Patent Publication Number: US-8539917-B2

Title: Variable compression ratio apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority to and the benefit of Korean Patent Application No. 10-2010-0113838 filed Nov. 16, 2010, the entire contents of which application is incorporated herein for all purposes by this reference. 
     BACKGROUND OF INVENTION 
     1. Field of Invention 
     The present invention relates to a variable compression ratio apparatus. More particularly, the present invention relates to a variable compression ratio apparatus which changes compression ratio of an air-fuel mixture in a combustion chamber according to a driving condition 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 excessively advanced 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 condition of the 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. 
     According to a conventional variable compression ratio apparatus, a variable compression ratio is achieved by changing a length of a connecting rod which connects a piston to a crankshaft. Such types of a variable compression ratio apparatus include a plurality of links connecting a piston with the crankshaft, and combustion force is directly transmitted to the links. So, durability of the links deteriorates. 
     It becomes known to a person skilled in the art through various experimental results conducted to a conventional variable compression ratio apparatus that operation reliability is high in a case that a distance between a crank pin and a piston pin is changed by using an eccentric bearing. If hydraulic pressure, however, is used for rotating the eccentric bearing, a rotating angle of the eccentric bearing in each cylinder or hydraulic pressure applied to each cylinder is different. So, a compression ratio in a cylinder is different from that in another cylinder and a time required for changing the compression ratio according to the driving condition of the engine is varied in each cylinder. 
     Since a plurality of links is used for rotating the eccentric bearing, moving mass may increase. Therefore, load applied to the eccentric bearing becomes increase and balance weight becomes heavier. 
     Further, since additional space for mounting the plurality of links is necessary at one side portion of the engine, installability of the engine may be deteriorated. 
     The information disclosed in this Background 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. 
     SUMMARY OF INVENTION 
     The present invention has been made in an effort to provide a variable compression ratio apparatus having advantages of reducing moving mass as a consequence of minimizing the number of links for rotating an eccentric bearing. 
     Various aspects of the present invention provide for a variable compression ratio apparatus which can be mounted at an engine without increasing a volume thereof is provided. 
     Various aspects of the present invention provide for a variable compression ratio apparatus in which link members for rotating a connecting rod and link members for rotating an eccentric bearing are kinematically separated and combustion force of air-fuel mixture delivered to the link members can be minimized is provided. 
     A variable compression ratio apparatus according to various aspects of the present invention may be mounted at an engine receiving combustion force of an air-fuel mixture from a piston and rotating a crankshaft, and may change compression ratio of the air-fuel mixture. The variable compression ratio apparatus including a connecting rod having a small end and a big end, the small end being formed of an eccentric bearing hole concentrically so as to be rotatably connected to the piston through a piston pin, and the crankshaft is rotatably mounted at the big end, an eccentric link having one end to which an eccentric bearing rotatably mounted in the eccentric bearing hole concentrically is connected, an eccentric link slot being formed along a length direction thereof, a variable bar formed of a variable bar gear at one end portion thereof, and connected to the eccentric link through a variable bar pin movable along the eccentric link slot, and a variable gear engaged with the variable bar gear so as to move the variable bar to a predetermined direction reciprocally, wherein a piston pin hole is formed at the eccentric bearing eccentrically, and the piston pin is inserted in the piston pin hole such that the piston, the connecting rod, and the eccentric link are rotatably connected to each other. 
     In a case that the variable bar moves to the predetermined direction, the variable bar pin may move along the eccentric link slot so as to rotate the eccentric link. 
     The eccentric bearing may be integrally formed with the eccentric link. 
     The piston may be adapted to move upwardly or downwardly in a cylinder block liner, and the crankshaft may be adapted to rotate in a crank case. A sliding groove may be formed horizontally at a connecting portion of the cylinder block liner and the crank case such that the variable bar is movable in the sliding groove horizontally. 
     The variable compression ratio apparatus may further include an actuator, wherein the variable gear is rotated according to a driving condition of the engine by the actuator. 
     A variable compression ratio apparatus according to other aspects of the present invention may include a connecting rod having one end connected to the piston and the other end connected to the crankshaft so as to deliver the combustion force of the air-fuel mixture to the crankshaft, an eccentric link having one end to which an eccentric bearing mounted at the one end of the connecting rod is connected and an eccentric link slot formed along a length direction thereof, a piston pin eccentrically mounted at the one end of the connecting rod and the eccentric bearing so as to connect the connecting rod, the eccentric bearing, and the piston, and changes a distance between a center of the eccentric bearing and an upper end of the piston according to a rotation of the eccentric bearing, a variable bar formed of a variable bar gear at one end portion thereof, a variable gear engaged to the variable bar gear so as to move the variable bar to a predetermined direction reciprocally, and a variable bar pin connecting the variable bar with the eccentric link slot, and moving along the eccentric link slot so as to rotate the eccentric bearing in a case that the variable bar moves to the predetermined direction. 
     The eccentric bearing may be inserted in an eccentric bearing hole formed at the one end of the connecting rod concentrically, and the piston pin may be inserted in a piston pin hole formed at the eccentric bearing eccentrically. 
     The eccentric bearing may be integrally formed with the eccentric link. 
     The piston may be adapted to move upwardly or downwardly in a cylinder block liner, and the crankshaft may be adapted to rotate in a crank case. A sliding groove may be formed horizontally at a connecting portion of the cylinder block liner and the crank case such that the variable bar is movable in the sliding groove horizontally. 
     The variable compression ratio apparatus may further include an actuator, wherein the variable gear is rotated according to a driving condition of the engine by the actuator. 
     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, which together serve to explain certain principles of the present invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a cross-sectional view of an exemplary variable compression ratio apparatus according to the present invention which is operated at a low compression ratio. 
         FIG. 2  is a cross-sectional view of an exemplary variable compression ratio apparatus according to the present invention which is operated at a high compression ratio. 
     
    
    
     DETAILED DESCRIPTION 
     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. 
     As shown in  FIG. 1  and  FIG. 2 , a variable compression ratio apparatus  1  according to various embodiments of the present invention is mounted at an engine which receives combustion force of air-fuel mixture from a piston  10  and rotates a crankshaft  30 . The variable compression ratio apparatus  1  changes compression ratio of the air-fuel mixture according to a driving condition of the engine. 
     The engine includes a cylinder block liner  2  and a crank case  4 , and the crank case  4  is coupled to a lower portion of the cylinder block liner  2 . A sliding groove  6  is formed horizontally at a connecting portion of the cylinder block liner  2  and the crank case  4 . 
     The piston  10  is installed in the cylinder block liner  2  and moves upwardly or downwardly in the cylinder block liner  2  by the combustion force of the air-fuel mixture. A combustion chamber is formed between the piston  10  and the cylinder, and the air-fuel mixture is flowed into the combustion chamber and is burned. 
     The crankshaft  30  receives the combustion force from the piston  10  and converts the combustion force into torque so as to deliver it to a transmission. The crankshaft  30  is mounted in the crank case  4 . The crankshaft  30  includes a crank pin  32  formed eccentrically to the crankshaft  30 . In addition, a plurality of balance weights  34  is mounted at the crankshaft  30 . The balance weights  34  reduce rotation vibration that occurs when the crankshaft  30  rotates. 
     The variable compression ratio apparatus  1  includes a connecting rod  20 , an eccentric link  40 , a variable bar  50 , and a variable gear  60 . 
     The connecting rod  20  receives the combustion force from the piston  10  and delivers the combustion force to the crankshaft  30 . The connecting rod  20  according to various embodiments of the present invention is similar to a conventional connecting rod. That is, the connecting rod  20  includes a small end  22  at an upper portion thereof and a big end  24  at a lower portion thereof. The small end  22  is rotatably connected to the piston  10  through a piston pin  12 , and the big end  24  is rotatably connected to the crank pin  32  formed eccentrically to the crankshaft  30 . For this purpose, an eccentric bearing hole  26  is formed at the small end  22  concentrically, and a crank pin hole  28  is formed at the big end  24  such that the crank pin  32  is rotatably inserted in the crank pin hole  28 . Since the connecting rod  20  similar to the conventional connecting rod is used, a structure of a conventional engine may not be changed so as to mount the variable compression ratio apparatus. In addition, durability of link members forming the variable compression ratio apparatus may be improved by transmitting the combustion force of the air-fuel mixture mostly to the connecting rod  20 . 
     One end of the eccentric link  40  is rotatably connected to the small end  22  of the connecting rod  20 . For this purpose, an eccentric bearing  42  is connected to one end of the eccentric link  40 , and the eccentric bearing  42  is inserted in the eccentric bearing hole  26  concentrically. A piston pin hole  44  is formed eccentrically to the eccentric bearing  42  at the eccentric bearing  42 . The piston pin  12  is inserted in the piston pin hole  44  so as to rotatably connect the connecting rod  20  and the eccentric link  40  to the piston  10 . That is, a center axis of the eccentric bearing  42  (the same as a center axis of the eccentric bearing hole  26 ) is parallel with and is spaced by a predetermined distance from a center axis of the piston pin  12 . Therefore, if the eccentric bearing  42  rotates, a relative position of a center of the piston pin  12  to a center of the eccentric bearing hole  26  is changed. Thereby, a distance between a center Z of the eccentric bearing  42  and an upper end Y of the piston  10  is changed. Therefore, a position of the piston pin  12  to the crank pin  32  is changed and the compression ratio of the air-fuel mixture is changed. In this specification, the eccentric bearing  42  is integrally formed and/or monolithically formed with the eccentric link  40 , but is not limited to this. That is, the eccentric bearing  42  can be separately manufactured and be assembled to the eccentric link  40 . 
     In addition, an eccentric link slot  46  is formed at the eccentric link  40  along a length direction thereof. 
     The variable bar  50  is movably inserted in the sliding groove  6  formed at the connecting portion of the cylinder block liner  2  and the crank case  4 . A variable bar gear  52  is formed at one end portion of the variable bar  50 . A variable bar pin  48  is mounted at a middle portion of the variable bar  50  and is adapted to move along the eccentric link slot  46 . That is, the variable bar pin  48  connects the variable bar  50  with the eccentric link  40  such that the variable bar  50  and the eccentric link  40  can move relatively. Therefore, if the variable bar  50  moves horizontally in the sliding groove  6 , the variable bar pin  48  moves along the eccentric link slot  46  and rotates the eccentric link  40 . 
     The variable gear  60  is mounted at the connecting portion of the cylinder block liner  2  and the crank case  4  and engages with the variable bar gear  52 . The variable gear  60  rotates according to the driving condition of the engine so as to move the variable bar  50  horizontally. In addition, the variable gear  60  is connected to an actuator such as a motor, and operation of the actuator is controlled by a control portion. Therefore, if the control portion decides the compression ratio of the air-fuel mixture according to the driving condition of the engine, the control portion operates the actuator. The variable gear  60  rotates by the operation of the actuator and changes the compression ratio of the air-fuel mixture. 
     Hereinafter, operation of the variable compression ratio apparatus  1  according to various embodiments of the present invention will be described in detail. 
     As shown in  FIG. 1 , in a case that the variable compression ratio apparatus  1  operates at a low compression ratio, an upper end Y of the piston  10  is lower than that X of the cylinder block liner  2  at a top dead center (TDC). At this state, if the control portion rotates the variable gear  60  and moves the variable bar  50  to the left in the drawings, the variable bar pin  48  moves along the eccentric link slot  46  and rotates the eccentric link  40  clockwise. Accordingly, a position of the piston pin  12  is heightened and a high compression ratio is realized as shown in  FIG. 2 . 
     If the control portion rotates the variable gear  6  and moves the variable bar  50  to the right in the drawings in a state that the variable compression ratio apparatus  1  operates at the high compression ratio as shown in  FIG. 2 , the variable bar pin  48  moves along the eccentric link slot  46  and rotates the eccentric link  40  counterclockwise. Accordingly, the position of the piston pin  12  is lowered and the low compression ratio is realized as shown in  FIG. 1 . 
     In order to mount the variable compression ratio apparatus  1  according to various embodiments of the present invention to the engine, only the sliding groove  6  may be formed horizontally. Therefore, structure and volume of the engine is hardly changed. That is, the variable compression ratio apparatus  1  according to various embodiments of the present invention can be applied to a conventional engine easily. 
     As described above, since an eccentric link and a variable bar move so as to rotate an eccentric bearing, moving mass may be minimized according to various embodiments of the present invention. Therefore, load applied to the eccentric bearing may be reduced and weight of a balance weight need not to increase. 
     In addition, a variable compression ratio apparatus may be mounted at an engine by forming a sliding groove at a connecting portion of a cylinder block liner and a crank case. Therefore, volume of the engine may not increase and the variable compression ratio apparatus can be easily mounted without a change in structure of a conventional engine. 
     Furthermore, durability of link members may be improved by directly delivering combustion force of air-fuel mixture to a connecting rod. 
     For convenience in explanation and accurate definition in the appended claims, the terms upper or lower, front or rear, inside or outside, and etc. 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.