Abstract:
A variable length connecting rod  13  for changing a compression ratio of an engine is provided. The connecting rod  13  includes a first locking assembly  36  for locking the connecting rod  13  in a first effective length setting corresponding to a high compression ratio. The connecting rod  13  further includes a second locking assembly  38  for releasably locking the connecting rod  13  in a second effective length setting corresponding to a low compression ratio. When a length change is initiated, hydraulic fluid unlocks one of the locking assemblies  36, 38,  allowing inertial force to effect the length change during an engine cycle. At completion of a length change, the other locking assembly  36, 38  automatically locks. The locking assemblies  36, 38  are self-contained units that are assembled to a bearing retainer  24.

Description:
BACKGROUND OF INVENTION 
     This invention relates generally to a connecting rod for an internal combustion engine, and particularly, to a variable length connecting rod that can vary a compression ratio of the engine. 
     The “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 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 thus the compression ratio 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. 
     One known system for changing the compression ratio of an engine utilizes a connecting rod whose effective length can be varied. Those skilled in the art will recognize that varying the effective length of a connecting rod allows the compression ratio of an associated engine cylinder to be varied. In particular, the apparatus includes a bearing retainer disposed between a connecting rod and a corresponding crankpin, the bearing retainer has an inner surface in communication with the crankpin and an outer surface in communication with the connecting rod. The connecting rod is axially movable relative to the bearing retainer along a longitudinal axis of the connecting rod to effect a selective displacement of the connecting rod relative to the bearing retainer. The displacement causes a change in the effective length of the connecting rod and the compression ratio of the internal combustion engine. A locking mechanism is provided in cooperation with the bearing retainer and the connecting rod for maintaining the connecting rod at a selected position relative to the bearing retainer. The selected position corresponds to a selected compression ratio of the internal combustion engine. The locking mechanism is housed in an “extruded portion” on the side of a connecting rod. The extruded portion includes a hydraulically actuated lock pin that can engage a corresponding aperture in the bearing retainer to lock the connecting rod relative to the bearing retainer. 
     A problem associated with the known connecting rod is that the overall width of the connecting rod having the extruded portion for the locking mechanism is wider than a conventional “constant length” connecting rod. Thus, to accommodate the extruded portion, clearance grooves are machined in the counterweights of the crankshaft to allow the extruded portion of the connecting rod to move therethrough. Thus, utilizing the known connecting rod requires additional machining of “stock” crankshafts which increases manufacturing costs and the assembly time. 
     SUMMARY OF INVENTION 
     The aforementioned limitations and inadequacies of conventional connecting rods are substantially overcome by the inventive connecting rod for selectively varying a compression ratio of an internal combustion engine. The connecting rod has a variable effective length and integrates a locking mechanism within the body of the connecting rod without utilizing an extruded portion for the locking mechanisms. 
     The inventive connecting rod includes a body portion extending along a first axis having an aperture extending therethrough generally perpendicular to the first axis and parallel to a crankpin axis. The connecting rod further includes a bearing retainer disposed in the aperture between the body portion and a crankpin of the engine. The aperture is configured to allow selective displacement of the body portion along the first axis relative to the bearing retainer. The displacement causes a change in the effective length of the body portion and the compression ratio of the engine. The connecting rod further includes a first locking mechanism contained within the aperture of the body portion and operably disposed between the bearing retainer and the body portion. The first locking mechanism has a first locking element that extends into a first gap formed between first and second opposing surfaces of the body portion and the bearing retainer, respectively, to create a first compression fit. The compression fit locks the body portion at a first position relative to the bearing retainer. The first position corresponds to a first selected compression ratio of the engine. 
     The inventive connecting rod in accordance with the present invention provides a substantial advantage over conventional systems and methods. In particular, the connecting rod integrates a locking mechanism within the body of the connecting rod without utilizing extruded portions to hold the locking mechanisms. Thus, the connecting rod can be utilized with conventional crankshafts with minimal additional machining being required on the crankshafts. Thus, the inventive connecting rod provides for reduced manufacturing costs and a reduction in assembly time as compared with known variable length connecting rods. 
     Another advantage associated with the inventive connecting rod is that the connecting rod is lighter than known variable effective length connecting rods because no extruded housings are utilized for the locking mechanisms. 
     Still another advantage associated with the inventive connecting rod is that the locking mechanism is compressively loaded between the body portion and the bearing retainer (i.e., creates a compression fit) to lock the bearing retainer relative to the body of the connecting rod. The compression fit results in decreased bending of the locking member as compared with known locking members having shear loading between two members of the connecting rod. 
    
    
     BRIEF DESCRIPTION OF DRAWINGS 
     FIG. 1 is perspective view of a connecting rod constituting an exemplary embodiment of the invention, with the connecting rod positioned relative to a bearing retainer to have an effective length that provides a high compression ratio. 
     FIG. 1A is a partial perspective view of the connecting rod shown in FIG. 1 with the connecting rod positioned relative to a bearing retainer to have an effective length that provides a low compression ratio. 
     FIG. 2 is a fragmentary perspective view of the large end of the connecting rod, broken away to show more detail of one of its two locking assemblies. 
     FIG. 3 is another fragmentary perspective view of the large end of the connecting rod, with the rod being shown in cross section substantially at its medial plane. 
     FIG. 4 is a view looking in same general direction as FIG. 2, with the locking assembly shown in exploded view on a larger scale to illustrate detail. 
     FIG. 5 is an enlarged perspective view of certain elements of the locking assembly, namely a guide and two spring-biased locking members. 
     FIG. 6 is an enlarged fragmentary perspective view of a portion of the bearing retainer on which a locking assembly is disposed. 
     FIG. 7 is a perspective view of another element of the locking assembly by itself, namely a cover. 
     FIG. 8 is a bottom plan view of a locking member of the locking assembly by itself. 
     FIG. 9 is a view in the direction of arrow  9  in FIG.  8 . 
     FIG. 10 is a view in the direction of arrow  10  in FIG.  9 . 
     FIG. 11 is a bottom plan view of a guide of the locking assembly by itself. 
     FIG. 12 is a view in the direction of arrow  12  in FIG.  11 . 
     FIG. 13 is a cross section view generally in the direction of line  13 — 13  in FIG.  2 . 
    
    
     DETAILED DESCRIPTION 
     FIGS. 1 and 1A show an embodiment of a variable length connecting rod  13  for varying a compression ratio of an internal combustion engine. Connecting rod  13  comprises a large end  14  for journaling on a crankpin of a crankshaft (not shown). Connecting rod  13  further includes a small end  16  for journaling on a central portion of a wrist pin (not shown) for coupling the connecting rod  13  to a piston (not shown). The connecting rod  13  may be utilized with the engine described in commonly owned U.S. patent application Ser. No. 09/690,961 entitled “System And Method For Varying The Compression Ratio Of An Internal Combustion Engine” filed Oct. 18, 2000, which is incorporated herein in its entirety. 
     Connecting rod  13  comprises a fixed length body portion  19  formed by rod portions  20  and  26  that are fastened together by fasteners  25 . Rod portion  20  comprises a small end  16  and a middle portion  22  that extends from the small end  16  to large end  14 . The connecting rod  13  further includes a bearing retainer  24  which is assembled onto a crankpin (not shown) of a crankshaft (not shown) with its centerline CL concentric with that of the crankpin. Bearing retainer  24  is captured between a generally semi-circular portion of rod portion  20  at large end  14  and a generally semi-circular cap that forms rod portion  26 . Body portion  19  and bearing retainer  24  are constructed to allow body portion  19  to move a short distance on bearing retainer  24 , thereby changing the effective length of connecting rod  13  by re-positioning the centerline of large end  14  relative to the centerline of bearing retainer  24 . FIG. 1 shows connecting rod  13  locked in a longer length setting that provides a higher compression ratio in an engine cylinder. FIG. 1A shows a shorter length setting that provides a smaller compression ratio in an engine cylinder. 
     Referring to FIG. 1, a bearing (not shown) resides within bearing retainer  24  to function as a bearing surface between the inside diameter (I.D.) of the bearing retainer  24  and the outside diameter (O.D.) of the crankpin (not shown). The bearing may be constructed as disclosed in commonly owned U.S. patent application Ser. No. 09/690,951, filed on Oct. 18, 2000 which is incorporated herein in its entirety. In particular, the bearing may be constructed as shown in FIGS. 9A,  9 B of U.S. patent application Ser. No. 09/690,951 where the bearing resides within the bearing retainer. Referring again to FIG. 1, the crankpin is girdled by the bearing retainer  24  as the retainer  24  turns on the crankpin in response to crankshaft rotation. Referring to FIG. 2, the bearing retainer  24  includes two circumferentially continuous channels C 1 , C 2 . The bearing also includes two series of circumferentially spaced apart through-holes through which hydraulic fluid can enter the channels C 1 , C 2  from the crankpin. 
     Connecting rod  13  includes two locking assemblies  36 ,  38 . Locking assembly  36  is disposed at large end  14  between small end  16  and a centerline CL. Locking assembly  38  is disposed at large end  14  diametrically opposite locking assembly  36  relative to centerline CL. As illustrated, assemblies  36 ,  38  may have identical configurations. 
     Referring to FIGS. 4-6, locking assembly  36  comprises several parts including two locking members, or lock pins  36 P 1 ,  36 P 2 , two bias springs  3651 ,  36 S 2 , a guide, or base,  36 G, and a cover  36 C, the latter two parts forming an enclosure of the assembly. 
     Locking assembly  38  comprises the same parts as locking assembly  36 , namely two locking members or lock pins, two bias springs, a guide, or base, and a cover. Only some of the elements of assembly  38  are illustrated for purposes of clarity. 
     Locking assembly  36  locks connecting rod  13  in a longer effective length setting, while locking assembly  38  locks the connecting rod  13  in a shorter effective length setting. Referring to FIG. 1, when connecting rod  13  has a longer length setting, a gap  37  exists between an edge of guide  36 G and the confronting edge of a notch  35 . The confronting edge is formed in rod portion  20  in one face of body portion  19  at the middle of the semi-circular portion of large end  14 . A distal end of locking member  36 P 1  protrudes from locking assembly  36  to fit very closely in gap  37  to create a compression fit that prevents body portion  19  from moving on bearing retainer  24  and thus prevents shortening the effective length of the connecting rod  13 . If connecting rod  13  were rotated 180° about a long axis in FIG. 1 to reveal an opposite face, the opposite face would appear identical to the one shown. Thus, gap  37  is also present on the opposite face where an end of locking member  36 P 2  protrudes into gap  37 . As shown in FIG. 1, the two locking members  36 P 1 ,  36 P 2  thereby lock the connecting rod  36  in the longer length setting. Force acting in a sense tending to shorten the length of the connecting rod  13  results in the application of a compression force to the extended portions of locking members  36 P 1  and  36 P 2  and the portions of guide  36 G that underlie the extended portions of the locking members. In this way, the locking assembly locks the connecting rod without shearing force being exerted on the members  36 P 1 ,  36 P 2  and guide  36 G. 
     Referring to FIG. 1A, when connecting rod  13  has a shorter length setting, a gap  39  exists between an edge of guide  36 G of locking assembly  38  and the confronting edge of a notch  35 . The confronting edge is formed in rod portion  26  in one face of body portion  19  at the middle of the semi-circular portion of large end  14  formed by the rod portion  26 . As illustrated in FIG. 1, when connecting rod  13  is locked in the longer length setting, gap  39  is closed. Further, the locking members  36 P 1 ,  36 P 2  of locking assembly  38  are retracted into the locking assembly enclosure. 
     As illustrated, bearing retainer  24  may be generally circular, and includes features for accommodating locking assemblies  36 ,  38 . At the location of each locking assembly  36 ,  38 , the bearing retainer  24  has a flat mounting surface  40  for the respective guide  36 G. Referring to FIG. 2, guide  36 G of locking assembly  36  is disposed flat against surface  40 . Locking members  36 P 1 ,  36 P 2  are disposed on guide  36 G, and cover  36 C fits over members  36 P 1 ,  36 P 2  to hold the members between cover  36 C and guide  36 G. Formations  42  and  44  of bearing retainer  24  are disposed adjacent respective sides of mounting surface  40 . 
     Formations  42 ,  44  serve multiple purposes as described below. One purpose is to provide for the precise locating and the secure attachment of cover  36 C to the bearing retainer  24 . A second purpose is to guide the fixed length connecting rod  19  on bearing retainer  24  when the connecting rod effective length is changed. A third purpose is to allow two semi-circular elements  24 A,  24 B that form bearing retainer  24  to be fastened together at a diagonal parting plane  46 . 
     Referring to FIG. 3, parting plane  46  illustrates the position where the two elements  24 A,  24 B are joined. Each element  24 A,  24 B includes an apertured ear  48  that abuts a mating surface  50  in formation  44  of the opposite element at parting plane  46 . The threaded shank of a headed screw  52  passes through the aperture of each ear  48  and threads into a tapped blind hole that extends into formation  44  from surface  50 . The screw  52  is tightened so that its head forces ear  48  against surface  50 , thereby securing the two elements  24 A,  24 B together at parting plane  46 . 
     Referring to FIGS. 1,  2 ,  3 , cap  26  and the semi-circular portion of rod portion  20  at large end  14  have grooves that fit closely onto formations  42 ,  44  to provide the small relative movement of the body portion  19  on bearing retainer  24 . The small relative movement allows the effective connecting rod length to change along the direction of a straight line  53 . As shown in FIG. 3, line  53  perpendicularly intersects centerline CL of bearing retainer  24 . 
     Referring to FIG. 4, formation  42  has a tapped hole  54  that is proximate mounting surface  40  and parallel to line  53 . Hole  54  provides for fastening of one end of cover  36 C to the bearing retainer  24  by means of a headed screw  55 . Formation  44  also has a circular through-hole  57  that is proximate mounting surface  40  and parallel to centerline CL. Hole  57  provides for fastening of the other end of cover  36 C to the bearing retainer  24  by means of a pressed-in cylinder such as a roll pin  58 . 
     Referring to FIG. 7, cover  36 C comprises a rectangular-shaped top  60  and sides  62 ,  64  that depend from opposite lengthwise side margins of top  60 . Sides  62 ,  64  have equal nominal height. At the lengthwise end portion of cover  36 C that is proximate formation  44 , sides  62 ,  64  have respective aligned circular through-holes  66 ,  68  of equal diameters with that of through-hole  57 . At the lengthwise end portion of cover  36 C that is proximate formation  42 , top  60  comprises a through-hole  70 . When cover  36 C and bearing retainer  24  are assembled together, the threaded shank of screw  55  passes through hole  70  and threads into hole  54 . The screw is tightened to seat its head flush with top  60  securing the cover to the bearing retainer. At the end of cover  36 C proximate formation  44 , through-holes  66 ,  68  register with opposite ends of through-hole  57 , and roll pin  58  is pressed in the three aligned holes to secure that end of the cover to the bearing retainer. Side  62  has a rectangular through-notch  63  that interrupts its bottom edge to provide clearance for locking member  36 P 1  when the cover is assembled over it. Likewise side  64  has a rectangular through-notch  65  that interrupts its bottom edge to provide clearance for locking member  36 P 2  when the cover is assembled over member  36 P 2 . 
     Referring to FIGS. 5,  11 ,  12 , guide  36 G has opposite parallel faces, and a generally straight rectangular ridge  72  that runs parallel to centerline CL. Ridge  72  protrudes centrally from one face of guide  36 G that is disposed against mounting surface  40 . Mounting surface  40  comprises a central straight through-slot  74  into which ridge  72  closely fits to accurately locate guide  36 G on the mounting surface. The faces of formations  42 ,  44  at the sides of mounting surface  40  also aid in locating the guide. 
     The other face of guide  36 G that is disposed toward top  60  of cover  36 C comprises a straight, generally rectangular ridge  76  that runs parallel to bearing retainer centerline CL. Ridge  76  protrudes centrally from the face opposite ridge  72 . The portion of guide  36 G to one side of ridges  72 ,  76  comprises a rectangular notch  77  that extends between top and bottom faces of the guide  36 G to endow the guide with spaced-apart, parallel arms  78 ,  80  that run perpendicular to the bearing retainer centerline. In similar fashion, the portion of guide  36 G to the opposite side of ridges  72 ,  76  comprises a rectangular notch  79  that extends between top and bottom faces of the guide to endow the guide  36 G with spaced-apart, parallel arms  82 ,  84  that run perpendicular to the bearing retainer centerline opposite arms  78 ,  80  thereby giving the guide  36 G a general H-shape as shown in FIG.  11 . 
     Referring to FIGS. 8,  9 ,  10 , locking member  36 P 1  comprises a generally rectangular body  90  having an essentially flat top surface  91  and an essentially flat bottom surface  92 . Surface  92  is divided into two surface portions  92 A,  92 B by a somewhat rectangular bar  94  that is transverse to the length of the locking member  36 P 1 . Bar  94  depends from bottom surface  92  of body  90  and is disposed in notch  77  between arms  78  and  80 . Bar  94  comprises opposite side surfaces  94 A,  94 B. A central area of surface  94 B and an adjoining central area of surface portion  92 B are formed to provide a recess  96  that serves to seat and locate one end of spring  36 S 1 . For locking member  36 P 1 , the opposite end of spring  36 S 1  bears against a surface  78 A of arm  78  that faces surface  94 B. Top  60  of cover  36 C overlies top surface  91  of body  90 . One side surface of body  90  confronts the side surface of ridge  76  while the opposite side surface of body  90  confronts the surface of formation  42  that adjoins mounting surface  40 . A recess  98  is formed centrally in side surface  94 A of bar  94 . 
     Referring to FIG. 5, locking member  36 P 2  is identical to locking member  36 P 1 , arm  82  is identical to arm  80 , and arm  84  is identical to arm  78 . Spring  3 GS 2  is disposed between arm  84  and locking member  36 P 2  with one end of spring  36 S 2  bearing against a surface  84 A of arm  84  that faces surface  94 B. Locking member  36 P 2  is arranged in relation to guide  36 G, cover  36 C, and formation  44  in the same manner as locking member  36 P 1  is arranged relative to the guide, the cover and formation  42 . The difference is that the two locking members  36 P 1 ,  36 P 2  operate in opposite directions, as will be explained in greater detail below. 
     Referring to FIGS. 1,  2 ,  4 ,  5 , a locked condition of locking assembly  36  is illustrated. As shown locking members  36 P 1 ,  36 P 2  are extended during the locked condition. To extend locking members  36 P 1 ,  36 P 2 , springs  36 S 1  and  36 S 2  force the bars  94  of the respective locking members  36 P 1 ,  36 P 2  against the respective arms  80 ,  82  with surfaces  94 A constituting stop surfaces that abut stop surfaces  80 A,  82 A of the arms  80 ,  82 . As a result, the lengthwise end of body  90  of locking member  36 P 1  opposite spring  36 S 1  protrudes from notch  63  to end essentially flush with the outer end surface of guide  36 G which is common to both arms  80 ,  84 . Further, the lengthwise end of body  90  of locking member  36 P 2  opposite spring  36 S 2  protrudes from notch  65  to end essentially flush with the outer end surface of guide  36 G which is common to both arms  78 ,  82 . 
     When locking assembly  36  is operated to an unlocked condition, the two locking members  36 P 1 ,  36 P 2  are retracted along respective straight lines (i.e. they translate) toward the interior of the locking assembly enclosure, resiliently compressing the respective bias springs  36 S 1 ,  36 S 2  in the process. As locking member  36 P 1  retracts, its surface portion  92 A slides across the top surface of arm  80 . As locking member  36 P 2  retracts, its surface portion  92 A slides across the top surface of arm  82 . The top surfaces of bodies  90  slide across the bottom surface of cover top  60 . Inboard side surfaces of the locking members  36 P 1 ,  36 P 2  slide across ridges  72  and  76 , and outboard side surfaces slide across the respective surfaces of formations  42  and  44  that adjoin mounting surface  40 . The protruding ends of the locking members  36 P 1 ,  36 P 2  retract into notches  63 ,  65 . 
     Referring to FIGS. 5,  6 , bearing retainer  24  includes a first passage  100  that extends from channel C 1  to notch  79  between arms  82  and  84 . It also comprises a second passage  102  that extends from channel C 2  to notch  79 . Each passage  100 ,  102  opens to notch  79  at a different location. In particular, passage  100  opens proximate arm  82  while passage  102  opens proximate arm  84 . 
     Bearing retainer  24  further comprises a third passage  104  that extends from channel C 1  to notch  77  between arms  78  and  80 . It also comprises a fourth passage  106  that extends from channel C 2  to the same notch, and importantly, each passage  104 ,  106  opens to notch  77  at a different location. In particular, passage  104  opens proximate arm  80  while passage  106  opens proximate arm  78 . Each of passages  100 ,  102  extends straight from the respective channel C 1 , C 2 . However, creating a straight passage for passages  104 ,  106  may not be possible in the available space. Therefore, passages  104 ,  106  may have to be slant drilled to establish the required communication with the proper channel. 
     Operation of the two locking members  36 P 1 ,  36 P 2  of locking assembly  36  to the unlocked condition is accomplished by the delivery of hydraulic fluid under pressure through channel C 1  and passages  100 ,  104 . With the two locking members  36 P 1 ,  36 P 2  in locked condition, hydraulic fluid is delivered through the respective notches  79 ,  77  in guide  36 G to respective confined spaces that are provided by the respective recess  98  in each locking member. The hydraulic pressure acts on the surface of each recess  98  to create a force opposite that of the respective bias spring  36 S 1 ,  36 S 2 . The hydraulic force is great enough to retract each locking member  36 P 1 ,  36 P 2  against the spring force. 
     As the locking members  36 P 1 ,  36 P 2  retract, their ends move out of the respective gaps  37  thereby unlocking the assembly to allow an effective length change of body portion  19 . Because the opposite locking assembly  38  is already unlocked, the length change occurs as soon as the inertial force acting along the length of the connecting rod  13  becomes sufficiently great. When the length change concludes, connecting rod  13  has a slightly shorter overall effective length there by resulting in a lower compression ratio. 
     Referring to FIGS. 1A and 5, when the length change is completed, locking assembly  38  automatically locks. The fact that locking assembly  38  will automatically lock can be appreciated from consideration of its identical construction with locking assembly  36 . One difference however between the two assemblies  36 ,  38  is that at locking assembly  38 , channel C 1  supplies hydraulic fluid to recess  96  for extending the two locking members  36 P 1 ,  36 P 2  of mechanism  38 , and channel C 2  supplies hydraulic fluid to recess  98  for retracting the locking members  36 P 1 ,  36 P 2 . This can be seen in FIG. 13 which shows locking assembly  36  locked and locking assembly  38  unlocked. Hence, channel C 1  is communicated to the two spaces of locking assembly  38  where the two bias springs are disposed. This allows hydraulic pressure in channel C 1  to act on surfaces  94 B of the two locking members  36 P 1 ,  36 P 2  of locking assembly  38  at the same time that the pressure is also acting to retract the two locking members  36 P 1 ,  36 P 2  of locking assembly  36 . 
     As the length change is ending, gaps  39  open sufficiently wide to cease interfering with the extension of locking members  36 P 1 ,  36 P 2  of assembly  38 . The locking members  36 P 1 ,  36 P 2  are immediately forced to translate to their extended positions by both spring force and hydraulic force, to fit closely in the open gaps. When the increased hydraulic pressure in channel C 1  ceases, the springs  36 S 1 ,  36 S 2  of locking assembly  38  keep the locking members in locked condition. Although the locking members  36 P 1 ,  36 P 2  of locking assembly  36  are no longer being forced into retraction by hydraulic pressure, the closure of gap  37  that occurred during the length change now presents an interference to their extension by the bias springs, and hence they remain retracted in the unlocked condition. Force acting in a sense tending to lengthen the connecting rod  13  results in the application of force of compression to the extended portions of locking members  36 P 1 ,  36 P 2  of locking assembly  38  and the portions of guide  36 G that underlie the extended portions of the locking members  36 P 1 ,  36 P 2 . Thus, locking assembly  38  locks the connecting rod  13  without shearing force being exerted on its two locking members  36 P 1 ,  36 P 2  and guides  36 G. 
     The connecting rod  13  is lengthened by increasing hydraulic pressure in channel C 2 . Assembly  38  is unlocked in the same manner as assembly  36  was unlocked when the length was decreased. The length change is accomplished by inertial force, and assembly  36  automatically re-locks upon completion of the length change. The hydraulic pressure increase in channel C 2  can be discontinued. Because the length change occurs within one engine cycle and increased hydraulic pressure is discontinued after the connecting rod has been re-locked in the new length, the increased pressure for performing a length change is in the nature of a pulse. 
     From the foregoing description, several aspects of operation may be recognized. A first aspect is that the locking of one assembly is sufficient to lock the connecting rod in one of two possible lengths. A second aspect is that it is not possible for both locking assemblies to be locked at the same time. A third aspect is that a length change is initiated by unlocking a locked assembly so that both locking assemblies are unlocked. A fourth aspect is that one of the assemblies will automatically lock the connecting rod upon completion of a length change. 
     The hydraulic control systems disclosed in commonly owned U.S. patent application Ser. No. 09/799,305, filed on Mar. 5, 2001, which is incorporated herein in its entirety, may be utilized for operating the connecting rod  13 . In one embodiment, passages  30 ,  32  illustrated in FIG. 1 of U.S. patent application Ser. No. 09/799,305 may selectively supply hydraulic fluid to grooves C 1  and C 2 , respectively, in FIG. 2 of the present application to adjust an effective length of connecting rod  13 . 
     A method for assembling a connecting rod  13  to a crankshaft (not shown) of an engine in accordance with the present invention is also provided. Referring to FIGS. 1,  2 , the method includes attaching first locking mechanism  36  to first portion  24 A of bearing retainer  24 . The method further includes attaching second locking mechanism  38  to second portion  24 B of bearing retainer  24 . The method further includes securing first and second portions  24 A,  24 B around a crankshaft (not shown) of the engine. The method further includes inserting first rod portion  20  over first locking mechanism  36  for mechanism  36  to be received in a portion of an aperture defined by first rod portion  20 , until a top surface of mechanism  36  abuts an inner surface of first rod portion  20 . The method further includes inserting second body portion  26  over second locking mechanism  38  for mechanism  38  to be received in a portion of the aperture defined by second rod portion  26 , until a top surface of second locking mechanism  38  abuts an inner surface of second rod portion  26 . Further, while inserting second rod portion  26  over second locking mechanism  38 , moving first and second locking members  36 P 1 ,  36 P 2  inwardly toward one another to an unlocked position. Finally, the method includes securing first rod portion  20  to second rod portion  26 . The first and second rod portions  20 ,  26  may be secured using conventional bolts, screws, or other attachment means known to those skilled in the art. 
     The inventive method for assembling a connecting rod  13  to an engine crankshaft represents a significant advantage over known assembly methods for variable compression connecting rods. In particular, the method allows the locking mechanisms  36 ,  38  to be attached to a respective portion of the bearing retainer  24  prior to the bearing retainer  24  being attached to an engine crankshaft. The inventive assembly method is much simpler and faster than known assembly methods that first attach the bearing retainer to the crankshaft and thereafter assemble at least a portion of the locking mechanisms to the bearing retainer or connecting rod within the limited space of the engine. 
     The inventive connecting rod  13  also provides a substantial advantage over conventional connecting rods for variable compression engines. In particular, the inventive connecting rod  13  integrates locking mechanisms  36 ,  38  completely within the body of the connecting rod  13  without utilizing extruded housing portions to contain the lock mechanisms. Thus, the inventive connecting rod  13  can be utilized with conventional crankshafts with minimal additional machining being required on the crankshafts, resulting in reduced manufacturing costs. Further, the inventive connecting rod  13  is lighter than known variable length connecting rods because no extruded housing is needed for the locking mechanisms. Still further, the connecting rod  13  utilizes a locking member that is compressively loaded between the body portion  19  and the bearing retainer  24 . The compressive loading reduces the possibility of bending the locking member while maintaining a locked position as compared to known connecting rods that have locking members that are shear loaded between a body portion and a bearing retainer.