Patent Publication Number: US-7591238-B2

Title: Variable valve-operating device

Description:
TECHNICAL FIELD 
   The present invention relates to a variable valve-operating device for an internal combustion engine, and more particularly to a variable valve-operating device that is capable of mechanically changing the operating characteristic of a valve. 
   BACKGROUND ART 
   A known conventional variable valve-operating device disclosed, for instance, by Japanese Patent Laid-open No. 2004-100555 mechanically changes the valve lift amount and valve timing in accordance with the operation of an internal combustion engine. 
   In the variable valve-operating device disclosed by Japanese Patent Laid-open No. 2004-100555, a camshaft is provided with two rotary cams, and a first rotary cam opens/closes a first intake valve of two intake valves positioned in a cylinder whereas a second rotary cam opens/closes a second intake valve. A variable valve transmission mechanism, which comprises a four-bar linkage, is positioned between the first rotary cam and first intake valve and between the second rotary cam and second intake valve. 
   The four-bar linkage for the above variable valve-operating device comprises an input arm, which has an input section that comes into contact with a rotary cam; a transmission arm, which is coupled to the input arm in a swingable manner; a swing arm, which is coupled to the transmission arm in a swingable manner, is capable of swinging around a rotary control shaft, and transmits a driving force, which is transmitted from a rotary cam, to an output section that opens/closes an intake valve; and a control arm, which rotates around the rotary control shaft and is coupled to the input arm in a swingable manner. The operating characteristic of an intake valve can be mechanically changed by controlling the attitude of the four-bar linkage to change the positional relationship between a rotary cam and input section. 
   Further, the above variable valve-operating device includes a coupling mechanism, which couples the four-bar linkage (first linkage) for the first intake valve to the four-bar linkage (second linkage) for the second intake valve, and a mechanism for maintaining the second linkage&#39;s attitude for providing the maximum operating angle of the second intake valve when the first and second linkages are uncoupled. The coupling mechanism comprises a through-hole, which is formed in the control arm of each four-bar linkage, and a coupling pin, which is to be inserted into the through-hole. The mechanism for maintaining the second linkage&#39;s attitude at the time of uncoupling comprises a through-hole that is formed in a stationary plate, a through-hole that is formed in the control arm (second control arm) of the second linkage, and the above-mentioned coupling pin. 
   The coupling pin is constantly engaged with the through-hole in the second control arm. The coupling pin can move toward the control arm (first control arm) of the first linkage and toward the stationary plate while it is engaged with the through-hole in the second control arm. When the coupling pin moves toward the first control arm and becomes inserted into the through-hole in the first control arm, the second control arm is coupled to the first control arm via the coupling pin. When the control arms are coupled, the first and second linkages assume the same attitude at all times. In this instance, control can be exercised so that the first and second valves have the same operating characteristic. 
   On the contrary, when the coupling pin moves toward the stationary plate and becomes inserted into the through-hole in the stationary plate, the second control arm is coupled to the stationary plate via the coupling pin. When the second control arm and stationary plate are coupled, the attitude of the second linkage is fixed. When the attitude of the first linkage is controlled to change the positional relationship between a rotary cam and input section, only the operating characteristic of the first valve can be mechanically changed with the operating characteristic of the second valve remaining unchanged. 
   In other words, the above variable valve-operating device can selectively provide the first and second intake valves with the same operating characteristic or with different operating characteristics. In this manner, the operating characteristics of the first and second intake valves, particularly, the lift amounts of these valves, can be rendered different from each other. Therefore, different intake flow rates can be employed to invoke a swirling flow within a combustion chamber. This makes it possible to provide stable combustion in the combustion chamber. 
   DISCLOSURE OF THE INVENTION 
   As described above, the second intake valve can control its operating characteristic in two different modes. In a variable control mode, the operating characteristic varies with the rotation position of the rotary control shaft. In a fixed control mode, on the other hand, a great operating angle is constantly employed without regard to the rotation position of the rotary control shaft. However, when the operating characteristic control mode for the second intake valve is to be changed from variable control to fixed control, it is necessary to perform two operations. More specifically, it is necessary to extract the coupling pin from the through-hole in the first control arm and insert the coupling pin into the through-hole in the stationary plate. Similarly, when the mode is to be changed from fixed control to variable control, it is necessary to perform two operations. More specifically, it is necessary to extract the coupling pin from the through-hole in the stationary plate and insert the coupling pin into the through-hole in the first control arm. 
   To perform the above two operations smoothly, it is preferred that the positions of the through-hole in the first control arm, the coupling pin, and the through-hole in the stationary plate agree perfectly with each other when the operating characteristic control mode changes. However, such perfect positional agreement cannot easily be achieved from the viewpoint of machining accuracy. Even if perfect positional agreement is achieved due, for instance, to simultaneous machining, distortion may occur during an actual operation. In addition, such positional agreement is also affected, for instance, by the control accuracy of the rotary control shaft. In reality, therefore, it is difficult to precisely align the positions of the through-holes and coupling pin. 
   Further, while the above two operations are sequentially performed, the coupling pin is disengaged from the first control arm and from the stationary plate for a brief moment. In this instance, the second control arm is free. Therefore, if any external force is applied, the position of the second control arm around the rotary control shaft may change, thereby displacing the coupling pin from a through-hole targeted for coupling. 
   The present invention has been made in view of the above circumstances. It is an object of the present invention to provide a variable valve-operating device that is capable of changing the operating characteristic control mode from variable control to fixed control or from fixed control to variable control through the use of a simple structure, and making such a mode change without malfunction. 
   In accomplishing the above object, according to a first aspect of the present invention, there is provided a variable valve-operating device comprising: a valve positioned on an intake side or on an exhaust side of an internal combustion engine; a first drive cam installed over a camshaft; a control shaft positioned parallel with the camshaft and being capable of changing the rotation position continuously or stepwise; a swing cam arm installed over the control shaft in a rotatable manner to swing around the control shaft; a swing cam surface formed on the swing cam arm and coming into contact with a valve support member, which supports the valve, to push the valve in a lifting direction; a slide surface formed on a swing member to face the first drive cam; an intermediate member sandwiched between the first drive cam and the slide surface, and coming into contact with a circumferential surface of the first drive cam; pushing means for pushing the swing cam arm in the circumferential direction of the control shaft so as to press the slide surface against the intermediate member; an interlock mechanism for moving the intermediate member along the circumferential surface of the first drive cam in coordination with the rotation of the control shaft to change the position of the intermediate member in relation to the center of the camshaft; a second drive cam installed over the camshaft so as to be aligned with the first drive cam; an input arm installed over the control shaft in a rotatable manner, positioned adjacent to the swing cam arm, and swinging upon receipt of a driving force input from the second drive cam; and coupling means for coupling the swing cam arm to the input arm. 
   While the swing cam arm is uncoupled from the input arm, the first aspect of the present invention transmits the rotary motion of the camshaft from the first drive cam to the slide surface of the swing cam arm via the intermediate member. Further, the rotary motion is transmitted from the swing cam arm to the valve. When the rotation position of the control shaft is changed, the rotation of the control shaft is transmitted to the intermediate member via the interlock mechanism. The intermediate member moves along the circumferential surface of the first drive cam while it is sandwiched between the first drive cam and slide surface. When the position of the intermediate member changes in relation to the camshaft, the position of the intermediate member on the slide surface changes. This causes the swing angle and initial swing position of the swing cam arm to change, thereby changing the valve lift amount. Further, when the position of the intermediate member changes in relation to the camshaft, the swing timing of the swing member changes in relation to the rotation of the camshaft. This causes the valve timing to change. 
   Meanwhile, when the coupling means couples the swing cam arm to the input arm, the rotary motion of the camshaft is transmitted from the second drive cam to the swing cam arm via the input arm. Further, the rotary motion is transmitted from the swing cam arm to the valve. The valve&#39;s operating characteristic prevailing in this instance is mechanically determined by the shapes of the second drive cam, input arm, and swing cam arm and by the positional relationship among them. A constant operating characteristic is maintained without regard to the rotation position of the control shaft. 
   As described above, according to the first aspect of the present invention, the operating characteristic control mode for the valve can be switched from variable control to fixed control simply by allowing the coupling means to couple the swing cam arm and input arm. Further, the operating characteristic control mode for the valve can be switched from fixed control to variable control simply by uncoupling the swing cam arm and input arm. 
   According to a second aspect of the present invention, there is provided the variable valve-operating device as described in the first aspect, wherein a setting for the lift amount of the valve that is obtained when the second drive cam swings the swing cam arm while the swing cam arm and the input arm are coupled by the coupling means is not smaller than a maximum lift amount setting for a situation where the first drive cam swings the swing cam arm. 
   When the coupling means couples the swing cam arm and input arm, the second aspect of the present invention generates a valve lift amount that is not smaller than the maximum lift amount for causing the first drive cam to swing the swing cam arm. Therefore, the swing cam arm that is swinging does not interfere with the intermediate member. 
   According to a third aspect of the present invention, there is provided the variable valve-operating device as described in the first or second aspect, wherein the coupling means couples the swing cam arm and the input arm when an insertable pin provided for either the swing cam arm or the input arm is inserted into a pin hole in the mating arm; and wherein the positions of the pin hole and the pin coincide with each other when the control shaft rotates beyond a normal use range and toward a great lift side in a situation where the swing cam arm and the input arm are not coupled. 
   According to the third aspect of the present invention, the swing cam arm and input arm can be coupled by using a simple structure in which the pin is to be inserted into the pin hole. When the rotation position of the control shaft is within the normal use range, the position of the pin hole does not coincide with that of the pin. Therefore, the valve does not erroneously switch to a fixed operation while it is performing a variable operation. Further, the influence of a lift amount difference upon the intake air amount decreases with an increase in the lift amount. Therefore, even when the control shaft is rotated beyond the normal use range and toward a great lift side to move the intermediate member toward a great lift side for valve operation change purposes, the intake air amount does not significantly change. 
   According to a fourth aspect of the present invention, there is provided the variable valve-operating device as described in the third aspect, wherein the positions of the pin hole and the pin coincide with each other while the swing cam arm is a zero lift position in which the valve does not lift. 
   According to the fourth aspect of the present invention, the pin is inserted into the pin hole while the swing cam arm is in a zero lift position in which the valve is not lifted. Therefore, the pin can be properly inserted into the pin hole. This makes it possible to properly change the operating characteristic control mode from variable control to fixed control. 
   According to a fifth aspect of the present invention, there is provided the variable valve-operating device as described in the first or second aspect, wherein the coupling means couples the swing cam arm and the input arm when an insertable pin provided for either the swing cam arm or the input arm is inserted into a pin hole in the mating arm; and wherein the position of the pin can be aligned with the position of the pin hole while a driving force for the pin, which is supplied to the pin before coupling of the swing cam arm and the input arm, is maintained. 
   According to the fifth aspect of the present invention, a driving force is supplied to the pin before a change in the operating characteristic control mode. Therefore, when the position of the pin coincides with that of the pin hole, the pin is immediately inserted into the pin hole. This makes it possible to properly change the operating characteristic control mode from variable control to fixed control. 
   According to a sixth aspect of the present invention, there is provided the variable valve-operating device as described in the fifth aspect, further comprising: an oil path for supplying drive hydraulic oil to the pin provided in the control shaft; and a discharge valve for discharging the hydraulic oil from the oil path; wherein the oil path doubles as a lubricating oil path for supplying lubricating oil between the control shaft and the swing cam arm and/or the input arm; and wherein the discharge valve is normally closed, opened when the pin is extracted from the pin hole to uncouple the swing cam arm and the input arm, and closed again when the position of the pin is displaced from the position of the pin hole. 
   According to the sixth aspect of the present invention, the lubricating oil path can double as the hydraulic oil path. Therefore, the oil path configuration for the entire device can be simplified. Further, according to the sixth aspect of the present invention, the pin can be extracted from the pin hole when the discharge valve is opened to discharge the hydraulic oil from the oil path and decrease the hydraulic pressure applied to the pin. Furthermore, the driving force of the pin can be retained for subsequent coupling when the discharge valve is closed to increase the hydraulic pressure applied to the pin. 
   According to a seventh aspect of the present invention, there is provided the variable valve-operating device as described in the fifth aspect, further comprising: an oil path for supplying drive hydraulic oil to the pin provided in the control shaft; and an open/close valve for opening/closing the oil path; wherein the open/close valve is normally closed, opened when the pin is inserted into the pin hole to couple the swing cam arm and the input arm, and closed again when the pin is extracted from the pin hole to uncouple the swing cam arm and the input arm. 
   According to the seventh aspect of the present invention, the driving force for lodging the pin in the pin hole can be supplied when the open/close valve opens to increase the hydraulic pressure applied to the pin. Further, the pin can be extracted from the pin hole when the open/close valve closes to decrease the hydraulic pressure applied to the pin. Furthermore, the seventh aspect of the present invention supplies the hydraulic oil to the pin only when the swing cam arm and input arm are to be coupled. Therefore, the hydraulic oil can be saved by reducing the amount of hydraulic oil leakage from a sliding gap. 
   In accomplishing the above object, according to a eighth aspect of the present invention, there is provided a variable valve-operating device comprising: a first valve and a second valve aligned with each other and positioned on the intake side or the exhaust side of a cylinder in an internal combustion engine; a first drive cam installed over a camshaft; a control shaft positioned parallel with the camshaft and being capable of changing the rotation position continuously or stepwise; a first swing cam arm provided for the first valve to swing around the control shaft; a second swing cam arm provided for the second valve and being capable of swinging independently of the first swing cam arm; swing cam surfaces formed on the first swing cam arm and the second swing arm, and coming into contact with a valve support member, which supports the first valve and the second valve, to push the first valve and the second valve in a lifting direction; slide surfaces formed on the first swing cam arm and the second swing cam arm to face the first drive cam; an intermediate member sandwiched between the first drive cam and the slide surfaces of the first swing cam arm and of the second swing cam arm, and coming into contact with a circumferential surface of the first drive cam; a first pushing means for pushing the first swing cam arm in the circumferential direction of the control shaft so as to press the slide surface of the first swing cam arm against the intermediate member; a second pushing means for pushing the second swing cam arm in the circumferential direction of the control shaft so as to press the slide surface of the second swing cam arm against the intermediate member; an interlock mechanism for moving the intermediate member along the circumferential surface of the first drive cam in coordination with the rotation of the control shaft to change the position of the intermediate member in relation to the center of the camshaft; a second drive cam installed over the camshaft so as to be aligned with the first drive cam; an input arm installed over the control shaft in a rotatable manner, positioned adjacent to the second swing cam arm, and swinging upon receipt of a driving force input from the second drive cam; and coupling means for coupling the second swing cam arm to the input arm. 
   According to the eighth aspect of the present invention, while the second swing cam arm and input arm are uncoupled, the rotary motion of the camshaft is transmitted from the first drive cam to the slide surfaces of the first and second swing cam arms via the intermediate member and converted to the swing motion of the first and second swing cam arms. The swing motion of the first swing cam arm is transmitted from its swing cam surface to the valve support member and converted to the lift motion of the first valve. The swing motion of the second swing cam arm is transmitted from its swing cam surface to the valve support member and converted to the lift motion of the second valve. 
   When the rotation position of the control shaft is changed, the rotation of the control shaft is transmitted to the intermediate member via the interlock mechanism. The intermediate member then moves along the circumferential surface of the first drive cam while it is sandwiched between the first drive cam and the slide surfaces of the first and second swing cam arms. When the position of the intermediate member changes in relation to the camshaft, the position of the intermediate member on the slide surfaces changes. This causes the swing angles and initial swing positions of the first and second swing cam arms to change, thereby changing the lift amounts of the first and second valves. Further, when the position of the intermediate member changes in relation to the camshaft, the swing timing of the first and second swing cam arms changes in relation to the phase of the camshaft. This invokes a change in the valve timing of the first and second valves. 
   Meanwhile, when the coupling means couples the second swing cam arm and input arm, the rotary motion of the camshaft is transmitted from the second drive cam to the second swing cam arm via the input arm. The swing motion of the second swing cam arm is transmitted from its swing cam surface to the valve support member and converted to the lift motion of the second valve. The second valve&#39;s operating characteristic prevailing is mechanically determined by the shapes of the second drive cam, input arm, and second swing cam arm and by the positional relationship among them. A constant operating characteristic is maintained without regard to the rotation position of the control shaft. 
   On the other hand, the rotary motion of the camshaft is transmitted from the first drive cam to the first swing cam arm via the intermediate member. Therefore, when the control shaft rotates, causing the position of the intermediate member to change in relation to the camshaft, the swing angle and initial swing position of the first swing cam arm change. The swing motion of the first swing cam arm is transmitted from its swing cam surface to the valve support member and converted to the lift motion of the first valve. Therefore, the operating characteristic of the first valve varies with the rotation position of the control shaft as is the case where the second swing cam arm and input arm are uncoupled. 
   As described above, the eighth aspect of the present invention can change the operating characteristic control mode for the second valve from variable control to fixed control simply when the coupling means couples the second swing cam arm and input arm, and change the operating characteristic control mode for the second valve from fixed control to variable control simply when the coupling means uncouples the second swing cam arm and input arm. This makes it easy to properly switch from a dual valve variable control mode, in which the operating characteristics of the first and second valves vary with the rotation position of the control shaft, to a single valve variable control mode, in which the operating characteristic of the first valve varies with the rotation position of the control shaft while the operating characteristic of the second valve is fixed. Switching from the single valve variable control mode to the dual valve variable control mode can also be made easily and properly. 
   According to a ninth aspect of the present invention, there is provided the variable valve-operating device as described in the eighth aspect, wherein a setting for the lift amount of the valves that is obtained when the second drive cam swings the second swing cam arm while the second swing cam arm and the input arm are coupled by the coupling means is not smaller than a maximum lift amount setting for a situation where the first drive cam swings the second swing cam arm. 
   According to the ninth aspect of the present invention, when the coupling means couples the second swing cam arm and input arm, the lift amount setting for the second valve is not smaller than the maximum lift amount for causing the first drive cam to swing the second swing cam arm. Therefore, the second swing cam arm that is swinging does not interfere with the intermediate member. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a side view illustrating the configuration of a variable valve-operating device according to a first embodiment of the present invention. 
       FIG. 2  is an exploded perspective view illustrating a variable valve mechanism and fixed valve mechanism in the variable valve-operating device shown in  FIG. 1 . 
       FIG. 3  is an exploded perspective view illustrating the configuration of an arm coupling mechanism in the variable valve-operating device shown in  FIG. 1 . 
       FIG. 4  is a schematic cross-sectional view that is taken along section A-A of  FIG. 1  to illustrate the variable valve mechanism. 
       FIG. 5A  illustrates a lift operation that the variable valve-operating device shown in  FIG. 1  performs to close a valve. 
       FIG. 5B  illustrates a lift operation that the variable valve-operating device shown in  FIG. 1  performs to open a valve. 
       FIG. 6A  illustrates a lift amount change operation that the variable valve-operating device shown in  FIG. 1  performs to give a great lift. 
       FIG. 6B  illustrates a lift amount change operation that the variable valve-operating device shown in  FIG. 1  performs to give a small lift. 
       FIG. 7A  illustrates an operation that is performed to couple a great lift arm to a second swing cam arm. 
       FIG. 7B  illustrates an operation that is performed to couple the great lift arm to the second swing cam arm. 
       FIG. 8  is a schematic diagram illustrating a lift operation that the variable valve-operating device performs while the great lift arm is uncoupled from the second swing cam arm. 
       FIG. 9  presents graphs illustrating the relationship between the valve timing and lift amount of a right- or left-hand valve that prevails while the great lift arm is uncoupled from the second swing cam arm. 
       FIG. 10  is a schematic diagram illustrating a lift operation that the variable valve-operating device performs while the great lift arm is coupled to the second swing cam arm. 
       FIG. 11  presents graphs illustrating the relationship between the valve timing and lift amount of the right- or left-hand valve that prevails while the great lift arm is coupled to the second swing cam arm. 
       FIG. 12  illustrates the configuration of a hydraulic system for operating a pin according to the first embodiment of the present invention. 
       FIG. 13  illustrates the relationship between the engine speed and the hydraulic pressure in the hydraulic system shown in  FIG. 12 . 
       FIG. 14  is a flowchart illustrating a hydraulic control routine that is executed in the first embodiment of the present invention to switch from dual valve variable control to single valve variable control. 
       FIG. 15  is a flowchart illustrating a hydraulic control routine that is executed in the first embodiment of the present invention to switch from single valve variable control to dual valve variable control. 
       FIG. 16  illustrates the configuration of a hydraulic system for operating a pin according to a second embodiment of the present invention. 
       FIG. 17  illustrates the relationship between the engine speed and the hydraulic pressure in the hydraulic system shown in  FIG. 16 . 
       FIG. 18  is a flowchart illustrating a hydraulic control routine that is executed in the second embodiment of the present invention to switch from dual valve variable control to single valve variable control. 
       FIG. 19  is a flowchart illustrating a hydraulic control routine that is executed in the second embodiment of the present invention to switch from single valve variable control to dual valve variable control. 
   

   BEST MODE FOR CARRYING OUT THE INVENTION 
   First Embodiment 
   A first embodiment of the present invention will now be described with reference to  FIGS. 1 to 15 . 
   [Configuration of a Variable Valve-operating Device According to the First Embodiment] 
     FIG. 1  is a side view illustrating the configuration of a variable valve-operating device according to the first embodiment of the present invention.  FIGS. 2 and 3  are exploded perspective views illustrating the variable valve-operating device. FIG.  4  is a schematic cross-sectional view that is taken along section A-A of  FIG. 1 . As indicated in  FIGS. 2 and 4 , a camshaft  20  of the variable valve-operating device has two drive cams  22 ,  24  per cylinder. Two valves  4 L,  4 R are symmetrically positioned on the right- and left-hand sides of a drive cam (first drive cam)  22 . These valves  4 L,  4 R are arranged on either the intake side or exhaust side of a cylinder. Variable valve mechanisms  30 L,  30 R are respectively provided between the first drive cam  22  and the valves  4 L,  4 R to interlock the lift motion of the valves  4 L,  4 R with the rotary motion of the first drive cam  22 . Another drive cam (second drive cam)  24  is positioned so that the second valve  4 R is sandwiched between the first drive cam  22  and second drive cam  24 . A fixed valve mechanism  70  is provided between the second drive cam  24  and second valve  4 R to interlock the lift motion of the second valve  4 R with the rotary motion of the second drive cam  24 . The variable valve-operating device makes it possible to select either the variable valve mechanism  30 R or fixed valve mechanism  70  as the mechanism with which the lift motion of the second valve  4 R is to be interlocked. 
   (1) Details of Variable Valve Mechanism Configuration 
   The configurations of the variable valve mechanisms  30 L,  30 R will now be described in detail. Since the right- and left-hand variable valve mechanisms  30 L,  30 R are basically symmetrical with respect to the first drive cam  22 , their configuration will be described without distinguishing between the right- and left-hand variable valve mechanisms  30 L,  30 R. This document and the accompanying drawings use the term “variable valve mechanism  30 ” when the right- and left-hand variable valve mechanisms  30 L,  30 R are not distinguished from each other. Similarly, symmetrically arranged parts such as the valves  4 R,  4 L and the components of the variable valve mechanisms  30 L,  30 R are assigned reference numerals without the symbols R and L except when the right- and left-hand parts particularly need to be distinguished from each other. 
   In the variable valve-operating device, the valve  4  is supported by a rocker arm  10  as shown in  FIG. 1 . The variable valve mechanism  30  is positioned between the first drive cam  22  and rocker arm  10  to continuously vary the interlock between the rotary motion of the first drive cam  22  and the swing motion of the rocker arm  10 . 
   The variable valve mechanism  30  includes a control arm  50 , which is supported by the camshaft  20  in a rotatable manner. An intermediate arm  58  is attached to the control arm  50  in a rotatable manner. The intermediate arm  58  is placed at a position that is displaced from the center of the camshaft  20  on which the control arm  50  turns. The intermediate arm  58  has a connection pin  56 , which is positioned across both ends of the fulcrum side of the intermediate arm  58 . The connection pin  56  is supported by the control arm  50  in a rotatable manner. The leading end of the intermediate arm  58  is positioned toward a control shaft  32  with the connection pin  56  used as a fulcrum. A coupling shaft  64 , which is positioned in parallel with the camshaft  20 , is fastened to the leading end of the intermediate arm  58 . A first roller  60  and second rollers  62  are supported by the coupling shaft  64  in a rotatable manner. The second rollers  62  have a smaller diameter than the first roller  60 . As shown in  FIG. 2 , a pair of second rollers  62  are positioned on both sides of the first roller  60 . A pair of control arms  50  are positioned on both sides of the first drive cam  22 . The right- and left-hand control arms  50  support the intermediate arm  58  (a front control arm  50  is not shown in  FIG. 1 ). 
   An arced, large-diameter gear  52  is positioned between the right- and left-hand control arms  50 . The large-diameter gear  52  is fastened on both sides thereof to the right- and left-hand control arms  50 . The large-diameter gear  52  is formed around the rotation center of the control arms  50 , that is, along an arc that is concentric with the camshaft  20 . The position of the large-diameter gear  52  on the control arms  50  is virtually opposite the position of the connection pin  56  with respect to the turning center of the control arms  50 . 
   The variable valve mechanism  30  includes the control shaft  32 , which is positioned in parallel with the camshaft  20 . The rotation position of the control shaft  32  can be arbitrarily controlled by an actuator (e.g., a motor), which is not shown but functions as a control shaft drive device. A small-diameter gear  34 , which is concentric with the control shaft  32 , is formed on the outer circumference of the control shaft  32 . The small-diameter gear  34  meshes with the large-diameter gear  52 , which is mounted on the control arm  50 . Therefore, the rotation of the control shaft  32  is input to the control arm  50  via the small-diameter gear  34  and large-diameter gear  52 . The small-diameter gear  34  and large-diameter gear  52  constitute a speed reduction mechanism that decelerates the rotation of the control shaft  32  and transmits the decelerated rotation to the control arm  50 . 
   Swing cam arms  40  are supported by the control shaft  32  in a swingable manner. A pair of swing cam arms  40  are positioned on both sides of the small-diameter gear  34  as shown in  FIGS. 2 to 4 . The swing cam arm (first swing cam arm)  40 L that is positioned to the left of the small-diameter gear  34  is a component part of the variable valve mechanism  30 L. The swing cam arm (second swing cam arm)  40 R that is positioned to the right of the small-diameter gear  34  is a component part of the variable valve mechanism  30 R. These swing cam arms  40  are arranged so that their leading ends are directed upstream in the rotation direction of the first drive cam  22 . In the present embodiment, the camshaft  20  rotates clockwise as indicated by an arrow in the figure. A slide surface  46 , which comes into contact with the second rollers  62  described later, is formed on the side that opposes the first drive cam  22  for the swing cam arm  40 . The slide surface  46  is gradually curved toward the first drive cam  22 . Further, the distance of the slide surface  46  from the center of the first drive cam  22  increases with an increase in the distance from the center of the control shaft  32 , which is the swing center. 
   A swing cam surface  42  ( 42   a ,  42   b ) is formed opposite with the slide surface  46  of the swing cam arm  40 . The swing cam surface  42  comprises a non-operating surface  42   a  and an operating surface  42   b , which have different profiles. The non-operating surface  42   a  is a circumferential surface of a cam base circle and formed in such a manner that the distance from the center of the control shaft  32  is uniform. On the other hand, the operating surface  42   b  is provided at the leading end of the swing cam arm  40 . It is connected to the non-operating surface  42   a  smoothly and in a continuous manner, and formed so that the distance from the center of the control shaft  32  (that is, the cam height) gradually increases with a decrease in the distance to the leading end of the swing cam arm  40 . This document simply uses the term “swing cam surface  42 ” when the non-operating surface  42   a  and operating surface  42   b  are not distinguished from each other. 
   A spring seat  48  is formed on the swing cam arm  40 . A lost motion spring  36  is hooked at its one end onto the spring seat  48 . The lost motion spring  36  is fastened at the other end to a stationary part of the internal combustion engine. The swing cam arm  40  is pushed in such a manner that the spring force received from the lost motion spring  36  rotates the slide surface  46  toward the first drive cam  22  (counterclockwise in  FIG. 1 ). 
   The intermediate arm  58  is positioned between the first drive cam  22  and the slide surface  46  of the swing cam arm  40  so as to direct its leading end toward the control shaft  32 . The first roller  60 , which is supported by the intermediate arm  58  in a rotatable manner, is positioned in the rotation plane of the first drive cam  22 . The left-hand second roller  62 L is positioned in the swing plane of the left-hand swing cam arm  40 L. The right-hand second roller  62 R is positioned in the swing plane of the right-hand swing cam arm  40 R. The spring force of the aforementioned lost motion spring  36  works to press the slide surface  46  against the second rollers  62  and press the first roller  60 , which is coupled to the second rollers  62  via the coupling shaft  64 , against the first drive cam  22 . Consequently, the first roller  60  and second rollers  62  are sandwiched between the slide surface  46  and first drive cam  22  for positioning purposes. 
   As described above, the first roller and second rollers  62  are connected to the control arm  50  via the intermediate arm  58 , and sandwiched between the slide surface  46  and first drive cam  22 . Therefore, when the control arm  50  rotates around the camshaft  20 , the first roller  60  and second rollers  62  rotate around the camshaft  20  while maintaining contact with the circumferential surface of the first drive cam  22 . Since the rotation of the control arm  50  is interlocked with the rotation of the control shaft  32  via the small-diameter gear  34  and large-diameter gear  52 , the rotations of the first roller  60  and second rollers  62  around the camshaft  20  are also interlocked with the rotation of the control shaft  32 . In the present embodiment, the small-diameter gear  34 , large-diameter gear  52 , control arm  50 , and intermediate arm  58  constitute an interlock mechanism that moves the first roller  60  and second rollers  62 , which are intermediate members, along the circumferential surface of the first drive cam  22  in coordination with the rotation of the control shaft  32 . 
   The aforementioned rocker arm  10  is positioned below the swing cam arm  40 . The rocker arm  10  is provided with a rocker roller  12 , which faces the swing cam surface  42  of the swing cam arm  40 . The rocker roller  12  is mounted on the middle part of the rocker arm  12  in a rotatable manner. A valve shaft  2  is mounted on one end of the rocker arm  10  to support the valve  4 . The other end of the rocker arm  10  is supported by a hydraulic lash adjuster  6  in a rotatable manner. A valve spring (not shown) pushes the valve shaft  2  in a closing direction, that is, in the direction of pushing the rocker arm  10  upward. Such a pushing force and the force exerted by the hydraulic lash adjuster press the rocker roller  12  against the swing cam surface  42  of the swing cam arm  40 . 
   (2) Details of Fixed Valve Mechanism Configuration 
   The configuration of the fixed valve mechanism  70  will now be described in detail. 
   As shown in  FIGS. 2 and 4 , the fixed valve mechanism  70  is positioned between the second drive cam  24  and the second swing cam arm  40 R. The fixed valve mechanism  70  interlocks the swing motion of the second swing cam arm  40 R with the rotary motion of the second drive cam  24 . It includes a great lift arm (input arm)  72 , which is driven by the second drive cam  24 , and an arm coupling mechanism  78 , which couples the great lift arm  72  to the second swing cam arm  40 R. 
   The great lift arm  72  is aligned with the second swing cam arm  40 R, is mounted on the control shaft  32 , and can rotate independently of the second swing cam arm  40 R. An input roller  74 , which comes into contact with the circumferential surface of the second drive cam  24 , is supported by the great lift arm  72  in a rotatable manner. A lost motion spring (not shown) is hooked onto the great lift arm  72 . The force exerted by the lost motion spring presses the input roller  74  against the circumferential surface of the second drive cam  24 . 
   The great lift arm  72  is provided with a pin  80  that can be inserted into and extracted from the second swing cam arm  40 R. The great lift arm  72  is also provided with a hydraulic chamber  88 , which has an opening that is positioned toward the second swing cam arm  40 R. The pin  80  is fit into the hydraulic chamber  88 . An oil path  90 , which allows hydraulic oil to flow, is connected to the hydraulic chamber  88 . When the hydraulic oil is supplied to the inside of the hydraulic chamber  88  from the oil path  90 , the resulting hydraulic pressure pushes the pin  80  from the hydraulic chamber  88  to the second swing cam arm  40 R. 
   The second swing cam arm  40 R is formed with a pin hole  86  opening toward the great lift arm  72 . The pin  80  and pin hole  86  are positioned on the same arc that is formed around the control shaft  32 . Therefore, when the second swing cam arm  40 R is positioned at a predetermined rotation position with respect to the great lift arm  72 , the position of the pin hole  86  coincides with that of the pin  80 . A return spring  84  and a piston  82  are placed in the pin hole  86  with the return spring  84  positioned at the innermost end. When the position of the pin hole  86  coincides with that of the pin  80 , the pin  80  comes into contact with the piston  82 . If, in this instance, the force exerted by the return spring  84  to press the piston  82  is greater than the force exerted by the hydraulic pressure in the hydraulic chamber  88  to press the pin  80 , the pin  80  moves into the pin hole  86  in such a manner as to push the piston  82  inward within the pin hole  86 . When the pin  80  is inserted into the pin hole  86 , the swing cam arm  40 R and great lift arm  72  are coupled via the pin  80 . In other words, the pin  80 , hydraulic chamber  88 , oil path  90 , pin hole  86 , return spring  84 , and piston  82  constitute the arm coupling mechanism  78 . 
   [Basic Operation of the Variable Valve-operating Device According to the Present Embodiment] 
   The basic operation of the variable valve-operating device, which is configured as described above, will now be described with reference to  FIGS. 5A ,  5 B,  6 A, and  6 B. 
   (1) Valve Lift Operation of the Variable Valve Mechanism 
   First of all, the operation that the variable valve mechanism  30  performs to lift the valve  4  will be described with reference to  FIGS. 5A and 5B .  FIG. 5A  shows a state of the variable valve mechanism  30  in which the valve  4  is closed during a lift operation.  FIG. 5B  shows a state of the variable valve mechanism  30  in which the valve  4  is fully open during a lift operation. 
   In the variable valve mechanism  30 , the rotary motion of the first drive cam  22  is first input to the first roller  60 , which comes into contact with the first drive cam  22 . The first roller  60  and the second rollers  62  are supported by the intermediate arm  58 . Therefore, they swing around the connection pin  56 , which serves as the fulcrum of the intermediate arm  58 . The resulting swing motion is then input to the slide surface  46  of the swing cam arm  40 , which comes into contact with the second rollers  62 . The slide surface  46  is constantly pressed against the second rollers  62  by the force exerted by the lost motion spring  36 . Therefore, the swing cam arm  40  swings around the control shaft  32  in coordination with the rotation of the first drive cam  22 , which is transmitted via the second rollers  62 . 
   More specifically, when the camshaft  20  rotates in the state shown in  FIG. 5A , the position at which the first roller  60  contacts the first drive cam  22  approaches the apex of the first drive cam  22  as indicated in  FIG. 5B . The first roller  60  is then relatively pushed downward by the first drive cam  22 , and the slide surface  46  of the swing cam arm  40  is pushed downward by the second rollers  62 , which are integral with the first roller  60 . This causes the swing cam arm  40  to rotate clockwise around the control shaft  32  (see  FIGS. 5A and 5B ). 
   When the swing cam arm  40  turns so that the position at which the rocker roller  12  contacts the swing cam surface  42  moves from the non-operating surface  42   a  to the operating surface  42   b , the rocker arm  10  is pushed downward in accordance with the distance between the position of the rocker roller  12  on the operating surface  42   b  and the center of the control shaft  32 . The rocker arm  10  then swings clockwise around a point of support provided by the hydraulic lash adjuster  6 . This causes the rocker arm  10  to lower and open the valve  4 . When the position at which the first roller  60  contacts the first drive cam  22  reaches the apex of the first drive cam  22  as indicated in  FIG. 5B , the amount of turning the swing cam arm  40  is maximized to maximize the lift amount of the valve  4 . 
   When the camshaft  20  further rotates until the position at which the first roller  60  contacts the first drive cam  22  passes the apex of the first drive cam  22 , the swing cam arm  40  turns counterclockwise around the control shaft  32  due to the force exerted by the lost motion spring and valve spring. When the swing cam arm  40  turns counterclockwise, the position at which the rocker roller  12  contacts the swing cam surface  42  moves toward the non-operating surface  42   a . This decreases the lift amount of the valve  4 . When the position at which the rocker roller  12  contacts the swing cam surface  42  later switches from the operating surface  42   b  to the non-operating surface  42   a  as indicated in  FIG. 5A , the lift amount of the valve  4  decreases to zero, that is, the valve  4  closes. 
   (2) Lift Amount Change Operation of the Variable Valve Mechanism 
   The lift amount change operation performed by the variable valve mechanism  30  will now be described with reference to  FIGS. 6A and 6B .  FIG. 6A  shows a maximum lift state of the variable valve mechanism  30  in which the variable valve mechanism  30  operates to give a great lift to the valve  4 .  FIG. 6B  shows a maximum lift state of the variable valve mechanism  30  in which the variable valve mechanism  30  operates to give a small lift to the valve  4 . 
   When the lift amount is to be changed from the lift amount shown in  FIG. 6A  to the lift amount shown in  FIG. 6B , the control shaft  32  is rotated in the same direction as the camshaft  20  in a state shown in  FIG. 6A  (rotated clockwise). The rotation of the control shaft  32  is transmitted to the control arm  50  via the small-diameter gear  34  and large-diameter gear  52  to rotate the control arm  50  to the rotation position indicated in  FIG. 6B . When the control arm  50  rotates, the second rollers  62 , which are coupled to the control arm  50  via the intermediate arm  58 , move along the slide surface  46  and away from the control shaft  32 . At the same time, the first roller  60 , which is integral with the second rollers  62 , moves along the first drive cam  22  and upstream in the rotation direction of the first drive cam  22 . 
   When the second rollers  62  move away from the control shaft  32 , the distance between the swing center of the swing cam arm  40  and the contact position P 2  at which the second rollers  62  contact the slide surface  46  increases, thereby decreasing the swing angle of the swing cam arm  40 . The reason is that the swing angle of the swing cam arm  40  is in inverse proportion to the distance between the swing center and the contact position P 2 , which is a driving force input point. When the swing angle of the swing cam arm  40  decreases, the final contact position P 3  that the rocker roller  12  can reach moves over the operating surface  42   b  and toward the non-operating surface  42   a , thereby reducing the lift amount of the valve  4 . Further, the crank angle during which the rocker roller  12  is positioned on the operating surface  42   b  is the operating angle of the valve  4 . However, when the final contact position P 3  moves toward the non-operating surface  42   a , the operating angle of the valve  4  decreases. Furthermore, since the first roller  60  moves along the first drive cam  22  and upstream in the rotation direction of the first drive cam  22 , the contact position P 1  of the first roller  60  that prevails when the camshaft  20  is at the same rotation position moves toward the advance side of the first drive cam  22 . This advances the swing timing of the swing cam arm  40  in relation to the phase of the first drive cam  22 . As a result, the valve timing (maximum lift timing) advances. 
   When, on the other hand, the lift amount is to be changed from the lift amount shown in  FIG. 6B  to the lift amount shown in  FIG. 6A , the control shaft  32  is rotated in a direction opposite the rotation direction of the camshaft  20  (rotated counterclockwise) in a state shown in  FIG. 6B  to rotate the control arm  50  to the rotation position shown in  FIG. 6A . This moves the second rollers  62  toward the control shaft  32 , reduces the distance between the swing center of the swing cam arm  40  and the contact position P 2  at which the second rollers  62  contact the slide surface  46 , and increases the swing angle of the swing cam arm  40 . When the swing angle of the swing cam arm  40  increases, the final contact position P 3  that the rocker roller  12  can reach moves toward the leading end of the operating surface  42 , thereby increasing the lift amount and operating angle of the valve  4 . In this instance, the contact position P 1  of the first roller  60  that prevails when the camshaft  20  is at the same rotation position moves toward the retard side of the first drive cam  22 . This retards the swing timing of the swing cam arm  40  in relation to the rotation of the first drive cam  22 . As a result, the valve timing retards. 
   [Interlock Switching Operation of the Variable Valve-operating Device According to the Present Embodiment] 
   When the arm coupling mechanism  78  in the variable valve-operating device according to the present embodiment couples the great lift arm  72  to the second swing cam arm  40 R, the fixed valve mechanism  70  can be selected instead of the variable valve mechanism  30 R as the mechanism with which the lift motion of the second valve  4 R is to be interlocked. When, on the contrary, the arm coupling mechanism  78  uncouples the great lift arm  72  from the second swing cam arm  40 R, the variable valve mechanism  30 R can be selected instead of the fixed valve mechanism  70  as the mechanism with which the lift motion of the second valve  4 R is to be interlocked. The interlock switching operation of the variable valve-operating device according to the present embodiment will now be described in detail with reference to  FIGS. 7A to 15 . 
   (1) Coupling the Great Lift Arm to the Second Swing Cam Arm 
   As described earlier, the positions of the pin  80  and pin hole  86  coincide with each other when the swing cam arm  40 R is positioned at a predefined rotation position in relation to the great lift arm  72 . When the positions of the pin  80  and pin hole  86  coincide with each other, the pin  80  is inserted into the pin hole  86  so that the great lift arm  72  is coupled to the second swing cam arm  40 R. To avoid an erroneous operation of the arm coupling mechanism  78 , therefore, it is necessary to set the swing angle of the second swing cam arm  40 R so that the position of the pin  80  coincides with that of the pin hole  86  only when the great lift arm  72  is coupled to the second swing cam arm  40 R. 
     FIGS. 7A and 7B  illustrate an operation that is performed to couple the great lift arm  72  to the second swing cam arm  40 R. When the great lift arm  72  is not coupled to the second swing cam arm  40 R, the swing angle of the second swing cam arm  40 R is set so that the positional relationship between the pin  80  and pin hole  86  is as indicated in  FIG. 7A . When, on the other hand, the great lift arm  72  is coupled to the second swing cam arm  40 R, the swing angle of the second swing cam arm  40 R is set so that the positional relationship between the pin  80  and pin hole  86  is as indicated in  FIG. 7B . 
   The “pin position” shown in  FIGS. 7A and 7B  represents the outermost position on the valve closing side that prevails when the second drive cam  24  drives the great lift arm  72  to reciprocate the pin  80  along the arc. When the pin  80  is at the “pin position,” the input roller  74  is in contact with the cam base circle of the second drive cam  24 . While the input roller  74  is in contact with the cam base circle, the great lift arm  72  is stationary. While the great lift arm  72  is stationary, the pin  80  is at the “pin position.” Since the swing angle of the great lift arm  72  is constantly fixed without regard to the rotation position of the control shaft  32 , the “pin position” remains fixed without regard to the rotation position of the control shaft  32 . 
   On the other hand, the swing angle of the second swing cam arm  40 R varies with the rotation position of the control shaft  32 . As described earlier, when the control shaft  32  rotates so as to increase the lift amount and operating angle of the second valve  4 R, the swing angle of the second swing cam arm  40 R increases. When the control shaft  32  rotates so as to decrease the lift amount and operating angle of the second valve  4 R, the swing angle of the second swing cam arm  40 R decreases. The “second great lift position” shown in  FIG. 7A  represents the outermost position on the valve closing side that prevails when the rotation position of the control shaft  32  is set for the maximum lift angle within the normal use range with the swing angle of the second swing cam arm  40 R set to the maximum angle within the normal use range to reciprocate the pin hole  86  along the arc. When the pin hole  86  is at the “second great lift position,” the first roller  60  is in contact with the cam base circle of the first drive cam  22  and the second swing cam arm  40 R is at a zero lift position at which the second valve  4 R will not be lifted. While the first roller  60  is in contact with the cam base circle of the first drive cam  22 , the second swing cam arm  40 R is stationary at the zero lift position. 
   As indicated in  FIG. 7A , the “second great lift position” is between the “pin position” and the inside in the swing direction of the second swing cam arm  40 R. The “second great lift position” corresponds to the maximum lift of the second valve  4 R within the normal use range, and the swing angle of the second swing cam arm  40 R decreases when the lift amount of the second valve  4 R is adjusted for a smaller lift. Therefore, when the rotation position of the control shaft  32  is within the normal use range, the position of the pin  80  does not coincide with that of the pin hole  86 . In other words, the great lift arm  72  will not be erroneously coupled to the second swing cam arm  40 R. 
   When the great lift arm  72  and the second swing cam arm  40 R are to be coupled, the control shaft  32  is rotated beyond the normal use range and toward the great lift side in order to move the position of the second rollers  62  on the slide surface  46  toward the great lift side. This increases the swing angle of the swing cam arm  40 R, and ensures that the outermost position on the valve closing side that prevails when the pin hole  86  moves along the arc moves outward beyond the “second great lift position.” The “first great lift position” shown in  FIG. 7B  represents the position of the pin hole  86  that prevails when the swing angle of the second swing cam arm  40 R is increased beyond the normal use range as described above, and is adjusted for the “pin position” on the side toward the pin  80 . Consequently, when the swing angle of the second swing cam arm  40 R is changed to place the pin hole  86  at the “first great lift position,” the position of the pin  80  coincides with that of the pin hole  86 , thereby making it possible to couple the great lift arm  72  to the second swing cam arm  40 R. 
   (2) Dual Valve Variable Control Exercised with the Great Lift Arm Uncoupled from the Second Swing Cam Arm 
     FIG. 8  is a schematic diagram illustrating a lift operation that is performed while the great lift arm  72  and the second swing cam arm  40 R are uncoupled. As indicated in  FIG. 8 , while the pin  80  is not engaged in the pin hole  86  and the great lift arm  72  is not coupled to the second swing cam arm  40 R, the rotary motion of the camshaft  20  is transmitted from the first drive cam  22  to the slide surface  46 L of the first swing cam arm  40 L via the first roller  60  and second roller  62 L, and converted to the swing motion of the first swing cam arm  40 L. The swing motion of the first swing cam arm  40 L is transmitted to the rocker arm  10 L and then converted to the lift motion of the first valve  4 L. 
   The rotary motion of the camshaft  20  is also transmitted from the first drive cam  22  to the slide surface  46 R of the second swing cam arm  40 R via the first roller  60  and second roller  62 R, and converted to the swing motion of the second swing cam arm  40 R. The swing motion of the second swing cam arm  40 R is transmitted to the rocker arm  10 R and then converted to the lift motion of the second valve  4 R. 
   When the control shaft  32  (not shown in  FIG. 8 ) rotates, the first roller  60  and the second rollers  62 L,  62 R move along the circumferential surface of the first drive cam  22  in accordance with the rotation position of the control shaft  32 . As a result, the position of the second roller  62 L on the slide surface  46 L changes. This causes the swing angle and initial swing position of the first swing cam arm  40 L to change, thereby changing the lift amount of the first valve  4 L. Similarly, the position of the second roller  62 R on the slide surface  46 R also changes. This causes the swing angle and initial swing position of the second swing cam arm  40 R to change, thereby changing the lift amount of the second valve  4 R. It means that the first valve  4 L and the second valve  4 R can change their lift amounts in accordance with the rotation of the control shaft  32 . In this instance, the lift amount of the first valve  4 L is always equal to the lift amount of the second valve  4 R as shown in  FIG. 8 . 
   Further, since the first roller  60  changes its position in relation to the camshaft  20 , the first swing cam arm  40 L and second swing cam arm  40 R change their swing timing in relation to the rotation of the camshaft  20 . As a result, the first valve  4 L and second valve  4 R change their valve timing in accordance with the rotation of the control shaft  32 . In this instance, the valve timing of the first valve  4 L is always the same as that of the second valve  4 R. 
     FIG. 9  presents graphs illustrating the relationship between the lift amount and valve timing of the valves  4 L,  4 R that the variable valve-operating device according to the present embodiment provides while the great lift arm  72  is uncoupled from the second swing cam arm  40 R. The left-hand graph in  FIG. 9  illustrates the relationship between the lift amount and valve timing of the first valve  4 L, whereas the right-hand graph illustrates the relationship between the lift amount and valve timing of the second valve  4 R. While the great lift arm  72  is uncoupled from the second swing cam arm  40 R, variable control can be exercised over the lift amount and valve timing of both the left- and right-hand valves  4 L,  4 R as indicated in  FIG. 9 . In other words, dual valve variable control can be exercised. In the dual valve variable control mode, the valve timing can be retarded in accordance with an increase in the lift amounts of the valves  4 L,  4 R, and advanced in accordance with a decrease in the lift amounts of the valves  4 L,  4 R. 
   (3) Single Valve Variable Control Exercised with the Great Lift Arm Coupled to the Second Swing Cam Arm 
     FIG. 10  is a schematic diagram illustrating a lift operation that is performed while the great lift arm  72  and the second swing cam arm  40 R are coupled. As indicated in  FIG. 10 , while the pin  80  is engaged in the pin hole  86  and the great lift arm  72  is coupled to the second swing cam arm  40 R, the rotary motion of the camshaft  20  is transmitted from the second drive cam  24  to the second swing cam arm  40 R via the great lift arm  72 . The swing motion of the second swing cam arm  40 R is transmitted to the rocker arm  10 R and then converted to the lift motion of the second valve  4 R. 
   As described earlier, the great lift arm  72  and the second swing cam arm  40 R are coupled when the control shaft  32  rotates to move the position of the second roller  62 R on the slide surface  46 R beyond the normal use range and toward the great lift side. As indicated in  FIGS. 6A and 6B , the initial swing position of the second swing cam arm  40 R (the swing position prevailing when the first roller  60  is in contact with the cam base circle of the first drive cam  22 ) moves toward the great lift side. Therefore, the initial swing position of the second swing cam arm  40 R that prevails when the great lift arm  72  is coupled to the swing cam arm  40 R is beyond the maximum initial swing position within the normal use range. The distance between the circumferential surface of the first drive cam  22  and the slide surface  46 R of the second swing cam arm  40 R becomes large as the initial swing position of the second swing cam arm  40 R moves toward the great lift side. Therefore, when the great lift arm  72  is coupled to the swing cam arm  40 R, the slide surface  46 R does not interfere with the second roller  62 R within the normal movement range of the second roller  62 R when the second swing cam arm  40 R swings. In other words, the operating characteristic of the second valve  4 R is mechanically determined by the shapes of the second drive cam  24 , great lift arm  72 , and second swing cam arm  40 R and by the positional relationship among them. A constant operating characteristic is always maintained without regard to the rotation position of the control shaft. 
   On the other hand, the rotary motion of the camshaft  20  is transmitted from the first drive cam  22  to the first swing cam arm  40 L via the first roller  60  and second roller  62 L. Therefore, when the control shaft  32  rotates to change the positions of the first roller  60  and second roller  62 L in relation to the camshaft  20 , the first swing cam arm  40 L changes its swing angle, initial swing position, and swing timing. Since the swing motion of the first swing cam arm  40 L is transmitted to the rocker arm  10 L and then converted to the lift motion of the first valve  4 L, the operating characteristic of the first valve changes in accordance with the rotation position of the control shaft  32  as is the case where the great lift arm  72  is uncoupled from the swing cam arm  40 R. 
     FIG. 11  presents graphs illustrating the relationship between the lift amount and valve timing of the valves  4 L,  4 R that the variable valve-operating device according to the present embodiment provides while the great lift arm  72  is coupled to the swing cam arm  40 R. The left-hand graph in  FIG. 11  illustrates the relationship between the lift amount and valve timing of the first valve  4 L, whereas the right-hand graph illustrates the relationship between the lift amount and valve timing of the second valve  4 R. While the great lift arm  72  is coupled to the swing cam arm  40 R, control is exercised so that the second valve  4 R is provided with a fixed lift amount and valve timing, and variable control can be exercised over the lift amount and valve timing of the first valve  4 L, as indicated in  FIG. 11 . In other words, single valve variable control can be exercised when the great lift arm  72  is coupled to the swing cam arm  40 R. In the single valve variable control mode, the lift amount of the second valve  4 R is fixed so that it is not smaller than the maximum lift amount setting for causing the first drive cam  22  to swing the second swing cam arm  40 R. Therefore, when the lift amount of the first valve  4 L is changed to control the lift amount difference between the two valves  4 L,  4 R, the swirl control can be exercised over an air-fuel mixture flow within a cylinder. 
   (4) Hydraulic Control for Switching between Dual Valve Variable Control and Single Valve Variable Control 
   The control exercised over the hydraulic pressure to be supplied to the pin  80  will now be described. Control mode switching from dual valve variable control to single valve variable control or from single valve variable control to dual valve variable control is achieved by controlling the hydraulic pressure supply to the pin  80  to couple the great lift arm  72  to the second swing cam arm  40 R or uncouple the great lift arm  72  from the second swing cam arm  40 R. 
     FIG. 12  illustrates the configuration of a hydraulic system for operating the pin  80 . As shown in  FIG. 12 , an oil path  92  is formed in the control shaft  32 , and connected to a sliding gap between the control shaft  32  and great lift arm  72  and to a sliding gap between the control shaft  32  and second swing cam arm  40 R. A pump  100  is installed upstream of the oil path  92 . Lubricating oil, which is pressurized by the pump  100 , is supplied to the sliding gaps between the control shaft  32  and arms  72 ,  40 R via the oil path  92 . In the present embodiment, another oil path  90  is used to connect the lubricating oil path  92  to the hydraulic chamber  88  in the great lift arm  72 . This oil path  90  supplies part of the lubricating oil flow in the oil path  92  to the hydraulic chamber  88 . The lubricating oil supplied in this manner then functions as the hydraulic oil for applying hydraulic pressure to the pin  80 . When the lubricating oil path  92  doubles as the oil path for the hydraulic oil, the oil path configuration for the entire device can be simplified. 
   The pump  100  is driven by the internal combustion engine; therefore, the hydraulic pressure is influenced by the engine speed as indicated in  FIG. 13 . In a situation where the hydraulic pressure is not raised due to a low engine speed, the pin  80  cannot be inserted into the pin hole  86  against the force that the return spring  84  exerts to push the piston  82  even when the position of the pin  80  coincides with that of the pin hole  36 . Therefore, the controller for controlling the variable valve-operating device inhibits the great lift arm  72  from being coupled to the second swing cam arm  40 R before the hydraulic pressure reaches a predetermined pressure P 1  due to an increase in the engine speed. The predetermined pressure P 1  should be equivalent to a hydraulic pressure for promptly inserting the pin  80  into the pin hole  86 . For example, the predetermined pressure P 1  can be obtained by multiplying the maximum spring force of the return spring  84  by the pin pressure reception area. 
   When, on the other hand, the great lift arm  72  is to be uncoupled from the second swing cam arm  40 R, the pin  80  is extracted from the pin hole  86 . In this instance, it is necessary to decrease the hydraulic pressure in the hydraulic chamber  88  so that the piston  82  pushes the pin  80  back into the hydraulic chamber  88 . However, since the pump  100  is driven by the internal combustion engine, it is difficult to decrease the hydraulic pressure by controlling the rotation speed of the pump  100 . In the present embodiment, therefore, a discharge path  102  is provided to expel the lubricating oil from the oil path  92 . When the great lift arm  72  is to be uncoupled from the second swing cam arm  40 R, the lubricating oil is discharged via the discharge path  102  to lower the hydraulic pressure of the lubricating oil flow in the oil path  92 , thereby reducing the force applied by the hydraulic pressure to push the pin  80 . The discharge path  102  is provided with a solenoid valve (discharge valve)  104 , which opens/closes the discharge path  102 . An orifice  106  is positioned downstream of the solenoid valve  104  in the discharge path  102 . The orifice  106  restricts the rate of lubricating oil flow from the discharge path  102  so that at least the minimum required amount of lubricating oil is supplied to the arms  72 ,  40 R. 
     FIGS. 14 and 15  are flowcharts illustrating specific details of the hydraulic control that is exercised by the variable valve-operating device according to the present embodiment. The flowchart in  FIG. 14  illustrates a hydraulic control routine that is executed to switch from dual valve variable control to single valve variable control. The flowchart in  FIG. 15  illustrates a hydraulic control routine that is executed to switch from single valve variable control to dual valve variable control. 
   If an instruction for single valve variable control is issued to the controller for the variable valve-operating device while dual valve variable control is exercised, the controller for the variable valve-operating device executes the routine shown in  FIG. 14  to exercise hydraulic control. First of all, step  100  is performed to judge whether the predetermined pressure P 1  is reached by the hydraulic pressure of the lubricating oil flow in the oil path  92  (controlled hydraulic pressure). The hydraulic pressure is measured by a hydraulic pressure sensor in the internal combustion engine. No subsequent step is performed until the hydraulic pressure reaches the predetermined pressure P 1 . A standby state persists until the judgment result obtained in step  100  indicates that the predetermined pressure P 1  is reached. 
   When the hydraulic pressure exceeds the predetermined pressure P 1 , the control shaft  32  rotates to move the position of the second roller  62 R on the slide surface  46 R toward the great lift side, and change the swing angle of the second swing cam arm  40 R to place the pin hole  86  in the “first great lift position” (step  102 ). Next, step  104  is performed to wait until one cycle elapses (the crankshaft makes two revolutions) while the rotation position of the control shaft  32  is maintained at the position set in step  102 . When the second swing cam arm  40 R swings to the above swing angle, the pin hole  86  passes the “first great lift position” without fail before the elapse of one cycle. In such an instance, the position of the pin  80  coincides with that of the pin hole  86  so that the hydraulic pressure in the hydraulic chamber  88  generates a driving force to promptly insert the pin  80  into the pin hole  86 . This ensures that the great lift arm  72  is completely coupled to the second swing cam arm  40 R. 
   After the elapse of one cycle, the control shaft  32  rotates in a direction opposite to the rotation direction employed in step  102  until the rotation position of the control shaft  32  reverts to the normal use range (step  106 ). The second roller  62 R then completely leaves the slide surface  46 R of the second swing cam arm  40 R, thereby allowing the second drive cam  24  to drive the second swing cam arm  40 R. Consequently, the second valve  4 R is set for a fixed lift amount and valve timing. On the other hand, the first swing cam arm  40 L is driven by the first drive cam  22  as is the case with the dual valve variable control mode so that variable control can be exercised over the lift amount and valve timing of the first valve  4 L by rotating the control shaft  32 . Subsequently, the controller exercises single valve variable control over the variable valve-operating device (step  108 ). 
   If an instruction for dual valve variable control is issued to the controller for the variable valve-operating device while single valve variable control is exercised, the controller for the variable valve-operating device executes the routine shown in  FIG. 15  to exercise hydraulic control. In the first step (step  200 ), the control shaft  32  rotates beyond the normal use range and toward the great lift side to adjust its rotation position to a position that corresponds to the “first great lift position.”. 
   In the next step (step  202 ), the solenoid valve  104  turns ON to start to discharge the lubricating oil via the discharge path  102 . After the solenoid valve  104  is turned ON, step  204  is performed to judge whether the hydraulic pressure of a lubricating oil flow in the oil path  92  (controlled hydraulic pressure) is lower than the predetermined pressure P 1 . No subsequent step is performed until the hydraulic pressure drops below the predetermined pressure P 1 . A standby state persists until the judgment result obtained in step  204  indicates that the hydraulic pressure of the lubricating oil flow in the oil path  92  is lower than the predetermined pressure P 1 . 
   When the hydraulic pressure drops below the predetermined pressure P 1 , step  206  is performed to wait until one cycle elapses (the crankshaft makes two revolutions) while the rotation position of the control shaft  32  is maintained at the position set in step  200 . Since the hydraulic pressure is below the predetermined pressure P 1 , the piston  82  pushes the pin  80  out of the pin hole  86 . When one cycle elapses, the pin  80  leaves the pin hole  86 . This completely uncouples the great lift arm  72  from the second swing cam arm  40 R. 
   After the elapse of one cycle, the control shaft  32  rotates in a direction opposite to the rotation direction employed in step  200  until the rotation position of the control shaft  32  reverts to the normal use range (step  208 ). This brings the second roller  62 R into contact with the slide surface  46 R of the second swing cam arm  40 R so that the second swing cam arm  40 R is driven by the first drive cam  22  as is the case with the first swing cam arm  40 L. In other words, when the control shaft  32  rotates, variable control can be exercised over the lift amount and valve timing of the valves  4 L,  4 R. When the rotation position of the control shaft  32  reverts to the normal use range, the solenoid valve  102  turns OFF to stop the discharge of lubricating oil from the discharge path  102  (step  210 ). Subsequently, the controller exercises dual valve variable control over the variable valve-operating device (step  212 ). 
   [Advantages of the Variable Valve-operating Device According to the Present Embodiment] 
   As described above, the variable valve-operating device according to the present embodiment can change the operating characteristic control mode for the second valve  4 R from variable control to fixed control simply by coupling the great lift arm  72  to the second swing cam arm  40 R, and change the operating characteristic control mode for the second valve  4 R from fixed control to variable control simply by uncoupling the great lift arm  72  from the second swing cam arm  40 R. This makes it easy to properly switch from the dual valve variable control mode, in which the operating characteristics of the first valve  4 L and second valve  4 R can be changed in accordance with the rotation position of the control shaft  32 , to the single valve variable control mode, in which the operating characteristic of the first valve  4 L can be changed in accordance with the rotation position of the control shaft  32  while the operating characteristic of the second valve  4 R is fixed. It is also easy to properly switch from the single valve variable control mode to the dual valve variable control mode. 
   According to the variable valve-operating device according to the present embodiment, the great lift arm  72  can be coupled to the second swing cam arm  40 R by using an extremely simple structure that inserts the pin  80  into the pin hole  86 . Further, the position of the pin hole  86  does not coincide with that of the pin  80  while the rotation position of the control shaft  32  is within the normal use range. Therefore, the second valve  4 R does not erroneously switch to a fixed operation while it is engaged in a variable operation. 
   Further, the aforementioned “pin position” and “first great lift position” are defined with reference to the zero lift positions of the arms  40 R,  72 . Therefore, the pin  80  can be inserted into the pin hole  86  while the arms  40 R,  72  are stationary. Therefore, the variable valve-operating device according to the present embodiment can properly couple the great lift arm  72  to the second swing cam arm  40 R. 
   When the control mode changes from dual valve variable control to single valve variable control, the control shaft  32  rotates beyond the normal use range and toward the great lift side. Therefore, the lift amount of the second valve  4 R temporarily increases above the maximum lift amount for the normal use range. However, the influence of the lift amount difference upon the intake air amount decreases toward the great lift side. Therefore, a lift amount change at the time of a control mode change does not significantly change the intake air amount. 
   Furthermore, the parts required for exercising single valve variable control in addition to dual valve variable control are limited to the great lift arm  72  and arm coupling mechanism  78 , which constitute the fixed valve mechanism  70 . Therefore, the variable valve-operating device according to the present embodiment has the advantage that the number of parts can be minimized. Moreover, the great lift arm  72  is positioned just next to the second swing cam arm  40 R. When compared to a situation where the fixed valve mechanism  70  is not furnished, the length in axial direction merely increases by the length of the great lift arm  72 . Therefore, the variable valve-operating device according to the present embodiment is also advantageous in that an undue increase in the size of the entire device can be avoided. 
   Second Embodiment 
   A second embodiment of the present invention will now be described with reference to  FIGS. 16 to 19 . 
   The variable valve-operating device according to the second embodiment differs from the variable valve-operating device according to the first embodiment in the hydraulic system configuration for pin operation. The second embodiment is equal to the first embodiment in the basic configuration and operation of the variable valve mechanism and fixed valve mechanism. Such configuration and operation can be depicted by  FIGS. 1 to 11 . The subsequent description mainly deals with the differences from the first embodiment. 
     FIG. 16  illustrates the configuration of a hydraulic system for operating the pin  80 . As shown in  FIG. 16 , the oil path  92  is formed in the control shaft  32  to connect with a sliding gap between the control shaft  32  and great lift arm  72  and with a sliding gap between the control shaft  32  and second swing cam arm  40 R. In the second embodiment, a hydraulic oil path  94  is formed in the control shaft  32  in addition to the lubricating oil path  92 . The hydraulic oil path  94  is connected to the hydraulic chamber  88  in the great lift arm  72  via the oil path  90 . A pump  110  is installed upstream of the oil path  94 . Hydraulic oil pressurized by the pump  110  is supplied to the hydraulic chamber  88  via the oil path  94  to apply hydraulic pressure to the pin  80 . The pump  110  may double as the pump for supplying lubricating oil to the oil path  92 . 
   A solenoid valve (discharge valve)  112 , which opens/closes the oil path  94 , is installed downstream of the pump  110  in the oil path  94 . When the solenoid valve  112  opens, hydraulic oil is supplied to the hydraulic chamber  88  via the oil path  94  so that the hydraulic pressure applied to the pin  80  increases. When, on the other hand, the solenoid valve  112  closes, the hydraulic oil supply to the oil path  94  is shut off. The hydraulic oil in the oil path  94  leaks little by little through the sliding gap between the control shaft  32  and great lift arm  72 . Therefore, when the hydraulic oil supply is shut off, the hydraulic pressure in the oil path  94  lowers to reduce the hydraulic pressure applied to the pin  80 . Consequently, the great lift arm  72  can be coupled to the second swing cam arm  40 R by opening the solenoid valve  112 , and the great lift arm  72  can be uncoupled from the second swing cam arm  40 R by closing the solenoid valve  112 . As described above, the solenoid valve  112  opens only when the great lift arm  72  is to be coupled to the second swing cam arm  40 R. As a result, the hydraulic oil can be saved by reducing the amount of hydraulic oil leakage from the sliding gap. 
   Hydraulic pressure is relieved from the hydraulic chamber  88  and oil path  94  when the solenoid valve  112  is closed. Therefore, a certain amount of standby time T is required between the instant at which the solenoid valve  112  is opened again and the instant at which the hydraulic pressure reaches the predetermined pressure P 1 , as indicated in  FIG. 17 . The standby time T varies with the temperature because it is influenced by the viscosity of hydraulic oil. If the predetermined pressure P 1  is not reached by the hydraulic pressure, the pin  80  cannot be inserted into the pin hole  86  against the force that is exerted by the return spring  84  to push the piston  82  no matter whether the position of the pin  80  coincides with that of the pin hole  36 . Therefore, the controller for controlling the variable valve-operating device inhibits the great lift arm  72  from being coupled to the second swing cam arm  40 R during the time interval between the instant at which the solenoid valve  112  opens and the instant at which the hydraulic pressure reaches the predetermined pressure P 1 . 
     FIGS. 18 and 19  are flowcharts illustrating the specific details of hydraulic control that is exercised by the variable valve-operating device according to the present embodiment. The flowchart in  FIG. 18  shows a hydraulic control routine that is executed to switch from dual valve variable control to single valve variable control. The flowchart in  FIG. 19  shows a hydraulic control routine that is executed to switch from single valve variable control to dual valve variable control. 
   If an instruction for single valve variable control is issued to the controller for the variable valve-operating device while dual valve variable control is exercised, the controller for the variable valve-operating device executes the routine shown in  FIG. 18  to exercise hydraulic control. In the first step (step  300 ), the control shaft  32  rotates to move the position of the second roller  62 R on the slide surface  46 R toward the great lift side and change the swing angle of the second swing cam arm  40 R so as to place the pin hole  86  at the “second great lift position.” 
   In the next step (step  302 ), the solenoid valve  112  turns ON to start to supply the hydraulic oil into the oil path  94  while the rotation position of the control shaft  32  is maintained at the position set in step  300 . After the solenoid valve  112  is turned ON, step  304  is performed to judge whether the predetermined pressure P 1  is reached by the hydraulic pressure (controlled hydraulic pressure) of the hydraulic oil flow in the oil path  94 . No subsequent step is performed until the hydraulic pressure reaches the predetermined pressure P 1 . A standby state persists until the judgment result obtained in step  304  indicates that the predetermined pressure P 1  is reached. 
   When the hydraulic pressure reaches the predetermined pressure P 1 , the control shaft  32  rotates to further shift the position of the second roller  62 R on the slide surface  46 R toward the great lift side and change the swing angle of the second swing cam arm  40 R so as to place the pin hole  86  at the “first great lift position” (step  306 ). The next step (step  308 ) is performed to wait until one cycle elapses (the crankshaft makes two revolutions) while the rotation position of the control shaft  32  is maintained at the position set in step  306 . When the second swing cam arm  40 R swings to the above swing angle, the pin hole  86  passes the “first great lift position” without fail before the elapse of one cycle. In such an instance, the position of the pin  80  coincides with that of the pin hole  86  so that the hydraulic pressure in the hydraulic chamber  88  generates a driving force to promptly insert the pin  80  into the pin hole  86 . This ensures that the great lift arm  72  is completely coupled to the second swing cam arm  40 R. 
   After the elapse of one cycle, the control shaft  32  rotates in a direction opposite to the rotation direction employed in step  306  until the rotation position of the control shaft  32  reverts to the normal use range (step  310 ). The second roller  62 R then completely leaves the slide surface  46 R of the second swing cam arm  40 R, thereby allowing the second drive cam  24  to drive the second swing cam arm  40 R. Consequently, the second valve  4 R is set for a fixed lift amount and valve timing. On the other hand, the first swing cam arm  40 L is driven by the first drive cam  22  as is the case with the dual valve variable control mode so that variable control can be exercised over the lift amount and valve timing of the first valve  4 L by rotating the control shaft  32 . Subsequently, the controller exercises single valve variable control over the variable valve-operating device (step  312 ). 
   If an instruction for dual valve variable control is issued to the controller for the variable valve-operating device while single valve variable control is exercised, the controller for the variable valve-operating device executes the routine shown in  FIG. 19  to exercise hydraulic control. In the first step (step  400 ), the control shaft  32  rotates beyond the normal use range and toward the great lift side to adjust its rotation position to a position that corresponds to the “first great lift position.” 
   In the next step (step  202 ), the solenoid valve  112  turns OFF to shut off the hydraulic oil supply to the oil path  94 . After the solenoid valve  112  is turned OFF, step  404  is performed to judge whether the hydraulic pressure of a hydraulic oil flow in the oil path  94  (controlled hydraulic pressure) is lower than the predetermined pressure P 1 . No subsequent step is performed until the hydraulic pressure drops below the predetermined pressure P 1 . A standby state persists until the judgment result obtained in step  404  indicates that the hydraulic pressure of the hydraulic oil flow in the oil path  94  is lower than the predetermined pressure P 1 . 
   When the hydraulic pressure drops below the predetermined pressure P 1 , step  406  is performed to wait until one cycle elapses (the crankshaft makes two revolutions) while the rotation position of the control shaft  32  is maintained at the position set in step  400 . Since the hydraulic pressure is lower than the predetermined pressure P 1 , the piston  82  pushes the pin  80  out of the pin hole  86 . The pin  80  leaves the pin hole  86  before the elapse of one cycle. This completely uncouples the great lift arm  72  from the second swing cam arm  40 R. 
   After the elapse of one cycle, the control shaft  32  rotates in a direction opposite to the rotation direction employed in step  400  until the rotation position of the control shaft  32  reverts to the normal use range (step  408 ). This brings the second roller  62 R into contact with the slide surface  46 R of the second swing cam arm  40 R again. The second swing cam arm  40 R is then driven by the first drive cam  22  as is the case with the first swing cam arm  40 L. In other words, when the control shaft  32  rotates, variable control can be exercised over the lift amount and valve timing of the two valves  4 L,  4 R. Subsequently, the controller exercises dual valve variable control over the variable valve-operating device (step  410 ). 
   Other 
   While the present invention has been described in terms of preferred embodiments, it should be understood that the invention is not limited to the foregoing preferred embodiments, and that variations may be made without departure from the scope and spirit of the invention. For example, the following modifications may be made to the preferred embodiments of the present invention. 
   In the foregoing embodiments, the great lift arm  72  is provided with the pin  80 , and the second swing cam arm  40 R is provided with the pin hole  86 . However, an alternative is to provide the great lift arm  72  with the pin hole  86  and the second swing cam arm  40 R with the pin  80 . Further, the foregoing embodiments use hydraulic pressure to drive the pin  80 . However, electromagnetic force or other driving force may alternatively be used. 
   In the foregoing embodiments, the control arm  50  is mounted on the camshaft  20  in a swingable manner, and interlocked with the control shaft  32  via the small-diameter gear  34  and large-diameter gear  52 . Alternatively, however, the control arm  50  may be fastened to the control shaft  32  so that the control arm  50  and control shaft  32  rotate as an assembly. The control arm  50  may be coupled to the rollers  60 ,  62  via the intermediate arm that is mounted on the control arm in a swingable manner. Even when such an alternative configuration is employed, the rollers  60 ,  62  can be moved along the circumferential surface of the first drive cam  22  in accordance with the rotation of the control shaft  32 . 
   In the foregoing embodiments, the present invention is applied to a one-cam two-valve drive type valve-operating device. However, the present invention can alternatively be applied to a one-cam one-valve drive type valve-operating device. Further, the present invention can be applied to a direct acting or other valve-operating device as well as to a rocker arm type valve-operating device, which is described in conjunction with the foregoing embodiments.