each locking projection  115  further includes two arcuate or curved surfaces  134  that extend between the engaging surfaces  132 . With such a configuration, each locking projection  115  may have a cross-section that is defined by two generally parallel lines joined by two semicircles. When a particular locking element  112  is in the locked position, one of the engaging surfaces  132  is engaged with a generally planar surface  136  of the bearing retainer  69 , and the other engaging surface  132  is engaged with a generally planar surface  138  of the body portion  70 . 
     Each locking mechanism  108  and  110  may further include one or more springs  140  and one or more cover plates  142  that are attachable to the bearing retainer  69 . Each spring  140  is disposed between and engaged with a respective locking element  112  and a respective cover plate  142 . Furthermore, each spring  140  is configured to urge a respective locking element  112  toward the locked position. In the embodiment shown in FIG. 7, each spring  140  is disposed at least partially in a cylindrical aperture  120  of a respective locking element  112 . Each cover plate  142  is attachable to the bearing retainer  69 , such as with fasteners, and is configured to retain a respective spring  140  and a cylindrical portion  114  of respective locking element  112  within a respective cylindrical bore  80 ,  82 ,  90  or  92 . 
     Referring to FIGS. 3 through 6, a method for mounting the connecting rod assembly  32  on the crankshaft  36  will now be described. The method includes mounting first locking mechanism  108  on first section  74  of bearing retainer  69 . The method further includes mounting second locking mechanism  110  on second section  75  of bearing retainer  69 . The method further includes positioning bearing  71  around crankpin  34  of crankshaft  36 , and then securing first and second sections  74  and  75  around the bearing  71  and crankpin  34 , such as with fasteners or by any other suitable means. Next, the method involves positioning second section  104  of body portion  70  over second locking mechanism  110 , such that second locking mechanism  110  is received in a portion of an aperture defined by second section  104 . The method further includes positioning first section  103  of body portion  70  over first locking mechanism  108 , such that first locking mechanism  108  is received in a portion of an aperture defined by first section  103 . Next, the method involves moving the locking elements  112  of the first locking mechanism  108  to the unlocked position. The method further includes securing first section  103  to second section  104  in any suitable manner, such as with fasteners  106 . Fasteners  106  may be, for example, bolts or screws. 
     Referring to FIGS. 2 and 5 through  8 , operation of the system  10  will now be described in detail. First, the engine controller  16  may determine under which compression ratio mode the engine  12  is currently operating. This may be accomplished, for example, by sensing combustion pressure and/or by using the position sensors  59 . When the engine controller  16  determines that it is desirable to change the compression ratio of the engine  12 , based on one or more operating parameters such as engine speed and load, the engine controller  16  may control operation of fluid supply system  14  so as to supply pressurized oil from the high pressure pump  39  and/or accumulator  51  to the connecting rod assemblies  32 . For example, if the engine controller  16  determines that it is desirable to change from high compression ratio mode shown in FIG. 6 to low compression ratio mode shown in FIG. 5, the engine controller  16  may open first valve  44  of fluid supply system  14  for a predetermined amount of time, such as 100 to 300 milliseconds, while keeping second valve  46  closed. As a result, pressurized oil is routed through first passage arrangement  40 , and a pressure differential is created across the first and second passage arrangements  40  and  42 , respectively, which activates the locking mechanisms  108  and  110  of the connecting rod assemblies  32 . 
     More specifically, referring to FIG. 6, pressurized oil from first passage arrangement  40  may travel through first crankshaft passage arrangement  144  and first bearing aperture or apertures (not shown) in bearing  71 , and then into first channel  76  of bearing retainer  69 . Next, pressurized oil passes through second unlocking fluid passages  127  of bearing retainer  69  and into cylindrical bores  90  and  92  and first fluid passages  122  of second locking mechanism  110 . The pressurized oil acts on the locking elements  112  of the second locking mechanism  110  so as to cause the locking elements  112  to move from the locked position shown in FIG. 6 to the unlocked position shown in FIG.  5 . 
     With both locking mechanisms  108  and  110  in the unlocked position, the body portion  70  is able to move axially relative to the bearing retainer  69  from the extended position shown in FIG. 6 to the unextended position shown in FIG.  5 . Such movement occurs as a result of inertia of the body portion  70 . Once the body portion  70  reaches the unextended position, pressurized oil from first channel  76  acts on first locking mechanism  108  so as to move the locking elements  112  of the first locking mechanism  108  to the locked positions. More specifically, pressurized oil passes through first locking fluid passages  126  of bearing retainer  69  and into cylindrical bores  80  and  82  and second fluid passages  124  of first locking mechanism  108 . The pressurized oil acts on the locking elements  112  of the first locking mechanism  108  so as to cause the locking elements  112  to move from the unlocked position shown in FIG. 6 to the locked position shown in FIG.  5 . 
     When the engine controller  16  determines that it is desirable to change back to high compression mode, the engine controller  16  may control operation of the fluid supply system  14  so as to route pressurized oil through the second passage arrangement  42 . Next, pressurized oil may travel through second crankshaft passage arrangement  146  and second bearing aperture or apertures (not shown) in bearing  71 , and then into second channel  77  of bearing retainer  69 . Pressurized oil passing from second channel  77 , through first unlocking fluid passages  125 , then acts on the first locking mechanism  108  so as to move the associated locking elements  112  to the unlocked position, thereby allowing the body portion  70  to move from the unextended position shown in FIG. 5 to the extended position shown in FIG.  6 . Once the body portion  70  reaches the extended position, pressurized oil passing from second channel  77 , through second locking fluid passages  128 , acts on second locking mechanism  110  so as to cause the associated locking elements  112  to move to the locked positions shown in FIG.  6 . 
     The connecting rod assembly  32  of the invention includes several beneficial aspects. First, as shown in the FIGS. 5 and 6, the locking mechanisms  108  and  110  may be disposed entirely between the bearing retainer  69  and the body portion  70 , so that no additional housing portions, such as extruded housing portions, are required to contain the locking mechanisms  108  and  110 . Thus, the connecting rod assembly  32  can be utilized with conventional crankshafts with minimal, if any, additional machining being required on the crankshafts. 
     Further, each locking element  112  is compressively loaded, rather than shear loaded, between the bearing retainer  69  and the body portion  70  when the locking element  112  is in the locked position. Such compressive loading reduces the possibility of bending the locking elements  112 . 
     In addition, because the cylindrical portions  114  of the locking elements  112  mate with the cylindrical bores  80 ,  82 ,  90  and  92 , the locking elements  112  may exhibit smooth lateral movement. In other words, the cylindrical bores  80 ,  82 ,  90  and  92  may act as guides for controlling lateral movement of the locking elements  112 . 
     Furthermore, because the connecting rod assembly  32  may be manufactured with close tolerances between the cylindrical portions  114  and the cylindrical bores  80 ,  82 ,  90  and  92 , fluid leakage around the cylindrical portions  114  may be minimized. Similarly, because the locking projections  115  closely mate with the extension apertures  84 ,  86 ,  94  and  96 , fluid leakage from the cylindrical bores  80 ,  82 ,  90  and  92  may be minimized. 
     While embodiments of the invention have been illustrated and described, it is not intended that these embodiments illustrate and describe all possible forms of the invention. Rather, the words used in the specification are words of description rather than limitation, and it is understood that various changes may be made without departing from the spirit and scope of the invention.