Patent Publication Number: US-6655330-B2

Title: Offset variable valve actuation mechanism

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 variously-configured mechanical and/or electromechanical devices, collectively referred to hereinafter as variable valve actuation (VVA) mechanisms. Several examples of particular embodiments of VVA mechanisms are detailed in commonly-assigned U.S. Pat. No. 5,937,809, the disclosure of which is hereby incorporated herein by reference. 
     Generally, a conventional VVA mechanism includes a rocker arm that is displaced in a generally radial direction by an input cam of a rotating input shaft, such as the engine camshaft. 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 cam followers, such as, for example, direct acting cam followers or roller finger followers. 
     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 and, via the rocker arm and link arms, pivots the output cams to a base angular orientation that corresponds to the desired valve lift profile. 
     A conventional VVA mechanism is typically disposed between and actuates a pair of functionally corresponding valves, such as, for example, a pair of intake valves, of an engine cylinder. Thus, the rocker arm, link arms, output cams, and frame members of the VVA mechanism must all be accommodated within the space between the corresponding valves. However, cam support bearings are also conventionally disposed between the valves of each cylinder. Locating the cam support bearings between the valves places the bearings more proximate to deflection forces imposed upon the camshaft that result from valve actuation, and thereby provides the camshaft with additional stiffness. Further, locating the cam support bearings between the valves enables the cylinder head bolts to be located more conveniently. 
     In order to accommodate VVA mechanisms, however, engine cylinder heads must typically be redesigned to relocate the cam support bearings. More particularly, the cam support bearings are typically relocated from between the valves of each cylinder to a position between the cylinders in order to accommodate the VVA mechanisms in the spaces between the valves. Similarly, the cylinder head bolts must also be relocated. Relocating the cam bearings reduces camshaft stiffness and thereby potentially results in undesirable deflection of the camshaft. Relocating the cylinder head bolts may also be problematic in that a less effective coupling of the cylinder head to the engine may result. 
     Therefore, what is needed in the art is a VVA mechanism that is configured for being installed between adjacent engine cylinders. 
     Furthermore, what is needed in the art is a VVA mechanism that is installed within an engine without requiring relocation of the cam support bearings. 
     Moreover, what is needed in the art is a VVA mechanism that is installed within an engine without requiring relocation of the cylinder head bolts. 
     SUMMARY OF THE INVENTION 
     The present invention provides a variable valve actuation mechanism that is configured for being disposed between adjacent engine cylinders, and thus does not require relocation of the cam support bearings or the cylinder head bolts. 
     The invention comprises, in one form thereof, an output cam having a first output cam lobe and a second output cam lobe. A body portion adjoins and axially separates the first and second output cam lobes. The body portion includes an outer surface. A portion of the outer surface is configured for being pivotally engaged by a cam support bearing. 
     An advantage of the present invention is that it is operably disposed between adjacent engine cylinders and thus does not require the cam support bearings to be relocated. 
     A further advantage of the present invention is that it does not require relocation by of the cylinder head bolts. 
    
    
     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 one embodiment of the invention in conjunction with the accompanying drawings, wherein: 
     FIG. 1 is a perspective view of one embodiment of a variable valve actuation (VVA) mechanism of the present invention operably installed within an internal combustion engine; 
     FIG. 2 is a perspective view of the VVA mechanism of FIG. 1; 
     FIG. 3 is a front view of the VVA mechanism of FIG. 1; and 
     FIG. 4 is a perspective view of the output cam of FIG.  1 . 
    
    
     Corresponding reference characters indicate corresponding parts throughout the several views. The exemplification set out herein illustrates one preferred embodiment of the invention, in one form, and such exemplification is not to be construed as limiting the scope of the invention in any manner. 
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring now to FIG. 1, there is shown one embodiment of a VVA of the present invention. Generally, VVA mechanism  10  is operably installed between adjacent cylinders of engine  12 , thereby avoiding the need to relocate the cam support bearings and cylinder head bolts (not shown in FIG. 1) from the space between the valves of each cylinder in engine  12 . 
     Engine  12  includes input shaft or camshaft  14  (hereinafter referred to as camshaft  14 ) having central axis A, control shaft  16  having central axis S, and cylinders  20 ,  22  and  24 . Valves  20   a  and  20   b ,  22   a  and  22   b , and  24   a  and  24   b , are associated with cylinders  20 ,  22  and  24 , respectively. Cam support bearing  26   a  is disposed between valves  20   a  and  20   b , cam support bearing  26   b  is disposed between valves  22   a  and  22   b , and cam support bearing  26   c  is disposed between valves  24   a  and  24   b.    
     Referring now to FIGS. 2 and 3, camshaft  14  is an elongate shaft member having input or opening cam lobe  28  and closing cam lobe  30 . Input cam lobe  28  and closing cam lobe  30  are disposed between cylinders  20  and  22  of engine  12 , and actuate valves  22   a ,  22   b  of cylinder  22  in a manner that will be more particularly described hereinafter. Opening cam lobe  28  and closing cam lobe  30  are disposed or paired in a predetermined angular relation relative to each other and relative to central axis A. Camshaft  14  is driven to rotate by, for example, a crankshaft (not shown) of engine  12 . Input and closing cam lobes  28  and  30 , respectively, rotate as substantially one body with camshaft  14 . For the sake of clarity, only one pair of input and closing cam lobes  28  and  30  is shown. However, it should be understood that a respective input cam lobe  28 , a respective closing cam lobe  30 , and a respective VVA mechanism  10  are also provided for each of cylinders  20  and  24 . 
     VVA mechanism  10 , as is more particularly described hereinafter, is operably installed between cylinders  20  and  22 , and actuates valves  22   a  and  22   b  of cylinder  22 . VVA mechanism  10  includes frame members  32   a ,  32   b , rocker arm  34 , link arm  36  and output cam  38 . For purposes of clarity, a single variable valve mechanism  10  is illustrated in the figures and discussed hereinafter. 
     Frame members  32   a  and  32   b  are configured as split or two-piece frame members. Generally, the pieces (not referenced) of each frame member  32   a ,  32   b , are positioned on their respective and opposing sides or portions of camshaft  14  and then coupled together with the corresponding pieces by fasteners (not referenced), thereby pivotally coupling frame members  32   a  and  32   b  to camshaft  14 . More particularly, frame member  32   a  is disposed on a first side of the paired input and closing cam lobes  28  and  30 , respectively, and frame member  32   b  is disposed on a second side of paired input and closing cam lobes  28  and  30 , respectively. Frame members  32   a  and  32   b  at respective first ends (not referenced) thereof are pivotally coupled by respective coupling means  42   a ,  42   b , such as, for example, shaft clamps, to control shaft  16 . Frame members  32   a  and  32   b  at respective second ends (not referenced) thereof are pivotally coupled, such as, for example, by pins, to a first end of rocker arm  34 . Frame member  32   a  is thereby pivotally disposed upon camshaft  14 , and frame member  32   b  is pivotally disposed upon output cam  38  as will be more particularly described hereinafter. 
     Thus coupled together and pivotally mounted, frame members  32   a ,  32   b  are not rotated by the rotation of camshaft  14 . Rather, camshaft  14  is free to rotate about central axis A and relative to split frame members  32   a ,  32   b , and frame members  32   a ,  32   b  are free to pivot relative to camshaft  14  and central axis A thereof. 
     Rocker arm  34 , as is known in the art, carries one or more rollers or slider pads (not shown) that engage each of input and closing cam lobes  28  and  30 . Rocker arm  34  is coupled, such as, for example, by pins, at a first end (not referenced) thereof to link arm  36  and at a second end (not referenced) thereof to each of frame members  32   a ,  32   b.    
     Link arm  36  is an elongate arm member that is pivotally coupled, such as, for example, by pins, at a first end (not referenced) thereof to output cam  38  and at a second end (not referenced) thereof to rocker arm  34 . 
     Output cam  38  is pivotally disposed upon camshaft  14 . More particularly, and as best shown in FIG. 4, output cam  38  is configured as a split or two-piece cam, and includes a first or top piece  52  and a second or bottom piece  54 . Pieces  52  and  54  are elongate semi-cylindrical members each having a respective first and second end (not referenced) adjoining and spaced apart by body portion  52   a  and  52   b , respectively. Pieces  52  and  54  are positioned on radially opposite sides or portions of camshaft  14  and then coupled together by fasteners (not referenced), to thereby pivotally dispose output cam  38  on camshaft  14 . 
     First/top piece  52  at a first end thereof defines link-accepting feature  56  (FIG. 4) having opposing walls  56   a ,  56   b  that define substantially concentric bores  58   a ,  58   b . The first end of link  36  is disposed between walls  56   a ,  56   b  such that an orifice (not shown) formed through link  36  is aligned with bores  58   a ,  58   b . Output cam  38  is pivotally coupled to link  36  by coupling means, such as, for example, a pin, received within bores  58   a ,  58   b  and an orifice (not shown) in the first end of link  36 . The first and second ends of first/top piece  52  include bores and flanges (not referenced) that enable first/top piece  52  and second/bottom piece  54  to be coupled together by fasteners, such as, for example, bolts, inserted through corresponding bores and flanges (not referenced) formed in second/bottom piece  54 . 
     Second/bottom piece  54  defines dual cam lobes of output cam  38 . More particularly, each of the first and second ends of second/bottom piece  54  includes a respective cam lobe surface or portion  62 ,  64  that is affixed to and/or integral with second/bottom piece  54 . With output cam  38  pivotally disposed on camshaft  14 , cam lobe portions  62 ,  64 , are configured for engaging cam followers  72 ,  74  (FIGS.  2  and  3 ), respectively, to thereby actuate valves  22   a ,  22   b , respectively. 
     It should be particularly noted that a portion of body portions  52   a  and  52   b  of output cam  38 , when operably installed in engine  12 , are disposed intermediate an inner surface (not referenced) of cam support bearing  26   b  and an outer surface (not referenced) of camshaft  14 . More particularly, an inside surface (not referenced) of cam support bearing  26   b  engages a portion of the outer surface (not referenced) of body portions  52   a  and  52   b . Output cam  38  is free to undergo pivotal movement relative to the inside surface of cam support bearing  26   b . The inside surface of output cam  38  pivotally engages camshaft  14 . Thus, cam support bearing  26   b  provides support to camshaft  14  via output cam  38 . Body portions  52   a  and  52   b  of output cam  38  extend axially in both directions from the interface thereof with cam support bearing  26   b  and camshaft  14  such that cam lobe portions  62  and  64  are disposed on opposite sides of cam support bearing  26   b  and on opposite sides of input and closing cam lobe pair  28 ,  30 . 
     It should further be particularly noted that frame member  32   b  is pivotally disposed upon body portions  52   a  and  52   b  of output cam  38 , rather than being pivotally disposed upon camshaft  14  as in a conventional VVA. More particularly, the pieces (not referenced) of frame member  32   b  are positioned on their respective and opposing sides or portions of output cam body portions  52   a  and  52   b , and then coupled together by fasteners (not referenced) to thereby pivotally coupling frame members  32   a  and  32   b  to output cam  38 . Thus coupled together and pivotally disposed upon output cam  38 , frame member  32   b  is not pivoted or rotated by the pivoting of output cam  38  nor by the rotation of camshaft  14 . Rather, camshaft  14  and output cam  38  are free to rotate about central axis A and relative to split frame member  32   b , and frame member  32   b  is free to pivot relative to camshaft  14 , central axis A thereof, and output cam  38 . 
     In use, VVA mechanism  10  operates in a generally similar manner as a conventional cam link variable valve actuating mechanism in regard to varying the lift profiles of the valves actuated thereby. Generally, a desired valve lift profile for associated valves  22   a ,  22   b  is obtained by placing control shaft  16  in a predetermined angular orientation relative to central axis S thereof, which, in turn, pivots output cam  38  relative to central axis A. Thus, the desired portion of the lift profiles of output cam lobe portions  62  and  64  are disposed within the pivotal oscillatory range of output cam  38  relative to cam followers  72 ,  74 . As output cam  38  is pivotally oscillated, the desired portions of the lift profiles of output cam lobe  38  engage cam followers  72  and  74  to thereby actuate valves  22   a  and  22   b  according to the desired lift profile. 
     It should be particularly noted that output cam  38  actuates both valves  22   a  and  22   b , which are disposed on opposite sides of cam support bearing  26   b . As stated above, the first end of output cam  38  is pivotally coupled to link  36 . As rocker arm  34  is displaced by the rotation of input cam  28 , thereby pulling and/or pushing on link arm  36 , the resultant torque causes the entire elongate output cam  38  to pivotally oscillate relative to central axis A. Each of cam lobe portions  62  and  64  pivot as substantially one body with output cam  38 , and thus cam lobe portions  62  and  64  are also pivotally oscillated relative to central axis A. Cam lobe portions  62  and  64  are disposed on opposite sides of cam support bearing  26   b , and actuate valves  22   a ,  22   b , respectively, as output cam  38  is pivotally oscillated. Since link  36  is pivotally coupled to just one (i.e., the first) end of output cam  38 , and since cam lobe portions  62  and  64  are disposed on opposite sides of cam support bearing  26   b , VVA mechanism  10  is referred to as an offset VVA. Further, since VVA mechanism  10  is offset relative to cylinder  22 , i.e., the cylinder with which it is operably associated, it is referred to as an offset VVA. 
     It should further be particularly noted that the outside surface (not referenced) of output cam body portions  52   a  and  52   b  are disposed between cam lobe portions  62  and  64 . Body portions  52   a ,  52   b  are supported by cam bearings  26   b  in the cylinder head of engine  12 , and thus provide support for camshaft  14 . More particularly, the inner surfaces of each body portion  52   a  and  52   b  are in pivotal engagement with the outer surface of camshaft  14 . At least a portion of the outer surface of body portions  52   a  and  52   b  are in pivotal engagement with the inside surface of cam support bearing  26   b . Thus, camshaft  14  is provided with support and added stiffness by output cam  38 , which, in turn, is supported by cam support bearing  26   b  and cam bearing  26   b  in the cylinder head of engine  12 . 
     In the embodiment shown, VVA mechanism  10  is configured as a cam link and/or desmodromic variable valve actuation mechanism. However, it is to be understood that the VVA mechanism of the present invention can be alternately configured, such as, for example, as a non-desmodromic mechanism. 
     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.