Abstract:
A variable compression ratio apparatus may include: a piston pin; a small diameter eccentric cam disposed on a piston; a large diameter eccentric cam disposed between the small diameter eccentric cam and a small end portion of a connecting rod; a first plunger movably disposed in a first plunger space inside the piston pin; a second plunger movably disposed in a second plunger space formed inside the piston pin; and first and second oil injection nozzles disposed at a lower portion of the piston. In particular, the first and second oil injection nozzles control a control position of the first and second plungers by supplying hydraulic pressure to an end portion of the first plunger and the other portion of the second plunger through first and second guide passages formed inside the piston by injecting oil to the lower portion of the piston.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims priority to and the benefit of Korean Patent Application No. 10-2016-0040401, filed on Apr. 1, 2016, the entire contents of which are incorporated herein by reference. 
       FIELD 
       [0002]    The present disclosure relates to an internal combustion engine. More particularly, the present disclosure relates to a variable compression ratio apparatus to improve fuel efficiency. 
       BACKGROUND 
       [0003]    The statements in this section merely provide background information related to the present disclosure and may not constitute prior art. 
         [0004]    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. 
         [0005]    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. 
         [0006]    A variable compression ratio (VCR) apparatus changes the compression ratio of an air-fuel mixture according to a driving condition of the engine. 
         [0007]    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 inhibit or prevent occurrence of knocking and improve engine output. 
         [0008]    The above information disclosed in this Background section is only for enhancement of understanding of the background of the present disclosure and therefore it may contain information that does not form the prior art that is already known to a person of ordinary skill in the art. 
       SUMMARY 
       [0009]    The present disclosure provides a variable compression ratio apparatus which may improve performance and decrease fuel consumption by changing compression ratio in multistep and controlling the compression ratio more precisely. 
         [0010]    The present disclosure also provides a variable compression ratio apparatus that has very little power loss since the number of oil path decreases and the loss of oil pressure for changing compression ratio is small by controlling oil control plunger using the oil-jet injection nozzle which is arranged under a piston. 
         [0011]    As described above, a variable compression ratio apparatus according to one form of the present disclosure may include: a piston pin connecting a piston and a small end portion of a connecting rod, a small diameter eccentric cam disposed at an outer circumference surface of the piston in an eccentric state with a center axis of the piston pin, a large diameter eccentric cam disposed between an outer circumference surface of the small diameter eccentric cam and an inner circumference surface of the small end portion of the connecting rod in an eccentric state with a center axis of the piston pin, a first plunger movably disposed in a first plunger space formed at a side inside the piston pin so as to control a rotational position of the small diameter eccentric cam by controlling oil supplied to first and second chambers formed between the outer circumference surface of the small diameter eccentric cam and an inner circumference surface of the large diameter eccentric cam according to a control position, a second plunger movably disposed in a second plunger space formed at the other side inside the piston pin so as to control a rotational position of the large diameter eccentric cam by controlling oil supplied to third and fourth chambers formed between an outer circumference surface of the large diameter eccentric cam and the inner circumference surface of the small end portion according to a control position, and first and second oil injection nozzles disposed at a side and the other side of a lower portion of the piston, respectively, and controlling the control position of the first and second plungers by supplying hydraulic pressure to an end portion of the first plunger and the other portion of the second plunger through first and second guide passages formed inside the piston by injecting oil to the lower portion of the piston. 
         [0012]    A first pocket may be formed at a lower side of the piston, and a first guide passage is formed inside the piston so as to deliver oil from the first pocket to the end portion of the first plunger, and a second pocket may be formed at the other lower side of the piston, and a second guide passage is formed inside the piston so as to deliver oil from the second pocket to the other end of the second plunger. 
         [0013]    The first and second oil-jet injection nozzles may control positions of the first and second plungers by injecting oil to the first and second pockets and delivering oil to the end portion of the first plunger and the other portion of the second plunger through the first guide passage and the second guide passage. 
         [0014]    A groove that is divided into the first chamber and the second chamber by a first protrusion protruded from a side of an outer circumference surface of the small diameter eccentric cam may be formed on the inner circumference surface of the large diameter eccentric cam, and a groove that is divided into the third chamber and the fourth chamber by a second protrusion protruded from a side of an outer circumference surface of the large diameter eccentric cam may be formed on the inner circumference surface of the small end portion of the connecting rod. 
         [0015]    The first and second plungers may be respectively disposed at a side and the other side of inside of the valve body that penetrates a center portion of the piston pin in a length direction. 
         [0016]    The apparatus may further include a first return spring disposed inside the valve body so as to elastically support the first plunger in a side, and a second return spring disposed inside the valve body so as to elastically support the second plunger in the other side. 
         [0017]    A first check space may be formed at an end portion of inside of the first plunger, and a second check space may be formed at the other end portion of inside of the first plunger, a first check space connection passage may be formed inside the first plunger to connect the first check space with the second check space, a portion on which the first check space and the second check space are formed on an outer circumference surface of the first plunger may contact an inner circumference of the first plunger space, a first small diameter portion may be formed at the center portion where the first check space connection passage is formed in a predetermined gap with the first plunger space, in the first check space connection passage, a first open passage passing through an outer circumference surface may be formed, in the first plunger, a first check passage that goes through outside is formed, and in the second check space, a second check passage that goes through outside may be formed, in the valve body, a first supply passage connected to the first small diameter portion at all times and supplied with hydraulic pressure from the connecting rod may be formed, a second chamber connection passage may be formed, that is connected to the second check passage and connected to the second chamber through a side from an inner circumference surface to an outer circumference surface of the valve body, in a state that the first plunger is moved to a side by the first return spring, and a first chamber connection passage may be formed, that is connected to the first check passage and connected to the first chamber through a side from the inner circumference surface to the outer circumference surface of the valve body, in a state that the first plunger is moved to the other side by the first oil-jet injection nozzle. 
         [0018]    A third check space may be formed at an end portion of inside of the second plunger, and a fourth check space may be formed at the other end portion of inside of the second plunger, a second check space connection passage may be formed inside the second plunger to connect the third check space with the fourth check space, a portion on which the third check space and the fourth check space are formed on an outer circumference surface of the second plunger may contact an inner circumference of the second plunger space, a second small diameter portion may be formed at the center portion where the second check space connection passage is formed in a predetermined gap with the second plunger space, in the second check space connection passage, a second open passage passing through an outer circumference surface may be formed, in the second plunger, a third check passage that goes through outside may be formed, and in the fourth check space, a fourth check passage that goes through outside is formed, in the valve body, a second supply passage connected to the second small diameter portion at all times and supplied with hydraulic pressure from the connecting rod may be formed, a fourth chamber connection passage may be formed, that is connected to the third check passage and connected to the fourth chamber through a side from an inner circumference surface to an outer circumference surface of the valve body, in a state that the second plunger is moved to the other side by the second return spring, and a third chamber connection passage may be formed, that is connected to the fourth check passage and connected to the third chamber through a side from the inner circumference surface to the outer circumference surface of the valve body, in a state that the first plunger is moved to the other side by the second oil-jet injection nozzle. 
         [0019]    The apparatus may include a first check valve disposed in the first check space, inhibiting or preventing hydraulic pressure being transferred to the check space connection passage from the first check space, and a second check valve disposed in the second check space, inhibiting or preventing hydraulic pressure being transferred to the check space connection passage from the second check space. 
         [0020]    The apparatus may include a third check valve disposed in the third check space, inhibiting or preventing hydraulic pressure being transferred to the first check space connection passage from the third check space, and a fourth check valve disposed in the fourth check space, inhibiting or preventing hydraulic pressure being transferred to the second check space connection passage from the fourth check space. 
         [0021]    The apparatus may include first and second oil-jet control valves controlling oil injected from the first and second oil-jet injection nozzles, and a control unit controlling the first and second oil-jet control valves according to an operation condition. 
         [0022]    A bent hole may be formed in the valve body for releasing hydraulic pressure therein to outside with being opened in the first and second plunger spaces in the first and second return springs to outside. 
         [0023]    The first, second, third and fourth check valves may include a ball disposed in the oil passage, and a check spring for elastically supporting the ball. 
         [0024]    The apparatus may further include an oil pump for pumping oil to the first and second oil-jet control valve. 
         [0025]    A main oil supply passage may be formed inside the connecting rod, oil supplied to the main oil supply passage may be supplied to a side of the first and second plungers, and the oil supplied to the main oil supply passage may be transferred to each of the first, second, third and fourth chambers, thereby controlling rotational position of the small diameter eccentric cam or the large diameter eccentric cam according to a position of the first and second plungers. 
         [0026]    According to the present disclosure, maximum four steps of variable compression ratio may be implemented using the large diameter eccentric cam and the small diameter eccentric cam, the accuracy in control may be improved by embedding a plunger for hydraulic pressure control. 
         [0027]    Further, by controlling the position of the plunger using the oil-jet injected from the oil-jet injection nozzle that is disposed under the piston, the oil path may become relatively simple, and the efficiency in control may be improved. 
         [0028]    Herein, a technical effect not described herein may be realized in the process of implementing the present disclosure, and such a technical effect not described herein is included in the technical effect of the present disclosure. 
         [0029]    Further areas of applicability will become apparent from the description provided herein. It should be understood that the description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure. 
     
    
     
       DRAWINGS 
         [0030]    In order that the disclosure may be well understood, there will now be described various forms thereof, given by way of example, reference being made to the accompanying drawings, in which: 
           [0031]      FIG. 1  is schematic diagram illustrating a variable compression ratio apparatus according to one form of the present disclosure; 
           [0032]      FIG. 2  is a cross-sectional view of a portion where the piston and the connecting rod are connected in a variable compression ratio apparatus according to one form of the present disclosure; 
           [0033]      FIG. 3  is a side view illustrating a piston pin of a variable compression ratio apparatus according to the present disclosure; 
           [0034]      FIG. 4  is a cross-sectional view in a length direction of the piston pin along A-A line of  FIG. 3  in a variable compression ratio apparatus; 
           [0035]      FIG. 5  is a cross-sectional view in a length direction of the piston pin along B-B line of  FIG. 3  in a variable compression ratio apparatus; 
           [0036]      FIG. 6  is a schematic diagram illustrating a variable compression ratio apparatus according to one form of the present disclosure; 
           [0037]      FIGS. 7A-7D  are cross-sectional views illustrating each of the operation modes of a variable compression ratio apparatus according to one form of the present disclosure; and 
           [0038]      FIGS. 8A-8D  are cross-sectional views illustrating the portion that the piston and the connecting rod are connected in each of the operation modes in a variable compression ratio apparatus according to the present disclosure. 
       
    
    
       [0039]    The drawings described herein are for illustration purposes only and are not intended to limit the scope of the present disclosure in any way. 
       DETAILED DESCRIPTION 
       [0040]    The following description is merely exemplary in nature and is not intended to limit the present disclosure, application, or uses. It should be understood that throughout the drawings, corresponding reference numerals indicate like or corresponding parts and features. 
         [0041]    However, since the size and the thickness of each element shown in the drawings are represented in arbitrary scale for the convenience of description, the present disclosure is not limited thereto, and the thickness is enlarged in order to clearly represent several parts and regions. 
         [0042]    Further, in order to clearly describe the exemplary forms of the present disclosure, the part that is not in relation to the description is omitted. 
         [0043]    The term “first”, “second”, or the like is used for distinguishing elements that have the same title, but the titles are not limited to the order. 
         [0044]    Referring to  FIG. 1 , a variable compress ratio apparatus includes: a connecting rod  120 , a piston pin  105 , a piston  100 , a small end portion  135 , a big end portion  125 , a small diameter eccentric cam  110 , a large diameter eccentric cam  115  and a crank pin  130 . 
         [0045]    The small end portion (small diameter portion)  135  of the connecting rod  120  is connected to the piston  100  through the piston pin  105 , and the large end portion (large diameter portion)  125  is connected to the crank pin  130  of the crank shaft. 
         [0046]    The piston pin  105  connects the piston  100  with the connecting rod  120  through the piston  100  and the small end portion  135  of the connecting rod  120 . 
         [0047]    In addition, the small diameter eccentric cam  110  has a ring structure, and the piston pin  105  slidably penetrates the small diameter eccentric cam  110 . And the large diameter eccentric cam  115  has a ring structure, and is engaged between the outer surface of the small diameter eccentric cam  110  and the inner surface of the small end portion  135 . 
         [0048]    In one form of the present disclosure, the hydraulic pressure of the oil supplied through the connecting rod  120  rotates each of the small diameter eccentric cam  100  and the large diameter eccentric cam  115 , and control the position of the piston pin  105  and the piston  100  upwardly and downwardly, thereby implementing low compression ratio and high compression ratio in multistep mode. 
         [0049]    Furthermore, inside the piston pin  105 , a plunger is located to control the rotational position of the small diameter piston  100  and the large diameter piston  100 . The detailed structure thereof is referred to  FIG. 4  and  FIG. 5 . 
         [0050]      FIG. 2  is a cross-sectional view of a portion where the piston and the connecting rod are connected in a variable compression ratio apparatus according to the present disclosure. 
         [0051]    Referring to  FIG. 2 , the variable compression ratio apparatus includes: a connecting rod  120 , a main oil supply passage  200 , a large diameter eccentric cam  115 , a small diameter eccentric cam  110 , a piston pin  105 , a first protrusion  250 , a second protrusion  255 , a first chamber  205 , a second chamber  220 , a third chamber  210  and a fourth chamber  215 . 
         [0052]    Through the main oil supply passage  200  that is formed inside the connecting rod  120 , oil is supplied to the plunger disposed inside the piston pin  105 . The plunger supplies the oil to each of the first chamber  205 , the second chamber  220 , the third chamber  210 , or the fourth chamber  215 , and controls the rotational position of the small diameter eccentric cam  110  and the large diameter eccentric cam  115 . 
         [0053]    The first protrusion  250  is protruded from one side of the outer circumference of the small diameter eccentric cam  110 , and the first protrusion  250  divides the groove that is formed on the inner circumference of the large diameter eccentric cam  115  into the first chamber  205  and the second chamber  220 . In addition, the second protrusion  255  is protruded from a side of the outer circumference of the large diameter eccentric cam  115 , and the second protrusion  255  divides the groove that is formed on the inner circumference of the small end portion  135  into the third chamber  210  and the fourth chamber  215 . 
         [0054]    In one form, when oil is supplied to the first chamber  205  and the oil in the second chamber  220  is returned, the small diameter eccentric cam  110  rotates clockwise and the piston pin  105  is lowered. In addition, when oil is supplied to the third chamber  210  and the oil in the fourth chamber  215  is returned, the large diameter eccentric cam  115  rotates clockwise and the piston pin  105  is lowered. 
         [0055]    On the other hand, when oil is supplied to the second chamber  220  and the oil in the first chamber  205  is returned, the small diameter eccentric cam  110  rotates counter clockwise and the piston pin  105  is raised. In addition, when oil is supplied to the fourth chamber  215  and the oil in the third chamber  210  is returned, the large diameter eccentric cam  115  rotates counter clockwise and the piston pin  105  is raised. 
         [0056]      FIG. 3  is a side view illustrating a piston pin of a variable compression ratio apparatus. 
         [0057]    Referring to  FIG. 3 , at a center part in the length direction of the piston pin, the valve body  300  is inserted, and a plunger is dispose inside the valve body  300 . In another form, the plunger may be installed inside the piston pin  105  without the valve body  300 . 
         [0058]      FIG. 4  is a cross-sectional view in a length direction of the piston pin along A-A line of  FIG. 3  in a variable compression ratio apparatus. 
         [0059]    Referring to  FIG. 4 , the piston pin  105  includes: a first plunger space  400 , a second check valve  402 , a first open passage  415 , a first supply passage  405 , a first check valve  420 , a first plunger  410 , a valve body  300 , a first check space  435 , a first oil-jet passage  425 , a first check passage  430 , a first check space connection passage  440 , a first small diameter portion  490 , a second check passage  450 , a second chamber connection passage  455 , a second check space  445 , a first return spring  460 , a second return spring  461 , a third check space  436 , a fourth chamber connection passage  456 , a third check passage  431 , a second small diameter portion  491 , a second check space connection passage  441 , a fourth check passage  451 , a second oil-jet passage  426 , a fourth check space  446 , and a second plunger  411 . 
         [0060]    At a center portion in the length direction of the piston pin  105 , the valve body  300  is disposed. At an end portion of the valve body  300 , a first plunger space is formed, and at the other end portion of the valve body  300 , a second plunger space  401  is formed. The first plunger  410  is fixed in the first plunger space  400 , and the second plunger  411  is fixed in the second plunger space  401 . 
         [0061]    In an end portion of the first plunger  410 , the first check space  435  is formed, and in the other portion of the first plunger  410 , the second check space  445  is formed. The first check space connection passage  440  that connects the first check space  435  and the second check space  445  is formed in the first plunger  410 . 
         [0062]    In the first plunger  410 , the first small diameter portion  490  is formed, which corresponds to the first check space connection passage  440 , and the outer circumference except the first small diameter portion  490  contacts the inner circumference of the valve body  300 . 
         [0063]    In the first check space connection passage  440 , the first open passage  415  that goes through the outside is formed. And, in the first check space  435 , the first check passage  430  that goes through the outside is formed, and in the second check space  445 , the second check passage  450  is formed. 
         [0064]    The first check valve  420  is disposed inside the first check space  435 . The first check valve  420  inhibits or prevents the oil in the first check space  435  from being discharged to the first check space connection passage  440 , and the oil in the first check space connection passage  440  inflows into the first check space  435 . 
         [0065]    In addition, the second check valve  402  is disposed inside the second check space  445 . The second check valve  402  inhibits or prevents the oil in the second check space  445  from being discharged to the first check space connection passage  440 , and the oil in the first check space connection passage  440  inflows into the second check space  445 . 
         [0066]    The oil supplied through the main oil supply passage  200  of the connecting rod  120  is supplied to the space that corresponds to the first small diameter portion  490  of the first plunger  410  through the piston pin  105  and the first supply passage  405  that is formed in the valve body  300 . And, the second check passage  450  is selectively connected to the second chamber  220  through the second chamber connection passage  455  that is formed in the valve body  300 . 
         [0067]    In one form of the present disclosure, the first return spring  460  connects the second check passage  450  with the second chamber connection passage  455  by elastically supporting the first plunger  410  in an end direction, and receives the oil-jet of the first oil-jet injection nozzle  615  (in  FIG. 6 ) through the first oil-jet passage  425  that is formed at an end portion of the piston pin  105  and the valve body  300 . 
         [0068]      FIG. 5  is a cross-sectional view in a length direction of the piston pin along B-B line of  FIG. 3  in a variable compression ratio apparatus. In comparison with  FIG. 4 , the detailed description for the similar or the same part is omitted, and main different points will be described. 
         [0069]    Referring to  FIG. 5 , in an end portion of the second plunger  411 , the third check space  436  is formed, and in the other end portion thereof, the fourth check space  446  is formed. The second check space connection passage  441  that connects the third check space  436  with the fourth check space  446  is formed in the second plunger  411 . 
         [0070]    In the second plunger  411 , the second small diameter portion  491  is formed, which corresponds to the second check space connection passage  441 , and the outer circumference surface except the second small diameter portion  491  contacts the inner circumference surface of the valve body  300 . 
         [0071]    In the second check space connection passage  441 , the second open passage  416  that goes through the outside is formed. And, in the third check space  436 , the third check passage  431  that goes through the outside is formed, and in the fourth check space  446 , the fourth check passage  451  is formed. 
         [0072]    Inside the third check space  436 , the third check valve  421  is disposed. The third check valve  421  inhibits or prevents the oil in the third check space  436  from being discharged to the second check space connection passage  441 , and the oil in the second check space connection passage  441  inflows into the third check space  436 . 
         [0073]    In addition, the fourth check valve  403  is disposed inside the fourth check space  446 . The fourth check valve  403  inhibits or prevents the oil in the fourth check space  446  from being discharged to the second check space connection passage  441 , and the oil in the second check space connection passage  441  inflows into the fourth check space  446 . 
         [0074]    Referring to  FIG. 4  and  FIG. 5 , the oil supplied through the main oil supply passage  200  of the connecting rod  120  is supplied to the space that corresponds to the second small diameter portion  491  of the second plunger  411  through the piston pin  105  and the second supply passage  406  formed in the valve body  300 . And, the fourth check passage  451  is selectively connected to the third chamber  210  through the third chamber connection passage  506  formed in the valve body  300 , and the first check passage  430  is selectively connected to the first chamber  205  through the first chamber connection passage  505  that is formed in the valve body  300 . 
         [0075]    In one form, the second return spring  461  may connect the third check passage  431  with the fourth chamber connection passage  456  by elastically supporting the second plunger  411  in the other end direction, and receive the oil-jet of the second oil-jet injection nozzle  616  (in  FIG. 6 ) through the second oil-jet passage  426  formed at an end portion of the piston pin  105  and the valve body  300 . 
         [0076]      FIG. 6  is a schematic diagram illustrating a variable compression ratio apparatus. 
         [0077]    Referring to  FIG. 6 , at a side of a lower portion edge of the piston  100 , a first pocket  605  is formed, and at the other side of the lower portion edge thereof, a second pocket  606  is formed. A first guide passage  625  is formed from the first pocket  605  to the valve body  300 , and a second guide passage  626  is formed from the second pocket  606  to the valve body  300 . 
         [0078]    At a side of a lower portion of the piston  100 , a first oil-jet injection nozzle  615  is disposed, and at the other side of the lower portion of the piston  100 , a second oil-jet injection nozzle  616  is disposed. The first oil-jet injection nozzle  615  is disposed to inject oil to the first pocket  605 , and the second oil-jet injection nozzle  616  is disposed to inject oil to the second pocket  606 . 
         [0079]    Further, a first oil-jet control valve  610  is disposed to control the oil that is pumped by an oil pump  620 , and injects oil through the first oil-jet injection nozzle  615 . The second oil-jet control valve  611  is disposed to control the oil that is pumped by the oil pump  620 , and injects oil through the second oil-jet injection nozzle  616 . 
         [0080]    In addition, the control unit  600  controls the injection of oil-jet by controlling the first oil-jet control valve  610  and the second oil-jet control valve  611  according to a driving condition. 
         [0081]      FIGS. 7A-7D  are cross-sectional views illustrating each of the operation modes of a variable compression ratio apparatus. 
         [0082]    Referring to  FIG. 7A , the oil is not injected from the first oil-jet injection nozzle  615 , and the first plunger  410  is located at an end portion in the valve body  300  by the first return spring  460 . And, the oil is not injected from the second oil-jet injection nozzle  616 , and the second plunger  411  is moved to a right direction in the valve body  300  by the second return spring  461 . 
         [0083]    And, the oil supplied through the main oil supply passage  200  is supplied to the second chamber  220  through the first open passage  415  of the first plunger  410 , the first check space connection passage  440  and the second check valve  402 , and the oil in the first chamber  205  is returned to the second chamber  220  through the first open passage  415 , the first check space connection passage  440  and the second check valve  402  by the pressure change applied to the piston  100 . Accordingly, the small diameter eccentric cam  110  rotates clockwise in  FIG. 2 . 
         [0084]    In addition, the oil supplied through the main oil supply passage  200  is supplied to the fourth chamber  215  through the second open passage  416  of the second plunger  411  and the third check valve  421 , and the oil in the third chamber  210  is returned to the fourth chamber  215  through the second open passage  416  and the third check valve  421  by the pressure change. Accordingly, the large diameter eccentric cam  115  rotates counter clockwise in  FIG. 2 . 
         [0085]    Referring to  FIG. 7B , the oil is not injected from the first oil-jet injection nozzle  615 , and the first plunger  410  is located at an end portion in the valve body  300  by the first return spring  460 . And, the oil is injected from the second oil-jet injection nozzle  616 , and the second plunger  411  is moved to a left direction in the valve body  300 . 
         [0086]    And, the oil supplied through the main oil supply passage  200  is supplied to the second chamber  220  through the first open passage  415  of the first plunger  410 , the first check space connection passage  440  and the second check valve  402 , and the oil in the first chamber  205  is returned to the second chamber  220  through the first open passage  415 , the first check space connection passage  440  and the second check valve  402  by the pressure change applied to the piston  100 . Accordingly, the small diameter eccentric cam  110  rotates clockwise in  FIG. 2 . 
         [0087]    In addition, the oil supplied through the main oil supply passage  200  is supplied to the third chamber  210  through the second open passage  416  of the second plunger  411  and the fourth check valve  403 , and the oil in the fourth chamber  215  is returned to the third chamber  210  through the second open passage  416  and the fourth check valve  403  by the pressure change. Accordingly, the large diameter eccentric cam  115  rotates counter clockwise in  FIG. 2 . 
         [0088]    Referring to  FIG. 7C , the oil is injected from the first oil-jet injection nozzle  615 , and the first plunger  410  is located at the other end portion (right side) in the valve body  300 . And, the oil is not injected from the second oil-jet injection nozzle  616 , and the second plunger  411  is moved to a right direction in the valve body  300 . 
         [0089]    And, the oil supplied through the main oil supply passage  200  is supplied to the second chamber  220  through the first open passage  415  of the first plunger  410 , the first check space connection passage  440  and the first check valve  420 , and the oil in the second chamber  220  is returned to the first chamber  205  through the first open passage  415 , the first check space connection passage  440  and the first check valve  420  by the pressure change applied to the piston. Accordingly, the small diameter eccentric cam  110  rotates counter clockwise in  FIG. 2 . 
         [0090]    In addition, the oil supplied through the main oil supply passage  200  is supplied to the fourth chamber  215  through the second open passage  416  of the second plunger  411  and the third check valve  421 , and the oil in the third chamber  210  is returned to the fourth chamber  215  through the second open passage  416  and the third check valve  421  by the pressure change. Accordingly, the large diameter eccentric cam  115  rotates counter clockwise in  FIG. 2 . 
         [0091]    Referring to  FIG. 7D , the oil is injected from the first oil-jet injection nozzle  615 , and the first plunger  410  is located at the other end portion (right side) in the valve body  300 . And, the oil is not injected from the second oil-jet injection nozzle  616 , and the second plunger  411  is moved to a right direction in the valve body  300 . 
         [0092]    And, the oil supplied through the main oil supply passage  200  is supplied to the second chamber  220  through the first open passage  415  of the first plunger  410 , the first check space connection passage  440  and the first check valve  420 , and the oil in the second chamber  220  is returned to the first chamber  205  through the first open passage  415 , the first check space connection passage  440  and the first check valve  420  by the pressure change applied to the piston  100 . Accordingly, the small diameter eccentric cam  110  rotates counter clockwise in  FIG. 2 . 
         [0093]    In addition, the oil supplied through the main oil supply passage  200  is supplied to the fourth chamber  215  through the second open passage  416  of the second plunger  411  and the fourth check valve  403 , the oil in the fourth chamber  215  is returned to the third chamber  210  through the second open passage  416  and the fourth check valve  403  by the pressure change. Accordingly, the large diameter eccentric cam  115  rotates clockwise in  FIG. 2 . 
         [0094]      FIGS. 8A-8D  are cross-sectional views illustrating the portion that the piston and the connecting rod are connected in each of the operation modes in a variable compression ratio apparatus. 
         [0095]      FIG. 8A  corresponds to  FIG. 7C , and the small diameter eccentric cam  110  and the large diameter eccentric cam  115  rotate counter clockwise. Accordingly, high compression ratio is implemented. 
         [0096]      FIG. 8B  corresponds to  FIG. 7A , and the small diameter eccentric cam  110  rotates clockwise and the large diameter eccentric cam  115  rotates counter clockwise. Accordingly, the first middle compression ratio is implemented. 
         [0097]      FIG. 8C  corresponds to  FIG. 7D , and the small diameter eccentric cam  110  rotates counter clockwise and the large diameter eccentric cam  115  rotates clockwise. Accordingly, the second middle compression ratio is implemented. 
         [0098]      FIG. 8D  corresponds to  FIG. 7B , and the small diameter eccentric cam  110  rotates clockwise and the large diameter eccentric cam  115  rotates clockwise. Accordingly, low compression ratio is implemented. 
         [0099]    As described above, four steps of variable compression ratio may be implemented using the large diameter eccentric cam  115  and the small diameter eccentric cam  110 , the accuracy in control may be improved by embedding a plunger for hydraulic pressure control. 
         [0100]    Further, by controlling the position of the plunger using the oil-jet injected from the oil-jet injection nozzle that is disposed under the piston  100 , the oil path may become relatively simple, and the efficiency in control may be improved. 
         [0101]    While the present disclosure has been described in connection with exemplary forms, it is to be understood that the present disclosure is not limited to the disclosed forms. On the contrary, it is intended to cover various modifications and equivalent arrangements by a skilled person in the art included within the spirit and scope of the forms of the present disclosure. 
         [0000]    
       
         
               
             
               
               
             
           
               
                   
               
               
                 &lt;Description of symbols&gt; 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 100: piston 
                 105: piston pin 
               
               
                 110: small diameter eccentric cam 
                 115: large diameter eccentric cam 
               
               
                 120: connecting rod 
                 125: big end portion 
               
               
                 130: crank pin 
                 135: small end portion 
               
               
                 200: main oil supply passage 
                 205: first chamber 
               
               
                 210: third chamber 
                 215: fourth chamber 
               
               
                 220: second chamber 
                 300: valve body 
               
               
                 400: first plunger space 
                 401: second plunger space 
               
               
                 402: second check valve 
                 403: fourth check valve 
               
               
                 410: first plunger 
                 411: second plunger 
               
               
                 405: first supply passage 
                 406: second supply passage 
               
               
                 415: first open passage 
                 416: second open passage 
               
               
                 420: first check valve 
                 421: third check valve 
               
               
                 425: first oil-jet passage 
                 426: second oil-jet passage 
               
               
                 430: first check passage 
                 431: third check passage 
               
               
                 435: first check space 
                 436: third check space 
               
               
                 445: second check space 
                 446: fourth check space 
               
               
                 450: second check passage 
                 451: fourth check passage 
               
               
                 440: first check space connection passage 
               
               
                 441: second check space connection passage 
               
               
                 455: second chamber connection passage 
               
               
                 456: fourth chamber connection passage 
               
               
                 460: first return spring 
                 461: second return spring 
               
               
                 505: first chamber connection passage 
                 506: third chamber connection passage 
               
               
                 600: control unit 
                 605: first pocket 
               
               
                 606: second pocket 
                 610: first oil-jet control valve 
               
               
                 611: second oil-jet control valve 
                 615: first oil-jet injection nozzle 
               
               
                 616: second oil-jet injection nozzle 
                 620: hydraulic pump 
               
               
                 625: first guide passage 
                 626: second guide passage 
               
               
                 250: first protrusion 
                 255: second protrusion 
               
               
                 490: first small diameter portion 
                 491: second small diameter portion