Patent Publication Number: US-6988473-B2

Title: Variable valve actuation mechanism having an integrated rocker arm, input cam follower and output cam body

Description:
TECHNICAL FIELD 
   The present invention relates to variable valve actuating mechanisms. 
   BACKGROUND OF THE INVENTION 
   Modern internal combustion engines may incorporate advanced throttle control systems, such as, for example, intake valve throttle control systems, to improve fuel economy and performance. Generally, intake valve throttle control systems control the flow of gas and air into and out of the engine cylinders by varying the timing and/or lift (i.e., the valve lift profile) of the cylinder valves in response to engine operating parameters, such as engine load, speed, and driver input. For example, the valve lift profile is varied from a relatively high-lift profile under high-load engine operating conditions to a reduced/lower low-lift profile under engine operating conditions of moderate and low loads. 
   Intake valve throttle control systems vary the valve lift profile through the use of various mechanical and/or electromechanical configurations, collectively referred to herein as variable valve actuation (VVA) mechanisms. Several examples of particular VVA mechanisms are detailed in commonly-assigned U.S. Pat. No. 5,937,809, the disclosure of which is incorporated herein by reference. Generally, a conventional VVA mechanism includes a rocker arm that carries a cam follower. The cam follower engages an input cam of a rotary input shaft, such as the engine camshaft. The cam follower and thus the rocker arm are displaced in a generally radial direction by the input cam, and a pair of link arms transfers the displacement of the rocker arm to pivotal oscillation of a pair of output cams relative to the input shaft or camshaft. Each of the output cams is associated with a respective valve. The pivotal oscillation of the output cams is transferred to actuation of the valves by associated cam followers, such as, for example, direct acting cam followers or roller finger followers. One or more return springs biases the rocker arm cam follower into engagement with the input cam lobe. 
   A desired valve lift profile is obtained by orienting the output cams in a starting or base angular orientation relative to the cam followers and/or the central axis of the input shaft. The starting or base angular orientation of the output cams determines the portion of the lift profile thereof that engages the cam followers as the output cams are pivotally oscillated, and thereby determines the valve lift profile. The starting or base angular orientation of the output cams is set via a control shaft that pivots a pair of frame members which, via the rocker arm and link arms, pivot the output cams to the desired base angular orientation. 
   Typically, the frame members and output cams of a conventional VVA mechanism are pivotally disposed upon the engine input or camshaft. Thus disposed, the frame members and output cams impose parasitic loads upon the driving torque of the engine input/camshaft. Such parasitic loads reduce engine power and fuel efficiency. Further, since the rocker arm is connected via the link arms to the output cams, the return spring must provide sufficient force to overcome the inertia presented by these components in order to maintain the rocker arm cam follower in contact with the input cam lobe, and must be stiff enough to do so at relatively high engine-operating speeds. The design of a spring having sufficient force and stiffness, and yet small enough to fit within the limited space available in a modern engine, requires complex spring designs and relatively expensive materials. Moreover, the relatively large number of component parts and critical interfaces within a conventional VVA mechanism make their manufacture and assembly relatively complex, labor intensive and costly. 
   Therefore, what is needed in the art is a VVA mechanism that has fewer component parts and is therefore easier to manufacture and assemble. 
   Furthermore, what is needed in the art is a VVA mechanism that places little or no parasitic load upon the driving torque of the engine input/camshaft, and thereby improves engine power and fuel efficiency. 
   Moreover, what is needed in the art is a VVA mechanism that reduces the stiffness required of the return spring by reducing the effective mass of the components of the VVA, thereby enabling an increase in the maximum engine operating speed at which the VVA can be used. 
   SUMMARY OF THE INVENTION 
   The present invention provides a variable valve actuation mechanism that integrates the output cam and input cam follower into one body. 
   The present invention includes, in one form thereof, a control shaft assembly and a body. The control shaft assembly is pivotable relative to a pivot axis. The body is pivotally disposed on the control shaft assembly, and includes an input cam follower and at least one output cam surface. The input cam follower engages an input cam lobe, and the output cam surface engages a corresponding output cam follower. A spring engages the body and biases the input cam follower into engagement with the input cam lobe. 
   An advantage of the present invention is that there are fewer component parts and it is therefore easier to manufacture and assemble. 
   A further advantage of the present invention is that little or no parasitic load is imposed upon the driving torque of the engine input/camshaft, and engine power and fuel efficiency are thus improved. 
   A still further advantage of the present invention is that the stiffness required of the return spring is reduced due to a reduction in the effective mass of the components of the VVA. 
   An even further advantage of the present invention is that the reduced effective mass of the components enables use at higher engine operating speeds. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above-mentioned and other features and advantages of this invention, and the manner of attaining them, will become apparent and be better understood by reference to the following description of the embodiments of the invention in conjunction with the accompanying drawings, wherein: 
       FIG. 1  is a side or end view of one embodiment of a Variable Valve Actuation (VVA) mechanism having an integrated rocker arm, input cam follower and output cam of the present invention in a full or substantially full-load position at a time prior to valve actuation; 
       FIG. 2  is a side or end view of the VVA mechanism of  FIG. 1  in a full or substantially full-load position at approximately the time of or during valve actuation; 
       FIG. 3  is a side or end view of the VVA mechanism of  FIG. 1  in a light-load position at a time prior to valve actuation; 
       FIG. 4  is a side or end view of the VVA mechanism of  FIG. 1  in a light-load position at approximately the time of or during valve actuation; 
       FIG. 5  is a perspective view of the spring of  FIG. 1 ; 
       FIG. 6  is a perspective, bottom view of the VVA mechanism of  FIG. 1 ; 
       FIG. 7  is a perspective view of the integrated input cam follower and output cam body of the VVA mechanism of  FIG. 1 ; 
       FIG. 8  is a perspective view of the VVA mechanism and control shaft assembly of  FIG. 1 ; 
       FIG. 9  is a detail view of  FIG. 8 ; and 
       FIG. 10  is a plot of an exemplary family of valve lift profiles obtained with the VVA mechanism of the present invention. 
   

   Corresponding reference characters indicate corresponding parts throughout the several views. The exemplifications set out herein illustrate one preferred embodiment of the invention, in one form, and such exemplifications are not to be construed as limiting the scope of the invention in any manner. 
   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Referring now to the drawings, and particularly to  FIG. 1 , there is shown one embodiment of a variable valve actuating (VVA) mechanism having an integrated rocker arm, input cam follower and output cam of the present invention in a full or substantially full-load position at a time prior to valve actuation. VVA mechanism  10  is operably installed in association with input shaft  12 , such as, for example, a camshaft, of engine  14 . Input shaft or camshaft  12  (hereinafter referred to as camshaft  12 ) is driven to rotate by and in timed relation to a crankshaft (not shown) of engine  14 . Camshaft  12  rotates relative to central axis A thereof, and includes cam lobe  16  that rotates as substantially one body with camshaft  12 . 
   VVA mechanism  10  includes spring  18 , integrated input cam follower and output cam body  20 , bearing insert  24 , and control shaft assembly  30 . Generally, and as is explained more particularly hereinafter, VVA mechanism  10  varies the valve lift of valves  32   a  and  32   b  (valve  32   b  shown in  FIG. 8 and 9  only) dependent at least in part upon the angular position of control shaft assembly  30 . 
   Spring  18 , as best shown in  FIG. 5 , is configured as a double helical torsion spring, and includes arm portions  33   a ,  33   b  that extend in a generally tangential direction from coil portions  34   a  and  34   b , respectively. Arm portions  33   a  and  33   b  form a central tab  36 , and tabs  38   a  and  38   b  extend from coil portions  34   a ,  34   b , respectively. As best shown in  FIGS. 1–4 ,  8  and  9 , and as will be more particularly described hereinafter, coil portions  34   a  and  34   b  are coiled around respective portions of control shaft assembly  30  and are disposed on opposite sides of integrated input cam follower and output cam body  20 . As will also be more particularly described hereinafter, central tab  36  is grounded to integrated input cam follower and output cam body  20 , and tabs  38   a  and  38   b  are grounded within corresponding features formed in respective portions of control shaft assembly  30 . 
   Integrated input cam follower and output cam body  20  (hereinafter referred to as integrated body  20 ), as best shown in  FIG. 7 , defines orifice  42  within which bearing insert  24  is disposed. A portion of control shaft assembly  30 , as will be more particularly described hereinafter, extends through bearing insert  24  and orifice  42  to thereby pivotally dispose integrated body  20  upon that portion of control shaft assembly  30 . Input cam follower  46 , such as, for example, a roller, is pivotally coupled by coupler  48 , such as, for example, a pin, to integrated body  20 . 
   Referring now to  FIG. 6 , integrated body  20  includes central recess  56 , within which central tab  36  of spring  18  is disposed to thereby couple spring  18  to integrated body  20 . Integrated body  20  further defines output cam surfaces  50   a  and  50   b  that include respective base circle/low-lift portions  52   a  and  52   b  ( FIG. 7 ) and respective high-lift/nose portions  54   a  and  54   b  ( FIG. 7 ) formed thereon, such as, for example, by grinding. Output cam surfaces  50   a  and  50   b  are disposed in engagement with a corresponding output cam follower  58   a  and  58   b  ( FIG. 8 ), such as, for example, roller finger followers. Integrated body  20  is constructed of, for example, surface hardened low-carbon steel, and is formed by, for example, stamping. 
   Bearing insert  24 , as discussed above, is disposed at least partially within orifice  42  of integrated body  20 , and a portion of control shaft assembly  30  is disposed within and extends through bearing insert  24 . Thus, bearing insert  24  is disposed and reduces friction between integrated body  20  and control shaft assembly  30 . Bearing insert  24  is configured, such as, for example, a needle bearing assembly. 
   Control shaft assembly  30 , as best shown in  FIG. 8 and 9 , includes pivot segments  60 ,  62 ,  64  and  66  alternating in an axial direction and interconnected with shaft segments  70 ,  72 ,  74  and  76 . Pivot segments  60 ,  62 ,  64  and  66  share a common central or pivot axis P, whereas shaft segments  70 ,  72 ,  74  and  76  share a common central or shaft axis S that is substantially parallel relative to and spaced apart from axis P. Pivot axis P and shaft axis S are each substantially parallel relative to and spaced apart from central axis A of input/camshaft  12  of engine  14 . Control shaft assembly  30  is constructed and/or fabricated of, for example, forged steel or cast iron. An actuator (not shown) pivots control shaft assembly  30  relative to pivot axis P to thereby establish, as will be explained more particularly hereinafter, a desired valve lift profile. 
   Referring now to  FIG. 9 , each shaft segment  70 ,  72 ,  74  and  76  is disposed proximate to and associated with a corresponding one of the cylinders  80  of engine  14 . A respective assembly of spring  18 , integrated body  20  and bearing insert  24 , hereinafter referred to as actuation assemblies  90 , are associated with each of shaft segments  70 ,  72 ,  74  and  76 , and thereby with each cylinder  80 , to provide variable actuation of at least two of the valves of each cylinder  80  of engine  14 . As stated above, spring  18  includes tabs  38   a  and  38   b  that are grounded within corresponding features formed in respective portions of control shaft assembly  30 . More particularly, control shaft  30  defines spring-tab-receiving features  78   a  and  78   b , such as, for example, grooves or orifices, within which tabs  38   a  and  38   b  are disposed, thereby grounding spring  18 . 
   In use, input/camshaft  12  is driven to rotate in a counterclockwise direction and in timed relation to the crankshaft (not shown) of engine  14 . Cam lobe  16  engages input cam follower  46  of integrated body  20 . As input cam lobe  16  rotates from a position wherein its base circle portion engages input cam follower  46  ( FIGS. 1 and 3 ) to a position in which its peak-lift or nose portion engages input cam follower  46  ( FIGS. 2 and 4 ), integrated body  20  is caused to pivot in a clockwise direction relative to central shaft axis S. The pivoting of integrated body  20  causes output cam surfaces  50   a  and  50   b  to pivot relative to output cam followers  58   a  and  58   b , respectively. Spring  18  biases integrated body  20  in a counterclockwise direction thereby biasing input cam follower  46  into engagement with input cam lobe  16 . 
   The angular orientation of control shaft assembly  30  determines the lift profile, i.e., the amount of lift imparted to and the camshaft, angle at which the valve opening event occurs for that given amount of lift, of the associated valves of engine  14 . More particularly, the angular orientation of control shaft  30  determines the portion of output cam surfaces  50   a  and  50   b  that engage cam followers  58   a  and  58   b , respectively, during pivotal oscillation of integrated body  20 . Further, the angular orientation of control shaft  30  also establishes the relative orientation of and the distance separating shaft axis S and central axis A. All of the aforementioned variables, i.e., the portion of output cam surfaces  50   a  and  50   b  that engage cam followers  58   a  and  58   b , respectively, during pivotal oscillation of integrated body  20 , and the relative orientation of and the distance separating shaft axis S and central axis A, conjunctively determine the valve lift profile. 
   With control shaft  30  oriented to dispose VVA mechanism  10  in the full or substantially full load orientation as shown in  FIGS. 1 and 2 , output cam surfaces  50   a ,  50   b  are disposed such that substantially all of lift portions  54   a  and  54   b , respectively, are disposed within the fixed oscillatory range of movement of integrated body  20  relative to output cam followers  58   a  and  58   b , respectively. Thus, as integrated body  20  is pivotally oscillated, substantially the entire lift portions  54   a  and  54   b  engage output cam followers  58   a  and  58   b , respectively, and a high or substantially maximum amount of lift is imparted to the valves of engine  14 . 
   Conversely, with control shaft  30  oriented to dispose VVA mechanism  10  in the low-load orientation as shown in  FIGS. 3 and 4 , output cam surfaces  50   a  and  50   b  are disposed such that substantially none of the lift portions  54   a  and  54   b , respectively, are disposed within the fixed oscillatory range of movement of integrated body  20  relative to output cam followers  58   a  and  58   b . Thus, as integrated body  20  is pivotally oscillated, output cam followers  58   a  and  58   b  are engaged only or substantially only by the base circle or low lift portions  52   a  and  52   b , and a low or substantially minimum amount of lift is imparted to the valves of engine  14 . 
   As stated above the pivoting of control shaft assembly  30 , in addition to orienting output cam surfaces  50   a  and  50   b  relative to cam followers  58   a  and  58   b , respectively, establishes the relative orientation of and the distance separating shaft axis S and central axis A. As control shaft assembly  30  is pivoted relative to pivot axis P, pivot segments  60 ,  62 ,  64  and  66  undergo substantially pure pivotal movement relative to pivot axis P. As pivot segments  60 ,  62 ,  64  and  66  are pivoted relative to pivot axis P they do not move substantially toward or away from input shaft  12 . Conversely, since shaft segments  70 ,  72 ,  74  and  76  are substantially concentric relative to shaft axis S but are eccentric relative to pivot axis P, shaft segments  70 ,  72 ,  74  and  76  move in a generally arced manner and in a direction generally toward and/or away from input/camshaft  12  as control shaft assembly  30  is pivoted relative to pivot axis P. 
   The movement of shaft segments  70 ,  72 ,  74  and  76  generally toward and/or away from input shaft  12  and/or central axis A thereof is best seen by comparing the orientation of shaft axis S of shaft segments  70 ,  72 ,  74  and  76  relative to central axis A of input/camshaft  12  shown in  FIGS. 1 and 2  with the orientation of shaft axis S relative to central axis A as shown in  FIGS. 3 and 4 . More particularly, as shown in  FIGS. 1 and 2  wherein VVA mechanism  10  is depicted in the high-load position, shaft axis S and central axis A are at a minimum or substantially minimum relative separation and are oriented in a generally horizontal plane relative to each other. 
   Conversely, as shown in  FIGS. 3 and 4  wherein VVA mechanism  10  is depicted in the low-load position, control shaft  30  has been pivoted from approximately twenty (20°) to approximately thirty (30°) degrees in a clockwise direction from the high-load orientation shown in  FIGS. 1 and 2  and, as a result of this clockwise pivoting of control shaft  30 , shaft axis S and central axis A are separated by a maximum or substantially maximum distance. Further, the two axes no longer occupy a generally horizontal plane. Rather, shaft axis S has moved down and away from central axis A, and the two axes now occupy a plane that is at an angle of approximate two (2°) to approximately three (3°) degrees below horizontal. 
   The separation between and orientation of shaft axis S relative to central axis A determine the portion of the lift profile of input cam lobe  16  that is in engagement with input cam follower  46  at a given angle of rotation of input/camshaft  12 , and thereby determine at least in part the timing or phasing of the valve opening event relative to the angle of input/camshaft  12  rotation. Further, the separation between and orientation of shaft axis S relative to central axis A determine at least in part the orientation of integrated body  20  relative to output cam followers  58   a ,  58   b , and thereby determine which portions of output cam surfaces  50   a ,  50   b  engage cam followers  58   a ,  58   b , respectively, during pivotal oscillation of integrated body  20 . Thus, the separation between and orientation of shaft axis S relative to central axis A as determined by the angular orientation of control shaft assembly  30  determine the valve lift profile. 
   It should be particularly noted that control shaft assembly  30  is pivoted in a substantially continuous manner between the maximum-lift or full-load orientation ( FIGS. 1 and 2 ) and low-load orientation ( FIGS. 3 and 4 ) to thereby provide substantially continuous adjustment of the amount of lift imparted to the valves of engine  14 , as depicted by the exemplary family of valve lift curves shown in  FIG. 10 . 
   In the embodiment shown, input cam follower  46  is configured as a roller that is pivotally coupled by coupler  48 , such as, for example, a pin, to integral body  20 . However, it is to be understood that integral body  20  can be alternately configured, such as, for example, with a slider-pad-type cam follower that is integral and monolithic with and/or otherwise attached to integral body  20 . 
   While this invention has been described as having a preferred design, the present invention can be further modified within the spirit and scope of this disclosure. This application is therefore intended to cover any variations, uses, or adaptations of the present invention using the general principles disclosed herein. Further, this application is intended to cover such departures from the present disclosure as come within the known or customary practice in the art to which this invention pertains and which fall within the limits of the appended claims.