Abstract:
To provide peak cylinder pressure control, an eccentric bearing is biased toward a first angular position wherein an attached piston is raised to a maximum compression ratio position in the cylinder. The compression ratio may remain constant at lower loads and above until a predetermined force generated by cylinder pressure is reached. At this point, the force acting on the eccentric lever arm or eccentricity of the bearing overcomes the restraining biasing force, causing the eccentric bearing to rotate in the connecting rod to move the eccentric end of the rod outward, away from the cylinder. This motion effectively shortens the length of the connecting rod and moves the piston downward relative to a connected crankpin. In this manner, the effective compression ratio of the cylinder is temporarily reduced and the pressure developed in the cylinder is controlled by the mechanical mechanism.

Description:
TECHNICAL FIELD  
         [0001]    This invention relates to reciprocating piston internal combustion engines and more particularly to a mechanism for controlling maximum cylinder pressures in such engines.  
         BACKGROUND OF THE INVENTION  
         [0002]    It is known in the art relating to reciprocating piston engines to provide means for limiting maximum cylinder pressures by allowing for some compressive adjustment of the position of the piston relative to its connecting rod. In one prior art arrangement, a preloaded compression spring is provided between the piston and its connecting rod attachment. In another, the piston is mounted on an oil pressure cushion which is connected with a relief valve to control the maximum oil pressure. In both cases, maximum engine cylinder pressure is limited by relative downward movement of the piston on the connecting rod when the maximum desired cylinder pressure is reached.  
           [0003]    The provision of mechanisms to limit cylinder pressures can allow the use of higher compression ratios in the cylinder which provide improved efficiency when the engine is operated at lower and medium load conditions. At higher loads, the downward motion of the piston relative to the connecting rod operates to limit maximum cylinder pressures, reducing the rate of pressure rise and resulting in smoother and quieter engine operation without damage from the effects of the higher compression ratio provided in lower load operating conditions. Other mechanisms proposed have included eccentric connecting rod bearings or piston pins which are rotated or oscillated as the piston reciprocates to vary the effective connecting rod length. Means for adjusting the phase of oscillation allows control of maximum piston compression ratio. However the prior art methods for accomplishing these results are considered to excessively complicate piston and connecting rod design.  
         SUMMARY OF THE INVENTION  
         [0004]    The present invention utilizes a sandwiched element in the form of an eccentric bearing rotatably mounting the connecting rod on a crankpin of the crankshaft or, alternatively on a wrist pin of the piston. If desired, eccentric bearings could be utilized in both the crankpin and wrist pin locations.  
           [0005]    In carrying out the preferred embodiment, the eccentric bearing is mounted in the connecting rod with the center of the outer diameter that rotatably engages the connecting rod offset by a predetermined eccentricity from the inner diameter of the bearing, which engages the crankpin. The eccentricity defines an effective lever arm acting from the center of the connecting rod bore around the center of the crankpin bore.  
           [0006]    When load is applied to the piston, the eccentricity tends to force the center of the connecting rod bore from a position longitudinally upward from a lateral axis of the crankpin relative to the connecting rod (a crankpin axis parallel to the lateral axis of the connecting rod bore) toward a position longitudinally downward from the relative lateral crankpin axis. This lowers the position of the piston in the cylinder and reduces the effective compression ratio. The amount of rotational force developed on the eccentric bearing is dependent both on the length and position of the eccentric lever arm as well as on the force applied against the lever arm by the engine cylinder pressures and other forces.  
           [0007]    To provide pressure control, the eccentric bearing may be provided with an extending lever or cam which is biased toward a first angular position by a preloaded compression (or tension) spring. The spring rotates the bearing to a first position against a stop, with the connecting rod and attached piston raised to the highest compression ratio position in the cylinder. The compression ratio may remain constant at lower loads and above until a predetermined force generated by cylinder pressure is reached.  
           [0008]    At this point, the force acting on the eccentric lever arm or eccentricity of the bearing overcomes the restraining force of the spring, causing the eccentric bearing to rotate in the connecting rod to move the eccentric end of the rod outward, away from the cylinder. This motion effectively shortens the length of the connecting rod and moves the piston downward relative to the connected crankpin. In this manner, the effective compression ratio of the cylinder is temporarily reduced and the pressure developed in the cylinder is controlled by the mechanical mechanism.  
           [0009]    These and other features and advantages of the invention will be more fully understood from the following description of certain specific embodiments of the invention taken together with the accompanying drawings. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]    In the drawings:  
         [0011]    [0011]FIG. 1 is a transverse cross-sectional view through a simplified mechanism representing a single cylinder of an internal combustion engine according to the invention;  
         [0012]    [0012]FIG. 2 is a cross-sectional end view of a connecting rod for the engine having an eccentric bearing orientated in a first angular position;  
         [0013]    [0013]FIG. 2A is an enlarged view of the first angular position of eccentricity;  
         [0014]    [0014]FIG. 3 is a view similar to FIG. 2 but having the eccentric bearing oriented in a second angular position representing a reduced compression ratio;  
         [0015]    [0015]FIG. 3A is a view similar to FIG. 2A showing the second angular position of eccentricity;  
         [0016]    [0016]FIG. 4 is an isometric view illustrating a piston connecting rod and bearing assembly;  
         [0017]    [0017]FIG. 5 is a cross-sectional end view of an alternative embodiment of connecting rod with an eccentric bearing according to the invention;  
         [0018]    [0018]FIG. 6 is a view similar to FIG. 5 but showing an alternative operational mode of the FIG. 5 embodiment; and  
         [0019]    [0019]FIG. 7 is a longitudinal cross sectional view through the connecting rod and bearing in the initial position of FIG. 6 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0020]    Referring first to FIG. 1 of the drawings in detail, numeral  10  generally indicates, in simplified form, an internal combustion engine including a cylinder block  12  internally defining a cylinder  14  closed at an upper end by a cylinder head  16 . Below the cylinder  14  the cylinder block defines a crankcase  18  closed at the bottom by an oil pan  20 . The cylinder block supports a longitudinally extending crankshaft  22  having at least one eccentric crankpin  24  journaling the lower end  26  of a connecting rod  28 . An upper end  30  of the connecting rod carries a piston pin  32  which connects with a piston  34  reciprocably mounted in the cylinder  14 .  
         [0021]    As is best shown in FIGS.  2 - 4 , an eccentric bushing or bearing  36  is provided between the lower end  26  of the connecting rod  28  and the outer surface of the crankpin  24 . Bearing  36  includes a central portion  38  having a cylindrical inner diameter  40  which engages the outer surface of the crankpin  24 , not shown in FIGS.  2 - 4 . The central portion  38  also includes a cylindrical outer diameter  42  which engages a longitudinal bore  44  formed in the lower end  26  of the connecting rod. The crankpin  24  is conventionally rotatable within the bearing inner diameter  40  and the bearing outer diameter  42  is also rotatable within the bore  44  of the connecting rod.  
         [0022]    As is best shown in the enlarged views of FIGS. 2A and 3A, the inner diameter  40  of the bearing is centered on a longitudinal axis  46  which is colinear with the axis of the crankpin  24 . The outer diameter of the bearing is centered on a separate longitudinal axis  48  which is colinear with the axis of the bore  44  of the connecting rod lower end. In accordance with the invention, the axis  48  of the outer diameter is eccentrically displaced from the axis  46  of the inner diameter by a distance or eccentricity  50  extending along a common plane  52  which passes through both axes  46 ,  48  and through the bearing wall at opposite points  53 ,  54  of maximum and minimum thickness. Thus, the eccentricity  50  effectively acts as a lever arm of the corresponding axis  48  of the connecting rod acting around the corresponding axis  46  of the crankpin.  
         [0023]    As installed in the engine, this thick wall portion  53  of the bearing is positioned initially above and substantially to one side laterally of the lateral and longitudinal axes  56 ,  57  of the crankpin  24  which are parallel to the corresponding axes  58 ,  59  of the connecting rod bore  44 . Thus, the lever arm  50  could extend at an angle A of, for example, 25° longitudinally upward or counterclockwise from the lateral axis  56  in the initial or first position of the bearing as shown in FIGS. 2 and 2A. The actual angle of the lever arm  50  for a particular application would depend upon many factors and might vary within a range from about 75° longitudinally upward or counterclockwise from the lateral axis  56  to about coextensive with, or at 0° from, the lateral axis  56 .  
         [0024]    The lateral displacement of the lever arm  50  converts the downward force of combustion pressure acting on the piston and connecting rod to a torque acting to rotate the bearing  36  in a clockwise direction as shown in the figures. The possible rotation is from an initial position as shown in FIGS. 2 and 2A toward a second or final position as shown in FIGS.  3  and  3 A wherein the eccentric lever arm is rotated clockwise around the crankpin center  46  to an angle B of about 25° longitudinally downward, or clockwise from, the lateral axis  56  of the crankpin parallel with the axis  58  of the corresponding connecting rod bore  44 . Again, this second position could, depending on the application, have a range of from essentially colinear with the lateral coordinate to an angle of up to about 75° downward or clockwise from the lateral axis  56 .  
         [0025]    The eccentric bearing  36  includes, in addition to the central portion  38  with its eccentric diameters, front and rear flanges  60 ,  62 , shown in FIG. 4, which maintain the bearing within the connecting rod bore. The flanges also include radially extending levers  64 . The levers include bores  66  carrying a longitudinal pin  68  on which a pivotable bushing  70  is mounted. Bushing  70  connects with a lower spring seat  72  on which a compression spring  74  is seated. The spring is compressed against an upper spring seat  76  mounted in a recess  78  on the side of the connecting rod  28 . The spring  74  exerts a predetermined force against the spring seats which generates torque urging the eccentric bearing  36  in a counterclockwise direction as shown in the drawings to normally force the bearing to its initial or first position, shown in FIG. 2, wherein a stop  80  extending from the lower spring seat  72  engages a portion of the connecting rod lower end  26  to prevent further counterclockwise rotation of the bearing past its intended initial position.  
         [0026]    In operation of the engine in which connecting rods  28  are utilized, combustion in the cylinder  14  causes a downward force on the piston which is transferred through the connecting rod  28  to the crankpin  24 . There, the force is converted in part by the eccentric lever arm  50  to a torque acting to urge the eccentric bearing  36  in a clockwise direction from its initial position of FIG. 2. However, the force of the compression spring  74  is selected to overcome the rotational torque on the bearing at low and medium engine loads so that the initial compression ratio of the piston is maintained and efficient combustion and operation of the engine is provided.  
         [0027]    As the engine load increases, however, maximum cylinder pressures also increase to a point where the torque caused by the force of cylinder pressures exceeds the restraining force of the spring. Then, the cylinder pressures cause some rotation of the bearing in a clockwise direction, toward and possibly up to the full amount allowed, to the second position shown in FIG. 3 where the bearing has been fully rotated to a predetermined position established by a stop, such as by engagement of the spring seats  72 ,  76 . The resulting clockwise-rotation of the bearing causes the center of the connecting rod bore  44  to move downward relative to the center of the crankpin  24 , thus effectively shortening the length of the connecting rod and increasing top dead center clearance of the piston from the cylinder head.  
         [0028]    The result is a self actuated reduction in the effective compression ratio which limits the cylinder pressure to a desired maximum value while allowing operation at lower loads with an increased compression ratio above that which would be possible without a control on cylinder pressures as provided by the invention. It should be understood that when the peak pressure has been reduced, the spring  74  will return the eccentric bearing  36  to its initial position each cycle, so that a full expansion of the combustion gases and operation on the maximum permitted compression ratio will be obtained each engine cycle.  
         [0029]    Referring now to FIG. 5, wherein like numerals indicate like or corresponding components to those of the first described embodiment, numeral  82  generally indicates a connecting rod assembly according to the invention including a connecting rod  28  having an eccentric bearing  84  which includes an eccentric central portion  38  connected with flanges  86  which are formed with peripheral cam surfaces  88 . A coil compression spring  90  is positioned around the shank of the connecting rod  28  and engages an upper spring retainer  92  fixed to the rod inward of the piston pin end. A second spring retainer  94  is engaged by the spring and includes a lower surface  96  which engages the cam surfaces  88  of the flanges  86 .  
         [0030]    In operation in an engine, the central portion  38  of the bearing  84  could be positioned in approximately the same angular initial and final positions as described with respect to the embodiment of FIGS.  1 - 4 . With an intended angular travel of 50°, for example, the cam will then be positioned as shown in FIG. 5 with the compression spring urging the cam and attached bearing in a counterclockwise direction against a stop, not shown, to establish the initial position of the bearing.  
         [0031]    When peak combustion gas pressures become sufficiently high, the force exerted by these pressures will cause the bearing  84  to rotate clockwise, as described regarding the first embodiment, rotating the cam surfaces to compress the coil spring  90  until, at a maximum pressure, the spring will be compressed to a second position wherein the cam is rotated about 500 from its initial position acting against a stop, not shown. This action will, as in the case of the earlier described embodiment, cause a reduction of compression ratio and a limiting of cylinder pressures so that normal operation at lower and medium loads with a higher compression ratio is made possible.  
         [0032]    Upon the reduction of the compression pressures during the down stroke, the cam will again be returned to its initial position, restoring the connecting rod to its initial effective length and returning the system to normal operation until the next excessive peak pressure occurs.  
         [0033]    It should be understood that in relation to both of the described embodiments, the angles of rotation of the bearing may be varied over a wide range depending upon the various forces including combustion pressures and inertias of the mechanism which may be involved. For the embodiment of FIGS.  2 - 4 , the initial (first angular) position of the bearing, the connecting rod eccentricity might reasonably be practical within a range of from about 75 to 0 degrees longitudinally upward from the relative lateral crankpin axis (parallel with the lateral axis of the connecting rod bore). Correspondingly, the maximum displaced position of the bearing could reasonably extend from about 0 to 75 degrees downward from the relative lateral crankpin axis. The embodiment of FIG. 5 might support varying ranges.  
         [0034]    [0034]FIGS. 6 and 7 illustrate an alternative operational concept for the embodiment of FIG. 5. The eccentric bearing  84  is shown in an initial position at 0° downward from (coextensive with) the relative lateral crankpin axis and the cam surfaces  88  are positioned at the lowest lift position (smallest diameter) engaging the spring bearing surfaces  96 . In this position, the effective lever arm force is at a maximum while the restraining force of the cams is essentially zero except for friction of the eccentric bearing  84  in its central portion  38  and at the cam surfaces  88 . A relatively low but increasing cylinder pressure will thus begin counterclockwise rotation of the bearing  84  eccentricity (at the axis  48  of the outer diameter) downward toward its lowest point below the axis  46  of the crankpin.  
         [0035]    As the bearing rotates, the effective lever arm becomes smaller while gas pressures become larger. If angular rotation of the bearing results in sufficient inertia, the bearing may reach the lowest point where the pointed ends of the cam surfaces  88  are centered against the bearing surface  96  of the lower spring retainer  92 . There, piston compression ratio reaches its lowest value and the spring return force is greatest but the lever arm is aligned with the longitudinal axis  59  of the connecting rod so there is no resulting force to rotate the bearing in either direction.  
         [0036]    Here it is conjectured that the bearing will most likely not reach the lowest eccentric point or, if it does, will be carried past it by rotational inertia or by operational forces on the connecting rod  28  and the bearing  84 . In either case, the spring  90  will act upon the cam surfaces  88  to return the bearing  84  toward its higher positions as gas pressure is reduced, until the lowest position of the cam is reached in either direction of cam rotation. This mode of operation could be helpful in evening out wear on the cams as well as increasing the potential eccentric travel of the bearing and the resulting variation in compression ratio of the engine piston in its cylinder.  
         [0037]    It should be apparent however that the described embodiments, as well as obvious alternatives thereof, may be utilized to provide a limiting of combustion pressures in an engine cylinder by effectively reducing the compression ratio when the combustion pressure becomes excessive. The mechanism has the advantage of being controlled completely by the actual compression pressures themselves rather than by a position modifying means. Thus the invention provides a simplified compression ratio or pressure control mechanism which can be applied in extending the operating range and compression ratios of internal combustion engines.  
         [0038]    The foregoing illustrations have been limited to exemplary embodiments wherein an eccentric bearing is provided at the crankpin end of a connecting rod. It should be appreciated, however, that similar results could be obtained by the use of a rotatable eccentric bushing located at the piston pin end of a connecting rod. When combined with a suitable spring arrangement allowing reduction of the compression ratio at high peak pressures, the operation would be similar to that previously described.  
         [0039]    As used in the claims, the phrase “a lateral (or longitudinal) axis of the crankpin relative to the connecting rod” refers, for example as shown in FIGS. 2A and 2B, to a lateral axis  56  of the crankpin which is parallel with a corresponding lateral axis  58  of the connecting rod bore  44  (or to a longitudinal axis  57  of the crankpin which is parallel to a corresponding longitudinal axis  59  of the connecting rod).  
         [0040]    While the invention has been described by reference to certain preferred embodiments, it should be understood that numerous changes could be made within the spirit and scope of the inventive concepts described. Accordingly, it is intended that the invention not be limited to the disclosed embodiments, but that it have the full scope permitted by the language of the following claims.