Abstract:
Disclosed herein is a continuously variable valve lift system for an engine which is able to variably adjust valve lift and opening duration of intake and exhaust valves operated by the rotation of a cam shaft. The continuously variable valve lift system of the present invention has a compact structure, so that space required for the system in a cylinder head is reduced. Furthermore, the continuously variable valve lift system is provided at a position level with or below a position at which the cam shaft is installed, thus reducing the overall height of the cylinder head, thereby reducing the volume of the engine.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     The present application is based on, and claims priority from, Korean Application Serial Number 10-2005-0109123, filed on Nov. 15, 2005, the disclosure of which is hereby incorporated by reference herein in its entirety.  
       FIELD OF THE INVENTION  
       [0002]     The present invention relates to continuously variable valve lift systems for engines and, more particularly, to a continuously variable valve lift system for engines which is able to variably control opening and shutting times and periods of intake and exhaust valves operated by the rotation of a cam shaft.  
       BACKGROUND OF THE INVENTION  
       [0003]     As well known to those skilled in the art, it is impossible to vary valve lift or opening duration using typical cams provided in conventional engine systems. Furthermore, because the valve lift and opening duration are fixed as specific values, a fuel consumption ratio and power output of an engine cannot be optimized.  
         [0004]     In an effort to overcome the problems experienced with the conventional arts, recently, studies have been conduced on variation of opening and shutting times and periods of intake and exhaust valves in order to increase thermal efficiency and power output of engines. As part of these studies, a continuously variable valve lift system has been proposed.  
         [0005]     In detail, the continuously variable valve lift system is able to adjust opening and shutting times of intake and exhaust valves and factors such as valve lift, related to valve movement, such that they are optimized. For example, the system maximizes the inflow rate of the engine in a high-speed or high-loading condition that requires high output power. In a low-speed or low-loading condition in which it is important to increase a fuel consumption ratio or reduce exhaust gas, the system increases an EGR (exhaust gas recirculation) effect and minimizes throttle loss.  
         [0006]     However, in the conventional continuously variable valve lift system, structures of moving parts are complex. Furthermore, because the system requires a large space above a position at which a cam shaft is mounted in the cylinder head of the engine, the overall height of the cylinder head is increased.  
         [0007]     As a result, the volume of an engine having the conventional continuously variable valve lift system is increased. As well, due to an increase in space required for the cylinder head in an engine room, there is a spatial restriction in the installation of other elements in the engine room.  
       SUMMARY OF THE INVENTION  
       [0008]     Embodiments of the present invention provide a continuously variable valve lift system for an engine which is able to variably adjust valve lift and opening duration of intake and exhaust valves operated by the rotation of a cam shaft despite having a compact structure, so that the space required for the system in a cylinder head is reduced, and which is provided at a position level with or below the position at which the cam shaft is installed, thus reducing the overall height of the cylinder head, thereby reducing the volume of the engine.  
         [0009]     A continuously variable valve lift system according to an embodiment of the present invention includes a cam shaft which is provided in a cylinder head of an engine and rotated in conjunction with a crank shaft, with a plurality of cams provided on the cam shaft to open and shut intake and exhaust valves. A rotary adjuster is set such that a rotating angle thereof is variably adjusted depending on an operational condition of the engine, with first contact parts provided at predetermined positions on the rotary adjuster and having predetermined curvatures. Bearing members are compressed both by the cams and by the first contact parts of the rotary adjuster, such that moving tracks of the bearing members vary dependently with the cams and the first contact parts. Elastic members bring the bearing members into contact with the cams and the rotary adjuster. Rocker arms are in contact with and compressed by the bearing members and have second contact parts having predetermined curvatures. Each of the rocker arms is pivotably supported at a first end thereof by a lash adjuster and compresses at a second end thereof each of the intake and exhaust valves. The rotary adjuster is set such that a rotation center thereof is a level with or is lower than a rotation center of the cam shaft based on a lower surface of the cylinder head. The bearing members are disposed below the cam shaft and between the rotary adjuster and the rocker arms.  
         [0010]     The rotary adjuster may include a rotating shaft set such that a rotating angle thereof is adjusted by a step motor. A plurality of control cams may be provided at predetermined positions on the rotating shaft and oriented downwards. Each of the control cams may have the first contact part having the predetermined curvature. A rotating angle of the step motor may be adjusted by an electronic control unit (ECU) depending on a load of the vehicle when traveling.  
         [0011]     Each of the bearing members may include a support shaft disposed along a longitudinal center line of the bearing member. First contact rings may be rotatably fitted at predetermined positions over a circumferential outer surface of the support shaft, such that each of the first contact rings contacts each of the first contact parts of the rotary adjuster. Second contact rings may be rotatably fitted over the circumferential outer surface of the support shaft at positions close to inner sidewalls of the first contact rings, such that each of the second contact rings contacts each of the second contact parts of the rocker arms. A third contact ring may be rotatably fitted over the circumferential outer surface of the support shaft at a position close to inner sidewalls of the second contact rings and contact the associated cam. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]     For a better understanding of the nature and objects of the present invention, reference should be made to the following detailed description with the accompanying drawings, in which:  
         [0013]      FIG. 1  is a perspective view of a continuously variable valve lift system for engines, according to an embodiment of the present invention;  
         [0014]      FIG. 2  is an exploded perspective view of the continuously variable valve lift system of  FIG. 1 ;  
         [0015]      FIGS. 3 and 4  respectively are front and sectional views of the continuously variable valve lift system according to the present invention;  
         [0016]      FIG. 5  is a side view of  FIG. 3 ;  
         [0017]      FIG. 6  is a partially broken perspective view of a bearing member of the continuously variable valve lift system of  FIGS. 1 through 5 ;  
         [0018]      FIG. 7  is an exploded perspective view of the bearing member of  FIG. 6 ; and  
         [0019]      FIGS. 8 through 10  are views showing variation in valve lift during the operation of the continuously variable valve lift system according to the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0020]     Hereinafter, an embodiment of the present invention will be described in detail with reference to the attached drawings.  
         [0021]     As shown in  FIGS. 1 through 5 , a continuously variable valve lift system according to the embodiment of the present invention includes intake and exhaust valves  10  which are provided in a cylinder head of an engine, and a cam shaft  12  which is rotated in conjunction with a crank shaft and integrally has a plurality of cams  12   a  that function to open and shut the intake and exhaust valves  10 . The continuously variable valve lift system further includes a rotary adjuster  14 , which is disposed in the cylinder head, and a rotating angle of which is variably adjusted depending on an operational condition of the engine. First contact parts  16   a , having predetermined curvatures, are provided at predetermined positions on the rotary adjuster  14 . The continuously variable valve lift system further includes bearing members  18  which are provided in the cylinder head such that moving tracks of the bearing members  18  depend on and are varied by compression of the cams  12   a  and the first contact parts  16   a  of the rotary adjuster  14 , and elastic members  20  which bring the bearing members  18  into contact with the cams  12   a  and the rotary adjuster  14 . The continuously variable valve lift system further includes rocker arms  22 , each of which has second contact parts  22   a  having predetermined curvatures. The second contact parts  22   a  are in contact with and are compressed by each bearing member  18 , the moving track of which depends on and varies with both the profile of each cam  12   a , provided on the cam shaft  12 , and the profiles of the first contact parts  16   a  of the rotary adjuster  14 .  
         [0022]     Each of the rocker arms  22  is pivotably supported at a first end thereof by each hydraulic lash adjuster  24  and is coupled at a second end thereof to an upper end of each of the intake and exhaust valves  10  to compress the intake or exhaust valve  10 .  
         [0023]     In this embodiment, the rotation center of the rotary adjuster  14  is set such that it is not higher than the rotation center of the cam shaft  12  based on a lower surface of the cylinder head. In other words, the rotation center of the rotary adjuster  14  is the same as or is lower than the rotation center of the cam shaft  12 .  
         [0024]     Furthermore, the bearing members  18  are disposed below the cam shaft  12  and between the rotary adjuster  14  and the rocker arms  22 .  
         [0025]     Meanwhile, the rotary adjuster  14  includes a rotating shaft  14   a  which is rotatably installed in the cylinder head, and a rotating angle of which is adjusted by a step motor  26 , and control cams  16  which are provided at predetermined positions on the rotating shaft  14   a  and are oriented downwards. Each control cam  16  has a first contact part  16   a  having a predetermined curvature. The rotating angle of the step motor  26  is adjusted by an electronic control unit (ECU) according to the load of the vehicle when traveling. That is, the electronic control unit adjusts the rotating angle of the step motor  26  according to the load of the vehicle when traveling, so that the valve lift and the opening duration by rotation of the cam shaft  12  are adjusted.  
         [0026]     In this embodiment, each first contact part  16   a  integrally has a first guide surface which is convexly curved towards the associated bearing member  18 , and a second guide surface which extends from the first guide surface and is concavely curved with respect to the bearing member  18 .  
         [0027]     Furthermore, each elastic member  20  comprises a torsion spring which is fastened at a first end thereof to the cylinder head and is supported at second ends thereof by each bearing member  18 .  
         [0028]     The second contact parts  22   a  of each rocker arm  22  are curved in concave shapes with respect to the bearing member  18  to effectively receive compression force transferred from the associated bearing member  18 .  
         [0029]     As shown in  FIGS. 6 and 7 , each bearing member  18  includes a support shaft  18   a  which is disposed along a longitudinal center line of the bearing member  18 , and first contact rings  18   b  which are rotatably fitted over a circumferential outer surface of the support shaft  18   a  such that the first contact rings  18   b  are brought into contact with the associated first contact parts  16   a  of the rotary adjuster  14 . Each bearing member  18  further includes second contact rings  18   c  which are rotatably fitted over the support shaft  18   a  at positions close to inner sidewalls of the first contact rings  18   b  such that the second contact rings are brought into contact with the second contact parts  22   a  of each rocker arm  22 , and a third contact ring which is rotatably fitted over the support shaft  18   a  at a position close to inner sidewalls of the second contact rings  18   c  and is in contact with each cam  12   a.    
         [0030]     In this embodiment, a plurality of idle rollers  18   e  is provided between the support shaft  18   a  and the third contact ring  18   d  to ensure smooth rotation of the third contact ring  18   d  with respect to the support shaft  18   a.    
         [0031]     Furthermore, snap rings  19  are fitted over opposite ends of the support shaft  18   a  to prevent the first contact rings  18   b  from being removed from the support shaft  18   a  in an axial direction.  
         [0032]     As well, a stepped flange part  18   f , a cross-section of which is enlarged moving from the inside to the outside, is integrally provided on each of the opposite ends of the support shaft  18   a , so that each second end of the associated elastic member  20  is inserted and supported in a space defined between the stepped flange part  18   f  and the associated snap ring  19 .  
         [0033]     Therefore, in the continuously variable valve lift system of the present invention having the above-mentioned construction, as shown in  FIGS. 8 through 10 , when the step motor  26  rotates the rotating shaft  14   a  of the rotary adjuster  14  at a predetermined angle under the control of the electronic control unit, the setting angle of the first contact parts  16   a  of the control cams  16  provided on the rotary adjuster  14  varies.  
         [0034]     The cams  12   a  are rotated by the rotation of the cam shaft  12 , which contact the third contact rings  18   d  of the bearing members  18 , and compress the bearing members  18 . Then, the first contact rings  18   b  of the bearing members  18  are brought into contact with the first contact part  16   a  of the control cams  16  of the rotary adjuster  14 , and the second contact rings  18   c  of the bearing members  18  are brought into contact with the second contact parts  22   a  of the rocker arms  22 .  
         [0035]     In this case, the valve lift and the opening duration of the intake and exhaust valves  10  depend on and vary with the profiles of the cams  12   a , the profiles of the first contact parts  16   a  of the control cams  16  of the rotary adjuster  14  and the profiles of the second contact parts  22   a  of the rocker arms  22 .  
         [0036]     For example, as shown in  FIG. 8 , when the rotating angle of the rotating shaft  14   a  of the rotary adjuster  14  is at 0°, variation of valve lift and opening duration of the intake and exhaust valves  10  by the rotation of the cam shaft  12  is smallest. As shown in  FIG. 9  and  10 , when the rotating shaft  14   a  of the rotary adjuster  14  is rotated at 10° and 25° in a counterclockwise direction, that is, when the rotating angle of the rotating shaft  14   a  of the rotary adjuster  14  is increased, valve lift and opening duration of the intake and exhaust valves  10  are also gradually increased.  
         [0037]     As is apparent from the foregoing, in the present invention, elements of a continuously variable valve lift system, which is provided in a cylinder head of an engine and varies the valve lift and opening duration of intake and exhaust valves, are reduced to a rotary adjuster, a bearing member and a rocker arm, thus ensuring a compact layout in a design process.  
         [0038]     Furthermore, the reduced number of elements of the continuously variable valve lift system can reduce the weight of the system. Particularly, because the system is set such that the rotation center of a rotary adjuster is not higher than the rotation center of a cam shaft, the overall height of the cylinder head of the engine is not increased, so that the volume of the engine is reduced.