Abstract:
A valve train device is provided for swinging a rocker arm, which is pivotally disposed on a rocker arm support shaft. The device comprises a drive device for driving the rocker arm, an intermediate member disposed between the drive device and the rocker arm and configured to transfer movement of the drive device to the rocker arm, and a displacement device. The displacement device is configured to displace a contact point between the rocker arm and the intermediate member to continuously adjust at least one of the valve opening duration and valve lift.

Description:
PRIORITY INFORMATION 
     The present application is a continuation of PCT Application No. PCT/JP03/06202, filed on May 19, 2003, which claims priority under 35 U.S.C. § 119 to Japanese Patent Application No. 2002-143037, filed on May 17, 2002, and the entire contents of both of which are expressly incorporated by reference herein. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to an engine valve train device for continuously controlling an opening duration or a lift of a valve. 
     2. Description of the Related Art 
     Conventionally, engine valve train devices for continuously controlling an opening duration and a lift of a valve have been in practical use. For example, there has been proposed such a valve train device in JP-A-Sho59-500002, in which, to open and close intake and exhaust valves by cam shafts via rocker arms, a swinging member for each valve is disposed and swung by the camshaft, an intermediate roller is interposed between a swing cam face of the swinging member and the rocker arm, and the valve opening duration and the valve lift can be continuously changed by displacing the intermediate roller. 
     Now, in such conventional valve train devices, the shorter the valve opening duration, the smaller the lever ratio of the rocker arm, and, in contrary, the longer the valve opening duration, the larger the lever ratio of the rocker arm. Due to the larger lever-ratio for a longer valve opening duration, a distal end of the rocker arm presses against the valve, and the intermediate roller presses against the intermediate portion of the rocker arm. As a result, it is difficult to secure rigidity of the entire valve opening/closing device. In particular, accuracy of control over the valve opening duration and the valve lift is apt to reduce during operation at high engine speeds. Further, due to a smaller lever-ratio for a shorter valve opening duration, it is difficult to secure the valve lift for a shorter valve opening duration, which is disadvantageous for reduction of pumping loss and improvement of combustibility. Thus, controllability of valve opening and closing timing is also apt to worsen. 
     SUMMARY OF THE INVENTION 
     Therefore, an object of the invention is to provide a valve train device that is rigid, provides accurate control of the valve lift for shorter valve opening duration, and provides the ability to continuously control the valve opening and closing timing. 
     Accordingly, one embodiment of the present invention comprises a valve train device of an engine for swinging a rocker arm, which is pivotally disposed on a rocker arm support shaft. The valve opens and closes a valve opening in a combustion chamber. The device comprises a drive device for driving the rocker arm, an intermediate member disposed between the drive device and the rocker arm and configured to transfer movement of the drive device to the rocker arm, and a displacement device. The displacement device includes a moveable portion that is coupled to an arm. A portion of the arm movies about a first axis. The displacement device is configured such that at least one of the valve opening duration and valve lift is increased as the moveable portion is displaced farther from the first axis. 
     Accordingly, another embodiment of the present invention comprises a valve train device of an engine for swinging a rocker arm, which is pivotally disposed on a rocker arm support shaft. The valve opens and closes a valve opening in a combustion chamber. The device comprises a drive device for driving the rocker arm and an intermediate member disposed between the drive device and the rocker arm and configured to transfer movement of the drive device to the rocker arm. The device also includes displacement means for displacing a contact point between the rocker arm and the intermediate member to continuously adjust at least one of the valve opening duration and valve lift where at least one of the valve opening duration or valve lift is increased as the contact point is displaced further from the rocker arm support shaft. 
     For purposes of summarizing the invention, certain aspects, advantages and novel features of the invention have been described herein. It is to be understood that not necessarily all such advantages may be achieved in accordance with any particular embodiment of the invention. Thus, the invention may be embodied or carried out in a manner that achieves or optimizes one advantage or group of advantages as taught herein without necessarily achieving other advantages as may be taught or suggested herein. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A general architecture that implements various features of specific embodiments of the invention will now be described with reference to the drawing. The drawing and the associated descriptions are provided to illustrate embodiments of the invention and not to limit the scope of the invention. 
         FIG. 1  is a cross-sectional side view, showing a first embodiment of a valve train device in a first position. 
         FIG. 2  is a cross-sectional side view of the first embodiment of the device in a second position. 
         FIG. 3  is a front, perspective view of the first embodiment of the device. 
         FIG. 4  is a front view of the first embodiment of the device. 
         FIG. 5  shows a graph of a cam angle-lift characteristic curve of the first embodiment of the device. 
         FIG. 6  is a cross-sectional side view of a second embodiment of the device in a first position. 
         FIG. 7  is a cross-sectional side view of the second embodiment of the device in a second position. 
         FIG. 8  is a perspective view of a third embodiment of the device. 
         FIG. 9  is a front view of the third embodiment of the device. 
         FIG. 10  is a cross-sectional side view of a fourth embodiment of the. 
         FIG. 11  is a cross-sectional side view of a fifth embodiment of the device 
         FIG. 12  is a cross-sectional side view of the device of a fifth embodiment according to the invention. 
         FIG. 13  is a cross-sectional side view of a sixth embodiment of the device in a first position. 
         FIG. 14  is a cross-sectional side view of a sixth embodiment of the device in a second position. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Several embodiments of the invention are described with reference to the accompanying drawings. 
       FIGS. 1 through 5  describe a first embodiment.  FIG. 1  and  FIG. 2  are cross-sectional side views, showing a smaller opening state and a larger opening state on an intake valve side, respectively, of a valve train device of an engine.  FIG. 3  and  FIG. 4  are a front perspective view and a side view of the first embodiment, respectively.  FIG. 5  shows a cam angle—lift characteristic curve of the first embodiment. 
     In the embodiments described below, reference will be made to the intake valve. However, it should be appreciated that certain features and aspects of these embodiments may also be applied to an exhaust valve. It should also be appreciated that various features, aspects and advantages of the present invent may be used with engines having more than one intake valve and/or exhaust valve, and any of a variety of configurations including a variety of numbers of cylinders and cylinder arrangements (V, W, opposing, etc. 
     Referring to  FIG. 1 , reference numeral  1  denotes a valve device for opening and closing valve openings that open into a combustion chamber. The valve device is constituted as follows. A right and a left intake opening  2   b  are formed in a combustion recess  2   a  that is formed in a cylinder head  2  and that forms part of a combustion chamber on a ceiling side thereof. Each intake valve opening  2   b  is in fluid communication with an intake port  2   c , which in turn leads to an external connection port in an engine wall. Also, each intake valve opening  2   b  is opened and closed by a valve head  3   a  of an intake valve  3 . The intake valve  3  is normally biased by a valve spring  6  that is interposed between a retainer  4 , which is mounted at the top end of a valve stem  3   b  of the intake valve  3  and is prevented from moving axially, and a spring seat  5  that is placed on a seat surface of the cylinder head  2 . 
     A valve train device  7  is disposed over the intake valves  3  and is constituted such that an intake camshaft  8 , which functions as a swinging member driving device to swings each swinging member  9 . The swinging member  9  swings a rocker arm  11  through an intermediate rocker  10 , and the swinging movement of the rocker arm  11  forces the intake valve  3  to travel to and fro in its axial direction, thereby opening and closing the valve opening  2   b.    
     The intake camshaft  8  is arranged parallel to a crankshaft (not shown), supported for rotation and prevented from moving in both of its axial direction and a direction normal to the axial direction, by cam journals formed in the cylinder head  2  and corresponding cam caps mounted on an upper mating surface of the cam journals. The intake camshaft  8  is formed with one cam nose  8   c  which is in common with the right and left intake valves and consists of a base circle section  8   a  having a constant outside diameter and a lift section  8   b  having a predetermined cam profile. 
     The swinging member  9  includes a pair of swing arm portions  9   a ,  9   a , a swing cam face  9   b , a roller shaft  9   c , and swing roller  9   d . The pair of swing arm portions  9   a ,  9   a  is supported for free rotation by a swing shaft  12  that is arranged parallel to the intake camshaft  8  and is prevented from moving in its axial direction and a direction normal thereto. The swing cam face  9   b  is formed so as to connect both the distal ends (lower ends) of the paired swing arm portions  9   a ,  9   a . The roller shaft  9   c  is disposed midway of the swing arm portions  9   a  and parallel to the swing shaft  12  so as to pass through the right and left swing arm portions  9   a ,  9   a . The swing roller  9   d  is supported for rotation by the roller shaft  9   c , the swing roller  9   d  normally being in contact with the cam nose  8   c  for rotation. 
     The swing shaft  12  passes through the bases (upper end portion) of the swing arm portions  9   a  and swings. A pair of right and left balancing springs  13  of coil springs are mounted to the swing shaft  12 . Each balancing spring  13  has a first end  13   a  that engages an edge positioned on the opposite side of the camshaft and between the roller shaft  9   c  and the swing shaft  12  of the swing arm portions  9   a , and has a second end that engages the cylinder head  2 . The paired balancing springs  13  bias the swinging member  9  so that the swing roller  9   d  contacts the cam nose  8   c  of the intake camshaft  8 , to thereby avoid the weight of the swinging member  9  from acting on the valve spring  6 . 
     The swing cam face  9   b  is generally shaped as a plate, having a curved surface in a base circle section  9   e  and a lift section  9   f  which are connected to each other continuously. The swinging member  9  is arranged in a way that the base circle section  9   e  is located on a rocker shaft side  14  and the lift section  9   f  is located on the opposite side thereof. The base circle section  9   e  is an arc having a radius R 1  and a swinging axis (a) which is an axis of the swing shaft  12 . Accordingly, while the base circle section  9   e  is in contact with the swing roller  9   d  and the swinging angle of the swinging member  9  increases, the intake valve  3  remains in its fully closed position and is not lifted. 
     On the other hand, as the point of the lift section  9   f  which presses against the swinging roller  9   d  progresses toward an apex of the lift section  9   f  and the swinging angle of the swinging member  9  becomes larger, the intake valve  3  is lifted more. The lift section  9   f  is constituted with a ramp zone for a constant velocity, an acceleration zone for acceleration of velocity, and a lift zone for an approximately constant velocity. 
     The rocker arm  11  is formed in one body such that it has a cylindrical base  11   c , and right and left arm portions  11   d  extending forward (on the side of the intake valves). The base  11   c  is supported, for swing, by the rocker shaft  14  that is disposed parallel to the intake camshaft  8  and on the side of an axis of the cylinder. At the lower portion of the distal end of each arm portion  11   d  is formed a valve pressing face  11   a  so as to press against a shim  3   c  that is mounted to the upper end of a valve stem  3   b  of the intake valve  3 . In an upper peripheral portion of each arm portion  1   d  is formed a pressurized rocker face  11   b , which is pushed by a rocker pin  10   a  of the intermediate rocker  10 . The pressurized rocker face  11   b  is formed into an arc having a radius R 2  about the swinging axis (a) of the swinging member  9 , as seen in the direction of the camshaft with the valve being fully closed. 
     The rocker shaft  14  is constituted so that the angular position of the rocker shaft  14  is freely controlled by a drive mechanism (not shown). Midway of the rocker shaft  14  is formed an eccentric pin portion  14   a  that has a diameter smaller than any other portions and deviated outwardly in a radial direction from the axis b of the rocker shaft  14 . An engagement recess  10   c  formed in the base end of the intermediate arm portion  10   b  of the intermediate rocker  10  is rotationally engaged with the eccentric pin portion  14   a.    
     The intermediate rocker  10  is generally configured such that both distal ends of the paired right and left intermediate arm portions  10   b  are fixedly connected to each other by the rocker pin  10   a  extending in the direction of the camshaft, and the rocker roller  10   d  is rotationally supported by the rocker pin  10   a . The distal ends of the intermediate arm portions  10   b  may be coupled by engagement of the rocker pin  10   a . The rocker roller  10   d  rotationally contacts the swing cam face  9   b  of the swinging member  9 , and the rocker pin  10   a  slidably contacts the pressurized rocker face  11   b  of the rocker arm  11 . 
     Thus, a displacing device is constituted such that the drive mechanism varies the angular position of the rocker shaft  14  to move or displace the positions of both the intermediate rocker roller  10   d  of the intermediate rocker  10  and the intermediate rocker pin  10   a  along the pressurized rocker face  11   b.    
     A rocker lever ratio may be defined as Lv/Lc, where Lc is a distance between the swinging axis (b) of the rocker arm  11  and a straight line (A) which connects the swinging center (a) of the swinging member  9  and the point at which the swing cam face  9   b  contacts the intermediate rocker roller  10   d ; and Lv is a distance between the valve axis and the swinging center (b) of the rocker arm  11 . The lever ratio increases as the opening duration of the valve becomes shorter. 
     The drive mechanism changes the angular position of the rocker shaft  14  to move or displace the positions of the intermediate rocker roller  10   d  and the intermediate rocker pin  10   a  of the intermediate rocker  10  along the swing cam face  96  and the pressurized rocker face  11   b , causing the valve lift and the valve opening angle to change continuously. The drive mechanism controls the angular position of the rocker shaft  14  in such a manner that the valve opening angle and the valve lift increase as the valve opening increases in response to the opening of an acceleration pedal, for example. 
     Specifically, in  FIG. 1 , for example, in a small opening state in which the valve opening duration is shortest and the maximum valve lift is smallest, the rocker shaft  14  is rotated at a position where the eccentric pin portion  14   a  is farthest away from the swing cam face  9   b . The contact point (c) between the swing cam face  9   b  and the rocker roller  10   d  is therefore positioned farthest away from the lift section  9   f . Also, the rocker lever ratio (Lv/Lc) reaches its largest value because the contact point (c) is brought into a position closest to the swinging center (b) of the rocker arm  11 , and the distance Lc is shortest. For this state, a lift curve is therefore drawn as a curve C 1  shown in  FIG. 5 . 
     Meanwhile, in  FIG. 2 , for a large opening state in which the valve opening duration is longest and the maximum valve lift is largest, the rocker shaft  14  is rotated at a position where the eccentric pin portion  14   a  is closest to the swing cam face  9   b . The contact point (c′) between the swing cam face  9   b  and the intermediate rocker roller  10   d  is therefore positioned nearest to the lift section  9   f , and, more specifically, at a position close to a boundary between the lift section  9   f  and the base circle section  9   e . Also, the rocker lever ratio (Lv/Lc) reaches its smallest value because the contact point (c′) is remote from the swinging center (b) of the rocker arm  11  and the distance Lc is largest. For this state, a lift curve is therefore drawn as a curve C 3  shown in  FIG. 5 . With a transition from the small opening state to the large opening state, the lift curve is, as shown in  FIG. 6 , continuously changed from the curve C 1  to the curve C 3 . 
     In  FIG. 5 , lift curves C 1 ′ to C 3 ′ are comparative examples in case of a constant rocker lever ratio. This comparative device has the same large opening state as that of the present invention. The changes in the valve lift from the large opening state to the small opening state are comparatively shown. It is apparent from those curves that, in the comparative device, the lift curves show large drops of the valve lift from the curve C 3 ′ to C 2 ′ and to C 1 ′, and, in contrast, in this embodiment, the lift curves show that the lift drops are suppressed from the curve C 3  to C 2  and to C 1 . It is also clear that if the valve opening of the embodiment and the comparative device is the same, then the lift drop of the embodiment is smaller than that of the comparative devices. 
     In each lift curve of  FIG. 5 , outer portions outside of the valve opening duration represent a ramp zone in which the valve lift height corresponds to a valve clearance. Within this ramp zone, the valve is not opened due to the valve clearance in a cold state. However, the valve will be slightly opened nearly from the end of the ramp zone by thermal expansion of the valve stem in a hot operation of the engine. 
     In the embodiment, the swinging member  9  swings with the rotation of the camshaft  8 , and the swinging of the swinging member  9  causes the swing cam face  9   b  to push against the intermediate rocker roller  10   d , thereby oscillating the intermediate rocker member  10 . Then, the intermediate rocker pin  10   a  of the intermediate rocker member  10  oscillates the rocker arm  11  to open and close the intake valve  3 . 
     Subsequently, the rotation of the rocker shaft  14  continuously displaces the intermediate rocker roller  10   d  of the intermediate rocker member  10 , the swing cam face  9   b  of the intermediate rocker pin  10   a , and the contact point (c) with the pressurized rocker face  11   b , which allows the valve opening duration and the valve lift to be controlled continuously. 
     Further, this embodiment is highly versatile, since there is no phase lag between the valve lift curves in the large and small opening durations. In other words, common mechanisms and components may be used for a right bank and a left bank of a V-engine. 
     Using the rotational motion of the rocker shaft  14  to move the intermediate rocker member  10 , an extremely simple configuration can be obtained, resulting in an improvement of accuracy of control over the valve opening duration and the maximum valve lift. 
     For the purpose of displacing the contact point (c) using the rotational motion of the rocker shaft  14 , a constitution is adopted that the base end of the intermediate rocker member  10  is swingably coupled with the eccentric pin portion  14   a  formed midway of the rocker shaft  14 . The rotation of the rocker shaft  14  causes the intermediate rocker roller  10   d  and the intermediate rocker pin  10   a  to displace along the swing cam face  9   b  and the pressurized rocker face  11   b . As a result, with an extremely simple constitution, the valve opening duration and the valve lift can be changed continuously. 
     A relative slide which occurs between the intermediate rocker pin  10   a  of the intermediate rocker member  10  and the pressurized rocker face  11   b  of the rocker arm  11  when the valve is opened and closed can be considerably reduced, since the rocker shaft  14  as the swinging axis of the rocker arm  11 , and the eccentric pin portion  14   a  as the swinging axis of the intermediate rocker member  10  are positioned in proximity to each other. 
     Meanwhile, as shown in  FIG. 2 , for a large opening state in which the valve opening duration is long and the maximum valve lift is large, the intermediate rocker roller  10   d  and the intermediate rocker pin  10   a  of the intermediate rocker member  10  are displaced to the opposite sides of the rocker shaft. Accordingly, the rocker lever ratio (Lv/Lc) is small, to thereby push atop of the intake valve  3 . Bending moment acting on the rocker arm  11  is therefore reduced, resulting in an increase of rigidity of the entire valve opening and closing mechanism. 
     On the other hand, in a small opening state in which both the valve opening duration and the maximum valve lift are small, as shown in  FIG. 1 , the intermediate rocker roller  10   d  and the intermediate rocker pin  10   a  are displaced to the rocker shaft  14  side. Accordingly, the rocker lever ratio (Lv/Lc) is large, and it is therefore easy to secure the maximum valve lift, in spite of a short opening duration of the valve (Refer to the curves C 1  and C 1 ′, in  FIG. 5 ). From this, it is possible to contemplate reduction of pumping loss, improvement of combustion, prevention of the ramp velocity in the valve lift curve from lowering, and ability to control timing of the valve opening and closing. 
     Further, the swing roller  9   d  is disposed within a space defined by lines connecting between the swinging center (a) of the swinging member  9  and both ends of the swing cam face  9   b , as seen in the direction of the camshaft. As a result, bending moment generated due to a rotary force of the camshaft  8  at a portion for supporting the swing roller  9   d  can be caused to be smaller, compared with a conventional configuration in which a swing roller is supported at the distal end of a separate arm, for example, and the resultant rigidity of the swinging member is increased. 
     Furthermore, the balance springs  13  are provided for rotatably urging the swing member  9  in a direction that restricts the weight of the swing member  9  from working on the valve spring  6 , which urges the valve in a closed state. Therefore, disposing the swing member  9  does not increase load on the valve spring  6 . Thus, there is no need to increase the spring load of the valve spring  6 , thereby providing optimum follow-up characteristics of the valve at high engine speed. 
       FIGS. 6 and 7  are drawings for describing a second embodiment according to the invention, in which the same reference numerals and symbols as those in  FIGS. 1 and 2  represent the same parts or the equivalents. 
     The second embodiment is an example in which the camshaft is of crankshaft type. That is, a crankshaft (camshaft)  18  includes a drive shaft  19   a  and a disk-like cam plate  19   b , which is formed midway of the drive shaft  19   a  in one body and located eccentrically relative thereto. To the cam plate  19   b  is rotatably mounted a base  20   a  of a plate-like connecting rod  20 , the distal end  20   b  of which is also rotatably coupled with a roller shaft  9   c  of the swinging member  9 . 
     In the second embodiment, rotation of the drive shaft  19   a  eccentrically rotates the cam plate  19   b  about the axis (d). The connecting rod  20  oscillates the swinging member  9 , and this swinging motion causes the rocker arm  11  to open and close the intake valve  3  through the intermediate rocker member  10 . 
     In the second embodiment, since the camshaft is of a crankshaft type, it is possible to oscillate the swinging member  9  easily, securely with ability to follow exactly, the valve opening duration and the valve lift are controllable accurately, and any balancing spring is not needed. 
       FIGS. 8 and 9  are drawings for description of a third embodiment according to the invention, in which the same reference numerals and symbols as those in  FIGS. 1 and 2  represent the same parts or the equivalents. 
     The third embodiment is an example in which separate valve train devices  7 ,  7  are provided for the right and left intake valves  3 ,  3 ′, respectively. Specifically, it is constituted such that a left cam nose  8   c  and a right cam nose  8   c ′ oscillate a left swinging member  9  and a right swinging member  9 ′, respectively, which in turn oscillate a left rocker arm  11  and a right rocker arm  11 ′, respectively, which subsequently advance and retract the intake valves  3 ,  3 ′, respectively, to thereby open and close the intake valve openings  2   b ,  2   b′.    
     In the third embodiment, since the left and right valve train devices  7 ,  7 ′ are separately disposed, an appropriate geometry of the left and right cam noses  8   c ,  8   c ′, left and right swing cam faces  9   b ,  9   b ′, and left and right intermediate rockers  10 ,  10 ′ allow the intake valves  3 ,  3 ′ to operate at different open and close timings as well as with different amounts of valve lift. 
       FIG. 10  is a drawing for description of a fourth embodiment according to the invention, in which the same reference numerals and symbols as those in  FIGS. 8 and 9  represent the same parts or the equivalents. The fourth embodiment is an example in which a swing cam face  9   b  of a swinging member  9  presses against an intermediate rocker roller  10   d . A pressing portion  10   e  is provided so as to project sideward from a side face of the distal end of a intermediate arm portion  10   b  and overlap the rocker arm  11 . A pressing face  10   f  is formed in a lower surface of the distal end of the pressurized rocker face  11   b  of the rocker arm  11 . 
     In this embodiment, the intermediate rocker  10  has an intermediate arm portion  10   b , the base end of which is bifurcated and fitted in an eccentric pin portion  14   a . An engagement pin  10   g  is passed through the bifurcated portion to shut the eccentric pin portion  14   a . In such a way, the intermediate rocker  10  is rotationally coupled with a rocker shaft  14 . 
     As described above, the rocker arm  11  is not pressed directly by the intermediate rocker pin  10   a , but is pressed by the pressing face  10   f  that has a large curvature and is formed in the intermediate rocker  10 . It is therefore possible to relax contact stress on the rocker pressing face and also to reduce the number of parts to be required. 
     In the embodiments described thusfar, it has been described that the swinging member  9  is supported by the swing shaft  12  and the rocker arm  11  is supported by the rocker shaft  14 . However, in other embodiments, the swinging member  9  and the rocker arm  11  may be supported by a spherical pivot, respectively. 
     Also, it has been described that the drive device for swinging the swinging member  9  is a camshaft  8  or  18 . However, the drive device is not limited to the camshaft. In other embodiments, any other type of driving devices, such as a solenoid type or a cylinder type that are capable of swinging the swinging member  9  in response to the engine speed may be used. 
     Further, in the embodiments described, the displacing device for the intermediate rocker  10  is of eccentric pin type that is incorporated in the rocker shaft  14 . However, this displacing device is not limited to the eccentric pin type. Any other type of displacing device, such as a solenoid type or a cylinder type, may be used, which, in brief, are capable of displacing the intermediate rocker  10  so as to change the contact points between the rocker roller and rocker pin and the swing cam face and the pressurized rocker face. 
       FIGS. 11 and 12  are drawings that depict a fifth embodiment according to the invention, in which the same reference numerals and symbols as those in  FIGS. 1 to 10  represent the same parts or the equivalents. 
     The fifth embodiment is an example in which a roller  9   d  is attached to the swinging member  9  and rotationally contacts a cam nose  8   c  of a camshaft  8 . A relative length Lc′ between an axis (d) of a roller shaft  9   c  of a roller  9   d  and an axis (a) of a swing shaft  12  of the swinging member  9  is variable. The roller  9   d  is guided by changing the relative length in the direction D, which is inclined relative to a straight line (E) connecting the axis (a) with the axis (d). 
     Specifically, a lever ratio. Lv/Lc′ of the swinging member when the valve opening duration is short is determined to be larger than that when the valve opening duration is long, where Lc′ is defined as a relative distance between the axis (a) of the swing shaft  12  of the swinging member  9  and the axis (d) of a camshaft abutment portion (roller)  9   d  of the swinging member  9  which contacts with the cam nose  8   c , and Lv is defined as a distance between an axis (b) of a swing shaft  14  of the rocker arm  11  and the valve axis (B). 
     Midway of the swinging member  9  is formed a guide  9   g  which is an elongated slot through the swinging member  9 . A roller shaft  9   c  is passed through the guide  9   g  and is displaceable in the direction D. The roller shaft  9   c  has an axis (d) parallel to the swing shaft  12  and supports the roller  9   d  for rotation. 
     The guide  9   g  is formed in shape of an elongated slot for guiding the roller shaft  9   c  to a predetermined distance in the longitudinal direction of the guide  9   g . The guide direction (the axis of the guide) (D) is defined to be inclined relative to the straight line (E) which connects the axis (a) of the swinging member  9  and the axis (d) of the roller  9   d . More specifically, the guide  9   g  is guided in a way that the larger the relative length Lc′ becomes (the more close to the state shown in  FIG. 12 ), the more the guide  9   g  advances on the camshaft  8  side, and, on the contrary, the smaller the relative length Lc′ becomes (the more close to the state shown in  FIG. 11 ) the more the guide  9   g  retracts on the opposite side of the camshaft  8 . 
     The swinging member  9  is provided with a roller (abutment portion) variable mechanism  30  for varying the relative length Lc′ of the roller  9   d . The roller variable mechanism  30  includes a drive shaft  31  formed to have an axis (e) which is parallel to the axis (a) and positioned to be eccentric in a radial direction thereof and an arm  32  having one end  32   a  which is connected with the roller  9   c  and having the other end  32   b  which is coupled with a drive shaft  31  for rotation relative thereto. The other end  32   b  is formed to be bifurcated and provided with a pin  32   c  for preventing the drive shaft  31  from coming off. 
     Here, an actuator (not shown) for rotating the swing shaft  12  about the axis (a) is coupled with an outer, axial end of the swing shaft  12  and is connected to a control device for controlling an angular position of the swing shaft  12 , in response to the engine speed or engine load. 
     In the range of an idling operation or low-speed, low-load operation, as shown in  FIG. 11 , the actuator rotates the swing shaft  12  of the swinging member  9  to an angular position so that the axis (e) of the drive shaft  31  is positioned across the axis (a) of the swing shaft  12  from the roller  9   c . At this time, the roller  9   d  is brought into a right end position of the guide  9   g , which is the farthest position from the camshaft  8 , resulting in the shortest relative length Lc′ and the largest lever ratio (Lv/Lc′) of the swinging member. At this time, the roller  9   d  is positioned on the opposite side of the camshaft  8 . The swinging member  9  therefore contacts the rocker roller  10  at a right end (as shown in the drawing) of a base circle section  9   e  of the swing cam face of the swing ember  9 , resulting in the shortest opening duration and the smallest lift of the valve  3 . 
     As the engine speed and load become higher, as shown in  FIG. 12 , the actuator rotates the swing shaft  12  of the swinging member  9  to an angular position so that the axis (e) of the drive shaft  31  is positioned on the roller  9   c  side. 
     At this time, the roller  9   d  is brought into a left end position of the guide  9   g , which is the nearest position from the camshaft  8 , resulting in the longest relative length Lc′ and the smallest lever ratio (Lv/Lc′) of the swinging member. At this time, the roller  9   d  is positioned on the camshaft  8  side. The swinging member  9  therefore contacts the rocker roller  10  at a left end (as shown in the drawing) of a base circle section  9   e  of the swing cam face of the swing ember  9 , resulting in the longest opening duration and the largest lift of the valve  3 . 
     Also, in this embodiment, since a lever ratio Lv/Lc′ of the swinging member in the engine operation range of a short valve opening duration is determined to be larger than that in the engine operation range of a long opening duration, the same effects as described in  FIG. 5  are achieved. In other words, at the same valve opening, the valve lift drop is smaller than that in case of a constant lever ratio of the swinging member. 
     Further, since the roller variable mechanism  30  is constituted such that rotation of the swing shaft  12  of the swinging member  9  displaces the position of the drive shaft  31  and thus the position of the roller  9   d , the relative distance between the roller  9   d  as a camshaft abutment portion and the swinging shaft  12  can be changed with a simple constitution. 
     Furthermore, since the longitudinal axis (D) of the elongated slot like guide  9   g  for guiding the roller  9   d  to the predetermined position is inclined relative to the straight line (E) of the swinging member  9 , varying the relative distance Lc′ between the roller  9   d  and the swing shaft  12  also varies the valve lift and the valve opening duration. Appropriate settings of the inclination angle and inclination direction of the longitudinal axis (D) allow for optional selection of the valve lift and valve opening duration. 
     Since the abutment portion to the camshaft  8  is a roller  9   d  that contacts and rotates on the cam nose  8   c  of the camshaft  8 , it is possible to reduce the loss of the driving force transmitted from the camshaft  8  to the camshaft abutment. 
       FIGS. 13 and 14  are drawings for description of a sixth embodiment according to the invention, in which the same reference numerals and symbols as those in  FIGS. 11 and 12  represent the same parts or the equivalents. 
     In the sixth embodiment, a rocker arm  11  serves as the swinging member in each embodiment described above, and an relative distance Lc″ between the rotation axis (d) of the roller  9   d  driven by the camshaft  8  and the swinging axis (b) of the rocker arm  11  is variable. 
     Specifically, the rocker arm  11  is supported by a swing shaft  14  and swung about a swinging axis (b). The rocker arm  11  is biased by a biasing spring (not shown) in clockwise direction as shown in the drawing, to thereby normally press a rocker pressing face against the roller shaft  9   c , and press the roller  9   d  against a cam nose  8   c  of the camshaft  8 . The rocker arm  11  is formed with a cam face consisting of a base circle section  9   g  which is a concentric circle whose center is the swinging center (b) and does not lift the valve  3  with increase of the swinging angle, and a lift section  9   f  for lifting the valve  3  with increase of the swinging angle of the rocker arm  11  in counterclockwise, as shown in the drawing. The cam face presses and drives the valve  3  via a valve lifter  4   a  that is disposed at the top end of the valve  3 . 
     The rocker arm  11  is provided with a roller variable mechanism  30  for varying the relative distance Lc″. This roller variable mechanism  30  includes a drive shaft  31  that is formed at a position radially eccentric from the axis (b) of the swing shaft  14  and has an axis (e) parallel to the axis (b), and an arm  32  having one end  32   a  coupled with the roller shaft  9   c  and the other end  32   b  coupled with the drive shaft  31  for rotation relative thereto. The other end  32   b  is formed to be bifurcated and provided with a pin  32   c  for preventing the drive shaft  31  from coming off. 
     Here, an actuator (not shown) for rotating the swing shaft  14  about the axis (b) is coupled with an outer, axial end of the swing shaft  14  and is connected to a control device for controlling an angular position of the swing shaft  14 , in response to the engine speed or engine load. 
     Now, a rocker lever ratio Lv/Lc″ when the valve opening duration is short, where Lc″ is a relative distance between the axis (b) of the swing shaft  14  of the rocker arm  11  and the axis (d) of the roller  9   d , and when Lv is a distance between the axis (b) of the swing shaft  14  of the rocker arm  11  and the valve axis (B), is determined to be larger than that when the valve opening duration is large. 
     In the range of an idling operation or low-speed and low-load operation, as shown in  FIG. 13 , the actuator rotates the swing shaft  14  to an angular position so that the axis (e) of the drive shaft  31  is positioned across the axis (b) of the swing shaft  14  from the roller  9   c . At this time, the roller  9   d  is brought to the farthest position from the camshaft  8 , resulting in the shortest relative length Lc″ and the largest rocker lever ratio (Lv/Lc″). At this time, for the rocker arm  11  at start of an intake stroke, the base circle section  9   e  of the cam face contacts the valve lifter  4   a  at a portion of the base circle section  9   e  remote from the lift section  9   f . In a predetermined time duration at each of an initial and end stages of the intake stroke, the base circle section  9   e  contacts the valve lifter  4   a  and the valve  3  is not lifted, resulting in the shortest opening duration and the smallest valve lift of the valve  3 . 
     As the engine speed and load become higher, as shown in  FIG. 14 , the actuator rotates the swing shaft  14  so that the axis (e) of the drive shaft  31  is positioned on the roller  9   d  side, resulting in the longest relative length Lc″ and the smallest rocker lever ratio (Lv/Lc″). At this time, the rocker arm  11  contacts the valve lifter  4   a  nearly at the boundary between the base circle section  9   g  and the lift section  9   f  of the cam face. The lift section  9   f  contacts the valve lifter  4   a  immediately at the initial and end stages of the intake stroke, resulting in the longest opening duration and the largest lift of the valve  3 . 
     By the way, during the intake stroke, the contact point of between the cam face of the rocker arm  11  and the valve lifter  4   a  is changed in its position such that the contact point is displaced from one side to the other side and subsequently returns from the other side to the one side of the valve axis (B). Accordingly, in this embodiment, the lever length (Lv) is defined as a distance between the valve axis (B) and the axis (b) of the rocker arm  11 . 
     Thus, in this embodiment, since the rocker lever ratio Lv/Lc″ in the engine operation range of a short valve opening duration is determined to be larger than that in the engine operation range of a long opening duration, the same effects as described in  FIG. 5  are achieved. In other words, at the same opening of the valve, the valve lift drop is smaller than that in case of a constant rocker lever ratio. 
     Further, since the roller variable mechanism  30  is constituted such that rotation of the swing shaft  14  of the rocker arm  11  displaces the position of the drive shaft  31  and thus the position of the roller  9   d , the relative distance Lc″ can be changed with a simple constitution. 
     Since the camshaft abutment portion on the camshaft  8  is a roller  9   d  that contacts and rotates on the cam nose  8   c  of the camshaft  8 , it is possible to reduce the loss of the driving force transmitted from the camshaft  8  to the camshaft abutment portion. 
     According to the embodiments described above it is more efficient to secure the valve lift since the lever ratio is determined to be larger when the valve opening duration is shorter. It is therefore possible to reduce pumping loss, improve combustibility, suppress reduction of the ramp velocity, and improve the ability to control the valve opening and closing timing. 
     According to another embodiment, when the swing shaft is swung by the driving device, the rocker arm is swung by the swing of the swing shaft via the intermediate rocker member to open and close the valve. The opening duration and the lift of the valve can be adjusted continuously, since the contact point between the pressurized rocker face and the swing cam face of the intermediate rocker member is forced to displace. 
     Additionally, according to another embodiment, an action to increase the valve lift in spite of a shorter opening duration of the valve, is achieved since the rocker lever ratio (Lv/Lc) is determined to be larger for a shorter opening duration of the valve. Also, as described above, the swinging member lever ratio (Lv/Lc′) is determined to be larger for a shorter opening duration of the valve, and the rocker lever ratio (Lv/Lc″) is determined to be larger for a shorter opening duration of the valve. It is therefore possible to reduce pumping loss, suppress reduction in the ramp velocity, and improve combustibility and ability to control the valve opening and closing timing. 
     Also, according to another embodiment, the contact point between the pressurized rocker face and the intermediate rocker member is positioned approximately just above the valve axis since the rocker lever ratio is determined to be smaller for a longer opening duration of the valve. It is also possible to increase the rigidity as a whole of the valve opening and closing mechanism. 
     According to another embodiment, the intermediate rocker roller and the intermediate rocker pin are provided at the distal end of the intermediate arm portion; the camshaft is located across the swinging member from the rocker shaft of the rocker arm; the swinging member is located such that the base circle section of the swing cam face is located on the rocker shaft side; and the rocker lever ratio becomes larger as the intermediate rocker roller and the intermediate rocker pin are moved toward the rocker shaft side, and, in contrast, it becomes smaller as they are moved away from the rocker shaft side. The locker lever ratio (Lv/Lc) for a shorter opening duration of the valve can be determined to be larger than that for a longer opening duration of the valve. 
     Further, according to another embodiment, the intermediate rocker roller and the intermediate rocker pin can be displaced toward or away from the rocker shaft side, using a simple configuration, to continuously control the valve opening duration and the valve lift, since a connection recess formed in the base end of the intermediate rocker member is engaged with the eccentric pin provided midway of the rocker shaft to rotate the rocker shaft. 
     According to another embodiment 5, since the camshaft may be of crankshaft type having a cam plate, and the cam plate and the swinging member are connected via the connecting rod, the swinging member can be securely and easily driven with sufficient ability to follow and oscillate easily, resulting in improvement of accuracy to control the valve opening duration and the valve lift. 
     According to another embodiment, the relative distance between the camshaft abutment portion and the swinging axis can be changed with a simple constitution of the abutment displacing mechanism which includes a drive shaft having its axis displaceable relative to the swinging axis of the swinging member or the rocker member, and an arm portion having one end coupled with the camshaft abutment portion and the other end coupled with the drive shaft. 
     According to another embodiment, a guide portion for guiding the camshaft abutment portion to a given position is inclined relative to the radial direction of the camshaft. The range of the combination of the valve lift and the valve opening duration can be therefore extended due to the variable relative distance between the camshaft abutment portion and the swinging shaft. 
     According to another embodiment, since the camshaft abutment portion is a roller that contacts and rotates on the camshaft, it is possible to reduce loss of the driving force transmitted from the camshaft to the camshaft abutment portion. 
     Although the foregoing systems and methods have been described in terms of certain preferred embodiments, other embodiments will be apparent to those of ordinary skill in the art from the disclosure herein. Additionally, other combinations, omissions, substitutions and modifications will be apparent to the skilled artisan in view of the disclosure herein. While certain embodiments of the inventions have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. Indeed, the novel methods and systems described herein may be embodied in a variety of other forms without departing from the spirit thereof.