Patent Publication Number: US-2015068473-A1

Title: Multiple variable valve lift apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     The present application claims priority to Korean Patent Application No. 10-2013-0107885 filed on Sep. 9, 2013, the entire contents of which is incorporated herein for all purposes by this reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a multiple variable valve lift apparatus. More particularly, the present invention relates to a multiple variable valve lift apparatus for improving fuel consumption. 
     2. Description of the Related Art 
     Generally, an internal combustion engine receives fuel and air into a combustion chamber and generates power by combusting the fuel and the air. Herein, an intake valve is operated by drive of a camshaft, and air flows into the combustion chamber during when the intake valve is open. In addition, an exhaust valve is operated by drive of a camshaft, and air is exhausted from the combustion chamber while the exhaust valve is open. 
     Optimal operations of the intake valve or the exhaust valve are determined according to rotation speed of the engine. That is, lift and open/close timing of the valves are properly controlled according to rotation speed of the engine. A plurality of cams may be disposed at a camshaft such that a valve is operated by various lift for realizing suitable valve operation according to rotation speed of an engine. 
     In case that the plurality of cams are provided so as to drive the valve by various lift, the valve lift is changed as a cam portion forming the plurality of cams is moved along an axial direction of the camshaft such that one cam realizing the valve lift is selected according to situation. 
     Meanwhile, changing of the valve lift may be performed for changing open/close time of a valve as well as to select high or low of the valve lift. 
     However, if size of a cam lobe is entirely larger for increasing open time of a valve even though the high lift is not required, the valve lift is increased. In addition, mechanical friction is increased according to the valve lift is increased such that fuel consumption may be deteriorated. 
     The information disclosed in this Background of the Invention section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art. 
     SUMMARY OF THE INVENTION 
     Various aspects of the present invention are directed to providing a multiple variable valve lift apparatus having advantages of simultaneously improving fuel consumption and NVH (noise vibration harness) performance. 
     In an aspect of the present invention, a multiple variable valve lift apparatus connected with a valve opening and closing unit which is adapted to rolling-contact one end thereof with a cam and is operated to open or close by a rotation of the cam, and operating to select the cam which is rolling-contacted with the valve opening and closing unit for changing a valve lift, may include a normal cam rolling-contacting with the valve opening and closing unit so as to realize a normal lift of a predetermined valve, and a low cam rolling-contacting with the valve opening and closing unit so as to realize a valve lift which is lower and longer than the normal lift realized by the normal cam, wherein the normal cam or the low cam is selectively rolling-contacted to the valve opening/closing unit according to a driving state. 
     The valve is early opened and is lately closed to compare with the normal lift in the valve lift realized by the low cam. 
     The normal lift realized by that the normal cam is rolling-contacted with the valve opening and closing unit is a predetermined valve lift such that efficiency of an engine is improved when a vehicle is driven at a high speed and a normal speed. 
     The low cam realizes the valve lift by rolling-contacting with the valve opening and closing unit such that efficiency of an engine is improved when a vehicle is driven at a low speed. 
     The methods and apparatuses of the present invention may have other features and advantages which will be apparent from or are set forth in more detail in the accompanying drawings, which are incorporated herein, and the following Detailed Description, which together serve to explain certain principles of the present invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic diagram of a multiple variable valve lift apparatus according to an exemplary embodiment of the present invention. 
         FIG. 2  is a perspective view of a cam portion according to an exemplary embodiment of the present invention. 
         FIG. 3  is a graph showing valve lift by a normal cam and a LIVC cam according to an exemplary embodiment of the present invention. 
     
    
    
     It should be understood that the appended drawings are not necessarily to scale, presenting a somewhat simplified representation of various features illustrative of the basic principles of the invention. The specific design features of the present invention as disclosed herein, including, for example, specific dimensions, orientations, locations, and shapes will be determined in part by the particular intended application and use environment. 
     In the figures, reference numbers refer to the same or equivalent parts of the present invention throughout the several figures of the drawing. 
     DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS 
     Reference will now be made in detail to various embodiments of the present invention(s), examples of which are illustrated in the accompanying drawings and described below. While the invention(s) will be described in conjunction with exemplary embodiments, it will be understood that the present description is not intended to limit the invention(s) to those exemplary embodiments. On the contrary, the invention(s) is/are intended to cover not only the exemplary embodiments, but also various alternatives, modifications, equivalents and other embodiments, which may be included within the spirit and scope of the invention as defined by the appended claims. 
     An exemplary embodiment of the present invention will hereinafter be described in detail with reference to the accompanying drawings. 
       FIG. 1  is a schematic diagram of a multiple variable valve lift apparatus according to an exemplary embodiment of the present invention. 
     As shown in  FIG. 1 , a multiple variable valve lift apparatus  1  according to an exemplary embodiment of the present invention includes a camshaft  100 , cam portions  40  and  60 , a solenoid  10 , an operating unit  30  and  50 , an interlock unit  70 , and a pin operating unit  20 . Herein, the operating unit  30  and  50  and interlock unit  70  compose an operating portion which operates for changing valve lift, and the solenoid  10  and the pin operating unit  20  compose a control portion which controls the operation of the operating unit  30  and  50  and interlock unit  70 . 
     The camshaft  100  is a shaft which is rotated by rotation of a crankshaft of an engine. The camshaft  100  is well-known to a person of ordinary skill in the art such that a detailed description thereof will be omitted. 
     The cam portion  40  and  60  is a portion that a cam  41 ,  42 ,  48 ,  49 ,  61 ,  62 ,  68 , and  69  for operating an intake valve or an exhaust valve of an engine is formed, and is formed in a hollow cylinder shape having uniform thickness. In addition, the camshaft  100  is inserted into the hollow of the cam portion  40  and  60 . Thus, an entire shape of the cam portion  40  and  60  and the camshaft  100  is to be a shape that the cam portion  40  and  60  is protruded from an exterior circumference of the camshaft  100 . Herein, the hollow of the cam portion  40  and  60  is formed in a circle shape corresponding to an external circumference of the camshaft  100 . That is, an interior circumference of the cam portion  40  and  60  is contacted to an exterior circumference of the camshaft  100 . Furthermore, an interior circumference of the cam portion  40  and  60  is slid on an exterior circumference of the camshaft  100  such that the cam portion  40  and  60  is moved along an axial direction of the camshaft  100 . Meanwhile, the cam portion  40  and  60  is disposed to rotate together with the camshaft  100 . The composition that the cam portion  40  and  60  is movable along an axial direction of the camshaft  100 , and the cam portion  40  and  60  and the camshaft  10  are coupled with each other such that the cam portion  40  and  60  and the camshaft  100  are rotated together can be realized by types such as the spline according to design of a person of ordinary skill in the art. 
     The cam portion  40  and  60  includes two cam portions  40  and  60  which are a first cam portion  40  and a second cam portion  60 . Herein, the first cam portion  40  is adapted to operate a valve disposed at one cylinder, and the second cam portion  60  is adapted to operate a valve disposed at another cylinder. Further, the first cam portion  40  can be provided for two valves disposed at one cylinder, and the second cam portion  60  can be provided for two valves disposed another cylinder. 
     In  FIG. 1 , a multiple variable valve lift apparatus  1  which is adapted to operate a valve at two cylinders of a multi-cylinder engine having at least two cylinders is shown. Herein, the valve is the intake valve or the exhaust valve. 
     The first cam portion  40  includes a first low cam  41 , a first normal cam  42 , a second low cam  48 , a second normal cam  49 , and a first connecting portion  45 . 
     The first normal cam  42  and second normal cam  49  may be formed in a general cam shape that an exterior circumference of a cut-plane is formed in an oval shape such that one end thereof is relatively further protruded to compare with the other end thereof. Typically, the one end of the cam is called “cam lobe”, and the other end of the cam is called “cam base”. 
     The cam base is a base circle of a cam, a part of an external circumference of the cam, which is formed in an arc shape having uniform radius. In addition, the cam lobe is a part of an external circumference of the cam  41 ,  42 ,  48 , and  49  which pushes the valve opening/closing unit  5  from when opening of the valve is started to when closing of the valve is ended by rotation of the cam  41 ,  42 ,  48 , and  49 . Herein, the valve opening/closing unit  5  is a device that one end thereof is rolling-contacted with the cams  41 ,  42 ,  48 , and  49  so as to be operated to open/close the valves by the rotation of the cams  41 ,  42 ,  48 , and  49 . The valve opening/closing unit  5  is well-known to a person of an ordinary skill in the art such that a detailed description thereof will be omitted. 
     The first low cam  41  and the first normal cam  42  are formed to be close with each other, and the second low cam  48  and the second normal cam  49  are formed to be close with each other. In addition, the first low cam  41  and the first normal cam  42  are paired with each other so as to operate one valve, and the second low cam  48  and the second normal cam  49  are paired with each other so as to operate the other valve. 
     The first connecting portion  45  connects the pair of the first low cam  41  and the first normal cam  42  with the pair of the second low cam  48  and the second normal cam  49 . That is, the first connecting portion  45  is disposed between the pair of the first low cam  41  and the first normal cam  42  and the pair of the second low cam  48  and the second normal cam  49 , and the first cam portion  40  is monolithically molded. 
     Meanwhile, the cam lobes of the first and second normal cams  42  and  49  may be further protruded from an exterior circumference of the camshaft  100  to compare with the cam lobes of the first and second low cams  41  and  48 . In addition, the cam lobes of the first normal cam  42  and second normal cam  49  may be formed such that an engine has regular intake or exhaust timing that is predetermined by a person of an ordinary skill in the art. Herein, the valve lift for realizing the regular intake or exhaust timing predetermined by a person of an ordinary skill in the art will be called “normal lift”. Furthermore, the cam lobes of the first low cam  41  and the second low cam  41  are formed such that time from when opening of the valve is started to when closing of the valve is ended by rotation of the first low cam  41  and the second low cam  41  is relatively long to compare with the first normal cam  42  and second normal cam  49  and the first low cam  41  and the second low cam  41  realize the relative low valve lift to compare with the first normal cam  42  and second normal cam  49 . 
     Therefore, the normal lift of the valve is realized when the valve opening/closing unit  5  is connected with the normal cam  42  and  49  so as to rolling-contact with the normal cam  42  and  49 , and the low lift of the valve that open time thereof is increased is realized when the valve opening/closing unit  5  is connected with the low cam  41  and  48  so as to rolling-contact with the low cam  41  and  48 . Furthermore, the first and second normal cams  42  and  49  or the first and second low cams  41  and  48  for operating the valve are selected according to the first cam portion  40  moves along an axial direction of the camshaft  100 . 
     The second cam portion  60  includes a third low cam  61 , a third normal cam  62 , a fourth low cam  68 , a fourth normal cam  69 , and a second connecting portion  65 . 
     Herein, the descriptions regarding the third low cam  61 , the third normal cam  62 , the fourth low cam  68 , the fourth normal cam  69 , and the second connecting portion  65  are respectively corresponded to the descriptions regarding the first low cam  41 , the first normal cam  42 , the second low cam  48 , the second normal cam  49 , and the first connecting portion  45 , and thus will be omitted. 
     The solenoid  10  is provided so as to transform the rotation motion of the camshaft  100  to the rectilinear motion of the first cam portion  40  or the second cam portion  60 . That is, the first cam portion  40  or the second cam portion  60  is rectilinearly moved along an axial direction of the camshaft  100  according to the rotation motion of the camshaft  100  if the solenoid  10  is operated. Herein, the solenoid  10  operated to on or off by an electrical control the solenoid  10  is well-known to a person of an ordinary skill in the art such that a detailed description thereof will be omitted. 
     The operating unit  30  and  50  is formed in a cylinder shape having a hollow like to the first and second cam portions  40  and  60 , and the camshaft  100  is inserted into the hollow of the operating unit  30  and  50  such that the operating unit  30  and  50  is disposed on an exterior circumference of the camshaft  100 . In addition, the hollow of the operating unit  30  and  50  may be formed that an internal circumference of the operating unit  30  and  50  is corresponded with an external circumference of the camshaft  100 . Further, an external circumference of the operating unit  30  and  50  is formed in a circle shape having uniform radius. Furthermore, an interior circumference of the operating unit  30  and  50  is slid on an exterior circumference of the camshaft  100  such that the operating unit  30  and  50  is moved along an axial direction of the camshaft  100 , and the operating unit  30  and  50  is adapted to rotate together with the camshaft  100 . 
     The solenoid  10  includes a low lift solenoid  12  and a normal lift solenoid  14 , and the operating unit  30  and  50  includes a low lift operating unit  30  and a normal lift operating unit  50 . 
     The low lift operating unit  30  is integrally formed with the first cam portion  40  or is adapted to move together with the first cam portion  40 . In addition, the low lift operating unit  30  rotating together with the camshaft  100  is moved in one direction along an axial direction of the camshaft  100  according to the operation of the low lift solenoid  12 . Thus, the low lift that open time of the valve is relatively increased to compare with the normal lift. While it is shown that the low lift operating unit  30  is disposed at one end of the first low cam  41  in  FIG. 1 , it is not limited thereto in the disclosed embodiment. 
     For better comprehension and convenience of description, a forward direction will be defined a word as the one direction that the low lift operating unit  30  is moved for realizing the low lift of the valve and a reverse direction will be defined a word as an opposite direction of the forward direction. 
     The normal lift operating unit  50  is integrally formed with the second cam portion  60  or adapted to move together with the second cam portion  60 . In addition, the normal lift operating unit  50  rotating together with the camshaft  100  is moved in the other direction along an axial direction of the camshaft  100  according to the operation of the normal lift solenoid  14 . Thus, the normal lift of the valve is realized. While it is shown that the normal lift operating unit  50  is disposed at one end of the third normal cam  62  in  FIG. 1 , it is not limited thereto in the disclosed embodiment. 
     The interlock unit  70  is formed in a cylinder shape having a hollow like to the operating units  30  and  50  and the first and second cam portions  40  and  60 , and the camshaft  100  is inserted into the hollow of the interlock unit  70  such that the interlock unit  70  is disposed on an exterior circumference of the camshaft  100 . In addition, the hollow of the interlock unit  70  may be formed that an internal circumference of the interlock unit  70  is corresponded with an external circumference of the camshaft  100 . Further, an external circumference of the interlock unit  70  is formed in a circle shape having uniform radius. Furthermore, an interior circumference of the interlock unit  70  is slid on an exterior circumference of the camshaft  100  such that the interlock unit  70  is moved along an axial direction of the camshaft  100 , and the interlock unit  70  is adapted to rotate together with the camshaft  100 . 
     The interlock unit  70  is disposed between the integrally formed first cam portion  40  and the integrally formed second cam portion  60 . In addition, the interlock unit  70  performs a function that the first cam portion  40  and the second cam portion  60  are interlocked with each other. 
     The interlock unit  70  is operated to move in the forward direction if the low lift operating unit  30  moves in the forward direction. In addition, the integrally formed second cam portion  60  is pushed by the interlock unit  70  according to the interlock unit  70  is moved in the forward direction. Thus, the second cam portion  60  is moved in the forward direction. 
     The interlock unit  70  is operated to move in the reverse direction if the normal lift operating unit  50  moves in the reverse direction. In addition, the integrally formed first cam portion  40  is pushed by the interlock unit  70  according to the interlock unit  70  is moved in the reverse direction. Thus, the first cam portion  40  is moved in the reverse direction. 
     The pin operating unit  20  is provided for moving the interlock unit  70  along an axial direction of the camshaft  100 . In addition, the pin operating unit  20  includes a housing  21 , a hinge unit  22 , a first pin  24 , a second pin  25 , and a pin fixing unit  27 . 
     The housing  21  is a body of the pin operating unit  20  that the hinge unit  22 , the first pin  24 , the second pin  25 , and the pin fixing unit  27  are mounted thereat. 
     The hinge unit  22  is adapted to perform hinge motion around a hinge shaft  23  mounted to the housing  21 . 
     The first pin  24  and second pin  25  may be formed in a bar shape which is extended along one direction. 
     The first pin  24  is pushed by the hinge unit  22  according to the hinge motion of the hinge unit  22  such that the first pin  24  moves toward a direction to be protruded from the housing  21 . In addition, the hinge unit  22  is pushed by the first pin  24  according to the first pin  24  is to be positioned at its original position such that the hinge unit  22  performs the opposite hinge motion. Further, the second pin  24  is pushed by the hinge unit  22  according to the hinge unit  22  performs the opposite hinge motion such that the second pin  25  moves toward a direction to be protruded from the housing  21 . That is, the pin operating unit  20  is operated to interlock the first and second pins  24  and  25  with each other such that if one of the first pin  24  and the second pin  25  is to be positioned at original position to be not protruded from the housing  21 , the other of the first pin  24  and the second pin  25  is to be protruded from the housing  21 . 
     The pin fixing unit  27  is provided for fixing the pin positioned at original position of the first and second pin  24  and  25 . A hooking groove  29  is formed at the first and second pin  24  and  25  for hooking the pin fixing unit  27  on the state that the first pin  24  or second pin  25  is positioned at original position, and the pin fixing unit  27  performs reciprocating motion between the first pin  24  and the second pin  25  such that a part of the pin fixing unit  27  is seated at the hooking groove  29  for fixing the pin positioned at original position of the first pin  24  and the second pin  25 . 
     The pin fixing unit  27  is operated by a spring  28 . In addition, the pin fixing unit  27  is seated at the hooking groove  29  formed at the one of the first and second pins  24  and  25  by relatively small force generated by pushing of the spring  28  and is escaped from the hooking groove  29  by relatively strong force generated by operation of the first and second pins  24  and  25 . The hooking groove  29  and the part of pin fixing unit  27  contacted with the hooking groove  29  may be formed in a gradually curved surface such that the operation is easily performed. 
     The low lift operating unit  30 , the normal lift operating unit  50 , and the interlock unit  70  include the guide rail  32 ,  52 , and  72 . 
     The guide rail  72  of the interlock unit  70  is formed to be contacted with the first pin  24  or the second pin  25  protruded from the housing  21  by the operation of the pin fixing unit  27  and guide motion of the interlock unit  70 . That is, when the camshaft  100  rotates on the state that the first pin  24  or second pin  25  is inserted into the guide rail  72  of the interlock unit  70 , the interlock unit  70  is moved along an axial direction of the camshaft  100  according to the guide rail  72  guides relative movement of the first pin  24  or second pin  25  with the rotation of the interlock unit  70  that the first pin  24  or second pin  25  is moved along an exterior circumference of the interlock unit  70 . 
     The low lift solenoid  12  includes a connecting pin  16  protruded by a bar shape, and the connecting pin  16  is contacted with the guide rail  32  of the low lift operating unit  30  according the operation of the low lift solenoid  12 . In addition, the guide rail  32  of the low lift operating unit  30  is formed to contact with the connecting pin  16  and guide the motion of the low lift operating unit  30 . That is, when the camshaft  100  rotates on the state that the connecting pin  16  is inserted into the guide rail  32  of the low lift operating unit  30 , the low lift operating unit  30  is moved in the forward direction along an axial direction of the camshaft  100  according to the guide rail  32  guides relative movement of the connecting pin  16  with the rotation of the low lift operating unit  30  that the connecting pin  16  is moved along an exterior circumference of the low lift operating unit  30 . 
     The normal lift solenoid  14  includes a connecting pin  18  protruded by a bar shape, and the connecting pin  18  is contacted with the guide rail  52  of the normal lift operating unit  50  according to the operation of the normal lift solenoid  14 . In addition, the guide rail  52  of the normal lift operating unit  50  is formed to contact with the connecting pin  18  and guide the motion of the normal lift operating unit  50 . That is, when the camshaft  100  rotates on the state that the connecting pin  18  is inserted into the guide rail  52  of the normal lift operating unit  50 , the normal lift operating unit  50  is moved in the reverse direction along an axial direction of the camshaft  100  according to the guide rail  52  guides relative movement of the connecting pin  18  with the rotation of the normal lift operating unit  50  that the connecting pin  18  is moved along an exterior circumference of the normal lift operating unit  50 . 
     The guide rails  32 ,  52 , and  72  may be formed in a groove shape recessed from the exterior circumferences of the operating units  30  and  50  and the interlock unit  70 . In addition, the groove shape guide rails  32 ,  52 , and  72  are longitudinally formed along a circumferential direction of the operating units  30  and  50  and the interlock unit  70 . 
     Furthermore, the guide rails  32 ,  52 , and  72  are formed in a slanted shape as a set slope with reference to an axial direction of the camshaft  100  on an exterior circumference of the operating unit  30  and  50  or the interlock unit  70  such that the operating unit  30  and  50  and the interlock unit  70  are moved in one direction along an axial direction of the camshaft  100 . 
     The first cam portion  40 , the interlock unit  70 , and the second cam portion  60  are sequentially moved in the forward direction by the rotation of camshaft  100  according to the shape of the guide rail  32 ,  52 , and  72 . The successive motion is for minimizing interference between the cam portion  40  and  60  and the valve according to the change of the valve lift is performed by on the state that the cam base is contacted with the valve. 
     The low lift operating unit  30  and the first cam portion  40  is integrally moved toward the forward direction when the connecting pin  16  is moved along the guide rail  32  by the rotation of the low lift operating unit  30 . In addition, the first cam portion  40  moves in the forward direction and pushes the interlock unit  70  as a set distance toward the forward direction. 
     The interlock unit  70  is moved toward the forward direction according to the first pin  24  is moved along the guide rail  72  by rotation of the interlock unit  70  pushed as the set distance in the forward direction. In addition, the interlock unit  70  is contacted with the second cam portion  60 , and pushes the second cam portion  60  toward the forward direction such that the second cam portion  60  is moved in the forward direction. 
     Meanwhile, at least one of gap between the first cam portion  40  and the interlock unit  70  and between the second cam portion  60  and the interlock unit  70  is to be always disposed apart from each other. The disposing apart is for sequentially moving the first cam portion  40 , the interlock unit  70 , and the second cam portion  60  according to the interlock unit  70  is moved between the first cam portion  40  and the second cam portion  60 . In addition, the timings for changing the valve lifts of the cylinder which at the first cam portion  40  is disposed and the cylinder which at the second cam portion  60  is disposed are determined according to the disposing apart and the shape of the guide rails  32 ,  52 , and  72 . Further, the distance, that the interlock unit  70  moves along an axial direction, determined by the shape of the guide rail  72  is longer than the distance, that the low lift operating unit  30  moves along an axial direction, determined by the shape of the guide rail  32 . 
     The successive motions toward the reverse direction of the second cam portion  60 , the interlock unit  70 , and the first cam portion  40  are started according to the connecting pin  18  of the normal lift solenoid  14  is inserted into the guide rail  52  of the normal lift operating unit  50  with reference to the valve timing of the cylinder which at the second cam portion  60  is disposed, on the contrary to the successive motions toward the forward direction of the first cam portion  40 , the interlock unit  70 , and the second cam portion  60 . 
     The second cam portion  60 , the interlock unit  70 , and the first cam portion  40  are sequentially moved in the reverse direction by the rotation of camshaft  100  according to the shape of the guide rail  32 ,  52 , and  72 . The successive motion is for minimizing interference between the cam portion  40  and  60  and the valve according to the change of the valve lift is performed by on the state that the cam base is contacted with the valve. 
     The normal lift operating unit  50  and the second cam portion  60  is integrally moved toward the reverse direction when the connecting pin  18  is moved along the guide rail  52  by the rotation of the normal lift operating unit  50 . In addition, the second cam portion  60  moves in the reverse direction and pushes the interlock unit  70  as a set distance toward the reverse direction. 
     The interlock unit  70  is moved toward the reverse direction reverse direction the second pin  25  is moved along the guide rail  72  by rotation of the interlock unit  70  pushed as the set distance in the reverse direction. In addition, the interlock unit  70  is contacted with the first cam portion  40 , and pushes the first cam portion  40  toward the reverse direction such that the first cam portion  40  is moved in reverse direction. 
     Meanwhile, the distance, that the interlock unit  70  moves along an axial direction, determined by the shape of the guide rail  72  is longer than the distance, that the normal lift operating unit  50  moves along an axial direction, determined by the shape of the guide rail  52 . 
     The multiple variable valve lift apparatus  1  may be applied to an in-line four or more than four cylinder engine for operating valves respectively disposed at cylinders by equal to or more than four according to constituent elements such as the first and second cam portions  40  and  60  and the interlock unit  70  are further disposed thereat by the same type. 
     The multiple variable valve lift apparatus  1  applied to an in-line four or more than four cylinder engine is operated by only the two solenoids  12  and  14  too. In addition, the operation of the multiple variable valve lift apparatus  1  is started by the motion along axial direction of the one cam portion, and is performed according to the interlock units  70  and the cam portions are sequentially and alternately moved toward one direction. 
     According to the multiple variable valve lift apparatus  1 , the composition can be simple and the operations can be simultaneously efficient by the pin operating unit  20  and the interlock unit  70  moving along axial direction of the camshaft  100  by the operation of the pin operating unit  20 . In addition, interference between constituent elements can prevented as the cam portions  40  and  60  disposed at each cylinder are operated step by step by the interlock unit  70 . Furthermore, spatial utility can be improved and cost can be simultaneously reduced as a number of the solenoids  10  are to be minimized. 
     Meanwhile, It is not limited that the normal cams  42 ,  49 ,  62 , and  69  realizing the normal lift and the low cams  41 ,  48 ,  61 , and  68  realizing the low lift having the open time of the valve which is relatively longer to compare with the normal lift are the multiple variable valve lift apparatus  1  according to an exemplary embodiment of the present invention, and the normal cams  42 ,  49 ,  62 , and  69  and the low cams  41 ,  48 ,  61 , and  68  can be applied to the all multiple variable valve lift apparatus that the cam rolling-contacting with the valve opening/closing unit  5  is selected for changing the valve lift. 
       FIG. 2  is a perspective view of a cam portion according to an exemplary embodiment of the present invention. In addition, the first cam portion  40  is shown in  FIG. 2 . 
     Hereinafter, the cam portions  40  and  60  forming the low cams  41 ,  48 ,  61 , and  68  and the normal cams  42 ,  49 ,  62 , and  69  will be described in detail based on the first cam portion  40  shown in  FIG. 2 . That is, the first cam portion  40  will be representatively described about the cam portions  40  and  60  which may be additionally provided to the multiple variable valve lift apparatus  1 . 
     As shown in  FIG. 2 , a spline  44  is formed on an interior circumference of the cam portion  40  and  60 , and the low cams  41 ,  48 ,  61 , and  68  and the normal cams  42 ,  49 ,  62 , and  69  are formed on an exterior circumference of the cam portion  40  and  60 , and the cam portion  40  and  60  may be integrally formed with the operating unit  30  and  50 . 
     The cam lobes of the low cams  41 ,  48 ,  61 , and  68  are formed along external circumferences of the cam portion  40  and  60  on relatively wider range to compare with the cam lobes of the normal cams  42 ,  49 ,  62 , and  69 . Therefore, the time from when opening of the valve is started to when closing of the valve is ended by the rotation of the low cams  41 ,  48 ,  61 , and  68  is longer than the time from when opening of the valve is started to when closing of the valve is ended by the rotation of normal cams  42 ,  49 ,  62 , and  69 . 
     Herein, in case that the intake valve is opened/closed by the low cams  41 ,  48 ,  61 , and  68 , amount of effective air remained in the combustion chamber may be decreased and power loss of a piston performing reciprocal motion in a cylinder of an engine may be minimized according to air flowed into a combustion chamber in the low speed low load of an engine flows backward through an intake hole of an engine. 
     the operation for increasing the open time of the intake valve and for doing that the close timing the valve is later than a close timing of the valve by the normal cams  42 ,  49 ,  62 , and  69  is called “late intake valve close (LIVC)”, and the cam realizing the valve lift of the operation is called “LIVC cam”, and the LIVC and LIVC cam are well known to a person of an ordinary skill in the art. 
     Meanwhile, the low cams  41 ,  48 ,  61 , and  68  which are the LIVC cam according to an exemplary embodiment of the present invention are adapted to realize the valve lift which is lower than the normal lift. According to the low cams  41 ,  48 ,  61 , and  68 , mechanical friction may be decreased and fuel consumption may be improved to compare with case that the LIVC cam realizes the valve lift which is higher than the normal lift. 
     Hereinafter, it will be defined that the low cams  41 ,  48 ,  61 , and  68  according to an exemplary embodiment of the present invention have same mean with the LIVC cam. In addition, the valve lift realized by the LIVC cams  41 ,  48 ,  61 , and  68  will be called “LIVC lift”. 
       FIG. 3  is a graph showing valve lift by a normal cam and a LIVC cam according to an exemplary embodiment of the present invention. 
     In  FIG. 3 , horizontal axis is time of valve lift, and vertical axis is size of valve lift. In addition, a curved line C1 illustrated by a dotted line represents the normal lift, a curved line C2 illustrated by a solid line represents the LIVC lift. 
     As shown in  FIG. 3 , size L2 of the LIVC lift by the LIVC cams  41 ,  48 ,  61 , and  68  is smaller than size L1 of the normal lift by the normal cams  42 ,  49 ,  62 , and  69 . In addition, time of the LIVC lift by the LIVC cams  41 ,  48 ,  61 , and  68  is longer than by time of the normal lift the normal cams  42 ,  49 ,  62 , and  69 . Meanwhile, shapes of the LIVC cams  41 ,  48 ,  61 , and  68  is changed and applied by a person of an ordinary skill in the art such that size L2 of the LIVC lift is smaller than size L1 of normal lift and time of the LIVC lift is longer than time of the normal lift. 
     According to an exemplary embodiment of the present invention, required torque of the cam can be minimized as the LIVC lift is realized by the low lift to compare with the normal lift, and noise and vibration generated in an engine can be minimized as drive impact of the valve is reduced. In addition, the velocity of the intake air flowed into an engine may become fast, and combust stability may be ensured, and fuel consumption can be improved as the LIVC lift is realized by the low lift to compare with the normal lift. Furthermore, the valve overlap time that open times of the intake valves are overlapped with each other is maximized according to design freedom about open timing of the intake valve can be improved. 
     For convenience in explanation and accurate definition in the appended claims, the terms “upper”, “lower”, “inner” and “outer” are used to describe features of the exemplary embodiments with reference to the positions of such features as displayed in the figures. 
     The foregoing descriptions of specific exemplary embodiments of the present invention have been presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the invention to the precise forms disclosed, and obviously many modifications and variations are possible in light of the above teachings. The exemplary embodiments were chosen and described in order to explain certain principles of the invention and their practical application, to thereby enable others skilled in the art to make and utilize various exemplary embodiments of the present invention, as well as various alternatives and modifications thereof. It is intended that the scope of the invention be defined by the Claims appended hereto and their equivalents.