Abstract:
A valve actuation mechanism are disclosed, which is capable of controlling the lift of valves of an engine by more than three on/off combinations. In a preferred embodiment of the invention, the valve actuation mechanism is designed to control the opening and closing of engine valves by the use of an uncomplicated structure with minimum solenoid valves and hydraulic lines. By the valve actuation mechanism of the invention, not only the design of hydraulic line as well as that of space mechanism of an engine can be greatly simplified, but also the opening and closing of valves of an engine can be controlled thereby for enabling the engine to provide different valve lifts and thus satisfying different engine requirements, such as output power increasing, combustion efficiency improving, or cylinder deactivation.

Description:
FIELD OF THE INVENTION 
   The present invention relates to a valve actuation mechanism, and more particularly, to a valve actuation mechanism designed with simplified structure and oil circuit that is capable of selectively controlling the lift of valves of an engine by more than three on/off combinations. 
   BACKGROUND OF THE INVENTION 
   With the ever-increasing oil price, fuel economic efficiency and fuel-saving potentials of an engine are becoming more and more important. Recently, most fuel-saving researches are focused upon developing variable valve actuation mechanism since it is the foundation of various fuel-saving techniques, such as cylinder deactivation, engine down-sizing, and so on. 
   Fuel-saving can be achieved by changing valves&#39; lift, which is realized by methods listed as following:
         (1) Designing intake valves to synchronously enable a high or a low lift selected with respect to engine speeds: The valve lifts of two intake valves of an engine are optimized for matching the same with the engine speed, by which high valve lift is adopted for enhancing intake efficiency and thus helping to develop high-power output with less fuel consumption when the engine is operating at high speeds, and low valve lift is adopted when the engine is operating at low/median speeds for reducing fuel consumption since the intake flow speed is increased, the driving torque of camshaft is reduced and the combustion of the engine at idle is stabilized. The aforesaid design is commonly being adopted by Honda and used in its products, such as CIVIC and ACCORD. In addition, The Valvetronic system of BMW is the first variable valve timing system to offer continuously variable intake valve lift for optimizing the performance of engines.   (2) Designing one of two intake valves to enable a high lift while another enabling a low lift: Such design basically allows only one intake valve to be opened for intaking air when an engine is operating at a low/median speed, by which an intense swirl can be created inside its cylinder so as to improve combustion efficiency and thus improve fuel consumption. It is noted that when the engine is operating at high speeds, both of the two intake valves are enabled to perform at a high valve lift. The CB400F of Honda is the representative of such design. However, in order to avoid fuel from depositing at the closed intake valve when the engine is operating at a low/median speed and thus cause troubles, such as incorrect air/fuel ratio and carbon deposition, one intake valve is enabled with a high lift while another is enabled with a low lift.   (3) Deactivating partial valves from intaking: For large-volume engine or hybrid engine, it is preferred to reduce pump loss during cylinder deactivation that can be achieved by designing valves of a portion of a cylinder to be closed when the engine is operating at low speed. The Insight of Honda is the representative of such design.       

   Currently, there are various researches relates to valve lift control. One such research is disclosed in U.S. Pat. No. 4,523,550, which uses a valve actuation mechanism with adjustable valve disabling device for valve lift control, and is the design capable of enabling one of two intake valves with a high lift while another with a low lift, or enabling only one valve is opened while another is closed. Another such research is disclosed in U.S. Pat. No. 4,727,831, which uses the combinations of three cams and three rocker arms for controlling two valves capable of selectively operating in two operation modes, that is, enabling both valves with a high lift synchronously or enabling one of two intake valves with a high lift while another with a low lift. Further another such research is disclosed in U.S. Pat. No. 4,887,563, which uses the combinations of three cams and three rocker arms for controlling two valves capable of selectively operating in three operation modes, that is, enabling both valves with a high lift synchronously, or enabling one of two intake valves with a high lift while another with a low lift, or enabling one of two intake valves with a median lift while another with a low lift. 
   Although methods and apparatuses disclosed in the aforesaid patents are all capable of providing multiple operation modes of valve lift, they are all short for providing valve lift control capable of meeting every operation requirement of an engine as it is operating at a high speed for high-power output, or as it is operating at a median speed and requiring an vertex inside its cylinder for improving combustion efficiency, or as it is subject to a cylinder deactivation condition, or as it is stalled. Therefore, it is in need of a valve actuation mechanism that is freed from the shortcomings of prior arts. 
   SUMMARY OF THE INVENTION 
   It is the primary object of the present invention to provide a valve actuation mechanism, capable of controlling two intake valves of a cylinder to selectively operate in three operation modes, that is, enabling both valves with a high lift synchronously, or enabling one of two intake valves with a high lift while another with a low lift, or enabling both of two intake valves to close, that respectively satisfy different engine requirements, such as the engine is operating at a high speed for high-power output, as the engine is operating at a median speed and requiring an vertex inside its cylinder for improving combustion efficiency, and as the engine is subject to a cylinder deactivation condition. 
   It is another object of the invention to provide a valve actuation mechanism, capable of using combinations enabled by a switch pin device, no more than three oil circuits, and no more then two solenoid valves for controlling two intake valves of a cylinder to selectively operate in three operation modes, that is, enabling both valves with a high lift synchronously, and enabling one of two intake valves with a high lift while another with a low lift, and enabling both of two intake valves to close. 
   Yet, another object of the invention is to provide a low-cost valve actuation mechanism by the use of an uncomplicated structure with minimum oil circuit control. 
   Furthermore, another object of the invention is to provide a valve actuation mechanism, capable of using no more than three oil circuits and less then two solenoid valves for controlling valves of a cylinder to selectively operate in at least three operation modes, including enabling both valves with a high lift synchronously, and enabling one of two intake valves with a high lift while another with a low lift, and enabling both of two intake valves to close. 
   To achieve the above objects, the present invention provides a valve actuation mechanism, comprising: a first rocker arm, connect to a first valve; a second rocker arm, connected to a second valve; a first tappet, arranged at a side of the first rocker arm for enabling the same to be driven to move by a first cam; a second tappet, arranged at a side of the second rocker arm for enabling the same to be driven to move by a second cam; a first connecting unit, capable of selectively coupling the first rocker arm to the first tappet or the second rocker arm; and a second connecting unit, capable of selectively enabling the second rocker arm to connect to/separate from the second tappet. 
   Preferably, any one of the first and the second connecting units can be a switch pin device composed of an elastic member and a hydraulic-driven unit. In addition, the switch pin device is substantially being a device selected from the group consisting of a lock pin and an unlock pin. Moreover, any one of the first and the second connecting units can be a two-way hydraulic-driven pin. 
   In addition, to achieve the above objects, the present invention provides a valve actuation mechanism, comprising: a first rocker arm, connect to a first valve, capable of being driven to move by a first cam; a second rocker arm, connected to a second valve; a tappet, arranged at a position between the first and the second rocker arms, capable of being driven to move by a second cam; a first connecting unit, capable of selectively enabling the first rocker arm to connect to/separate from the tappet; and a second connecting unit, capable of selectively enabling the second rocker arm to connect to/separate from the tappet. 
   Preferably, the valve actuation mechanism further comprises: a power transmission unit, mounted on the first rocker arm at a position enabling the same to be sandwiched between the first rocker arm and the first cam and thus enabling power transmitted from the first cam to be received by the first rocker arm; wherein the power transmission unit further comprises: a can, having a throttling hole and a via hole formed thereon while enabling an accommodation space to be formed between the throttling hole and the via hole; a top pin, arranged in the via hole in a manner that an end of the top pin is oriented corresponding to the first cam while enabling the top pin to slide up and down the via hole; and an oil circuit control unit, connected to the throttling hole, capable of selectively performing a task selected from the group consisting of: filling an oil inside the accommodation space and enabling the oil containing in the accommodation space to be released. 
   In another preferred aspect, the valve actuation mechanism further comprises: a power transmission unit, sandwiched between the first rocker arm and the first cam for enabling power transmitted from the first cam to be received by the first rocker arm. The power transmission unit further comprises: a base, having a first accommodation space, a second accommodation space and a hydraulic channel containing a liquid; a first top pin with a recess formed at a side thereof, being arranged inside the first accommodation space while enabling the bottom thereof to connected to a first elastic member; and a second top pin, being arranged inside the second accommodation space while enabling a portion thereof to have connect with the hydraulic channel and the bottom thereof to connect to a second elastic member; wherein, an end of the second top pin is enabled to embed into/detach from the recess selectively by the action of the second elastic member and the liquid. 
   Other aspects and advantages of the present invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the present invention. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1A  is a schematic diagram showing a valve actuation mechanism according to a first embodiment of the invention. 
       FIG. 1B  is a schematic diagram illustrating the oil circuit control of  FIG. 1A . 
       FIG. 1C  shows a two-way hydraulic-driven pin used in a valve actuation mechanism of the invention. 
       FIG. 1D  shows a lock pin used in a valve actuation mechanism of the invention. 
       FIG. 1E  is a table showing various valve lift controls with respect to different settings of the valve actuation mechanism of  FIG. 1A . 
       FIG. 2A  is a schematic diagram showing a valve actuation mechanism according to a second embodiment of the invention. 
       FIG. 2B  shows an unlock pin used in a valve actuation mechanism of the invention. 
       FIG. 2C  is a schematic diagram showing a power transmission unit adopted by the valve actuation mechanism of  FIG. 2A . 
       FIG. 2D  is a schematic diagram illustrating the oil circuit control of  FIG. 2A . 
       FIG. 2E  is a table showing various valve lift controls with respect to different settings of the valve actuation mechanism of  FIG. 2A . 
       FIG. 3A  is a schematic diagram showing a valve actuation mechanism according to a third embodiment of the invention. 
       FIG. 3B  is a schematic diagram showing a power transmission unit adopted by the valve actuation mechanism of  FIG. 3A . 
       FIG. 3C  is a schematic diagram illustrating the oil circuit control of  FIG. 3A . 
       FIG. 3D  is a table showing various valve lift controls with respect to different settings of the valve actuation mechanism of  FIG. 3A . 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENT 
   For your esteemed members of reviewing committee to further understand and recognize the fulfilled functions and structural characteristics of the invention, several preferable embodiments cooperating with detailed description are presented as the follows. 
   It is intended to provide a valve actuation mechanism in the present invention, that is capable of controlling two intake valves of a cylinder to selectively operate in at least three operation modes, that is, enabling both valves with a high lift synchronously, or enabling one of two intake valves with a high lift while another with a low lift, or enabling both of two intake valves to close, that respectively satisfy different engine requirements, such as the engine is operating at a high speed for high-power output, as the engine is operating at a median speed and requiring an vertex inside its cylinder for improving combustion efficiency, and as the engine is subject to a cylinder deactivation condition. In addition, the foregoing at least three valve lift controls are realized by using no more than three oil circuits and less then two solenoid valves. 
   Please refer to  FIG. 1A , which is a schematic diagram showing a valve actuation mechanism according to a first embodiment of the invention. The valve actuation mechanism  1  of  FIG. 1A  is comprised of a first rocker arm  13 , a second rocker arm  14 , a first tappet  12 , a second tappet  15 , a first connecting unit  18  and a second connecting unit  19 . In which, the first rocker arm  13  is connect to a first valve  10  while the second rocker arm  14  is connected to a second valve  11 . In a preferred aspect, the first and the second valves  10 ,  11  are valves arranged on an engine cylinder that are capable of controlling the intake of the cylinder by the lift thereof. It is noted that the arrangement of the first and the second valves  10 ,  11  on the cylinder are known to those skilled in the art and thus are not described further herein. 
   The first tappet  12  is arranged at a side of the first rocker arm  13  for enabling the same to be driven to move by a first cam  16  while a second tappet  15  is arranged at a side of the second rocker arm  14  for enabling the same to be driven to move by a second cam  17 . In addition, the first cam  16  and the second cam  17  are all being driven to rotate by the rotation of a camshaft. In the first preferred embodiment of the invention, the first cam  16  is a Mid cam and the second cam  17  is a High cam, that is, the moving distance of the first tappet  12  caused by the first cam  16  is smaller than that of the second tappet  15  caused by the second cam  17 . Moreover, the first connecting unit  18 , which is a two-way hydraulic-driven pin, is capable of selectively coupling the first rocker arm  13  to the first tappet  12  or the second rocker arm  14 ; and the second connecting unit  19 , which is a lock pin, is capable of selectively enabling the second rocker arm  14  to connect to/separate from the second tappet  15 . 
   Please refer to  FIG. 1C  and  FIG. 1D , which respectively shows a two-way hydraulic-driven pin and a lock pin used in a valve actuation mechanism of  FIG. 1A . In  FIG. 1C , an accommodation space  180  is formed inside the two-way hydraulic-driven pin, whereas a plug  181 , having two oil baffle pads respectively attached to the two ends thereof, is arranged in the accommodation space  180 . As the accommodation space  180  is channeled with two oil circuits Pc and Pb, the plug  181  can be driven to move/slide in the accommodation space  180  by the pressure of the oil  9  caused by the activations of the two oil circuits Pc and Pb. As the plug  181  is driven to move to the left of the accommodation space  180 , the first rocker arm  13  is connected to the first tappet  12 , and as the plug  181  is driven to move to the right of the accommodation space  180 , the first rocker arm  13  is connected to the second rocker arm  14 . So that, the first connecting unit  18  is capable of selectively coupling the first rocker arm  13  to the first tappet  12  or the second rocker arm  14 . As seen in  FIG. 1A , when the oil circuit Pc is activated for enabling the oil pressure of Pc to be higher than that of the Pb, the plug  181  is driven to move to the right of the accommodation space  180  and thus the first rocker arm  13  is connected to the second rocker arm  14 ; and when the oil circuit Pb is activated for enabling the oil pressure of Pb to be higher than that of the Pc, the plug  181  is driven to move to the left of the accommodation space  180  and thus the first rocker arm  13  is connected to the first tappet  12 . 
   As seen in  FIG. 1D , the lock pin is substantially a plug  191  with a accommodation space  192  formed therein. In addition, an elastic member  193  is arranged in the accommodation space  192 , whereas an end of the elastic member  193  is abutted against the inner wall of the plug while another end thereof is connected to a sidewall. Moreover, an oil baffle pad  194  is attached to an end of the plug  194  while an end of the lock pin corresponding to such end is connect to an oil circuit Pa. Therefore, as the oil circuit Pa is activated for filling oil  9  into the lock pin, the pressurized oil  9  will push the oil baffle pad  194  and thus force the plug  191  to move to the right, so that the elastic member  193  will be compressed and thus a resilience force of the elastic member  193  is accumulated. When the oil circuit Pa is deactivated and thus the oil pressure exerting on the plug  191  is released, the accumulated resilience force of the elastic member  193  will force the plug  191  to move to the left. As seen in  FIG. 1A , by the movement of the lock pin, the second rocker arm  14  is capable of selectively being enabling to connect to or separate from the second tappet  15 . 
   Please refer to  FIG. 1B , which is a schematic diagram illustrating the oil circuit control of  FIG. 1A . In  FIG. 1B , an oil circuit control unit is designed and used for controlling the activations of the three oil circuits Pa, Pb, Pc. As seen in  FIG. 1B , two four-port two-way solenoid valves  40 ,  41  are used, in which the two ports, referring as A port and B port, are used as interfaces for connecting to working circuits, i.e. used for connecting to the three oil circuits Pa, Pb, Pc; and the port, referring as P port, is acting as pressure interface that is connected to a pump  42 ; and the port, referring as T port, is acting as a drain interface and is connected to an oil tank  43 . Moreover, a node indicated as a Y node on  FIG. 1B  is a joint connecting to a control valve. 
   As seen in  FIG. 1E , by the control of the three oil circuit Pa, Pb, Pc, a variety of connection statuses can be enabled through the first and the second connecting units  18 ,  19  that correspondingly various valve lifts of the first and the second valves  10 ,  11  can be realized. For instance, in  FIG. 1A , the first connecting unit  18  is enabled to connect the first rocker arm  13  with the second rocker arm  14  while the second connecting unit  19  is enabled to connect the second rocker arm  14  with the second tappet  15 . Therefore, when the first tappet  12  is driven to move by the rotation of the first cam  16 , the movement of the first tappet  12  will be a stand along movement since the first connecting unit  18  is not connected to the first tappet  12 . 
   However, when the second tappet  12  is driven to move by the rotation of the second cam  17 , the movement of the second tappet  15  will drive the second connecting unit  19  and therefore the first connecting unit  18  to move, and consequently the first rocker arm  13  the second rocker arm  14  are being driven to move as well since the second tappet  15  are connected to the second rocker arm  14  by the second connecting unit  19  while the second rocker arm  14  are connected to the first rocker arm  13  by the first connecting unit  18 . In this preferred embodiment, the second cam  17  is a high cam, so that the first valve  10  and the second valve  11  are both being enabled with a high valve lift. Hence, under the same principle, other valve lift controls with respect to different settings of the valve actuation mechanism of  FIG. 1A  can be seen in the table shown in  FIG. 1E . As seen in  FIG. 1E , the engine can produce a high-power output when the valve actuation mechanism enables both of the two valves  10 ,  11  with a high lift; an status of engine deactivation is enabled when both of the two valves  10 ,  11  are closed; and the engine is enabled to produce an intense swirl inside its cylinder or is stalled when one of two intake valves  10 ,  11  is enabled with a high lift while another with a low lift. 
   Please refer  FIG. 2A , which is a schematic diagram showing a valve actuation mechanism according to a second embodiment of the invention. The valve actuation mechanism  2  of  FIG. 2A  is comprised of a first rocker arm  22 , a second rocker arm  24 , a tappet  23 , a first connecting unit  25  a second connecting unit  27  and a power transmission unit  26 . In which, the first rocker arm  22 , being connect to a first valve  20 , is capable of being driven to move by a first cam  28  while the second rocker arm  22  is connected to a second valve  21  for enabling the same to control the lift of the second valve  21 . In a preferred aspect, the first and the second valves  20 ,  21  are valves arranged on an engine cylinder that are capable of controlling the intake of the cylinder by the lift thereof. It is noted that the arrangement of the first and the second valves  10 ,  11  on the cylinder are known to those skilled in the art and thus are not described further herein. The tappet  23  is sandwiched between the first rocker arm  22  and the second rocker arm  24  that can be driven to move by a second cam  29 . In addition, the first cam  28  and the second cam  29  are all being driven to rotate by the rotation of a camshaft. In this preferred embodiment of the invention, the first cam  28  is a Mid cam and the second cam  29  is a High cam, that is, the moving distance of the first rocker arm  22  caused by the first cam  28  is smaller than that of the second rocker arm  24  caused by the second cam  29 . 
   Moreover, the first connecting unit  25 , which is an unlock pin, is capable of selectively enabling the first rocker arm  22  to connect to/separate from the tappet  23 . Please refer to  FIG. 2B , which shows an unlock pin used in a valve actuation mechanism of  FIG. 2A . The unlock pin of  FIG. 2B  has an accommodation space  250  used for receiving a plug  252  while enabling an end of the accommodation space  250  to channel with an oil circuit Pb. In addition, a rod  251  connected to the plug  252  is extending out of the accommodation space  250  and thus out of the unlock pin, whereas a blocking panel  254  is attached to the out-extending end of the rod  251  while enabling the section of the rod  251  between the blocking panel  254  and the outer wall of the unlock pin to be ensheathed by an elastic member  253 . 
   Therefore, as the oil circuit Pb is activated for exerting a pressure upon the plug  252 , the plug  252  will be push to move toward the left for compressing the elastic member  253  and thus a resilience force of the elastic member  193  is accumulated. When the oil circuit Pb is deactivated and thus the oil pressure exerting on the plug  252  is released, the accumulated resilience force of the elastic member  253  will force the plug  252  to move to the right. As seen in  FIG. 2A , by the movement of the unlock pin controlled by the oil circuit Pb and the elastic member  253 , the first rocker arm  22  is capable of selectively enabling the first rocker arm  22  to connect to or separate from the tappet  23 . Similarly, the second connecting unit  27  is capable of selectively enabling the second rocker arm  24  to connect to or separate from the tappet  23 . In this preferred embodiment, the second connecting unit  27  is a lock pin, whose operational principle is illustrated with respect to  FIG. 1D  and thus is not described further herein. 
   Please refer to  FIG. 2C , which is a schematic diagram showing a power transmission unit adopted by the valve actuation mechanism of  FIG. 2A . The power transmission unit  26 , being mounted on the first rocker arm  22 , is comprised of a can  260 , a top pin  265  and an oil circuit control unit. The can  260  has a throttling hole  264  and a first via hole  262  formed thereon while enabling an accommodation space  261  to be formed between the throttling hole  264  and the first via hole  262 . the top pin  265  is arranged in the first via hole  262  in a manner that an end of the top pin  265  is oriented corresponding to the first cam  28  while enabling the top pin  265  to slide up and down the first via hole  262 . 
   Moreover, the oil circuit control unit is connected to the throttling hole  264  and is capable of selectively performing a task selected from the group consisting of: filling an oil inside the accommodation space  261  for pressurizing the top pin to move upwardly and enabling the oil containing in the accommodation space  261  to be released for causing the top pin  265  to move downwardly. If the top pin  265  is moved upward, the power of the first cam  28  can be received by the power transmission unit  26  and then transmitted to the first rocker arm  22  for enabling the same to move accordingly. As the diameter of the throttling hole  264  is specifically designed and specified, the oil containing in the accommodation space  261  will not leak even when the first cam  28  bangs on the top pin  265 . Thus, the power transmission unit  26  is considered to have good rigidity by the incompressibility of the oil. For instance, an throttling hole  264  with smaller than 2 mm diameter will enabling the power transmission unit  26  to sustain a force of 200N from the first cam  28 . If the oil containing in the accommodation space  261  is released and the top pin  265  is dropped, the driving force of the first cam  28  will not be received by the first rocker arm  22 . There is an oil circuit control illustrated in  FIG. 2D , however, it is only an illustration and the present invention is not limited thereby. 
   Please refer to  FIG. 2D , which is a schematic diagram illustrating the oil circuit control of  FIG. 2A . In  FIG. 2D , an oil circuit control unit  5  is designed and used for controlling the activations of the three oil circuits Pa, Pb, Pc. As seen in  FIG. 2D , two four-port two-way solenoid valves  50 ,  51  are used, in which the two ports, referring as A port and B port, are used as interfaces for connecting to working circuits, i.e. used for connecting to the three oil circuits Pa, Pb, Pc; and the port, referring as P port, is acting as pressure interface that is connected to a pump  52 ; and the port, referring as T port, is acting as a drain interface and is connected to an oil tank  53 . Moreover, a node indicated as a Y node on  FIG. 1B  is a joint connecting to a control valve. 
   As seen in  FIG. 2E , by the control of the three oil circuit Pa, Pb, Pc, a variety of connection statuses can be enabled through the first and the second connecting units  25 ,  27  that correspondingly various valve lifts of the first and the second valves  20 ,  21  can be realized. For instance, referring to  FIG. 2A  and  FIG. 2C , when the oil circuit Pc is exerting a pressure upon the power transmission unit  26  for forcing the top pin  265  to raise, and the same time that the first connecting unit  25  is enabled to separate the first rocker arm  22  from the tappet  23  while the second connecting unit  27  is enabled to separate the second rocker arm  24  from the tappet  23 , the rotation power of the first cam  28  will be received by the power transmission unit  26  and then transmitted to the first rocker arm  22 , however, the movement of first rocker arm  22  will be a stand along movement since the tappet  23  is not connected to the first rocker arm  22 . So that, only the first valve  20  is driven to perform a low lift as the first cam  28  is a Mid cam. 
   On the other hand, when the second cam  29 , being a high cam, is rotating and the tappet  23  is connected to the second rocker arm  24  by the second connecting unit  27 , the tappet  23  will be driven to move by the second cam  29  that further brings the second rocker arm  24  to move accordingly through the second connecting unit  27 , and eventually enables the second valve  21  with a high lift. Hence, under the same principle, other valve lift controls with respect to different settings of the valve actuation mechanism of  FIG. 2A  can be seen in the table shown in  FIG. 2E . 
   Please refer to  FIG. 3A , which is a schematic diagram showing a valve actuation mechanism according to a third embodiment of the invention. The valve actuation mechanism  3  of  FIG. 3A  is comprised of a first rocker arm  32 , a second rocker arm  24 , a tappet  33 , a first connecting unit  35 , a second connecting unit  37  and a power transmission unit  36 . In which, the first rocker arm  32 , being connect to a first valve  30 , is capable of being driven to move by a first cam  38  while the second rocker arm  32  is connected to a second valve  31  for enabling the same to control the lift of the second valve  31 . The tappet  33  is sandwiched between the first rocker arm  32  and the second rocker arm  34  that can be driven to move by a second cam  39 . It is noted that the connecting relations between the first cam  38 , the second cam  39 , the first rocker arm  32 , the second rocker arm  34 , the tappet  33 , the first connecting unit  35  and the second connecting unit  37  are the same as those illustrated in  FIG. 2A  and thus are not described further herein. 
   Please refer to  FIG. 3B , which is a schematic diagram showing a power transmission unit adopted by the valve actuation mechanism of  FIG. 3A . The power transmission unit  36 , being mounted on the first rocker arm  34 , is comprised of: a base  360 , having a first accommodation space  363 , a second accommodation space  365  and a hydraulic channel  367  containing a liquid; a first top pin  361  with a recess  3611  formed at a side thereof, being arranged inside the first accommodation space  363  while enabling the bottom thereof to connected to a first elastic member  364 ; and a second top pin  362 , being arranged inside the second accommodation space  365  while enabling a portion thereof to have connect with the hydraulic channel  367  and the bottom thereof to connect to a second elastic member  366 ; wherein, an end of the second top pin  362  is enabled to embed into/detach from the recess  3611  selectively by the action of the second elastic member  366  and the liquid. In a preferred aspect, the hydraulic channel  367  is connected to the oil circuit Pc of  FIG. 3A . 
   Operationally, when the first elastic member  364  of the power transmission unit  36  is not subjecting to any external force, the first top pin  361  is raised naturally thereby. Similarly, as not oil pressure is provided by the hydraulic channel  367  and thus the second elastic member  366  will not be subjected to any external force, the second top pin  362  will be pushed by move forward thereby that enable the top  3621  of the second top pin  362  to embed into the recess  3611 . By embedding the top  3621  of the second top pin  362  into the recess  3611  of the first top pin  361 , the first top pin  361  is fixed to a raised position, by which the first top pin  361  is able to have contact with the first cam  38  so as to transmit the driving force of the first cam  38  to the first rocker arm  32  for driving the same to move. However, when an oil pressure provided by the hydraulic channel  367  force the second top pin  362  to move to the right causing the top  3621  of the second top pin  362  to separate from the recess  3611  and as the rotating first cam  38  is contacting to the first top pin  361 , the force of the first cam  38  will be absorbed by the first elastic member  364  since the first top pin  361  is not supported by the second top pin  362  and thus the first rocker arm will not receive any power. 
   Please refer to  FIG. 3C , which is a schematic diagram illustrating the oil circuit control of  FIG. 3A . In  FIG. 3C , an oil circuit control unit  5  is designed and used for controlling the activations of the three oil circuits Pa, Pb, Pc. As seen in  FIG. 2D , two four-port two-way solenoid valves  60 ,  61  are used, in which the two ports, referring as A port and B port, are used as interfaces for connecting to working circuits, i.e. used for connecting to the three oil circuits Pa, Pb, Pc; and the port, referring as P port, is acting as pressure interface that is connected to a pump  62 ; and the port, referring as T port, is acting as a drain interface and is connected to an oil tank  63 . Moreover, a node indicated as a Y node on  FIG. 1B  is a joint connecting to a control valve. 
   As seen in  FIG. 3D , by the control of the three oil circuit Pa, Pb, Pc, a variety of connection statuses can be enabled through the first and the second connecting units  35 ,  37  that correspondingly various valve lifts of the first and the second valves  30 ,  31  can be realized. For instance, referring to  FIG. 3A  and  FIG. 3C , when the oil circuit Pc is not exerting any pressure upon the power transmission unit  36  so that the first top pin  361  is maintained at a raised position, and the same time that the first connecting unit  25  is enabled to separate the first rocker arm  32  from the tappet  23  since no oil pressure is provided by the oil circuit Pb; moreover, the second connecting unit  37  is enabled to separate the second rocker arm  34  from the tappet  23  also since no oil pressure is provided by the oil circuit Pa, the rotation power of the first cam  38  will be received by the power transmission unit  36  and then transmitted to the first rocker arm  32 , however, the movement of first rocker arm  32  will be a stand along movement since the tappet  33  is not connected to the first rocker arm  32 . So that, only the first valve  30  is driven to perform a low lift as the first cam  38  is a Mid cam. 
   On the other hand, when the second cam  39 , being a high cam, is rotating and the tappet  33  is connected to the second rocker arm  34  by the second connecting unit  37 , the tappet  33  will be driven to move by the second cam  39  that further brings the second rocker arm  34  to move accordingly through the second connecting unit  37 , and eventually enables the second valve  31  with a high lift. Hence, under the same principle, other valve lift controls with respect to different settings of the valve actuation mechanism of  FIG. 3A  can be seen in the table shown in  FIG. 3D . 
   To sum up, the present invention provides a valve actuation mechanism, capable of using no more than three oil circuits and no more then two solenoid valves for controlling valves of a cylinder to selectively operate in at least three operation modes, including enabling both valves with a high lift synchronously, and enabling one of two intake valves with a high lift while another with a low lift, and enabling both of two intake valves to close. 
   While the preferred embodiment of the invention has been set forth for the purpose of disclosure, modifications of the disclosed embodiment of the invention as well as other embodiments thereof may occur to those skilled in the art. Accordingly, the appended claims are intended to cover all embodiments which do not depart from the spirit and scope of the invention.