Abstract:
A variable valve system includes a camshaft in which a first lobe having a first height and a second lobe having a second height that is higher than the first height from a rotational center axis of the camshaft are formed; a first tappet that corresponds to the first lobe and that has a depression negatively formed in one side thereof; a second tappet corresponding to the second lobe and that is inserted into the depression; at least a pin positioned at the first tappet and fixing a position of the second tappet; and a hydraulic pressure control portion that transfers hydraulic pressure into the depression so as to move the second tappet upwards or downwards and to the pin so as to engage or disengage the first tappet with the second tappet.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims priority to and the benefit of Korean Patent Application No. 10-2007-0126237 filed in the Korean Intellectual Property Office on Dec. 6, 2007, the entire contents of which are incorporated herein by reference. 
       BACKGROUND OF THE INVENTION 
       [0002]    (a) Field of the Invention 
         [0003]    The present invention relates to a valve system, more particularly, the variable valve system equipped with a variable tappet. 
         [0004]    (b) Description of the Related Art 
         [0005]    Generally, technical developments are ongoing in a variety of fields of the vehicle industry. Among them, a field for improving fuel efficiency of an engine is important in aspects of environment and energy saving. 
         [0006]    An engine having CDA (cylinder de-activation) improves fuel efficiency by stopping function of some cylinders in an idle or low load driving condition. 
         [0007]      FIGS. 1A and 1B  show operating states of a valve system equipped with a general variable tappet. 
         [0008]    As shown, the valve system is equipped with a variable tappet. The variable tappet is provided on an upper end portion of a stem  1   a  of a valve. 
         [0009]    The variable tappet includes an inner tappet  3 , an outer tappet  5 , and a locking pin  7 . First cams  13  and a second cam  11  are formed on a camshaft  9 . 
         [0010]    The first cams  13  correspond to the outer tappet  5 , and the second cam  11  corresponds to the inner tappet  3 . 
         [0011]    The inner tappet  3  and the outer tappet  5  move together by the locking pin  7  as the locking pin  7  couples the outer tappet  5  and the inner tappet  3 , referring to  FIG. 1A . The stem  1   a  is moved by the first cams  13 . 
         [0012]    The inner tappet  3  and the outer tappet  5  may move separately, as the locking pin  7  is disengaged from the inner tappet  3 , referring to  FIG. 1B . The stem  1   a  is moved by the shorter second cam  11 . Further, the outer tappet  5  compresses a lost spring  1   b , so a movement of the stem  1   a  is restricted. 
         [0013]    The locking pin  7  is operated by hydraulic pressure. 
         [0014]    However, a movement of the valve by the first cam  13  is controlled by a movement of the outer tappet  5 , so there is a problem in that the overall length (L) of the variable tappets  3  and  5  is increased. 
         [0015]    The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art. 
       SUMMARY OF THE INVENTION 
       [0016]    The present invention has been made in an effort to provide a variable valve system having advantages of reducing length and weight of a variable tappet. 
         [0017]    A variable valve system includes: a camshaft in which a first lobe having a first height and a second lobe having a second height that is higher than the first height from a rotational center axis of the camshaft are formed; a first tappet that corresponds to the first lobe and that has a depression negatively formed in one side thereof; a second tappet corresponding to the second lobe and that is inserted into the depression; at least a pin positioned at the first tappet and fixing a position of the second tappet; and a hydraulic pressure control portion that transfers hydraulic pressure into the depression so as to move the second tappet upwards or downwards and to the pin so as to engage or disengage the first tappet with the second tappet, wherein an upper end face of the second tappet facing the second lobe is inserted into the depression by as much as a predetermined distance or protrudes out of the depression by as much as a predetermined distance according to a hydraulic pressure transferred from the hydraulic pressure control portion to the depression. 
         [0018]    The second tappet may be slidably coupled to an inner side of the depression, and the second tappet is elastically supported by a first spring. 
         [0019]    The variable valve system may further comprise a second spring supporting the pin that connects or disconnects the first tappet and the second tappet in accordance with hydraulic pressure supplied from the hydraulic pressure control portion. 
         [0020]    The variable valve system may further comprise a cylinder in which the pin is slidably coupled therein. 
         [0021]    At least a protrusion for restricting movement of the pin inwards may be formed inside the cylinder and at least a groove into which an end portion of the pin is inserted may be formed on an inner surface of the first tappet. 
         [0022]    The first lobes may be formed at both sides and the second lobe is formed between the first lobes and the depression is formed substantially in the middle of the first tappet. 
         [0023]    The pin may be provided at both end portions of the second spring and a stem connected to a valve for opening a port may be supported and moved by the first tappet. 
         [0024]    The hydraulic pressure control portion may include: a first oil path that fluidly communicates with the pin; and a second oil path that fluidly communicates between the pin and the depression. 
         [0025]    The hydraulic pressure control portion may further include a third oil path that fluidly communicates with the first oil path and a lower portion of the depression. 
         [0026]    As stated above, the length of a variable tappet is reduced and the weight thereof is small according to the valve system in an exemplary embodiment of the present invention. Accordingly, the valve system becomes compact and efficiency of an engine is improved. 
         [0027]    The above features and advantages of the present invention will be apparent from or are set forth in more detail in the accompanying drawings, which are incorporated in and form a part of this specification, and the following Detailed Description of the Invention, which together serve to explain by way of example the principles of the present invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0028]    The above and other features of the present invention will now be described in detail with reference to certain exemplary embodiments thereof illustrated the accompanying drawings which are given hereinbelow by way of illustration only, and thus are not limitative of the present invention, and wherein: 
           [0029]      FIG. 1A  shows a valve system equipped with a general variable tappet as locking pin couples outer tappet and inner tappet; 
           [0030]      FIG. 1B  shows a valve system equipped with a general variable tappet as locking pin is disengaged from inner tappet; 
           [0031]      FIG. 2  is a cross-sectional view showing a first state of a valve system equipped with a variable tappet according to an exemplary embodiment of the present invention; and 
           [0032]      FIG. 3  is a cross-sectional view showing a second state of a valve system equipped with a variable tappet according to an exemplary embodiment of the present invention. 
           [0033]      FIG. 4  is a cross-sectional view showing a valve system equipped with a variable tappet according to another exemplary embodiment of the present invention. 
       
    
    
       [0034]    It should be understood that the appended drawings are not necessarily to scale, presenting a somewhat simplified representation of various preferred features illustrative of the basic principles of the invention. The specific design features of the present invention as disclosed herein, including, for example, specific dimensions, orientations, locations, and shapes will be determined in part by the particular intended application and use environment. 
         [0035]    In the figures, reference numbers refer to the same or equivalent parts of the present invention throughout the several figures of the drawing. 
       DESCRIPTION OF REFERENCE NUMERALS INDICATING PRIMARY ELEMENTS IN THE DRAWINGS 
       [0000]    
       
         
           
               200 : camshaft 
               202 : stem 
               203 : depression 
               204 : valve 
               205 : cam unit 
               210 : first tappet 
               215 : second tappet 
               220 : first spring 
               225 : supporting portion 
               230 : pin 
               235 : groove 
               240 : second spring 
               250 ,  255 : oil path 
           
         
       
     
       DETAILED DESCRIPTION OF THE EMBODIMENTS 
       [0049]    Hereinafter reference will now be made in detail to various embodiments of the present invention, examples of which are illustrated in the accompanying drawings and described below. While the invention will be described in conjunction with exemplary embodiments, it will be understood that present description is not intended to limit the invention to those exemplary embodiments. On the contrary, the invention is 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. 
         [0050]    The drawings and description are to be regarded as illustrative in nature and not restrictive. Like reference numerals designate like elements throughout the specification. 
         [0051]    A valve system is explained according to an exemplary embodiment of the present invention referring to the accompanying drawings. 
         [0052]      FIG. 2  is a cross-sectional view showing a first state of a valve system equipped with a variable tappet according to an exemplary embodiment of the present invention. 
         [0053]    As shown in  FIG. 2 , a cam unit  205  is formed in a camshaft  200 , and includes first lobes  205   a  and a second lobe  205   b.    
         [0054]    The first lobes  205   a  have a first height L 1 , and the second lobe  205   b  has a second height L 2 . Here the second height L 2  is greater than the first height L 1 . Also, the first lobes  205   a  are formed at both sides of the cam unit  205 , and the second lobe  205   b  is positioned between the first lobes  205   a.    
         [0055]    A first tappet  210 , a second tappet  215 , a stem  202 , and a valve  204  are provided at a lower portion of the camshaft  200 . 
         [0056]    A depression  203  is negatively formed substantially in the middle of the first tappets  210 , and the second tappet  215  is complementarily inserted in the depression  203 . The stem  202  is directly connected to the first tappet  210 . Further, the valve  204  for opening/closing a port of a cylinder is formed in a lower end portion of the stem  202 . 
         [0057]    The first tappet  210  corresponds to the first lobe  205   a  and the second tappet  215  corresponds to the second lobe  205   b  in the present exemplary embodiment. 
         [0058]    A first oil path  250  and a second oil path  255  are formed in a lower portion of the first tappet  210 . Hydraulic pressure is transferred inside the depression  203  through the first oil path  250  and the second oil path  255 . The second tappet  215  moves in an upward direction or in a downward direction according to a supply of the hydraulic pressure. 
         [0059]    A supporting portion  225  is formed inside the depression  203 , and a first spring  220  is provided on the supporting portion  225 . The first spring  220  elastically supports the second tappet  215 . 
         [0060]    A first space  245  is formed inside the supporting portion  225 , and a second spring  240  is provided inside the first space  245 . The first oil path  250  fluidly communicates with the first space  245 , and the second oil path  255  is formed from the first space  245  to the depression  203  under the second tappet  215 . 
         [0061]    A cylinder  305  (referring to  FIG. 3 ) is provided at both sides of the first space  245 , and a pin  230  is installed in the cylinder  305  in  FIG. 3 . The pin  230  is connected or fixed to both end portions of the second spring  240 . 
         [0062]    The second spring  240  may elastically push the pin  230 . At least a protrusion  260  is formed along an inner surface of the first space  245  and the movement of the pin  230  may be supported by the protrusion  260 . 
         [0063]    The hydraulic pressure is supplied to the first oil path  250  such that a pressure of the first space  245  and the depression  203  is increased. Accordingly, the second tappet  215  moves in an upward direction and then the pin  230  moves to a groove  235  formed at an inner surface of the first tappet  210 . 
         [0064]    The second tappet  215  is in a first state in  FIG. 2 . That is, an upper end face of the second tappet  215  is inserted as much as a third length L 3  from an upper end face of the first tappet  210  inside the depression  203 . 
         [0065]    Further, the second tappet  215  is in a middle state ( 267 ) or a second state ( 265 ) according to a supply of the hydraulic pressure. An upper end face of the second tappet  215  has an equal height to an upper end face of the first tappet  210  in the middle state ( 267 ), and the upper end face of the second tappet  215  has a greater height of as much as L 1  to the upper end face of the first tappet  210  in the second state ( 265 ). 
         [0066]    The variable tappet according to an exemplary embodiment of the present invention has a length L 0  in the first state and a length L in the second state. The variable tappet according to the present exemplary embodiment has a shorter length of as much as L 1  compared to a general variable tappet. 
         [0067]      FIG. 3  is a cross-sectional view showing a second state of a valve system equipped with a variable tappet according to an exemplary embodiment of the present invention. 
         [0068]    As shown in  FIG. 3 , the second tappet  215  moves up by the hydraulic pressure that is supplied inside the depression  203 . Also, as a pressure of the first space  245  rises, the second spring  240  is elastically extended and the pins  230  move toward the first tappet  210  as explained hereinafter in detail. 
         [0069]    At least a groove  235  (referring to  FIGS. 2 and 3 ) may be formed in a lower portion of an inside surface of the first tappet  210  as an exemplary embodiment of the present invention. As a pressure to the first space  245  and depression  203  rises, the second tappet  215  moves upwards, the second spring  240  in the first space  245  is elastically extended and some portions of the pins  230  are inserted into the groove  235 . Accordingly, the pins  230  support a lower end portion of the second tappet  215  and thus restrict the downward movement of the second tappet  215 . 
         [0070]    As shown, the second tappet  215  protrudes from the upper end face of the first tappet  210  by as much as a fourth length L 4 . Accordingly, the variable tappet has an extended length L according to the present exemplary embodiment. Therefore, a distance that the stem  202  and the valve  204  move is equal to the length of the second length L 2  plus the fourth length L 4 . 
         [0071]    The hydraulic pressure can be supplied through the first oil path  250 , the first space  245 , and the second oil path  255  to the depression  203 . As another exemplary embodiment, a third oil path  300  may be further formed in a lower portion of the first tappet  210  as shown in  FIGS. 2 and 3  and thus the hydraulic pressure can be directly supplied to the depression  203  through the first oil path  250  and the third oil path  300 . 
         [0072]    However, when the hydraulic pressure descends through the first oil path  250 , the pins  230  are drawn out of the groove  235 . Further, the pins  230  move in a central direction to the protrusions  260  where the first space  245  is formed. The second tappet  215  descends when the pressure in the depression  203  falls. 
         [0073]      FIG. 4  is a cross-sectional view showing a valve system equipped with a variable tappet according to another exemplary embodiment of the present invention. 
         [0074]    As shown  FIG. 4 , a variable tappet according to another exemplary embodiment of the present invention includes a first tappet  400 , a groove portion  405 , a second tappet  410 , at least a cylinder  412 , an inner guide  420 , a first spring  415 , at least a second spring  430 , at least a pin  425 , an oil path  435  and a second oil path  440 . 
         [0075]    Groove portion  405  is formed at upper end portion of the first tappet  400 , traversing the center portion of the first tappet  400 . The second tappet  410  is assembled substantially at the center portion of the first tappet  400 . In the instant embodiment, the first lobe  205   a  is placed on upper portion of the first tappet  400  and the second lobe  205   b  is placed on the second tappet  410  positioned in the groove portion  405  of the first tappet  400 . 
         [0076]    The inner guide  420  is positioned in the second tappet  410  and outer circumference of the inner guide  420  is substantially fit into the inner circumference of the second tappet  410  as shown  FIG. 4 . 
         [0077]    First spring  415  is provided inside the second tappet  410  and thus supports elastically the second tappet  410 . 
         [0078]    Lower portion of the inner guide  420  is fixed to lower portion of the first tappet  400  and thus only the second tappet  410  moves up and down by the supplied hydraulic pressure as explained hereinafter. 
         [0079]    The cylinder  412  is formed substantially in the middle portion of the first tappet  400  and includes a guide  407  at one end of the cylinder  412  wherein the guide  407  is substantially near to inner circumference of the first tappet  400 . 
         [0080]    At least a pin  425  is provided inside the guide  407  and the second spring  430  attached to an end of the pin  425  is provided in the cylinder  412  wherein the other end of the second spring  430  is attached to the other end of the cylinder  412 . The second spring  430  is an extension spring for proving a restoring force. 
         [0081]    A second oil path  440  is provided at the other end of the cylinder  412 , fluidly communicating with the oil path  435  which supplies external hydraulic pressure to the pin  425 . 
         [0082]    From this configuration, while hydraulic pressure is not supplied through the oil path  435  and the second oil path  440 , the pin  425  stays inserted into the cylinder  412  by a restoring force of the second spring  430 . Accordingly the second tappet  410  may move up and down along the inner circumference of the first tappet  400 . 
         [0083]    In contrast, as the hydraulic pressure increases in the oil path  435  and the second oil path  440 , the second tappet  410  moves up by a hydraulic pressure supplied through the oil path  435  along a gap between the first tappet  400  and the inner guide  420  as shown  FIG. 4 . 
         [0084]    When the hydraulic pressure in the cylinder  405  increases sufficiently enough to overcome the restoring force of the second spring  430 , the pin  425  in the guide  407  of the cylinder  412  moves to the outer circumference of the inner guide  420  to a central direction of the inner guide  420  and thus the second tappet  410  that already moved up is locked by the pin  425 . The height of the second tappet  410  may be substantially the same as the height of the top portion of the first tappet  400  when the second tappet  410  is fully extended by external hydraulic pressure in an exemplary embodiment of the present invention. 
         [0085]    In contrast, as the hydraulic pressure in the cylinder  412  decreases, the pin  425  moves into the cylinder  412  by a restoring force of the second spring  430  such that the second tappet  410  moves down. 
         [0086]    Accordingly, when the second tappet  410  moves up, the lift amount of a valve is increased, and when the second tappet  410  moves down, the lift amount of a valve decreased. 
         [0087]    While this invention has been described in connection with what is presently considered to be practical exemplary embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, On the contrary, it is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.