Abstract:
A valve actuator system is capable of operating a number of valves with a single cam. The system includes a power shaft, a cam mounted around the power shaft and a gear train to drive the cam when the shaft rotates. Hydraulic actuator assemblies corresponding to the number of valves are radially positioned around the shaft axis for operation by the cam. Hydraulic tubes connect each actuator to a valve follower disposed adjacent to the respective valves. The cam profile pressing each actuator plunger in sequence as the cam rotates causes the hydraulic fluid to flow out of the actuator assembly, through the like-numbered pipe, and into the like-numbered follower assembly, which in turn causes the follower plunger to move the like-numbered valve from an open position or a closed position. This occurs sequentially for each valve.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application No. 62/039,815, filed on Aug. 20, 2014, entitled VALVE ACTUATOR SYSTEM CAPABLE OF OPERATING MULTIPLE VALVES WITH A SINGLE CAM, which is incorporated by reference herein in its entirety. 
    
    
     TECHNICAL FIELD 
     The present invention relates to a valve actuator system for an internal combustion piston engine. In particular, it relates to a valve actuator system that permits multiple valves to be operated by a single cam and can accommodate various piston arrangements and various engine firing orders. 
     BACKGROUND 
     Current engine designs such as those used in automotive and many other applications typically use an in-line or “V” arrangement of multiple pistons. Each intake and exhaust engine valve is opened and closed by a cam on one or more camshafts. Since each piston employs two or more valves, many cams are required for the engine. The camshafts are aligned parallel to the crankshaft that controls the oscillatory motion of the pistons. They extend approximately the entire length of the engine. The possible locations of the camshafts are limited due to the need to arrange them in concert with the valves they operate. 
     The arrangement of the camshafts is determined by the mechanical link between the cam and the valve the cam operates. The cam may operate directly on the valve, use a “push rod” and/or a “valve lifter” as a direct link between the cam and valve, or incorporate rocker arms to transfer the cam motion to the valve. A push rod is a small shaft that allows the cam and camshaft to be located some distance from the valve. A valve lifter is a small device that uses engine oil to maintain proper adjustment of the valve actuation mechanism. All of these options for valve actuation limit the practical locations for the cams and camshafts on the engine. 
     The rotation of each cam on each camshaft must be synchronized with the crankshaft in order for the valve to open and close at the proper position of the piston in the engine cycle. In four-stroke engines, the rotation of the camshaft is one-half as fast as the rotation of the crankshaft. Synchronization of the camshafts and crankshaft is accomplished in newer engines using timing belts or timing chains since the camshafts are often located too far from the crankshaft (for example, in the cylinder head) for them to be synchronized by gear arrangements alone. Timing belts can fail due to wear or breakage and require expensive replacement at specified intervals of operation. 
     SUMMARY 
     A first embodiment of the invention comprises a single cam, multiple valve actuators arranged radially about the cam, valve followers at each valve operated by the cam, and small tubes to transport hydraulic fluid as links between each actuator and the valve it operates. As the cam engages the valve actuator, a small piston in the actuator is displaced driving hydraulic fluid through the tube to the connected follower. Simultaneously a small piston in the valve follower is displaced to open the valve. After the cam high point passes the actuator piston, the actuator piston moves back to its starting point and the hydraulic fluid flows back into the valve actuator permitting the follower piston to return to its original position and the valve to close. The only fluid lost from the valve actuation system is any trivial seepage past the pistons. Any fluid lost is replaced by fluid from the hydraulic fluid source. This fluid source may be oil from the engine lubrication system. 
     The use of a hydraulic link between the actuator and the follower permits the valves and cam to be separated by a distance and location of the cam in an optimum place on the engine. This approach accommodates various cylinder arrangements and firing orders including ones that do not follow the traditional placement of cylinders in the “in line” or “V” configurations. The use of a hydraulic tube as the link between the cam location and valve location is similar to use of an electricity conducting wire as a link between a the spark generator in one location and a spark plug in another location. 
     The cam driving the actuators may be synchronized with the rotational component of the engine such as a crankshaft to open and close the valve at the appropriate phase of the engine combustion cycle. In typical four-cycle internal combustion engines, the cam rotates at one-half the rotational speed of the crankshaft. For example, the intake valve may open to allow air or a mixture of air and fuel to enter the combustion chamber and be closed the rest of the time. In another example, the exhaust valve may open to allow the products of combustion to exit the combustion chamber after the expansion cycle and be closed the rest of the time. Synchronization of the actuator and the engine may be accomplished by a mechanical interface. With the subject valve actuation system, one cam may be used to actuate all intake valves in a multi-cylinder engine and one cam used to actuate all exhaust valves. 
     If the actuator piston and the follower piston are the same size, the valve duplicates the action of the cam. If the pistons are not the same size, the valve action will be similar to that of the cam, but the follower action will either be amplified or reduced in comparison to the action of the cam. 
     A second embodiment includes followers for all intake or exhaust valves linked to an assembly consisting of one cam for all similar valves, and a set of reduction gears to synchronize the cams with a single power shaft that is rotationally connected to the crankshaft or its equivalent power shaft. Similarly, a second cam and set of reduction gears can be added to operate the other valves. The following example provides an illustration of the this embodiment based on an application to a 5-cylinder, four-stroke, piston engine with the cylinders arranged radially about a central power shaft and with the centerlines of the cylinders parallel to the centerline of the power shaft. The follower for each valve is linked with its actuator and a hydraulic fluid supply in the same manner as described for the first embodiment. 
     The configuration of the reduction gear set, cam, and actuators for the intake valves and the exhaust valves may be virtually mirror images of each other. A central camshaft that drives the two cams may be functionally fixed to the power shaft of the engine so that it rotates with a rotational speed proportional to the rotational speed of the power shaft. Each cam is connected to a set of planetary gears that reduce the rotational speed of the cam to one-half of the rotational speed of the central shaft. In this embodiment, the cam is part of the planetary gear carrier of its gear set. A single center (sun) gear mounted fixedly to the central shaft drives both sets of planetary gears and thereby each cam. The outside (ring) gear of each set is nominally fixed and does not rotate except to change valve timing. The proper relation of cam rotational speed and central shaft speed is obtained by proper ratio of size between the sun gear and the planetary gears. The ring gear is determined by the size of the sun gear and planetary gears. 
     A set of five actuators for one set of valves may be arranged radially about its cam. Similarly, a second set of actuators is arranged about the other cam. Each set of actuators is fastened to one of two parts of a housing that surrounds the central shaft. One part of the housing is held in place by fastening to a suitable structure such as a cylinder head. The central shaft extends through the housing and its rotation is fixed by the rotation of the engine power shaft. This housing also encases the reduction gears and cam for one set of valves. Part of the ring gear extends through the side of the housing. This part of the ring gear restrains the ring gear from rotating, but can be moved by the external device to change the timing of valves attached to the cam in this part of the housing. For demonstration purposes only, this set of valves may be selected as the intake valves. 
     The second set of actuators is mounted to the second part of the housing. The second part of the housing also surrounds the second set of reduction gears and cam. This part of the housing is similar to the first part except that it is mounted fixedly to the first part rather than to surrounding structure and the central shaft may not extend through the housing. When the housing is assembled, the arrangement of the gears, cam and actuators in the second part of the housing is virtually a mirror image of those in the first part of the housing except for the positions of the cams. The part of the ring gear extending from the ring gear of this set of gears permits the timing of the valves to be varied independently with respect to the timing of the valves operated by the cam in the first part of the housing. For demonstration purposes only, this set of valves may be selected as the exhaust valves. 
     The use of two sets of reduction gears in this configuration permits the independent variation of intake and exhaust valve timing. This capability is achieved with a nearly trivial increase of complexity when compared to a design without any variable valve timing. The simplicity is in stark contrast to the complexities in current engine designs. 
     All lubricating oil and leakage is directed through the bottom of the housing and back to the oil pan. The containment of engine oil makes it possible to keep the surrounding portion of the engine to be oil free and eliminates the need for oil containment covers as required in current engine designs. 
     The valve housing assembly, with or without the actuators attached, can be assembled and tested for correct timing prior to installation on an engine. This capability will simplify the engine assembly and maintenance process. 
     All of the features of this valve actuator assembly are accomplished without the need for timing belts, timing chains, or any other complex provisions. 
     A valve actuation system incorporating the above described features would be very difficult if not impossible using today&#39;s conventional technology. At least one camshaft would be required for each cylinder and independent variable valve timing would require added complexity. 
     A third embodiment is similar to the second except that each planetary gear reduction set that drives each cam is replaced by a linear set of reduction gears and the housing is modified to accommodate the difference in gear geometry 
     A drive gear replaces the sun gear used in the planetary gear system used in the second embodiment. The drive gear is fixedly attached to the central shaft and rotates with it. The drive gear drives one side of a double gear (idler gear) that is mounted on a lever through a bearing. The idler gear is allowed to rotate about the bearing stem on the lever. The second side of the idler gear drives a cam gear fixedly attached to its cam. One end of the lever is mounted so that the lever is allowed to rotate about the camshaft. The other end of the lever is restrained to prevent rotation of the lever about the camshaft except to vary valve timing. The sizes of the drive gear, both sides of the idler gear, and the cam gear are selected to result in the desired rotational speed of the cam in relation to the rotational speed of the central shaft. When the rotational speed of the central shaft is equal to the rotational speed of the engine power shaft, this ratio is ½. 
     The following gear sizes are an example where the central camshaft is fixedly attached to the engine power shaft. The side of the double gear in contact with the drive gear is twice the size of the drive gear and rotates at half the rotational speed of the camshaft and in the opposite direction. A third gear is fixedly attached to the cam. The second side of the double gear meshes with the third gear. The second side of the double gear and the third gear are of the same size. This combination of gears results in the cam rotation in the same direction as the camshaft but at half the rotational speed as required for proper cam operation. Other combinations of gear sizes to produce the same gear reduction are possible. 
     The end of the lever opposite the camshaft is restrained from movement except to vary valve timing. Movement of this end of the lever for the intake valve cam varies timing of the intake valves. Similarly, movement of the same end of the lever for the exhaust valve cam varies timing of the exhaust valves. 
     Minor changes to the housing design in the second embodiment are made to accommodate replacement of the ring gear and planetary gears in the second embodiment with the lever and an idler gear in the third embodiment. 
     A fourth embodiment is similar to the second embodiment except that the planetary gears are used in a different way to achieve the desired rotational speed of the cams. Small changes in the housing design from the second embodiment are made to accommodate the differences in cam/gear interfaces and addition of bearings between the cams and the central shaft. 
     Each cam is fixedly attached to its ring gear or the two are made as one unit. The cam rotates with the same rotational speed as the ring gear. In this embodiment, there is no rotation of the planetary gear carrier except to change valve timing. This arrangement of fixed and rotating gears permits a greater range of valve timing than the configuration in the second embodiment. 
     In this embodiment, the cams rotate in the opposite direction from the central shaft. This difference is easily accommodated by rerouting the hydraulic line from each actuator to the proper valve. The cam rotational speed of one-half the rotational speed of the central shaft is accomplished when the diameter of the ring gear is twice that of the sun gear. 
     Other features of this embodiment are the same as those in the second embodiment. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Reference is made to the following drawings for a more complete description of the four previously presented embodiments of the invention: 
         FIG. 1  is a schematic view of a valve actuator system in accordance with one aspect using a single cam to operate multiple valves; 
         FIG. 2  is another schematic view, further illustrating components comprising the valve actuator system of  FIG. 1 ; 
         FIG. 3  is a cross-section side view of a valve actuator system in accordance with another aspect, wherein the system includes two cams and a set of planetary gears; 
         FIG. 4  is a top view showing the general arrangement of the components in a planetary gear reduction system in accordance with one embodiment; 
         FIG. 5  is a schematic view showing the fluid lines connecting the cam actuators to the valve followers for all intake or exhaust valves in an engine configuration of five cylinders surrounding a central power shaft wherein the cylinder centerlines are parallel to the centerline of the power shaft in accordance with another embodiment; 
         FIG. 6  is a cross-section side view of a valve actuator system in accordance with yet another aspect, wherein the system includes two cams and a set of linear reduction gears; and 
         FIG. 7  is a cross-section side view of a valve actuator system in accordance with a further aspect, wherein the system includes two cams and an alternative set of planetary gears having a different arrangement from that shown in  FIG. 3 . 
     
    
    
     DETAILED DESCRIPTION 
     Referring now to the drawings, wherein like reference numbers are used herein to designate like elements throughout, the various views and embodiments of a valve actuator system using a single cam to operate multiple valves are illustrated and described. Also other embodiments of this valve actuator system are described. The figures are not necessarily drawn to scale, and in some instances the drawings have been exaggerated and/or simplified in places for illustrative purposes only. One of ordinary skill in the art will appreciate the many possible applications and variations based on the following examples of possible embodiments. 
     Referring now to  FIGS. 1 and 2 , there is illustrated an exemplary embodiment of a valve actuator system  100  in accordance with one aspect. Referring first to  FIG. 1 , in the illustrated embodiment four valve actuators  101  are arranged radially about a single cam  102 . Each actuator  101  is linked to its respective valve follower  103  by a small linking tube  104 , all of which are filled with a hydraulic fluid  116 . The follower  103  in turn causes the valve  105  to open and close in the same manner as the cam surface directs. Hydraulic fluid  116  (e.g., engine lubricating oil) transfers the force of the cam  102  from the actuator  101  to the follower  103  via the fluid-filled tube  104 . In  FIG. 1 , one valve (denoted  105 ′) is shown in the open position while all others are shown in the closed position. A more detailed description of the components and their operation is illustrated in  FIG. 2 . 
     Referring now also to  FIG. 2 , the cam  102  is connected to the engine crankshaft or other element (not shown) through a gear, belt, chain or other means so the cam causes the valve  105  to open and close in proper timing with the piston operation. In  FIG. 2 , the valve  105  is shown in the closed position. The actuator  101  comprises an actuator housing  106  that is mounted in a fixed position with relation to the cam  102 . One open end  107  of the housing  106  permits a plunger  108  to slide back and forth as the cam  102  forces it to open the valve  105  or permits it to return to the closed position. The plunger  108  fits snugly within the actuator housing  106  to prevent hydraulic fluid  116  from leaking unnecessarily past the housing  106 . The other end  110  of the actuator housing  106  connects with the linking tube  104 . The tube  104 , actuator  101  and follower  103  are filled with a hydraulic fluid  116 . 
     Referring still to  FIG. 2 , the distant end of the linking tube  104  connects with the valve follower housing  111 . The follower housing  111  is mounted in a fixed position in relation to the engine structure  115  around the valve  105 . As the cam  102  pushes the actuator plunger  108  into the actuator housing  106 , hydraulic fluid  116  is forced into the linking tube  104  and into the valve follower housing  111 , forcing the valve plunger  112  to extend and open valve  105 . The valve plunger  112  may be the same size as the actuator plunger  108  to replicate the motion produced by the cam  102 , or it may be larger for less motion than the motion of actuator plunger  108 , or it may be smaller to magnify the motion produced for actuator plunger  108  by the cam  102 . 
     Hydraulic fluid  116  may be supplied to the valve actuator system  100  from a source  117 , which may be the engine lubricating system, through supply tube  113 . A check valve  114  permits flow of fluid into the valve actuation system  100 , but it prevents fluid from being forced back into the fluid source  117  while the valve  105  is forced open. The hydraulic fluid supply pressure keeps the valve plunger  112  against the valve  105 , and the cam plunger  108  against the cam  102 . The supply pressure is kept lower than the pressure required to open the valve  105  so that the valve is only open when the cam  102  forces the cam plunger  108  into the actuator housing  106 . There is essentially no flow of hydraulic fluid  116  from the system  100 . This feature keeps power loss to a minimum. The hydraulic fluid supply  117  replaces any seepage around the actuator plunger  108  and the valve plunger  112 . There is no fluid accumulator in the valve actuation system  100 . The hydraulic fluid  116  simply flows from the actuator housing  106  to the follower housing  111  and back again. 
     Referring now to  FIG. 3 , there is illustrated a cross-section side view of a valve actuator system  300  in accordance with another embodiment (“second embodiment”). The system  300  includes two cams, a first cam  320  for operating all exhaust valves and a second cam  322  for operating all intake valves, and two sets of planetary gears  301   a ,  301   b  for matching the operation of the respective cams with the rotation of the central power shaft of the engine. A central shaft  315  is connected rotationally in concert with the crankshaft (or power shaft) of the engine. A single sun gear  316  fixedly connected to the central shaft  315  drives two sets of planetary gears (denoted, respectively, with “a” and “b”) to drive the exhaust and intake cams  320 ,  322  at the correct rotational speed. In this application, the ring gears  318   a ,  318   b  do not rotate except to vary valve timing. 
     Referring now to  FIG. 4 , a typical set  301  of planetary reduction gears is illustrated as may be used in the disclosed embodiments. In each set of planetary gears  301 , a sun gear  316  on a shaft  315  is in geared engagement with a set of multiple (in this case, three) planetary gears  317  that are concurrently in geared engagement with an enclosing ring gear  318 . The planetary gears  317  are rotatably attached through bearings to a carrier  319 , which carrier may also be rotatable around the shaft  315 . In various configurations, either the planet gears  317 , the ring gear  318  or the planet carrier  319  may be constrained against rotation to produce a rotational output from the remaining components when driven by the sun gear  316 . It will be appreciated that  FIG. 4  is intended only to illustrate the general layout of a planetary gear set, and the particular gear sizes and gear ratios illustrated in  FIG. 4  are not necessarily the gear sizes or gear ratios used in the embodiments described herein. 
     Returning to  FIG. 3 , a first set of gears,  317   a  and  318   a , and a first carrier  319   a  are used to drive the exhaust cam  320  by the sun gear  316 . In the illustrated embodiment, the exhaust cam  320  is fixedly mounted directly on the exhaust carrier  319   a . Unlike the sun gear  316 , which is fixed to the central shaft  315  to rotate with the central shaft, the exhaust carrier  319   a  and the exhaust cam  320  are rotatably mounted on the central shaft  315  to allow independent rotation with respect to the central shaft (although the carrier  319   a  and the cam  320  must rotate together). Each exhaust planet gear  317   a  is rotatably mounted on an axle bearing  302   a  of the exhaust carrier  319   a , and is simultaneously engaged on the inward side by the sun gear  316  and on the outward side by the exhaust ring gear  318   a . Relative rotational movement between the sun gear  316  and the ring gear  318   a  causes the planet gears  317   a  to simultaneously rotate on the axle bearing  302   a  of the carrier  319   a  and revolve around the sun gear. This revolution of the planet gears  317   a  causes the carrier  319   a  to rotate around the shaft  315 . The sizes of the gears  317   a  and  318   a  are determined by the requirement for the exhaust cam  320  to rotate at half the rotational speed of the central shaft  315 . The exhaust cam  320  is used to actuate all exhaust valves. Exhaust valve actuators  101 ′ are arranged radially about the central shaft  315  and the exhaust cam  320 . The exhaust actuator  101 ′ shown in  FIG. 3  is in the compressed state for an open exhaust valve  105 . An exhaust timing lever  321  extends outward from the exhaust ring gear  318   a , and may be used to selectively rotate the exhaust ring gear to vary the exhaust valve timing. 
     Referring still to  FIG. 3 , the component arrangement for operation of intake valves is similar to the one for operation of exhaust valves previously described. A second set of gears,  317   b  and  318   b , and a second carrier  319   b  are used to drive the intake cam  322  by the sun gear  316 . The intake cam  322  is fixedly mounted directly on the intake carrier  319   b . The intake carrier  319   b  and the intake cam  322  are rotatably mounted on the central shaft  315  to allow independent rotation with respect to the central shaft (although the carrier  319   b  and the cam  322  must rotate together). The intake planet gear  317   b  is rotatably mounted on an axle bearing  302   b  of the intake carrier  319   b , and is simultaneously engaged on the inward side by the sun gear  316  and on the outward side by the intake ring gear  318   b . Relative rotational movement between the sun gear  316  and the intake ring gear  318   b  causes the intake planet gears  317   b  to simultaneously rotate on the axle bearing  302   b  of the intake carrier  319   b  and revolve around the sun gear. This revolution of the intake planet gears  317   b  causes the intake carrier  319   b  to rotate around the shaft  315 . The sizes of the gears  317   b  and  318   b  are determined by the requirement for the intake cam  322  to rotate at half the rotational speed of the central shaft  315 . The intake cam  322  is used to actuate all intake valves. Intake valve actuators  101 ″ are arranged radially about the central shaft  315  and the intake cam  322 . The intake valve actuator  101 ″ shown in  FIG. 3  is in the extended state indicating a closed intake valve  105 . It should be noted that in the illustrated embodiment, the intake cam  322  leads the exhaust cam  320  by approximately 90 degrees. An intake timing lever  323  extends outward from the intake ring gear  318   b , and may be used to vary intake valve timing (independently of the exhaust valve timing). The two timing levers  321 ,  323  are shown in the same position for illustration purposes only. 
     The valve actuator assembly  300  may include a housing fabricated in two parts, e.g., an upper housing  325  and a lower housing  327 , to permit installation and orientation of components and verification of the configuration. In the illustrated embodiment, the respective actuator housings  106  of the intake valve actuator  101 ′ and the exhaust valve actuator  101 ″ are installed and oriented to the respective housing parts  325 ,  327  at fixed locations such that the outlet ports to the linking tubes  104  remain at respective fixed locations and respective fixed orientations relative to the housing  300 . Hydraulic oil  116  may be provided through the fitting  324  in the upper housing  325  at the top of the central shaft  315  for lubrication of the components. It is anticipated that all hydraulic oil  116  including oil for lubrication and purging air bubbles will be returned to a collection system through openings  326  at the bottom of the lower housing  327 . Similar provisions can be made with the follower installation. 
     Referring now to  FIG. 5 , a schematic diagram is provided of a valve actuator system  500  in accordance with another embodiment suitable for use on a four-cycle, five-cylinder piston engine  502  with the cylinders  504 - n  arranged radially around the central power shaft  315  that controls piston motion. For purposes of illustration, only one cam  102  is shown, and each cylinder  504 - n  is provided with only one valve follower  103 - n , but it will be appreciated that multiple cams may be placed on the shaft as previously described (e.g.,  FIG. 3 ) to actuate multiple types of valves per cylinder. The cam  102  is operatively connected to the central power shaft  315  to rotate with the power shaft. The cylinders  504 - n  in this embodiment are sequentially numbered  504 - 1 ,  504 - 2 ,  504 - 3 ,  504 - 4  and  504 - 5  in clockwise order and the cam  102  also rotates clockwise. Each cylinder  504 - n  is provided with a corresponding valve follower  103 - n  to be actuated by the cam  102  in order to open a corresponding valve (not shown) on the cylinder. Valve actuators  101 - n  are arranged radially about the central shaft  315  and the cam  102 . The dash-numbers on the valve actuators  101 - n  indicate the dash-number of the corresponding valve follower  103 - n  to which that the respective valve actuator  101 - n  is linked (e.g., actuator  101 - 1  is linked to follower  103 - 1 , actuator  101 - 2  is linked to follower  103 - 2 , etc.). The firing order for this arrangement is (1), (3), (5), (2), (4). The dashed lines  104 - n  indicate the corresponding hydraulic tube connections between the respective valve actuators  101 - n  and the corresponding valve followers  103 - n . The particular routes shown for the hydraulic lines  104 - n  are for illustration only; however, the interconnections are specific. 
     Valve actuation systems incorporating an integrated reduction gear set and multiple cam actuators with one or two cams as described in these embodiments can be expected to offer significant advantages over the current technology. Independent intake and exhaust valve timing are easily achieved. Such valve actuation systems can be designed, constructed and installed as a single unit in various locations and orientations. In many installations, the installation should be able to avoid the use of timing belts and timing chains with their risk of failure and requirements for replacement. Such valve actuation systems do not require lengthy camshafts with multiple cams and their location requirements; thereby freeing up design features not available in current technology engines. Such valve actuation systems can be especially advantageous with non-traditional cylinder arrangements, such as those illustrated in  FIG. 5 . Achieving an oil-free upper cylinder head will simplify the installation of spark plugs and their wiring. It avoids the problem of oil leaks that now occur with valve covers. 
     Referring now to  FIG. 6 , there is illustrated a valve actuation system  600  in accordance with another embodiment (“third embodiment”). Valve action system  600  is similar to the system  300  previously described, except that each set of planetary reduction gears  301  is replaced by a set of double idler gears mounted on a lever. The assembly housing  635 ,  637  is also modified to accommodate the different gear arrangement. If multiple cams are required, then separate gear trains may be provided for each cam, but all cams may be driven by the same power shaft. 
     In the illustrated embodiment, two cams  633  and  636  are provided, the cams being driven, respectively, by an “a” gear train and a “b” gear train. In this embodiment, the sun gear  316  of  FIG. 3  is replaced by a central drive gear  628  that drives both gear trains. The central drive gear  628  is fixed to the power shaft  315  and rotates with it. The “a” gear train includes a two-part idler gear  629   a  having two coaxial gear portions, a larger portion  610   a  and a smaller portion  612   a , wherein each portion has a different diameter. The larger gear portion  610   a  of the idler gear  629   a  engages the central drive gear  628  and rotates about the bearing  630   a  on an exhaust timing lever  631   a . The number of teeth on the larger portion  610   a  of the idler gear  629   a  is twice the number of the teeth on the drive gear  628 , resulting in a 2:1 gear ratio. Thus, the idler gear  629   a  rotates at half the rotational speed but in opposite directions as the drive gear  628  and the central shaft  315 . The smaller portion  612   a  of the idler gear  629   a  engages the gear section  632  of the exhaust cam  633 . The exhaust cam  633  rotates freely about the central shaft  315 . The smaller portion  612   a  of the idler gear  629   a  and the gear section  632  have the same number of teeth, resulting in a 1:1 gear ratio, so that both rotate at the same rotational speed but in opposite directions. The result is that the exhaust cam  633  rotates around the central shaft  315  in the same direction that the central shaft rotates, but at one-half the rotational speed. 
     During operation of the “a” gear train, the exhaust timing lever  631   a  is normally held in a fixed position; however, the timing lever can be moved in an arc around the central shaft  315  to vary the exhaust valve timing. In the illustrated embodiment, one end portion of the timing lever  631   a  (e.g., the right end portion in  FIG. 6 ) is constrained by the upper housing  635  (constraint not visible) to rotate about the central shaft  315 . An exhaust timing actuator connection  634  extends from the other end of the timing lever  631   a , and the gear bearing  630   a  is mounted on the timing lever between the two ends. To vary the exhaust timing, the timing lever  631   a  may be selectively rotated about the central shaft  315  by moving the timing actuator connection  634  in an arc. This arcing movement of the timing lever  631   a  causes the position of gear bearing  630   a  (upon which the idler gear  629   a  is mounted) to move in a similar arc about the central shaft  315  (while the idler gear stays in engagement with the central drive gear  628  and the gear section  632 ), thereby advancing or retarding the relationship between the angular position of the exhaust cam  633  and the angular position of the central drive gear  628  and power shaft  315  to adjust the exhaust timing. 
     Gear components of the “b” gear train (denoted with “b”) that drive the intake cam  636  may be substantially similar to the parts used to drive the exhaust cam  633 . In some embodiments, the intake cam  636  may be identical to the intake cam  633 , but in other embodiments it may be modified to better meet the requirements of intake valves as opposed to those of exhaust valves. The “b” gear train includes a two-part idler gear  629   b  having two coaxial gear portions, a larger portion  610   b  and a smaller portion  612   b , wherein each portion has a different diameter. The idler gear  629   b  may be identical to the idler gear  629   a , but this is not required, provided each gear produces the appropriate gear ratios. The larger gear portion  610   b  of the idler gear  629   b  engages the central drive gear  628  and rotates about the bearing  630   b  on an intake timing lever  631   b . The number of teeth on the larger portion  610   b  of the idler gear  629   b  is twice the number of the teeth on the drive gear  628 , resulting in a 2:1 gear ratio. Thus, the idler gear  629   b  rotates at half the rotational speed but in opposite directions as the drive gear  628  and the central shaft  315 . The smaller portion  612   b  of the idler gear  629   b  engages the gear section  638  of the intake cam  636 . The intake cam  636  rotates freely about the central shaft  315 . The smaller portion  612   b  of the idler gear  629   b  and the gear section  638  have the same number of teeth, resulting in a 1:1 gear ratio, so that both rotate at the same rotational speed but in opposite directions. The result is that the intake cam  636  rotates around the central shaft  315  in the same direction that the central shaft rotates, but at one-half the rotational speed. 
     During operation of the “b” gear train, the intake timing lever  631   b  is normally held in a fixed position; however, the timing lever can be moved in an arc around the central shaft  315  to vary the exhaust valve timing. In the illustrated embodiment, one end portion of the timing lever  631   b  (e.g., the right end portion in  FIG. 6 ) is constrained by the lower housing  637  (constraint not visible) to rotate about the central shaft  315 . An intake timing actuator connection  639  extends from the other end of the timing lever  631   b , and the gear bearing  630   b  is mounted on the timing lever between the two ends. To vary the intake timing, the timing lever  631   b  may be selectively rotated about the central shaft  315  by moving the timing actuator connection  639  in an arc. This arcing movement of the timing lever  63   b  causes the position of gear bearing  630   b  (upon which the idler gear  629   b  is mounted) to move in a similar arc about the central shaft  315  (while the idler gear stays in engagement with the central drive gear  628  and the gear section  638 ), thereby advancing or retarding the relationship between the angular position of the intake cam  636  and the angular position of the central drive gear  628  and power shaft  315  to adjust the intake timing. It will be appreciated that this arrangement allows the exhaust valve timing and the intake valve timing to be adjusted independently of one another. 
     Referring now to  FIG. 7 , there is illustrated a valve actuation system  700  in accordance with yet another embodiment (“fourth embodiment”). The embodiment of  FIG. 7  is substantially similar to the embodiment of  FIG. 3  (“second embodiment”) except that the planetary gear set uses a different configuration to achieve the desired rotational speed of the cams. In particular, in this fourth embodiment the ring gears rotate continuously and there is no rotation of the planetary gear carrier except to change valve timing, whereas in the second embodiment of  FIG. 3  the planetary gear carrier rotates continuously and there is no rotation of the ring gear except to change valve timing. This arrangement of fixed and rotating gears may permit a greater range of valve timing than the configuration in the second embodiment. Changes in the upper and lower housing  735 ,  737  from the second embodiment are also made to accommodate the differences in cam/gear interfaces and addition of bearings between the cams and the central shaft. 
     In the valve actuation system  700 , the exhaust cam  720  and the intake cam  722  are driven by separate gear trains (denoted “a” and “b”) similar to those previously described. A sun gear  316  is fixed to a central shaft  315  to rotate with the central shaft. The sun gear  316  engages a plurality of planet gears  717   a  and  717   b  from both gear trains. The planet gears  717   a  are rotatably mounted on axle bearings  702   a  of a first planetary gear carrier  719   a , and the planet gears  717   b  are rotatably mounted on axle bearing  702   b  of a second planetary gear carrier  719   b . An exhaust timing lever  721  extends from the planetary gear carrier  719   a , and an intake timing lever  723  extends from the planetary gear carrier  719   b . The timing levers  721 ,  723  prevent the rotation of the respective planetary gear carriers  719   a ,  719   b  except to change valve timing as further described herein. 
     Each cam  720 ,  722  is fixedly attached to a respective ring gear  718   a ,  718   b . In some embodiments, each cam and its respective ring gear are separately formed pieces connected together, whereas in other embodiments the two elements may be formed integrally as a single piece. Each cam  720 ,  722  and its connected ring gear  718   a ,  718   b  are rotatably mounted on the central shaft  315  to allow independent rotation with respect to the central shaft (although each cam/ring gear pair  720 / 718   a  and  722 / 718   b  must rotate together). Thus, each cam  720 ,  722  rotates with the same rotational speed as its respective ring gear  718   a ,  718   b.    
     The planet gears  717   a  engage the sun gear  316  on one side and the ring gear  718   a  on the other side. Since the planet gear carrier  719   a  is constrained from free rotation by the exhaust timing lever  721 , then rotation of the sun gear  316  drives rotation of the ring gear  718   a , and hence rotation of the exhaust cam  720 . The sizes of the gears  717   a  and  718   a  are determined by the requirement for the exhaust cam  720  to rotate at half the rotational speed of the central shaft  315 . Similarly, the planet gears  717   b  engage the sun gear  316  on one side and the ring gear  718   b  on the other side. Since the planet gear carrier  719   b  is constrained from free rotation by the intake timing lever  723 , then rotation of the sun gear  316  drives rotation of the ring gear  718   b , and hence rotation of the intake cam  722 . The sizes of the gears  717   b  and  718   b  are determined by the requirement for the exhaust cam  722  to rotate at half the rotational speed of the central shaft  315 . 
     The exhaust cam  720  may be used to actuate all exhaust valves (not shown). Exhaust valve actuators  101 ′ may be arranged radially about the central shaft  315  and the exhaust cam  720 . The exhaust timing lever  721  may be moved in an arc around the shaft  315  to vary the exhaust valve timing in a manner substantially similar to that described in connection with the second embodiment and with  FIG. 6  (“third embodiment”). Similarly, the intake cam  722  may be used to actuate all intake valves (not shown). Intake valve actuators  101 ″ may be arranged radially about the central shaft  315  and the intake cam  722 . The intake timing lever  723  may be moved in an arc around the shaft  315  to vary the intake valve timing. 
     In the illustrated embodiment of  FIG. 7 , the cams  720 ,  722  rotate in the opposite direction from the central shaft  315  and sun gear  316 . This directional difference is easily accommodated by rerouting the hydraulic lines  104 - n  ( FIG. 5 ) from each actuator  101 - n  to the proper valve follower  103 - n . A cam rotational speed of one-half the rotational speed of the central shaft  315  is accomplished when the diameter of the ring gears  718   a ,  718   b  is twice that of the sun gear  316 . 
     It will be appreciated by those skilled in the art having the benefit of this disclosure that valve actuator systems in accordance with the aspects and embodiments described herein may operate multiple valves with a single cam. It should be understood that the drawings and detailed description herein are to be regarded in an illustrative rather than a restrictive manner, and are not intended to be limiting to the particular forms and examples disclosed. On the contrary, included are any further modifications, changes, rearrangements, substitutions, alternatives, design choices, and embodiments apparent to those of ordinary skill in the art, without departing from the spirit and scope hereof, as defined by the following claims. Thus, it is intended that the following claims be interpreted to embrace all such further modifications, changes, rearrangements, substitutions, alternatives, design choices, and embodiments.