FIELD OF THE INVENTION 
     The present invention relates to a rocker system for push rod and overhead camshaft engines, more particularly to a variable compound rocker system having primary and secondary rocker assemblies adapted for varying valve lift. 
     BACKGROUND OF THE INVENTION 
     Traditional push rod internal combustion engines include a single camshaft disposed in the valley of the engine block for actuating the intake and exhaust valves via pushrods and rockers that pivot about a rocker shaft. A disadvantage of this design, however, is that no convenient method for varying the lift of the intake valves exists. It is desirable to vary the lift of the intake valves to increase engine performance in certain applications. For example, during start-up it would be advantageous to lower the lift of the intake valves to help decrease fuel emissions and improve fuel economy. Similarly, at high cruising speeds it would be advantageous to increase the lift of the intake valves to increase performance. Hence, a rocker system capable of varying the lift of the intake valves in an internal combustion engine is desired. Such systems are disclosed in U.S. Pat. No. 5,560,329, U.S. Pat. No. 6,041,746, U.S. Pat. No. 6,055,949, and U.S. Pat. No. 6,123,053. 
     Each of these patents however, disclose or suggest a system of cams and linkages moving in sequence to vary the intake valve lift events. A disadvantage apparent to these configurations is the need for many moving parts, which increases the risk of failure. Another disadvantage of these systems is the loss of energy due to frictional and rotational resistances apparent in such complex configurations. A further disadvantage to these systems is the need for very particular assembly procedures, which lacks economic efficiency. 
     Thus, a simplified variable compound rocker system that is fully contained within the cylinder head is desired. This ensures compactness of the engine block, easy adaptation to current production push rod and overhead camshaft engines, and minimal energy losses due to friction and gyro dynamics. 
     SUMMARY OF THE INVENTION 
     The present invention provides a compound rocker system for varying the lift of intake valves adaptable for push rod and overhead camshaft internal combustion engines for use in motor vehicles. The rocker system includes a rocker shaft, a plurality of primary rockers positioned on a plurality of eccentric rings, a plurality of secondary rockers, and a plurality of exhaust rockers, all positioned on the rocker shaft. The primary rockers are adapted to actuate the secondary rockers, and the secondary rockers are adapted to actuate the intake valves. Furthermore, an actuator assembly is adapted to incrementally rotate the rocker shaft, thus changing the attitude of the primary rockers causing a variance in the lift of the intake valves. This allows for increased performance in different applications. 
     Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein: 
     FIG. 1 is an isometric view of a preferred embodiment of the present invention. 
     FIG. 2 is an exploded view of a preferred embodiment of the present invention. 
     FIG. 3 is an end view of a preferred embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The following description of the preferred embodiments is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses. 
     Referring to FIGS. 1 and 2, a preferred embodiment of the variable compound rocker system  10  of the present invention is shown in isometric view and in exploded view, respectively, as adapted to an internal combustion engine  58  for use in a motor vehicle  60 . The variable compound rocker system  10  includes a rocker shaft  12  having an axis of rotation, whereby the rocker shaft  12  is rotatably supported on a plurality of cylinder head pedestals  14  and contained thereon by a plurality of rocker caps  16 . An eccentric ring  18  is also provided having an axis of rotation, an interior surface  42 , and an exterior surface  44  non-rotatably attached to the rocker shaft  12 . It should be appreciated that the eccentric ring  18  could be directly formed as part of the rocker shaft  12 , or as illustrated in FIG. 2, it could be assembled to the rocker shaft  12  by weld, press fit, pin, or other mechanical fastening means. 
     Further included in the system  10  is a primary rocker  20  having an interior surface  46  rotatably attached to the exterior surface  44  of the eccentric ring  18 . The primary rocker  20  includes a socket surface  54  for receiving an intake pushrod  22  and an engaging surface  24  for engaging a roller  32 . A secondary rocker  30  is positioned generally adjacent to the primary rocker  20  and includes a roller  32  in constant sliding engagement with the engaging surface  24  of the primary rocker  20 . The secondary rocker  30  further includes a first valve arm  26  in constant driving engagement with a first intake valve  28  and a second valve arm  34  in constant driving engagement with a second intake valve  36 . 
     The engaging surface  24  extends from the primary rocker  20  and includes a curved profile  25  for interaction with the roller  32  as best shown in FIG.  3 . The curved profile  25  includes a generally arcuate surface disposed at a distal end of the engaging arm  24  and a recess disposed adjacent the arcuate surface. The particular geometry of both the arcuate surface and the recess is governed by the geometry of the eccentric ring  18  such that as the eccentric ring  18  rotates, the roller  32  concurrently moves along the engaging surface  24  to maintain the intake valves  28  in a closed position. Specifically, as the rocker shaft  12  rotates in direction A, as shown in FIG. 3, the primary rocker  20  is caused to shift in a first direction generally away from the cylinder head pedestal  14  due to the eccentric relationship of the axis of rotation of the eccentric cam  18  and the axis of rotation of the rocker shaft  12 . As the primary rocker  20  moves sufficiently in the first direction, the roller  32  is caused to move along the curved profile  25  from the recess to the arcuate surface, thereby causing no rotation of the secondary rocker  30 , and preventing the rockers  26 , 34  from lifting from the valve tips. 
     FIGS. 1 and 2 also illustrate the system  10  including an exhaust rocker  38  positioned generally central between the first valve arm  26  and the second valve arm  34  and including an exhaust valve arm  40 . The system  10  further includes an exhaust pushrod  48  in constant driving engagement with a receiving surface (not shown) on the exhaust rocker  38  and an exhaust arm  40  having an exhaust spring  41  mounted thereto for actuating the exhaust valve  56 . Lastly, the system  10  includes an actuator assembly  50  in constant rotational engagement with the rocker shaft  12  for bi-directionally rotating the rocker shaft  12 . It should be appreciated that the actuator assembly  50  could be a generic phaser, a piston lever mechanism, or any other mechanical device capable of bi-directionally rotating the rocker shaft. It should further be appreciated that while FIGS. 1 and 2 illustrate a single piston application, the system  10  could be adapted to accommodate a conventional multi-piston engine by simply extending the rocker shaft  12  and providing additional single piston configurations thereon. It should further yet be appreciated that while FIGS. 1 and 2 illustrate a three-valve configuration, the system  10  can be adapted to accommodate any number of valve configurations. 
     Referring now to FIG. 3, the primary rocker  20  is shown in a low-lift mode. When the internal combustion engine is running, the intake  22  and exhaust  48  pushrods stroke in accordance with the rotation of a camshaft (not shown). The intake pushrod  22  strokes, thus rotating the primary rocker  20  in a clockwise direction. The engaging surface  24  of the primary rocker  20  forces the roller  32  and the secondary rocker  30  to also rotate in a clockwise direction. The secondary rocker  30  pivots about an axis approximately central to the rocker shaft  12 , forcing the first  26  and second  34  (see in FIGS. 1 and 2) valve arms to depress the first  28  and second  36  (seen in FIGS. 1 and 2) intake valves. Upon further rotation of the camshaft (not shown) the intake valve springs  52  force the secondary rocker  30  upward, and the intake pushrod  22  down, thus, closing the first  28  and second  36  intake valves. 
     From FIG. 3 it should be appreciated that when the actuator assembly  50  (shown in FIGS. 1 and 2) rotates the rocker shaft  12  in the direction of arrow A, the eccentric ring  18  rotates causing the attitude of the primary rocker  20  to change relative to the secondary  30  and exhaust  38  (shown in FIGS. 1 and 2) rockers, as previously discussed. This change in attitude results in an increase in the depression of the first  28  and second  36  intake valves when the intake pushrod  22  strokes. The engaging surface  24  is such that when the actuator assembly  50  rotates the rocker shaft  12  thus, rotating the eccentric ring  18 , the first  28  and second  36  intake valves remain closed due to the interaction of the roller  32  on the curved profile  25 , as illustrated in FIG.  3 . In a preferred embodiment, the actuator assembly  50  is a piston-lever assembly that rotates the rocker shaft  12  approximately ninety degrees. In another embodiment the actuator assembly  50  is a conventional phaser that rotates the rocker shaft  12  approximately ninety-degrees. It should be appreciated that while the embodiment described herein includes one ninety degree rotational increment of the rocker shaft  12 , an embodiment including any degree and number of rotational increments is included within the scope of the present invention. 
     Changing the attitude of the primary rocker  20  from the low-lift position to the high-lift position, as discussed above, decreases the depression of the first  28  and second  36  intake valves. Decreasing and increasing the intake valve depression decreases the engine emissions at startup and provides more power and efficiency during acceleration. It should be appreciated that while the system  10  described herein includes a two position rocker system  10 , systems capable of providing three or more positions are included within the scope of the present invention. It should also be appreciated that the actuator assembly  50  should be configured such that no actuation is required for the base operating condition of the system, i.e, the condition most commonly utilized. In a system having three or more rotational positions the base condition would most likely be a middle position. Lastly, it should be appreciated that while the description contained herein describes the system  10  adapted to a V-style internal combustion engine, the system  10  is also adaptable to an overhead camshaft internal combustion engine by replacing the pushrods with an overhead camshaft. 
     Accordingly, a simple rocker system that compactly fits within the cylinder head of a V-style or overhead camshaft internal combustion engine and is capable of varying intake valve lift events for increasing engine efficiency and performance characteristics is provided. Furthermore, a single-shaft rocker system capable of varying intake valve lift events via static means without suffering frictional or gyro dynamic energy losses is provided. 
     The description of the invention is merely exemplary in nature and, thus, variations that do not depart from the gist of the invention are intended to be within the scope of the invention. Such variations are not to be regarded as a departure from the spirit and scope of the invention.
A variable compound rocker system for varying the lift of intake valves of an internal combustion engine is provided. The system comprises a rocker shaft with eccentric rings non-rotatably attached thereto. Furthermore, the system includes primary rockers non-rotatably attached to the eccentric rings. The primary rockers have engaging surfaces for engaging rollers attached to secondary rockers. The rollers enable the primary rockers to actuate the secondary rockers, thus actuating the intake valves. The system further includes an actuator assembly adapted to incrementally rotate the rocker shaft, and thus the primary rockers. This incremental rotation of primary rockers changes their attitude causing the lift of the intake valves to vary, thus varying the engine performance characteristics.