Abstract:
A valve control system including a camshaft having first and second cam profiles, the valve control system comprising a rocker arm assembly ( 11 ) including a first rocker arm ( 13 ) having a first cam follower ( 15 ) in engagement with the first cam profile, and a second rocker arm ( 17 ) having a second cam follower ( 23,25 ) in engagement with the second cam profile. The engine includes a fulcrum location (P) operable to provide a source of pressurized fluid, and the first rocker arm includes a latch member ( 47 ) moveable between latched (FIG.  6 ) and unlatched conditions. The latch member is biased toward the latched condition by a fluid pressure in a chamber ( 51 ), and the first rocker arm defines a fluid passage ( 55 ) having a first end ( 57 ) in open fluid communication with the pressure source, and a second end ( 59 ) in open fluid communication with the pressure chamber ( 51 ).

Description:
BACKGROUND OF THE DISCLOSURE  
       [0001]     The present invention relates to valve control systems for internal combustion engines of the type in which the movement of an engine poppet valve is controlled in response to rotation of a cam shaft, and more particularly, to such a valve control system in which the cam shaft has a cam profile including both a high lift portion and a low lift portion.  
         [0002]     Even more specifically, the present invention relates to such a valve control system including a dual lift rocker arm assembly of the type having both a high lift cam follower and a low lift cam follower (for engagement with the high lift portion and the low lift portion, respectively, of the cam profile). Although the terms “high lift” and “low lift” can have various meanings when used in regard to valve control systems for engine poppet valves, it should be understood that, within the scope of the present invention, all that is required is that one cam profile provide a relatively higher lift of the engine poppet valve while the other cam profile provides a relatively lower lift of the engine poppet valve. Within the scope of the invention, the “low lift” could actually comprise zero lift, or could comprise some finite lift amount which is greater than zero lift, but somewhat (or substantially) less than the “high lift”.  
         [0003]     In a typical dual lift rocker arm assembly, of the type which is now well known in the art, there is provided an outer rocker arm and an inner rocker arm, with those two rocker arms typically being pivotally connected relative to each other toward one axial end thereof. In addition, the typical, prior art dual lift rocker arm assembly includes some sort of latch mechanism, operable to latch the inner rocker arm to the outer rocker arm, such that the two rocker arms move in unison about a fulcrum location, such as the ball plunger of a hydraulic lash adjuster. This “latched” condition, as described above, would typically, but not necessarily, correspond to the high lift mode of operation of the valve control system. When the latch mechanism is in the “unlatched” condition, the inner and outer rocker arm are free to pivot relative to each other, and this unlatched condition would typically, but not necessarily, correspond to the low lift mode of operation of the valve control system.  
         [0004]     Dual lift, latchable rocker arm assemblies are illustrated and described in U.S. Pat. Nos. 5,524,580; 5,584,267; and 5,697,333, all of which are assigned to the assignee of the present invention, and incorporated herein by reference.  
         [0005]     In the dual lift rocker arm assemblies of the above-incorporated patents, there is provided some sort of electromagnetic actuator for controlling the operation of the latching mechanism. Although such electromagnetic actuation of the latching mechanism has been found to operate in a generally satisfactory manner, the resulting need for a separate electromagnetic actuator for each rocker arm assembly would add substantially to the cost of the overall valve control system, and in many applications, would require much more space for “packaging” than is available in the typical engine cylinder head.  
         [0006]     Those skilled in the art have attempted to provide a means of actuation for the latching mechanism of a dual lift rocker arm assembly, which would overcome the prior art problems discussed above, by utilizing hydraulic pressure. Specifically, those skilled in the art have attempted to utilize, to control the latching mechanism, a variable hydraulic pressure within the plunger of the hydraulic lash adjuster, which serves as the fulcrum location for the rocker arm assembly. Such an actuation arrangement is illustrated and described in U.S. Pat. Nos. 5,544,626 and 6,668,779, both of which are incorporated herein by reference.  
         [0007]     Although the rocker arm assemblies of the above-incorporated patents, in the immediately preceding paragraph, do provide at least the potential for substantially improved actuation of the latching mechanism, the need to communicate the low pressure (control) fluid from the lash adjuster to the latching mechanism has somewhat complicated the design of the rocker arm assembly. This is especially true when it is recognized that there are various other design criteria for rocker arm assemblies which must be observed, in order to achieve the best possible overall performance of the valve control system. For example, in order to improve the dynamic behavior of the valve control system, it is desirable to reduce the inertia of the rocker arm assembly. One way of reducing the inertia is to locate as much of the mass of the rocker arm assembly as close as possible to the fulcrum location. Therefore, it is recognized that it is desirable to have the pivot axis, between the inner and outer rocker arms, disposed adjacent the fulcrum location, such that the torsion spring, which biases the rocker arms relative to each other, may also be near the fulcrum location.  
         [0008]     Unfortunately, in the dual rocker arm assembly of the above-incorporated U.S. Pat. No. 6,668,779, in order to utilize a control fluid from the hydraulic lash adjuster to control the latching mechanism, it was necessary to add a piston member (the only function of which was to move in response to changes in control pressure), with the movement of the piston member being transmitted from the piston member to the latching mechanism at the opposite end of the rocker arm assembly by means of a separate slider element, having no function other than to move the latching mechanism in response to movement of the piston member. The added cost and complexity of the arrangement in the rocker arm assembly of the &#39;779 patent, as well as the added mass and inertia of the assembly, make the overall assembly less than desirable commercially.  
       BRIEF SUMMARY OF THE INVENTION  
       [0009]     Accordingly, it is an object of the present invention to provide an improved valve control system, for controlling engine poppet valves, wherein the system is of the type including a dual lift rocker arm assembly which is able to overcome the above-discussed disadvantages of the prior art.  
         [0010]     It is a more specific object of the present invention to provide such an improved dual lift rocker arm assembly in which the latching mechanism is controlled by pressurized fluid from the hydraulic lash adjuster, but which does not require substantial added structure, cost, and weight in order to transmit changes in fluid pressure into movement of the latch mechanism.  
         [0011]     The above and other objects of the invention are accomplished by the provision of a valve control system for an internal combustion engine of the type including a cylinder head, and a poppet valve moveable relative to the cylinder head between open and closed positions, and a cam shaft having a first cam profile and a second cam profile formed thereon. The valve control system comprises a rocker arm assembly including a first rocker arm having a first cam follower in engagement with the first cam profile, and a second rocker arm having a second cam follower in engagement with the second cam profile. The valve control system further comprises the cylinder head including a fulcrum location operable to provide a source of pressurized fluid. The first rocker arm defines, toward a first axial end thereof, a fulcrum surface adapted for pivotal engagement with the fulcrum location. The first rocker arm further defines, adjacent the fulcrum surface, a pivot location whereby the second rocker arm pivots relative to the first rocker arm about the pivot location. The first rocker arm includes, toward a second axial end thereof, a latch assembly including a latch member moveable between latched and unlatched conditions, relative to a latch surface defined by an adjacent portion of the second rocker arm. A spring biases the latch member toward one of the latched and unlatched conditions, and the latch assembly defines a pressure chamber operable to bias the latch member toward the other of the latched and unlatched conditions.  
         [0012]     The improved valve control system is characterized by the first rocker arm defining a fluid passage having a first end in open fluid communication with the fulcrum surface, the first end of the fluid passage being operable to receive pressurized fluid from the source. The fluid passage has a second end in open fluid communication with the pressure chamber of the latch assembly. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]      FIG. 1  is a perspective view of a dual lift rocker arm assembly of the type which may utilize the present invention.  
         [0014]      FIG. 2  is a perspective view of the rocker arm assembly of  FIG. 1 , but taken from the opposite end, and looking upward.  
         [0015]      FIG. 3  is a view generally similar to that of  FIG. 2 , but showing only the inner rocker arm, and taken at a slightly different angle than  FIG. 2 .  
         [0016]      FIG. 4  is a side plan view, looking toward the side which is on the bottom in  FIG. 3 , showing primarily only the inner rocker arm.  
         [0017]      FIG. 5  is an axial cross-section, taken generally on line  5 - 5  of  FIG. 4 , of the inner rocker arm, including the fluid passage which comprises one important aspect of the invention.  
         [0018]      FIG. 6  is a greatly enlarged, fragmentary, axial cross-section, on a “vertical” plane, showing in greater detail the latch mechanism which comprises one aspect of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0019]     Referring now to the drawings, which are not intended to limit the invention,  FIG. 1  illustrates a dual lift rocker arm assembly, generally designated  11 , of the general type illustrated and described in U.S. Pat. No. 5,655,488, assigned to the assignee of the present invention and incorporated herein by reference. One reason for referring to the incorporated patent is that it shows the cam shaft, including the high lift and low lift cam profiles, as well as a portion of the cylinder head, and also shows the engine poppet valve, none of which are illustrated herein, for the sake of simplicity, and because such elements are well known to those skilled in the art, and do not require detailed description.  
         [0020]     Referring still to  FIG. 1 , the dual lift rocker arm assembly  11  of the present invention comprises an inner rocker arm  13  (also referred to hereinafter in the appended claims as a “first” rocker arm). The inner rocker arm  13  includes a roller follower  15  which, in the subject embodiment, would comprise the “low lift” cam follower, and would engage the low lift cam profile on the cam shaft. As may best be seen in  FIG. 6 , the roller follower  15  rotates about an axis designated “a”.  
         [0021]     Referring still primarily to  FIG. 1 , the dual lift rocker arm assembly  11  further comprises an outer rocker arm  17  (also referred to hereinafter in the appended claims as a “second” rocker arm). The outer rocker arm  17  includes a pair of sidewalls  19  and  21 , disposed on laterally opposite sides of the inner rocker arm  13 . The sidewalls  19  and  21  include a pair of pad portions  23  and  25 , respectively, and the pad portions  23  and  25  would comprise the “high lift” cam follower, and would engage the high lift cam profile on the cam shaft. As is well known in the art, the high lift cam profile, for use with the dual lift rocker arm assembly  11 , would comprise a pair of cam profiles, disposed on either side, axially, of the low lift cam profile.  
         [0022]     As may best be seen in  FIGS. 1 and 2 , the inner and outer rocker arms  13  and  17  are connected to each other, for relative pivotal movement, by means of a transversely-oriented shaft  27 . The shaft  27  (also shown in  FIGS. 4 and 5 ), has its end portions received within openings in the sidewalls  19  and  21  of the outer rocker arm  17  and has its middle portion disposed within a circular opening  29  (see  FIGS. 3 and 4 ) defined by the inner rocker arm  13 . In a surrounding relationship to portions of the shaft  27 , on either lateral side of the inner rocker arm  13 , are several turns of a torsion spring  31 , shown only in  FIGS. 1 and 2 . As is well known to those skilled in the art, the purpose of the torsion spring  31  is to bias the inner rocker arm  13  counterclockwise in  FIG. 1 , relative to the outer rocker arm  17 , about the shaft  27 .  
         [0023]     Referring now primarily to  FIG. 3 , the inner rocker arm  13  preferably comprises a single, unitary item which may be produced as a casting and subsequently machined, or may be produced as a powdered metal part. It should be understood by those skilled in the art that the present invention is not limited to the particular configuration of, or the process for manufacture of, the inner rocker arm  13 , and the configuration shown herein is by means of example only, except as will be noted hereinafter and in the appended claims.  
         [0024]     The inner rocker arm  13  defines a generally hemispherical fulcrum surface  33  which, as is well known to those skilled in the art, is adapted for engagement with a member which serves as a “fulcrum location”. By way of example only, the fulcrum location can comprise a ball plunger portion (identified as “P” in  FIG. 4 ) of a hydraulic lash adjuster, such that both the ball plunger portion and, where appropriate, the hydraulic lash adjuster itself (“fulcrum location”), may hereinafter bear the reference designation “P”. As is also now well known to those skilled in the art, the hydraulic lash adjuster is typically received within a cylindrical bore defined by the engine cylinder head (not shown herein for ease of illustration).  
         [0025]     Referring now primarily to  FIGS. 1, 3  and  5 , the inner rocker arm  13  defines, at its end axially opposite the circular opening  29 , a latch bore  35 , and disposed within the latch bore  35  is a latch assembly, generally designated  37  (shown only in  FIG. 6 ), and to be described in greater detail subsequently. It may be seen in  FIG. 6  that the inner rocker arm  13  defines a valve pad  38  (also shown in  FIG. 2 ) for engagement with the valve stem tip portion of the poppet valve. Disposed intermediate the opening  29  and the latch bore  35 , the inner rocker arm  13  defines a central open chamber  39  (see also  FIG. 3 ), the roller follower  15  being disposed in the open chamber  39 , rotatably mounted upon a roller shaft  41  (see  FIG. 4 ). Although the present invention is not limited to use with any particular configuration of rocker arm assembly, except where specifically otherwise noted in the appended claims, the invention is especially useful in the dual lift rocker arm assembly  11 , of the type shown herein, in which the fulcrum surface  33  is disposed toward one axial end of the inner rocker arm  13 , and the latch bore  35  is disposed toward the opposite axial end, with the roller follower  15  disposed axially therebetween, for reasons which will become apparent subsequently.  
         [0026]     Referring now primarily to  FIG. 6 , the latch assembly  37  includes a spring cage  43 , seated against a shoulder formed by the latch bore  35 , and with the spring cage  43  being trapped in the position shown by a latch bore plug  45 , which is preferably pressed into the latch bore  35 . Disposed within the latch bore  35 , and axially movable therein, is a latch member  47 , biased toward a retracted (“unlatched”) position by a generally conical latch spring  49 , which has its left end (in  FIG. 6 ) seated against an adjacent surface of the spring cage  43 . The latch assembly  37  defines a pressure chamber  51 , which comprises the region within the latch bore  35 , disposed axially between the latch bore plug  45  and the latch member  47 . When pressurized fluid is communicated into the pressure chamber  51 , the latch member  47  is biased to the left in  FIG. 6 , to the extended (“latched”) position, generally parallel to an axis A defined by the inner rocker arm  13 . In the latched position of the latch member  47 , a flat, planar upper surface of the latch member  47  engages an adjacent lower surface  52  defined by an endwall  53  of the outer rocker arm  17  (see also  FIG. 2 ).  
         [0027]     Referring again primarily to  FIGS. 3, 4  and  5 , the inner rocker arm  13  defines an axially-extending (i.e., generally parallel to the axis A of the rocker arm  13 ) bore  55 , an open end of which is visible in  FIG. 3 . As is best shown in  FIG. 5 , although somewhat schematically, an angled bore  57  is formed within, and defined wholly by, the inner rocker arm  13 . By way of example only, the angled bore  57  may be formed by drilling, with the drill bit entering the inner rocker arm  13  from the circular opening  29 , then proceeding until the bore  57  intersects the fulcrum surface  33  (or a bore extending somewhat vertically “upward” therefrom). The drill bit then continues until the resulting angled bore  57  is in open communication with the axially-extending bore  55 . Preferably, but not necessarily, when the shaft  27  is inserted into the opening  29 , the fit between the shaft  27  and the opening  29  is close enough (and perhaps even comprises a press-fit), such that the shaft  27  effectively “seals” the angled bore  57  from excessive fluid leakage. Those skilled in the art will understand that, for purposes of the present invention, absolute leakage-free sealing is not essential, but instead, all that is required is that the end of the angled bore  57  be sufficiently sealed to be able to build enough fluid pressure within the bore  55  and  57  to achieve the biasing of the latch member  47 .  
         [0028]     Referring now primarily to  FIGS. 4, 5  and  6 , another angled bore  59  is formed within, and defined wholly by, the inner rocker arm  13 . In the same manner as for the angled bore  57 , the angled bore  59  may be formed by drilling, with the drill bit entering the inner rocker arm  13  from above, and then through, the latch bore  35 , then proceeding until the angled bore  59  is in open fluid communication with the axially-extending bore  55 . Preferably, but not necessarily, the latch member  47  effectively “seals” the angled bore  59 , although, as in the case of the angled bore  57 , it is sufficient if the angled bore  59  is sealed enough such that pressure is able to build up within the pressure chamber  51 , sufficient to bias the latch member  47  to the latched position shown in  FIG. 6 . It should be noted that, in  FIG. 5 , the reference numeral “ 59 ” appears twice, including a schematic (centerline) representation of the angled bore, and a physical representation where the angled bore  59  intersects the axially-extending bore  55 . However, the angled bore  59  is also shown in  FIG. 6 , wherein just an upper terminal end of the bore  59 , “above” the latch bore  35 , is visible. It should be understood, when viewing  FIG. 6 , that the plane of the angled bore  59  does not coincide with the plane of  FIG. 6 , but instead is at an angle relative thereto.  
         [0029]     Thus, by means of the series of bores just described, pressurized fluid is enabled to flow from above the ball plunger portion P “down” (in  FIG. 4 ) through the angled bore  57 , into the axially-extending bore  55 , then flow to the left in  FIG. 5 , then flow “upward” (in  FIG. 4 ) through the angled bore  59 . The pressurized fluid in the bore  59  then flows into the pressure chamber  51 , because the angled bore  59  intersects the latch bore  35  “behind” the plane of the drawing in  FIG. 6 . It should be noted that, in the appended claims, there will be reference made to a “fluid passage” (the axially-extending bore  55 ), having a “first end” (angled bore  57 ) in communication with the source of pressurized fluid, and a “second end” (the angled bore  59 ) in communication with the pressure chamber  51  of the latch mechanism.  
         [0030]     Although not shown herein, it would be preferred to insert some sort of sealing ball or plug into the left end (in  FIG. 5 ) of the axially-extending bore  55 . There may also be a need to insert a sealing ball or plug into the upper end of the angled bore  59 . In accordance with one worthwhile aspect of the preferred embodiment of the invention, in spite of needing three separate bores (passages, etc.) to communicate pressurized fluid from the “source” of the pressurized fluid (ball plunger portion P) to the pressure chamber  51  of the latch mechanism  37 , at only two locations (left end of bore  55  and upper end of bore  59 ) are any extra sealing members perhaps required. This particular feature is significant in connection with reducing the overall manufacturing cost, and time of assembly of the invention.  
         [0031]     It should be understood by those skilled in the art that, although fluid communication from the HLA to the latch member is shown and described herein as being accomplished by means of the fluid bores  57 ,  55 , and  59 , the use of such an “integral” passage is not a limitation of the present invention. By way of example only, the required fluid communication could, within the scope of the invention, be accomplished by means of a separate tubular member, brazed or otherwise attached to the inner rocker arm  13  at two spaced apart locations, but providing fluid communication from the ball plunger portion P to the pressure chamber  51 . All that is essential to the present invention is that no extra (not otherwise needed) mechanical structure be required to “transmit” the effect of fluid pressure from the source (at one end of the inner rocker arm  13 ) to the latch assembly  37  (at the axially opposite end).  
         [0032]     Although the bore  55 ,  57  and  59  have been described above in connection with a forming process involving drilling of the bores, it should be understood that the invention is not so limited. For example, if the inner rocker arm  13  is formed as a powder metal part, the bores  55 ,  57  and  59  could be formed by inserted members which would be withdrawn from the PM die after the formation of the inner rocker arm, to allow the rocker arm to be removed from the die. Thus, those skilled in the art will understand that the particular method chosen to form the bore  55 ,  57  and  59  is not a significant feature of the invention, as long as pressurized fluid may be communicated from the fulcrum surface  33  to the pressure chamber  51 .  
         [0033]     The invention has been described in great detail in the foregoing specification, and it is believed that various alterations and modifications of the invention will become apparent to those skilled in the art from a reading and understanding of the specification. It is intended that all such alterations and modifications are included in the invention, insofar as they come within the scope of the appended claims.