Abstract:
A rocker arm assembly having an adjustably located cam roller that permits modification of valve timing for an internal combustion engine. An adjustment control shaft having an adjustment cam operates through a linkage to move the cam roller along the rocker arm and relative to the cam shaft of the engine.

Description:
BACKGROUND OF INVENTION 
     1. Field of the Invention 
     The present invention relates to a valve lifter rocker arm for an internal combustion engine. 
     2. Background Art 
     Valves for internal combustion engines are generally opened and closed to allow for the intake and exhaust of gases in cylinders of the engine. Valves are operated by various valve lifter mechanisms including rocker arms and roller finger follower assemblies. Timing valve opening and closing is important to maximize fuel efficiency, assure complete combustion, and maximize engine output. Adjusting valve timing can lead to improvements in fuel economy, engine emissions, torque and idle quality. 
     Many different approaches have been proposed for providing adjustable valve timing. Some prior art approaches include independent lifter control for each cylinder by means of electrical solenoids or by changing the pivot point for a rocker arm. Various other approaches have also been proposed. 
     There is a need for a system and apparatus for providing adjustable valve timing wherein the valve timing may be adjusted in a synchronized manner to minimize variation of timing from cylinder to cylinder. There is also a need for a simple and effective valve timing adjustment mechanism that may be used with intake or exhaust valves. There is also a need for a valve timing adjustment mechanism that is amenable to dual overhead cam and single overhead cam applications. There is a further need to provide a simple and effective way to deactivate cylinders by deactivating valve lifter operation selectively when a cylinder is not firing pursuant to a variable displacement engine operation strategy. 
     The above problems and objectives are addressed by the present invention as summarized below. 
     SUMMARY OF INVENTION 
     According to one aspect of the present invention, a valve timing system for an internal combustion engine having a rotating cam that operates at least one valve is provided. A rocker arm is pivotally attached to the engine. The rocker arm has a cam arm extending toward the rotating cam and a valve arm that contacts a valve stem. A cam roller is attached to the cam arm and is adjustable within a range of positions along the length of the cam arm. The cam roller is supported on the cam arm to selectively contact the rotating cam. A linkage is connected to the cam roller and the rocker arm. The linkage is used to adjust the position of the cam roller to change the timing of the valve of the engine. 
     According to another aspect of the present invention, a rocker arm assembly is provided for an internal combustion engine. The engine has at least one valve that is opened and closed in a timed manner to port combustion gases for a combustion chamber of the internal combustion engine. The internal combustion engine has at least one cam shaft and at least one cam that is rotated by the cam shaft in accordance with the operating cycle of the internal combustion engine. The cam has a lobe that is rotated to contact the rocker arm assembly to open and close the valve. The rocker arm assembly comprises a rocker arm pivotally secured to the engine that has a valve stem engaging arm and a cam engaging arm on opposite its ends. A roller is adjustably secured to the cam engaging arm and is held on the cam engaging arm in a position to contact the cam as it is rotated by the cam shaft. An adjustment link is provided for shifting the roller relative to the cam engaging arm to cause the roller to contact the lobe of the cam within a range of rotational positions relative to the cam shaft. 
     Other features of the invention include providing a cam arm that has a pair of spaced flanges between which the cam roller is secured. The cam roller is preferably rotatably secured to the cam arm. The cam roller may be secured to the cam arm by a shaft that extends through a slot formed in the cam arm. 
     The linkage comprises an adjustment link and a cam roller that is secured to the cam arm by a shaft that is engaged by one end of the adjustment link. The linkage may comprise at least one adjustment cam that is attached to an adjustment control shaft and the adjustment link. The adjustment control shaft may be rotated to rotate the adjustment cam relative to the rocker arm to cause the adjustment link to move the cam roller on the cam arm. 
     A bushing may be mounted on the adjustment control shaft and secured to the rocker arm wherein the bushing is rotatable relative to the adjustment control shaft and the rocker arm mounting shaft. 
     According to another aspect of the invention, the slot formed in the cam arm extends generally lengthwise relative to the cam arm. The one end of the slot in the cam arm may be curved away from the rotating cam so that the cam roller may be moved to a recessed position on the cam arm in which the cam roller does not contact the rotating cam. 
     These and other aspects of the valve timing system and rocker arm assembly of the present invention will be better understood in view of the attached drawings and following detailed description of the preferred embodiments of the invention. 
    
    
     BRIEF DESCRIPTION OF DRAWINGS 
     FIG. 1 is an elevation view of a rocker arm assembly shown in conjunction with a rotating cam and valve of an internal combustion engine; 
     FIG. 2 is an elevation view of a rocker arm assembly showing an adjustable cam roller in three different positions relative to the rotating cam of the engine; and 
     FIG. 3 is an exploded perspective view showing a rocker arm assembly and adjustment linkage for adjusting the position of the cam roller on the rocker arm assembly. 
    
    
     DETAILED DESCRIPTION 
     Referring now to FIG. 1, a rocker arm assembly, generally referred to by reference numeral  10 , is shown in conjunction with a cam lobe  12  of a camshaft  14  and a valve  16  having a valve stem  18 . The valve  16  is held normally closed by valve spring  20 . The rocker arm assembly  10  engages the valve stem  18  with a valve arm  22  when the cam lobe  12  lifts the cam arm  24 . The cam lobe  12  engages a cam roller  26  that is secured to the cam arm  24  as will be more specifically described below. 
     The location of the cam roller  26  on the cam arm  24  is adjusted by means of an adjustment control shaft  28  that includes at least one adjustment cam  30 . The adjustment control shaft also functions as the rocker arm mounting shaft that connects the shaft to the engine. The adjustment cam  30  is turned by the adjustment control shaft  28  to cause the adjustment link  32  to move the cam roller  26  along the length of the cam arm  24 . 
     Referring now to FIG. 2, a rocker arm assembly  10  is shown with the cam roller  26  shown in three different positions designated  1 ,  2  and  3  in FIG.  2 . Positions  1  and  2  are active roller positions, wherein the cam roller  26  contacts the cam lobe  12  as it is rotated by the camshaft  14 . Position  3  is an inactive position wherein the roller is recessed relative to the cam lobe  12 . When the cam roller  26  is in position  3 , the valve is not opened as the cam lobe  12  rotates. When the cam roller  26  is in position  3 , the rocker arm assembly  10  may function as a variable displacement engine control for deactivating the valve. 
     The position of the cam roller  26  is changed by rotating the adjustment control shaft  28 . As illustrated by positions  1  and  2 , the adjustment cam allows for adjustment as indicated by positions  1  and  2  during engine operation. As shown in FIG. 2, adjustment between positions  1  and  2  causes the center line of the roller  26  to move an incremental distance represented by the arrows labeled “dh” that represent the change in height as the roller is adjusted between positions  1  and  2 . The adjustment of the roller  26  also causes a change in the timing of valve opening represented by the arcuate arrow designated “α”. The center line of the roller  26  moves relative to the center line of the camshaft  14  by the amount indicated by “α” (change in angle). 
     When the roller  26  is moved, the distance between the center line of the adjustment control shaft  28  and the center line of the roller  26  is adjusted between lengths l 1  and l 2 . l 1  represents the distance between the center line of the roller  26  in position  1  and the adjustment control shaft  28 . l 2  represents the distance between the center line of the roller  26  in position  2  and the center of the adjustment control shaft  28 . As will be readily appreciated by one of ordinary skill in the art, by changing the distance between the center line of the adjustment control shaft  28  and the roller  26 , the timing of the valve opening is adjustable within the increment represented by α. As the roller is moved between positions  1  and  2 , the length of the valve arm  22  remains constant and is represented by arrow “l 3 ”. Similarly, the height of the valve opening changes slightly due to the change in the maximum height of the center line of the roller  26 . Depending upon the inclination of the cam arm  24 , the value for “α” may be modified. 
     Referring now to FIG. 3, the rocker arm assembly  10  is shown in conjunction with the adjustment control shaft  28 . The cam arm  24  is formed in two parts  24 ′ and  24 ″ with a space being provided between the two parts  24 ′,  24 ″ for receiving the cam roller  26 . The rocker arm assembly  10  is secured to a bushing  36  that is received on the adjustment control shaft  28  so that the adjustment control shaft may be rotated without affecting the operation or movement of the rocker arm assembly  10 . On either side of the bushing  36 , adjustment cams  30 ′ and  30 ″ are secured to teeth  38  formed on the adjustment control shaft  28  at spaced locations on either side of the bushing  36 . The adjustment cams  30 ′ and  30 ″ have corresponding toothed openings  40  that engage teeth  38  to secure the adjustment cams  30  to the adjustment control shaft  28 . As will be readily appreciated by one of ordinary skill in the art, the adjustment cams  30  may be connected by welding, swaging, keys, or by other attachment mechanisms to the adjustment control shaft  28 . 
     A pin  42  supports the cam roller  26  within slots  42 ′ and  42 ″. The pin  42  is moved along the slots  42 ′,  42 ″ when the adjustment links  32 ′,  32 ″ are moved by the adjustment cams  30 ′,  30 ″. The other end of the adjustment links  30 ′,  30 ″ are connected by pins  48 ′,  48 ″. Pins  48 ′ connect the links  32 ′,  32 ″ to the adjustment links  30 ′,  30 ″. 
     While the best mode for carrying out the invention has been described in detail, those familiar with the art to which this invention relates will recognize various alternative designs and embodiments for practicing the invention as defined by the following claims.