Abstract:
A variable compression ratio device having a piston, a crankshaft, a connecting rod including a small end portion connected to the piston, may include a piston pin fixed to the connecting rod and fixed thereto, a receiving hole formed inside the piston and rotatably receiving the piston pin, wherein the receiving hole includes a convex portion and a concave portion, at least a variable pin slidably coupled to the piston pin and slidably coupled to the interior circumference of the receiving hole, wherein the at least a variable pin has a protrusion, and an oil supply passage selectively supplying oil to apply hydraulic pressure to the at least a variable pin, wherein the protrusion of the at least a variable pin is selectively coupled to the convex portion or the concave portion of the receiving hole.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     The present application claims priority to Korean Patent Application No. 10-2009-0094824 filed on Oct. 6, 2009, the entire contents of which is incorporated herein for all purposes by this reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a variable compression ratio device, and more particularly to a variable compression ratio device that is capable of changing a compression ratio of a mixture in a combustion chamber corresponding to driving conditions of an engine. 
     2. Description of Related Art 
     Generally, thermal efficiency of combustion engines increases as the compression ratio thereof increases, and if ignition timing is advanced to some degree, thermal efficiency of spark-ignition engines increases. 
     However, if the ignition timing of the spark-ignition engines is advanced at a high compression ratio, abnormal combustion may occur and the engine may be damaged. Thus, the ignition timing cannot be advanced a large amount and accordingly engine output may deteriorate. 
     A variable compression ratio (VCR) apparatus changes the compression ratio of an air-fuel mixture according to a driving state of an engine. 
     The variable compression ratio apparatus raises the compression ratio of the air-fuel mixture at a low-load condition of the engine in order to improve fuel mileage. On the contrary, the variable compression ratio apparatus lowers the compression ratio of the air-fuel mixture at a high-load condition of the engine in order to prevent occurrence of knocking and improve engine output. 
     A conventional variable compression ratio apparatus can achieve a predetermined compression ratio of the air-fuel mixture according to a driving state of the engine, but it cannot achieve different strokes corresponding to intake/compression/expansion/exhaust strokes, respectively. 
     Particularly, if the expansion stroke is longer than that of the compression stroke, thermal efficiency may further improve. However, it is difficult to achieve a longer expansion stroke than compression stroke according to the conventional variable compression ratio apparatus. 
     In addition, a high compression ratio/low exhaust amount at a low load condition and a low compression ratio/high exhaust amount at a high load condition may be preferable in order to achieve low fuel consumption and high power output. 
     Herein, since oil pressure or an electric motor etc. must be provided as an actuator in order to change the compression ratio, a pump size is increased and electrical load is increased due to a large capacity electric motor. 
     The information disclosed in this Background of the Invention section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art. 
     BRIEF SUMMARY OF THE INVENTION 
     Various aspects of the present invention are directed to provide a variable compression ratio device having advantages of reducing the number of parts because of not using oil pressure or an electric motor for rotating an eccentric bearing. 
     In an aspect of the present invention, the variable compression ratio device having a piston, a crankshaft, a connecting rod including a small end portion rotatably connected to the piston and a large end portion rotatably connected to the crankshaft and converting reciprocative motion of the piston to rotary motion of the crankshaft, may include a piston pin that passes through the small end portion of the connecting rod and fixed thereto, a receiving hole formed inside the piston and rotatably receiving the piston pin therein, wherein the receiving hole includes a convex portion and a concave portion along an interior circumference thereof, at least a variable pin slidably coupled to an exterior circumference of the piston pin and slidably coupled to the interior circumference of the receiving hole, wherein the at least a variable pin has a protrusion at an exterior circumference thereof, and an oil supply passage selectively supplying oil to apply hydraulic pressure to the at least a variable pin so as to slidably move the at least a variable pin along the piston pin, wherein the protrusion of the at least a variable pin is selectively coupled to the convex portion or the concave portion of the receiving hole to change a distance between an upper surface of the piston and a center axis of the piston pin. 
     The concave and convex portions of the receiving hole may be formed in the piston by turns so as to be symmetrical with respect to the small end portion, and wherein the at least a variable pin constitutes a pair and are controlled so as to be moved closer to or farther from each other by the hydraulic pressure supplied from the oil supply passage. 
     The pair of variable pins are slidably coupled to both end portions of the piston pin and controlled to be moved closer to or farther from each other by the hydraulic pressure supplied from the oil supply passage. 
     The device may further include a flange protruding outwardly from respective variable pin and hydraulic pressure of the oil supply passage is selectively applied to one side of the flange to move the respective variable pin, and an elastic member supporting the other side of the flange, wherein the elastic member exerts an elastic force on the other side of the flange so as to move the pair of variable pins closer to each other when the hydraulic pressure of the oil supply passage is released. 
     The device may further include a sliding pin that is slidably coupled to the small end portion of the connecting rod and selectively moved by the hydraulic pressure of the oil supply passage to pressurize the one side of the flange to move the respective valve pin, wherein the oil supply passage is disposed inside the connecting rod and supplies the hydraulic pressure to an end of the sliding pin to move the respective variable pin. 
     The protrusion of the at least a variable pin may include an upper protrusion that is formed at an upper portion of the exterior circumference of the at least a variable pin so as to protrude eccentric upwardly from a central axis of the at least a variable pin, and a lower protrusion that is disposed at a lower portion of the exterior circumference of the at least a variable pin so as to protrude eccentric downwardly from the central axis of the at least a variable pin, wherein the upper protrusion and the lower protrusion are alternatively formed along a longitudinal axis of the at least a variable pin. 
     The convex portion may include an upper convex portion and an upper concave portion formed in sequence in an upper inner circumference of the receiving hole, and a lower convex portion and a lower concave portion formed in sequence in a lower inner circumference of the receiving hole, wherein the upper protrusion is selectively engaged with the upper convex or concave portion and the lower protrusion is selectively engaged with the lower concave or convex portion. 
     A horizontal thickness of the upper projection may be smaller than a horizontal thickness of the upper concave portion and a horizontal thickness of the lower projection is smaller than a horizontal thickness of the lower concave portion. 
     The upper and lower concave portions may be integrally formed with a circular shaped groove and the upper and lower convex portions are integrally formed with a circular shape between the upper and lower concave portions. 
     The upper protrusion may be engaged with the upper convex portion and the lower protrusion is engaged with the lower concave portion when the hydraulic pressure is released from the oil supply passage to decrease a distance between the upper surface of the piston and the center axis of the piston pin, and wherein the upper protrusion is engaged with the upper concave portion and the lower protrusion is engaged with the lower convex portion when the hydraulic pressure is applied to the at least a variable pin to increase a distance between the upper surface of the piston and the center axis of the piston pin. 
     The methods and apparatuses of the present invention have other features and advantages which will be apparent from or are set forth in more detail in the accompanying drawings, which are incorporated herein, and the following Detailed Description of the Invention, which together serve to explain certain principles of the present invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an exploded view of an exemplary variable compression ratio apparatus according to the present invention. 
         FIG. 2  is a cross-sectional view of an exemplary variable compression ratio apparatus according to the present invention. 
         FIG. 3  shows an operating state of an exemplary variable compression ratio apparatus according to the present invention. 
     
    
    
     It should be understood that the appended drawings are not necessarily to scale, presenting a somewhat simplified representation of various features illustrative of the basic principles of the invention. The specific design features of the present invention as disclosed herein, including, for example, specific dimensions, orientations, locations, and shapes will be determined in part by the particular intended application and use environment. 
     In the figures, reference numbers refer to the same or equivalent parts of the present invention throughout the several figures of the drawing. 
     DETAILED DESCRIPTION OF THE INVENTION 
     Reference will now be made in detail to various embodiments of the present invention(s), examples of which are illustrated in the accompanying drawings and described below. While the invention(s) will be described in conjunction with exemplary embodiments, it will be understood that present description is not intended to limit the invention(s) to those exemplary embodiments. On the contrary, the invention(s) is/are intended to cover not only the exemplary embodiments, but also various alternatives, modifications, equivalents and other embodiments, which may be included within the spirit and scope of the invention as defined by the appended claims. 
     An exemplary embodiment of the present invention will hereinafter be described in detail with reference to the accompanying drawings. 
       FIG. 1  is an exploded view of a variable compression ratio device according to an exemplary embodiment of the present invention. 
       FIG. 2  is a cross-sectional view of a variable compression ratio device according to an exemplary embodiment of the present invention. 
       FIG. 3  shows an operating state of a variable compression ratio device according to an exemplary embodiment of the present invention. 
     Referring to  FIG. 1 , a variable compression ratio device according to an exemplary embodiment of the present invention includes a piston  100  reciprocally moving inside a cylinder (not shown), a crankshaft  300  converting reciprocative motion of the piston  100  to rotary motion through a connecting rod  200  connected to the piston  100 , a piston pin  110  fixedly inserted in a small end portion  5  of the connecting rod  200 , and a variable pin  120  mounted around the piston pin  110 . 
     The piston pin  110  penetrates the inside of the piston  100 , and simultaneously the variable pin  120  is mounted around the piston pin  110 . 
     Further, a protrusion  121  is formed at an exterior circumference of the variable pin  120 , and receiving hole  101  is formed at an interior circumference of the piston  100  so as to correspond to the protrusion  121 . 
     Herein, the protrusion  121  includes an upper protrusion  121   a  and a lower protrusion  121   b  that are each eccentric. 
     The upper protrusion  121   a  is eccentric upwardly from a central axis of the variable pin  120 , and the lower protrusion  121   b  is eccentric downwardly from a central axis of the variable pin  120 . 
     Further, the variable pin  120  is slidably mounted at an exterior circumference of the piston pin  110  in an axial direction thereof, and the protrusion  121  is selectively engaged with concave portion  101   a  and  101   d  or convex portion  101   b  and  101   c  of the receiving hole  101 . 
     Therefore, the protrusion  121  is formed as an upper protrusion  121   a  and a lower protrusion  121   b , and the receiving hole  101  includes the upper concave portion  101   a  and an upper convex portion  101   b , the lower convex portion  101   c  and a lower concave portion  101   d , engaging or disengaging with the protrusion  121 . 
     Herein, a plurality of the upper concave portions  101   a  and the lower concave portion  101   d  are integrally formed at an interior circumference of the piston  100  as circular-shaped grooves, and the upper convex portion  101   b  and the lower convex portion  101   c  are integrally formed at an interior circumference of the piston  100  as circular-shape between the concave portions  101   a  and  101   d.    
     The upper protrusion  121   a  is formed so as to be selectively engaged or disengaged with the upper concave portion  101   a , and in this way, the lower protrusion  121   b  is formed so as to be selectively engaged or disengaged with the lower concave portion  101   d.    
     As shown in (A) of  FIG. 3 , when the lower protrusion  121   b  is engaged with the lower concave portion  101   d , the height of the piston  100  is increased. 
     At this time, the upper protrusion  121   a  upwardly supports the upper convex portion  101   b.    
     On the contrary, when the upper protrusion  121   a  is engaged with the upper concave portion  101   a , the height of the piston  100  is decreased. 
     The lower protrusion  121   b  also downwardly supports the lower convex portion  101   d.    
     Thus, as the variable pin  101  is slid, the upper protrusion  121   a  of the variable pin  101  or the lower protrusion  121   b  are selectively engaged with the upper concave portion  101   a  and lower concave portion  101   d  of the receiving hole  101 , so the height of the piston  100  is increased or decreased. 
     Further, flanges  123  are vertically formed at a surface facing each other between the variable pins  120 . 
     Herein, an elastic member  133  is formed such that both sides of the flanges  123  are moved closer to each other. 
     Thus, the elastic member  133  is formed as rectangular-shaped frame so as to inwardly exert a force on the flanges  123 . 
     Further, a pin hole  150  is formed at both surfaces of the small end portion  5  of the connecting rod  200 . 
     Sliding pins  140  are respectively inserted into both sides of the pin hole  150 . 
     Further, as shown in  FIG. 2 , an oil supply passage  210  is formed inside the small end portion  5  of the connecting rod  200  so as to communicate with the pin hole  150 . 
     Herein, an oil control valve  400  may be provided to supply oil to the oil supply passage  210 . 
     When the oil is supplied to the oil supply passage  210  by the oil control valve  400 , the sliding pins  140  are moved outwardly. 
     Hereinafter, an operation of the variable compression ratio device according to an exemplary embodiment of the present invention will be described. 
     As shown in  FIG. 3 , the flange  123  is pushed inwardly by the elastic force of the elastic member  133  when oil is not supplied from the oil control valve  400 , and the upper protrusion  121   a  upwardly supports the upper convex portion  101   b.    
     Therefore, the height of the piston  100  is maintained by the support of the protrusion  121 , wherein a distance between the upper surface of the piston  100  and a center axis of the piston pin  100  is increased. 
     That is, a high compression ratio for the compressed air is realized by the increase of the height of the piston  100 . 
     Meanwhile, as shown in (B) of  FIG. 3 , when oil is supplied to the oil supply passage  210  of the connecting rod  200  by the oil control valve  400 , the sliding pins  140  are moved farther from each other. 
     At this time, the sliding pin  140  supports an interior surface of each variable pin  120 , and then move the variable pins  120  outwardly against an elastic force of the elastic member  133  encompassing the variable pin  120 . 
     The variable pins  120  slide along an exterior circumference of the piston pin  110  so as to be farther from each other. 
     At this time, the upper protrusion  121   a  of the variable pin  120  is set into the upper concave portion  101   a , and the height of the variable pin  120  is changed as the height of the piston  100  is decreased as a distance of the upper protrusion  121   a  engaged with the upper concave portion  101   a  changes such that a distance between the upper surface of the piston  100  and a center axis of the piston pin  100  is decreased. 
     Thus, the height of the piston  100  is changed as the height of the piston pin  110  is disposed to be coaxial with the variable pin  120 . 
     Therefore, by changing the height of the piston  100 , the compression ratio of the cylinder is changed. 
     As can been seen from the forgoing, the variable compression ratio device according to an exemplary embodiment of the present invention has advantages of reducing the number of parts because of not using oil pressure or an electric motor for rotating an eccentric bearing. 
     Further, because only design of a connecting rod and a piston is needed, and not for a crankshaft, the design is simplified and web inertia of the crankshaft is minimized. 
     For convenience in explanation and accurate definition in the appended claims, the terms “upper”, “lower”, “interior”, “exterior”, “inner,” and “outer” are used to describe features of the exemplary embodiments with reference to the positions of such features as displayed in the figures. 
     The foregoing descriptions of specific exemplary embodiments of the present invention have been presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the invention to the precise forms disclosed, and obviously many modifications and variations are possible in light of the above teachings. The exemplary embodiments were chosen and described in order to explain certain principles of the invention and their practical application, to thereby enable others skilled in the art to make and utilize various exemplary embodiments of the present invention, as well as various alternatives and modifications thereof. It is intended that the scope of the invention be defined by the Claims appended hereto and their equivalents.