Abstract:
A variable compression ratio engine includes a control actuator which has a simple structure, seals well internally, and provides high reliability. In the variable compression ratio engine, a connecting rod is divided into at least two portions. A control rod is operatively connected to a juncture of the connecting rod. A support shaft position of the control rod is displaced. The control rod is operatively connected to a right cylinder rod of a piston-type double-acting hydraulic control cylinder. A piston section of the hydraulic control cylinder is configured to selectively move in accordance with displacement of the support shaft position of the control rod. A channel is used to connect two hydraulic chambers divided by the piston section. The channel is configured to selectively control the flow of hydraulic fluid from the right hydraulic chamber to the left hydraulic chamber, and vice versa.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     The present application claims priority under 35 U.S.C. 119 based on Japanese patent application 2003-193803, filed Jul. 8, 2003.  
       BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates to an engine having a variable compression ratio, and to methods of operating the engine. More particularly, the present invention relates to an engine in which the effective length of a connecting rod is made hydraulically adjustable to allow for adjustment of the compression ratio, and to methods of operating the described engine.  
         [0004]     2. Background Art  
         [0005]     Conventionally, it has been known that some vehicles such as cars may use a variable compression ratio engine, that provides an appropriate compression ratio according to driving conditions, by making an intermediate portion of a connecting rod flexibly adjustable. A flexing portion of the connecting rod needs to be movable while the engine is operating. Doing so requires a driving force of an actuator that exceeds the engine&#39;s inertia force, or an air-fuel mixture&#39;s explosion force acting on the flexing portion. Improving the control accuracy requires a large external energy or a complicated mechanism (see, e.g., Japanese published patent document JP-A 214770/2001).  
         [0006]     By contrast, another technology is described in Japanese published patent document JP-A 289079/2001. This technology uses the engine&#39;s inertia force and the air-fuel mixture&#39;s explosion force acting on an operating piston as a differently directed force alternately acting on the flexing portion of the connecting rod. This force is used to operate a control mechanism connected to the connecting rod&#39;s flexing portion via a control rod. The control mechanism comprises two arced spaces that are separated by a moving vane, and are filled with hydraulic fluid. The hydraulic fluid is selectively ported from one space to the other, via a check valve, against the above-mentioned differently directed force This makes it possible to change or retain a flexing orientation of the connecting rod.  
         [0007]     The technology described in Japanese published patent document JP-A 289079/2001 effectively uses the engine&#39;s inertia force and the air-fuel mixture&#39;s explosion force acting on the piston. There is an advantage of not requiring an extra power. However, the control mechanism is structured to be the two arced spaces that are separated by the moving vane. There are problems of complicating the structure and difficultly of ensuring sealability of the mechanism.  
         [0008]     Although the known variable compression ratio engines are useful, a need still esists for an improved variable compression ratio engine that has a simple structure, ensures sealability, and provides high reliability.  
       SUMMARY OF THE INVENTION  
       [0009]     To solve the above-mentioned problem, the present invention, according to a first aspect hereof, provides a variable compression ratio engine which divides a connecting rod into at least two portions, where the connecting rod converts vertical movement of a piston into rotary movement of a crankshaft. In the first aspect hereof, a control rod is operatively attached to a juncture of the connecting rod or to any one of a plurality of divided connecting rods. A support shaft position of the control rod may be displaced. The control rod is operatively connected to a cylinder rod of a piston-type, both rod type, double-acting hydraulic control cylinder. A piston section of the hydraulic control cylinder is configured to selectively move, in order to control displacement of a support shaft position of the control rod. According to another aspect hereof, a channel is used to connect two hydraulic chambers divided by the piston section, and the channel is configured to selectively control hydraulic fluid flow from the first hydraulic chamber to the second hydraulic chamber, and vice versa.  
         [0010]     The novel construction allows the connecting rod to be bent at a controlled angle, as will be described subsequently herein.  
         [0011]     A force is applied from the supporting position of the control rod to a cylinder rod attached to the piston of the hydraulic control cylinder. The hydraulic fluid flows through the channel from the first hydraulic chamber to the second hydraulic chamber, and vice versa. The piston section and the attached cylinder rod slide linearly, to change the flexing orientation of the connecting rod. The connecting rod orientation is held as follows. The channel is closed to prevent the hydraulic fluid from flowing through the hydraulic chambers. The piston section and the attached cylinder rod are prevented from sliding, to hold the flexing orientation of the connecting rod.  
         [0012]     The reciprocating piston-type hydraulic control cylinder is used to simplify the structure, improve the accuracy of fixing the compression ratio, and to promote internal sealability.  
         [0013]     A second aspect of the present invention is characterized in that part of the channel is provided with two branch channels which join downstream. The branch channels are provided with check valves having different directions; and a selector valve is used to choose between the branch channels.  
         [0014]     This construction enables the following. When the selector valve selects one of the branch channels, one check valve allows movement of the hydraulic fluid from the first hydraulic chamber to the second hydraulic chamber in the hydraulic control cylinder. When the selector valve selects the other branch channel, the other check valve allows movement of the hydraulic fluid from the second hydraulic chamber to the first hydraulic chamber in the hydraulic control cylinder.  
         [0015]     For a more complete understanding of the present invention, the reader is referred to the following detailed description section, which should be read in conjunction with the accompanying drawings. Throughout the following detailed description and in the drawings, like numbers refer to like parts. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0016]      FIG. 1  is a sectional view of an engine according to a selected illustrative embodiment of the present invention;  
         [0017]      FIG. 2  is a sectional detail view of part of the engine of  FIG. 1 , showing a position for a high compression ratio according to the selected embodiment of the present invention;  
         [0018]      FIG. 3  is a sectional detail view of part of the engine of  FIG. 1 , showing a position for a low compression ratio according to the selected embodiment of the present invention;  
         [0019]      FIG. 4  is a system diagram for the embodiment of the present invention;  
         [0020]      FIG. 5  is a partial system diagram for the embodiment of the present invention positioned to a high compression ratio; and  
         [0021]      FIG. 6  is a partial system diagram for the embodiment of the present invention positioned to a low compression ratio.  
     
    
     DETAILED DESCRIPTION  
       [0022]     Selected illustrative embodiments of the present invention will be described herein, with reference to the accompanying drawings. It should be understood that herein, only structures considered necessary for clarifying the present invention are described. Other conventional structures, and those of ancillary and auxiliary components of the system, are assumed to be known and understood by those skilled in the art.  
         [0023]     Referring now to  FIG. 1 , an engine  1  according to a selected illustrative embodiment of the invention is shown in cross-section. The engine  1  is usable for vehicles such as motorcycles and all-terrain vehicles, and is provided with structure and controls enabling it to operate with a variably adjustable compression ratio, as will be further described herein.  
         [0024]     The engine  1  includes a cylinder block  3 , which is attached to a crankcase  2 . The cylinder block  3  and crankcase  2  cooperate to define an engine block. A cylinder head  4  is mounted on top of the cylinder block  3 . A cylinder  5  is defined as a hollow cylindrical bore formed in the cylinder block  3 . A piston  6  is reciprocally movable in the cylinder  5 , along a two-way path extending in a substantially vertical direction.  
         [0025]     The cylinder head  4  is formed with an intake channel  7  and an exhaust channel  8  to provide respective flow paths for intake and exhaust air to travel to and from the cylinder  5 . Each channel aperture is provided with its own respective valve, including an intake valve  9  to open and close the intake channel  7 , and an exhaust valve  10  to open and close the exhaust channel  8 .  
         [0026]     A combustion chamber  12  is formed in the cylinder head  4  above an upper portion of the piston  6 . The combustion chamber  12  is defined as the space between the piston  6 , when it is positioned at top dead center, and a concave portion  11  of the cylinder head  4 .  
         [0027]     During operation of the engine  1 , the piston  6  is pressed downwardly, due to an explosion force generated by the ignition of an air-fuel mixture in the combustion chamber  12 . The air-fuel mixture is ignited by a spark plug (not shown) that pierces the cylinder head  4  and is provided with a tip end extending into the combustion chamber  12 . The vertical reciprocating motion of the piston  6  in the cylinder  5  is converted, via the connecting rod  13 , into rotary motion of a crankshaft  14 . The rotary motion is transmitted, not only to a transmission (not shown), but also to a valve train  15  for operating the intake valve  9  and the exhaust valve  10 .  
         [0028]     According to the practice of the present invention, the connecting rod  13  is subdivided into an upper rod member  16  and a lower rod member  17 . In the depicted embodiment, the bottom end of the upper rod member  16  is rotatably connected to a top end of the lower rod member  17  via a coupling pin  18 , provided parallel to an axial direction of the crankshaft  14 . The connecting rod  13  can flex in a dogleg shape at an intermediate portion thereof, designated as a flexing portion K. A small end SE of the connecting rod  13  is formed at the top end of the upper rod member  16 , and is rotatably attached to the piston  6  via a piston pin  19 . A big end BE of the connecting rod  13  is formed at the bottom end of the lower rod member  17 , and is rotatably attached to a crankpin  20 . Reference numeral  22  indicates the rotary center of the crankshaft  14 .  
         [0029]     A control rod  21  is connected, via the coupling pin  18 , to the flexing portion K of the connecting rod  13 , so as to adjust a flexing degree of the connecting rod  13 . The control rod  21  is an almost horizontally extending bar-shaped member. The compression ratio of the engine is able to be variably adjusted by moving the control rod  21  to vary the position of the coupling pin  18 , thereby adjusting the effective length of the connecting rod  13 . A base of the control rod  21  is axially supported by a pin  23  which is provided parallel to the crankshaft  14  at one end of a lever arm  25 , to be discussed in more detail below. The tip of the control rod  21  is joined to the connecting rod  13  via the coupling pin  18 , and is rotatably and axially supported by the juncture formed between the bottom end of the upper rod member  16  and the top end of the lower rod member  17 . As previously noted, the coupling pin  18  also connects the bottom end of the upper rod member  16  and the top end of the lower rod member  17  together. Accordingly, the control rod  21  regulates a locus of the flexing portion K for the connecting rod  13 .  
         [0030]     The pin  23  is provided at one end of the lever arm  25  supported by the crankcase  2 , and regulates the oscillation center of the control rod  21 . The lever arm  25  is a bent member formed in a dogleg shape. The lever arm  25  is rotatably supported in the crankcase  2  via a support shaft  26 , located approximately at the center of the lever arm  25 , and provided parallel to the crankshaft  14 . The support shaft  26  is substantially fixed in place in relation to the crankcase  2 .  
         [0031]     The upper end of the lever arm  25  is provided with the pin  23  that axially supports the base of the control rod  21 . The lower end of the lever arm  25  is operatively connected to an end of a right cylinder rod  28  of a hydraulic control cylinder  27 .  
         [0032]     When a piston section  35  of the hydraulic control cylinder  27  to be described is positioned to the neutral, the lever arm  25  is supported in the crankcase  2  so that a portion below the support shaft  26  moves almost downward. This provides almost the same horizontal pivot angle as that generated when the portion below the support shaft  26  of the lever arm  25  moves horizontally.  
         [0033]     The hydraulic control cylinder  27  is fixed, via a bracket  30 , to the crankcase  2  with a series of bolts  31 . The hydraulic control cylinder  27  is a piston-type, dual rod type, and double-acting hydraulic control cylinder. End caps  33  are fixed with bolts  34  at both ends of a cylindrical casing  32 . Inside the casing  32 , a piston section  35  is movably provided so as to slide along an inside surface of a cylindrical bore  52  formed inside of the casing  32 . Both ends of the piston section  35  are provided with respective cylinder rods extending outwardly therefrom, including a right cylinder rod  28  and a left cylinder rod  29  protruding from the corresponding end caps  33 . The piston section  35  and the left cylinder rod  29  are molded integrally.  
         [0034]     An outside periphery of the piston section  35  is provided with a seal  36  so as to be sealed against an inside peripheral surface of the bore  52  formed inside of the casing  32 . Insertion holes  37  are provided for the cylinder rods  28  and  29  corresponding to the end caps  33 . Inside peripheries of the insertion holes  37  are provided with seals  38  for sealing between the right cylinder rod  28  and the left cylinder rod  29 . Each end cap  33  has a boss  39  protruding into the casing  32 . An outside peripheral surface of the boss  39  is provided with a seal  40  in close contact with the inside peripheral surface of the bore  52  formed in the casing  32 .  
         [0035]     A vertical slot  41  is formed in a tip of the right cylinder rod  28 . A pin  42  is provided at the lower end of the lever arm  25 , and is inserted into the vertical slot  41 . The tips of the lever arm  25  and the right cylinder rod  28  are rotatably supported so as to enable free vertical movement of the pin  42  in the vertical slot. When the bottom end of the lever arm  25  pivots around the support shaft  26 , provision of the vertical slot  41  enables the pin  42  to allow a displacement below the shaft center of the right cylinder rod  28  in the hydraulic control cylinder  27 .  
         [0036]     As shown in  FIG. 2 , let us assume that the piston section  35  in the hydraulic control cylinder  27  is positioned at the left end of the casing  32 . In this case, the lever arm  25  pivots around the support shaft  26 , via the right cylinder rod  28 , moving the upper end thereof to the right as shown in the drawing. The control rod  21  accordingly moves to the right end of its travel range. This causes a small angle formed by the upper rod member  16  and the lower rod member  17  so that the flexing portion K approximates to be more straight. This also causes the longest distance between the piston pin  19  and the crankpin  20  for the connecting rod  13 , comprising the upper rod member  16  and the lower rod member  17 . As a result, the piston will travel to its highest level in the cylinder block  3 , and a compression ratio of the engine  1  becomes maximum. In this case, the compression ratio is found by adding a stroke volume to a combustion chamber volume and then dividing a result by the combustion chamber volume.  
         [0037]     On the other hand, as shown in  FIG. 3 , let us assume that the piston section  35  in the hydraulic control cylinder  27  is positioned at the right end of the casing  32 . In this case, the lever arm  25  rotates around the support shaft  26  via the right cylinder rod  28 , moving the upper end thereof to the left. The control rod  21 , accordingly, moves to the left end of its range of travel. This causes a larger angle formed by the upper rod member  16  and the lower rod member  17  so that the flexing portion K bends more remarkably. This also causes the shortest distance between the piston pin  19  and the crankpin  20  for the connecting rod  13  comprising the upper rod member  16  and the lower rod member  17 . As a result, the height of the piston at the top of its travel is reduced, and the compression ratio of the engine  1  becomes minimum.  
         [0038]     As shown in  FIG. 4 , the piston section  35  divides a hydraulic chamber, defined within the bore  52  of the casing  32 , into right and left chambers  43 ,  44 , respectively. In the casing  32 , a right hydraulic chamber  43  is formed surrounding the right cylinder rod  28 , to the right side of the piston section  35 . A left hydraulic chamber  44  is formed surrounding the left cylinder rod  29 , to the left side of the piston section  35 . The right hydraulic chamber  43  is connected to the left hydraulic chamber  44  via a channel  45 .  
         [0039]     Part of the channel  45  is provided with two branch channels  46  and  47  that join downstream. The branch channels  46  and  47  are respectively provided with check valves  48  and  49 , having different flow directions. The check valve  48  permits flow of the hydraulic fluid from the right hydraulic chamber  43  to the left hydraulic chamber  44 . The check valve  49  permits flow of the hydraulic fluid from the left hydraulic chamber  44  to the right hydraulic chamber  43 .  
         [0040]     A selector valve  50  operates under control of an Electronic Control Unit (ECU)  51 . Operating the selector valve  50  selects one of the branch channels  46  and  47 , and closes the other ( FIGS. 5 and 6 ) or closes both ( FIG. 4 ). The ECU  51  is omitted from  FIGS. 5 and 6 .  
         [0041]     More specifically,  FIG. 5  shows that the selector valve  50  closes the branch channel  46  and selects the branch channel  47 . This enables a position for the high compression ratio. In this case, the hydraulic fluid is allowed to move in the channel from the left hydraulic chamber  44  to the right hydraulic chamber  43  via the branch channel  47 .  FIG. 6  shows that the selector valve  50  closes the branch channel  47  and selects the branch channel  46 . This enables a position for the low compression ratio. In this case, the hydraulic fluid is allowed to move in the channel from the right hydraulic chamber  43  to the left hydraulic chamber  44  via the branch channel  46 .  FIG. 4  shows that the selector valve  50  closes both the branch channels  46  and  47  (hold position). The hydraulic fluid is prevented from moving between the left hydraulic chamber  44  and the right hydraulic chamber  43 , locking the hydraulic control cylinder  27 . While there has been described in  FIG. 4  that the piston section  35  is held at the center of the casing  32 , it is to be distinctly understood that the piston section  35  can be held at any position.  
         [0042]     The selector valve  50  is operated based on a signal from the ECU  51 . For this purpose, the ECU  51  is supplied with sensor signals for crank angles, engine speeds (Ne), intake manifold pressures (Pb), throttle angles, and the like.  
         [0043]     According to the above-mentioned embodiment, the engine  1  may need to change to the high compression ratio based on sensor signals for the crank angle, the engine speed, the intake manifold pressure, and the throttle angle supplied to the ECU  51 . In such case, the ECU  51  sends a signal to change the selector valve  50  to the high compression ratio position in  FIG. 5  and select the branch channel  47 . A vertical movement of the piston  6  applies a load on the lever arm  25  from the flexing portion K of the connecting rod  13  via the control rod  21 . A load is applied to the lever arm  25  to rotate it counterclockwise in vain, because the check valve  49  prevents movement of the hydraulic fluid from the right hydraulic chamber  43  to the left hydraulic chamber  44 .  
         [0044]     Let us assume that a load is applied to rotate the lever arm  25  clockwise. The check valve  49  permits movement of the hydraulic fluid from the left hydraulic chamber  44  to the right hydraulic chamber  43 . Consequently, the piston section  35  of the hydraulic control cylinder  27  moves to the left by pushing the hydraulic fluid out of the left hydraulic chamber  44  to the right hydraulic chamber  43 . This allows clockwise rotation of the lever arm  25 . The connecting rod  13  changes its orientation to the high compression ratio side as shown in  FIG. 5 . Then, setting the selector valve  50  to the hold position allows the connecting rod  13  to maintain the orientation for the high compression ratio.  
         [0045]     The engine may need to be changed to the low compression ratio. In such case, the ECU  51  outputs a signal to change the selector valve  50  to the low compression ratio position in  FIG. 6  and select the branch channel  46 . A vertical movement of the piston  6  applies a load on the lever arm  25  from the flexing portion K of the connecting rod  13  via the control rod  21 . A load is applied to the lever arm  25  to rotate it clockwise in vain because the check valve  49  prevents movement of the hydraulic fluid from the left hydraulic chamber  44  to the right hydraulic chamber  43 .  
         [0046]     Let us assume that a load is applied to rotate the lever arm  25  counterclockwise. The check valve  48  permits movement of the hydraulic fluid from the right hydraulic chamber  43  to the left hydraulic chamber  44 . Consequently, the piston section  35  of the hydraulic control cylinder  27  moves to the right by pushing the hydraulic fluid out of the right hydraulic chamber  43  to the left hydraulic chamber  44 . This allows counterclockwise rotation of the lever arm  25 . The connecting rod  13  changes its orientation to the low compression ratio side as shown in  FIG. 6 . Then, setting the selector valve  50  to the hold position allows the connecting rod  13  to maintain the orientation for the low compression ratio.  
         [0047]     When a desired compression ratio is obtained, setting the selector valve  50  to the hold position can hold the piston section  35  at that position. The engine  1  can operate at an optimum compression ratio.  
         [0048]     As a result, it is possible to efficiently use a driving force of the engine  1  acting on the lever arm  25 . The hydraulic fluid moves through the branch channel  46  or  47  selected by the selector valve  50  with the flowing direction restricted by the check valve  48  or the check valve  49 . This makes it possible to move the hydraulic control cylinder  27  in a specified direction. The connecting rod  13  can be maintained between the high compression ratio and the low compression ratio without applying an extra power.  
         [0049]     The reciprocating piston-type hydraulic control cylinder  27  is used to simplify the structure, improve the accuracy of fixing the compression ratio, and to ensure sealability for the seals  36  and  38 . It is possible to provide high durability and reliability after long-term use.  
         [0050]     That is to say, the seal  36  just needs to ensure sealability during simple reciprocating slides of the piston section  35 . The seal  38  just needs to ensure sealability during simple reciprocating slides of the right cylinder rod  28  and the left cylinder rod  29 . These are advantageous to ensuring sealability.  
         [0051]     The present invention is not limited to the above-mentioned embodiment. For example, the present invention can be applied to not only motorcycle engines, but also vehicle engines in general. There has been described the case where the control rod  21  is operatively connected to the coupling pin  18 , i.e., a junction between the upper rod member  16  and the lower rod member  17 . Further, the control rod  21  may be operatively connected to the upper rod member  16  and the lower rod member  17  near the coupling pin  18 .  
         [0052]     [Effects of the Invention] 
         [0053]     As mentioned above, the first aspect of the present invention allows the connecting rod to be bent as follows. A force is applied from the supporting position of the control rod to one of both cylinder rods attached to the piston of the hydraulic control cylinder. The hydraulic fluid flows through the channel from the the first hydraulic chamber to the second hydraulic chamber, and vice versa. The piston, i.e., the cylinder rod linearly slides to change the flexing orientation of the connecting rod. The connecting rod orientation is held as follows. The channel is closed to prevent the hydraulic fluid from flowing through the hydraulic chambers. The piston, i.e., the cylinder rod is prevented from sliding to hold the flexing orientation of the connecting rod. There is an effect of operating the engine at an optimum compression ratio by efficiently using the engine&#39;s inertia force and the air-fuel mixture&#39;s explosion force.  
         [0054]     Especially, the reciprocating piston-type hydraulic control cylinder is used to simplify the structure, improve the accuracy of fixing the compression ratio, and easily ensuring sealability. It is possible to provide high durability and reliability after long-term use.  
         [0055]     The second aspect of the present invention enables the following. When the selector valve selects one of the branch channels, one check valve allows movement of the hydraulic fluid from the first hydraulic chamber to the second hydraulic chamber in the hydraulic control cylinder. When the selector valve selects the other branch channel, the other check valve allows movement of the hydraulic fluid from the other check valve to the first hydraulic chamber in the hydraulic control cylinder. It is possible to easily ensure sealability and improve the accuracy of fixing the compression ratio even for the simple construction using the reciprocating piston-type hydraulic control cylinder. There is an effect of providing high reliability.  
         [0056]     Although the present invention has been described herein with respect to a number of specific illustrative embodiments, the foregoing description is intended to illustrate, rather than to limit the invention. Those skilled in the art will realize that many modifications of the preferred embodiment could be made which would be operable. All such modifications, which are within the scope of the claims, are intended to be within the scope and spirit of the present invention.