Abstract:
An electromechanical VVA system for controlling the poppet valves in the cylinder head of an internal combustion engine. The system varies valve lift, duration, and phasing in a dependent manner for one or more banks of engine valves. A rocker subassembly for each valve or valve pair is pivotably disposed on a control shaft between the camshaft and the roller finger follower. The control shaft may be displaced about a pivot axis outside the control shaft to change the angular relationship of the rocker subassembly to the camshaft, thus changing the valve opening, closing, and lift. A plurality of control shafts for controlling all valvetrains in an engine bank defines a control shaft assembly. The angular positions of the individual control shafts may be tuned to optimize the valve timing of each cylinder. The system is applicable to the intake and exhaust camshafts of diesel and gasoline engines.

Description:
TECHNICAL FIELD  
       [0001]     The present invention relates to valvetrains of internal combustion engines; more particularly, to devices for controlling the timing and lift of valves in such valvetrains; and most particularly, to a system for variable valvetrain actuation wherein electromechanical means for variable actuation is interposed between the engine camshaft and the valvetrain cam followers to vary the timing and amplitude of follower response to cam rotation.  
       BACKGROUND OF THE INVENTION  
       [0002]     One of the drawbacks inhibiting the introduction of a gasoline Homogeneous Charge Compression Ignited (HCCI) engine in production has been the lack of a simple, cost effective and energy efficient Variable Valvetrain Actuation (VVA) system to vary both the exhaust and intake events. Many electro-hydraulic and electro-mechanical “camless” VVA systems have been proposed for gasoline HCCI engines, but while these systems may consume less or equivalent actuation power at low engine speeds, they typically require significantly more power than a conventional fixed-lift and fixed-duration valvetrain system to actuate at mid and upper engine speeds. Moreover, the cost of these “camless” systems usually is on par with the cost of an entire conventional engine itself.  
         [0003]     As the cost of petroleum continues to rise from increased global demands and limited supplies, the fuel economy benefits of internal combustion engines will become a central issue in their design, manufacture, and use at the consumer level. In high volume production applications, applying a continuously variable valvetrain system to just the intake side of a gasoline engine can yield fuel economy benefits up to 10% on Federal Test Procedure—USA (FTP) or New European Driving Cycle (NEDC) driving schedules, based on simulations and vehicle testing. HCCI type combustion processes have promised to make the gasoline engine nearly as fuel efficient as a conventional, 4-stroke Diesel engine, yielding gains as high as 15% over conventional (non-VVA) gasoline engines for these same driving schedules. The HCCI engine could become strategically important to the United States and other countries dependent on a gasoline based transportation economy.  
         [0004]     Likewise, the use of a continuously variable valvetrain for both the intake and exhaust sides of a Diesel engine has been identified as a potential means to reduce the size and cost of future exhaust aftertreatment systems and a way to restore the lost fuel economy that these systems presently impose. By varying the duration of intake lift events, potential Miller-cycle type fuel economy gains are feasible. Also, with VVA on the intake side, the effective compression ratio can be varied to provide a high ratio during startup and a lower ratio for peak fuel efficiency at highway cruise conditions. Without intake side VVA, compression ratios must be compromised in a tradeoff between these two extremes. Exhaust side VVA can improve the torque response of a Diesel engine. Varying exhaust valve opening times can permit faster transitions with the turbocharger, reducing turbo lag. Exhaust VVA can also be used to expand the range of engine operation where pulse turbo-charging can be effective. Furthermore, varying exhaust valve opening times can be used to raise exhaust temperatures under light load conditions, significantly improving NOx adsorber efficiencies.  
         [0005]     VVA devices for controlling the poppet valves in the cylinder head of an internal combustion engine are well known.  
         [0006]     For a first example, U.S. Pat. No. 5,937,809 discloses a Single Shaft Crank Rocker (SSCR) mechanism wherein an engine valve is driven by an oscillatable rocker cam that is actuated by a linkage driven by a rotary eccentric, preferably a rotary cam. The linkage is pivoted on a control member that is in turn pivotable about the axis of the rotary cam and angularly adjustable to vary the orientation of the rocker cam and thereby vary the valve lift and timing. The oscillatable cam is pivoted on the rotational axis of the rotary cam.  
         [0007]     For a second example, U.S. Pat. No. 6,311,659 discloses a Desmodromic Cam Driven Variable Valve Timing (DCDVVT) mechanism that includes a control shaft and a rocker arm. A second end of the rocker arm is connected to the control shaft. The rocker arm carries a roller for engaging a cam lobe of an engine camshaft. A link arm is pivotally coupled at a first end thereof to the first end of the rocker arm. An output cam is pivotally coupled to the second end of the link arm, and engages a corresponding cam follower of the engine. A spring biases the roller into contact with the cam lobe and biases the output cam toward a starting angular orientation.  
         [0008]     A shortcoming of these prior art VVA systems is that both the SSCR device and the DCDVVT mechanism include two individual frame structures per each engine cylinder that are somewhat difficult to manufacture.  
         [0009]     Another shortcoming is that these mechanisms “hang” from the engine camshaft and thus create a parasitic load. The SSCR input rocker is connected through a link to two output cams that also ride on the input camshaft. Because the mechanism comprises four moving parts per cylinder, it is difficult to design a return spring stiff enough for high-speed engine operation that can still fit in the available packaging space.  
         [0010]     Still another shortcoming is that assembly and large-scale manufacture of the SSCR device would be difficult at best with its high number of parts and required critical interfaces.  
         [0011]     What is needed in the art is a simplified VVA mechanism that is not mounted on the engine camshaft, is easy to manufacture and assemble, and requires minimal packaging space in an engine envelope.  
         [0012]     It is a principal object of the present invention to provide variable opening timing, closing timing, and lift amplitude in a bank of engine intake or exhaust valves.  
         [0013]     It is a further object of the invention to simplify the manufacture and assembly of a VVA system for such variable opening, closing, and lift.  
         [0014]     It is a still further object of the invention to provide such a system which is not parasitic on the engine camshaft.  
       SUMMARY OF THE INVENTION  
       [0015]     Briefly described, the invention contained herein includes an electromechanical VVA system for controlling the poppet valves in the cylinder head of an internal combustion engine. The system varies valve lift, duration, and phasing in a dependent manner for one or more banks of engine valves. Using a single electrical rotary actuator per bank of valves to control the device, the valve lift events can be varied for either the exhaust or intake banks. The device comprises a hardened steel rocker subassembly for each valve or valve pair pivotably disposed on a control shaft between the engine camshaft and the engine roller finger follower. The control shaft itself may be displaced about a pivot axis outside the control shaft to change the angular relationship of the rocker subassembly to the camshaft, thus changing the valve opening, closing, and lift. A plurality of control shafts for controlling a plurality of valve trains for a plurality of cylinders in an engine bank may be assembled linearly to define a control crankshaft for all the valves in the engine bank. The angular positions of the control shafts for the plurality of cylinders may be tuned by mechanical means with respect to each other to optimize the valve timing of each cylinder in a cylinder bank. The valve actuation energy comes from a conventional mechanical camshaft that is driven by a belt or chain, as in the SSCR device disclosed in U.S. Pat. No. 5,937,809 device. An electrical, controlling actuator attached to the control shaft receives its energy from the engine&#39;s electrical system.  
         [0016]     Compared to prior art devices, an important advantage of the present mechanism is its simplicity. The input and output oscillators of prior art mechanical, continuously variable valvetrain devices, such as the SSCR and the DCDVVT, have been combined into one moving part. Due to its inherent simplicity, the present invention differs significantly from the original SSCR device in its assembly procedure for mass production. With only one oscillating member, the present invention accrues significant cost, manufacturing and mechanical advantages over these previous designs. Further, a VVA device in accordance with the present invention does not “hang” from the camshaft, as was the case with these other mechanisms and therefore is not a parasitic load on the camshaft. Since the present invention has only one moving part, its total mass moment of inertia is much lower and, hence, spring design is less challenging. Because mechanically there are fewer parts, there are fewer degrees of freedom in the mechanism. This simplifies the task of design optimization to meet performance criteria, by substantially reducing the number of equations required to describe the motion of the present device. Further, a device in accordance with the invention requires approximately one-quarter the total number of parts as an equivalent SSCR device for a similar engine application. With its cost advantages and design flexibility, the present device can easily be applied to the intake camshaft of a gasoline engine for low cost applications, or to both the intake and exhaust camshafts of a diesel or a gasoline HCCI engine. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0017]     The present invention will now be described, by way of example, with reference to the accompanying drawings, in which:  
         [0018]      FIG. 1   a  is an elevational drawing of a prior art valvetrain without VVA, showing the valve in the fully closed position;  
         [0019]      FIG. 1   b  is a drawing like that shown in  FIG. 1   a , showing the valve in a fully open position;  
         [0020]      FIG. 2   a  is an elevational drawing of an improved valvetrain equipped with VVA means in accordance with the invention, showing the VVA in maximum lift position and the valve in the fully closed position;  
         [0021]      FIG. 2   b  is a drawing like that shown in  FIG. 2   a , showing the VVA in maximum lift position and the valve in the fully open position;  
         [0022]      FIG. 3   a  is a drawing like that shown in  FIG. 2   a , showing the VVA in minimum lift position and the valve in the fully closed position;  
         [0023]      FIG. 3   b  drawing like that shown in  FIG. 3   a , showing the VVA in minimum lift position and the valve in the fully open position;  
         [0024]      FIG. 4  is an isometric drawing of four valvetrains for a four-cylinder engine bank, the valvetrains being equipped with VVA means linked together in accordance with the invention;  
         [0025]      FIG. 5  is a graph showing a family of lift curves for a valvetrain equipped with VVA means in accordance with the invention, the curves being bounded by maximum lift of the apparatus shown in  FIGS. 2   a  and  2   b , and by minimum lift of the apparatus shown in  FIGS. 3   a  and  3   b;    
         [0026]      FIGS. 6   a  and  6   b  are isometric views from above and below, respectively, of a metal stamping for forming a VVA rocker frame in accordance with the invention;  
         [0027]      FIGS. 7   a , 7   b , 7   c , 8   a , 8   b , 8   c  are isometric views showing progressive steps in the manufacture and assembly of a VVA rocker in accordance with the invention;  
         [0028]      FIG. 9   a  is an exploded isometric view of a VVA rocker sub-assembly and return spring;  
         [0029]      FIG. 9   b  is an exploded isometric view showing a first assembly of a VVA rocker sub-assembly and return spring onto a control shaft;  
         [0030]      FIG. 9   c  is an exploded isometric view showing assembly of a second control shaft onto the first assembly shown in  FIG. 9   b;    
         [0031]      FIG. 10   a  is an exploded isometric view showing joining of the elements shown in  FIG. 9   c;    
         [0032]      FIG. 10   b  is an exploded isometric view showing addition of a second VVA rocker sub-assembly onto the assembly shown in  FIG. 10   a;    
         [0033]      FIG. 11  is an elevational view of the valvetrains shown in  FIG. 4 ;  
         [0034]      FIG. 12  is a cross-sectional view taken along line  12 - 12  in  FIG. 11 ;  
         [0035]      FIG. 13  is a cross-sectional view taken along line  13 - 13  in  FIG. 11 ;  
         [0036]      FIGS. 14   a  through  14   d  are isometric views like that shown in  FIG. 4  but viewed from the opposite side, showing a sequence of air flow adjustment steps for tuning air flow to each individual engine cylinder; and  
         [0037]      FIG. 15  is an isometric view showing VVA means in accordance with the invention installed on all of the intake valves and all of the exhaust valves of an inline four cylinder engine. 
     
    
       [0038]     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  
       [0039]     The benefits and advantages of a VVA system in accordance with the invention may be better appreciated by first considering a prior art engine valvetrain without VVA.  
         [0040]     Referring to  FIGS. 1   a  and  1   b , a prior art valvetrain  100  comprises an input engine camshaft  2  having a cam lobe  4 . Lobe  4  is defined by a profile having a base circle portion  15 , an opening flank  6 , and a nose portion  22 . A roller finger follower (RFF)  18  includes a centrally mounted roller  17  for following cam lobe  4  and is pivotably mounted at a first socket end  19  on a hydraulic lash adjuster  20 . A second pallet end  21  of RFF  18  engages the stem end of an engine valve  5 . When RFF  18  is on the base circle portion  15 , valve  5  is closed, as shown in  FIG. 1 . As camshaft  2  rotates counterclockwise, RFF  18  begins to climb opening flank  6 , forcing valve  5  to begin opening. When RFF  18  reaches nose portion  22 , valve  5  is fully open, as shown in  FIG. 2 . Further rotation of camshaft  2  causes valve  5  to gradually close as RFF  18  moves down the closing flank of the cam lobe and returns to base circle portion  15 . Note that in prior art valvetrain  100 , the valve opening and closing timing and the height of valve lift are fixed by the cam lobe profile and are invariant.  
         [0041]     Referring now to  FIGS. 2   a - 11 , an improved VVA valvetrain system  200  in accordance with the invention includes a control shaft assembly  1  shown at the intake valve camshaft  2  of an inline 4-cylinder engine  102  which may be spark-ignited or compression-ignited. In the present exemplary arrangement, the valvetrains include two intake valves per cylinder.  
         [0042]     Control shaft assembly  1  manages an engine&#39;s gas exchange process by varying the angular position of its control shaft  1   a . In  FIGS. 2   a  and  2   b , system  200  is shown in its full engine load position, and in  FIGS. 3   a  and  3   b , system  200  is shown in its lowest engine load position. In  FIGS. 2   a , 3   a , a view of system  200  with the input camshaft on its base circle appears, and in  FIGS. 2   b , 3   b  a view with the input camshaft at its peak lift point appears. Note that actuator control shaft segment  38  has been removed for clarity in  FIGS. 2 and 3 .  
         [0043]     As shown in  FIGS. 2   a , 2   b , high lift events with full duration are produced by the system whenever the control shaft arms  3  are in the nearly vertical position indicated. (For convenience in the following discussion, such terms as vertical, horizontal, above, and below are used in the sense as the elements appear in the figures; of course, it will be recognized that in an actual installation the directional relationships among the elements may be different.)  
         [0044]     As seen in  FIG. 4 , at each engine cylinder is a cam lobe  4 , integral to a nodular cast iron input camshaft  2 , centered axially between two engine valves  5 . As input camshaft  2  rotates counter-clockwise, urged by an electromechanical rotary actuator (not shown) attached to an end of system  1 , opening flank  6  of cam lobe  4  pushes hardened steel rocker roller  7  down, causing the stamped steel rocker subassembly  8  to rotate in a clockwise direction. As rocker subassembly  8  rotates, it turns about a forged steel (or cast iron) control shaft rocker pivot pin  9  of the lift control shaft assembly  1 , one of which is located at each of the engine&#39;s cylinders. A mating bronze (or babbit) pivot bearing insert  10  facilitates rotation of rocker subassembly  8 . When in the full engine load mode of operation ( FIGS. 2   a , 2   b ), the locus of motion of rocker roller  7  is left of the centerline  7   a  of the input camshaft  2 . Clockwise rotation of rocker subassembly  8  advances the output cam profiles  12  ground onto the folded and carbonized rocker flanges  13 , 14  to where the radius of output cam  16  increases beyond that of the base circle portion  15  of the cam profile. The further that rocker subassembly  8  is rotated about control shaft rocker pivot pin  9 , the greater the lift imparted through finger follower rollers  17 . The left end of each finger follower  18  pivots about the ball shaped tip of a conventional hydraulic valve lash adjuster  20 . Pushing down on the centrally located finger follower roller  17  imparts lift to engine valve  5  via pallet  21  on RFF  18 .  
         [0045]     An important aspect and benefit of an improved VVA system in accordance with the invention is that no changes except relative location are required in the existing prior art camshaft, cam lobes, roller finger followers, hydraulic valve lifters, and valves. The only structural requirement in the engine is that the camshaft be removed farther from the HLA and RFF and offset slightly to permit insertion of VVA assembly  200  there between.  
         [0046]     When control shaft assembly  1  is in the full lift position as shown in  FIGS. 2   a ,  2   b , maximum lift is reached at engine valves  5  whenever rocker roller  7  reaches nose portion  22  of input cam lobe  4 . At this point, rocker subassembly  8  ceases to rotate in the clockwise direction. As input cam lobe  4  rotates further in the counter-clockwise direction, nose portion  22  of camshaft lobe  4  slips past rocker roller  7 , and helical torsion return spring  23  forces rocker subassembly  8  to rotate counter-clockwise. This counter-clockwise rotation, in turn, reduces lift produced between the output cam profiles  12  and finger follower rollers  17 . Eventually, as camshaft  2  continues to rotate counter-clockwise, rocker roller  7  reaches base circle portion  15  of input cam lobe  4 . Here, lift remains at zero, until the next engine event occurs in that cylinder. The motion described above produces a peak lift profile ( FIG. 5 , curve  210 ), similar to that produced by prior art system  100  as shown in  FIGS. 1   a , 1   b , to maximize gas flow to the engine.  
         [0047]     Short shank pins  25 , 27  in control shaft assembly  1  ride in matching holes (not shown), bored through the engine&#39;s camshaft bearing webs, integral to the cylinder head. An electromechanical actuator (also not shown) rotates control shaft assembly  1  about the center of these holes to vary engine load. Note that the centerlines  25   a  of the control shaft shank pins  25 , 27  coincide with the centerlines  17   a  of finger follower rollers  17 .  
         [0048]     Referring to  FIGS. 3   a , 3   b , if control shaft assembly  1  is rotated through an angle  202  clockwise on axis  17   a  from its full load position as shown in  FIG. 2   a  (such as would be desirable under light engine load conditions), for example through about 27.5°, assembly  1  produces minimal lift events with reduced duration (also see curve  212  in  FIG. 5 ). In this position ( FIGS. 3   a , 3   b ), control shaft rocker pivot pins  9  are in their closest proximity to input camshaft  2 , causing the loci of all rocker rollers  7  to oscillate just right of the centerline  7   a  of camshaft  2 . Likewise, when control shaft assembly  1  is in the light load position, finger follower roller  17  spends most of its time on base circle portion  15  of output cam profile  12 , just barely reaching opening flank  16  of the profile whenever rocker roller  7  is aligned with nose portion  22  of input camshaft lobe  4 . Thus, assembly  1  produces short and shallow lift events (see  FIG. 5 , curve  212 ), which minimizes gas flow to the engine.  
         [0049]     Variably rotating control shaft assembly  1  to intermediate rotational positions between full engine load position ( FIGS. 2   a , 2   b ) and minimum engine load position ( FIGS. 3   a , 3   b ) produces the remaining lift curves (not numbered) within the family depicted in  FIG. 5  between curves  210 , 212 .  
         [0050]      FIGS. 6   a  through  8   c  show sequential steps in formation of a stamped steel rocker subassembly  8 . Each low carbon steel rocker frame  28  is stamped from sheet stock in a series of forming operations that may include punching in the rocker pivot bearing holes  29  and initial roller pin holes  30 . Rocker flanges  13 , 14  are then carbonized to increase their hardness. Bronze pivot bearing insert  10  is then inserted into holes  29  and is held in place by assembly jigs (not shown) and fixed into permanent position in a copper brazing process  31 . In the next step ( FIG. 8   a ) of manufacture, bearing through-hole  32  for control shaft rocker pivot pin  9  and roller pin holes  30  are reamed to size and aligned with respect to the rocker flanges  13 , 14 . The final cam profiles  11 , 12  are ground onto the lower surfaces of rocker flanges  13 , 14 . A shaft spinning operation is employed to attach rocker roller  7 , needle bearings (not shown), and retaining pin  33 , providing a finished rocker sub-assembly  8  ( FIG. 8   c ).  
         [0051]     Engine cam  4  defines an input cam lobe to a valvetrain, and cam profiles  11 , 12  define a variable-output cam lobe of system  200  to RFF  18 .  
         [0052]     Referring now to  FIG. 4  and  FIGS. 9   a - c  and  10   a - b , the control shaft assembly  1  of assembly  200  can be assembled from individual, segments  34 , 35 , 36 , 37 , 38 , also referred to herein as control shaft sub-assemblies, to facilitate installation of the rocker sub-assemblies  8  and return springs  23 . As noted above, when all the forged steel segments are assembled, control shaft  1  defines a control crankshaft for system  200 . At three of the cylinder locations are modular unit-control shaft segments  35 , 36 , 37 , each comprising a slender control shaft rocker pivot pin  9 , a wider shoulder section  39 , and a pair of control arms  3 , 40  that straddle a head shank pin  26 . Control shaft assembly  1  is terminated at its ends by a drive end control shaft segment  34  and an actuator control shaft segment  38 , each of which has only one control shaft arm  3  and  40 , respectively. The drive end control shaft segment  34  also includes a control shaft rocker pivot pin  9  and a shoulder section  39 . All of the control shaft segments  34 - 38  contain diamond shaped, broached holes  41  for retention of the grounded end hooks  42  of return springs  23 .  
         [0053]     Prior to the final assembly of system  200 , the dual coils  43  of the helical, torsion return springs  23  are snapped in place over the closed middle section  44  and the pivot bearing insert  10  of each completed rocker sub-assembly  8  (see  FIG. 9   a ). During assembly of a control shaft sub-assembly, the pivot bearing insert  10  of each rocker subassembly  8  and a hardened steel collar  45  are slid over the control shaft rocker pivot pin  9 , while inserting one of the grounded end hooks  42  of each return spring into one of the broached holes  41  in the control shaft arms  3 . The rocker subassembly  8  and steel collar  45  are retained axially against each shoulder section  39  by a common, external type snap ring  46  and a matching groove  47  in the circumference of each control shaft rocker pivot pin  9 .  
         [0054]     At the free end of each control shaft rocker pivot pin  9  are machined flats  48 , 49  and a cylindrically shaped arched pocket  50  of radius R 1  (see  FIGS. 12 and 13 ). Correspondingly, and referring now to  FIGS. 10   a , 10   b , at the opposite end of the unit-control shaft segments  35 , 36 , 37  and the actuator control shaft segment  38  is a notched control arm  40 , complete with a mating arched flange  51  of radius R 1 , a blind, threaded hole  52  and an arm boss  53 . Centered in the arm boss  53  of each unit-control shaft segment  35 , 36 , 37  is a threaded, adjustment hole  54 . Also located in the free ends of the control shaft rocker pivot pins  9  for the drive end control shaft segment  34  and the first two unit-control shaft segments  35 , 36  are machined slots  55 . These permit rigid yet adjustable connections (see  FIGS. 10   b ,  11 , and  14   a - d ) between adjacent control shaft segments  34 - 37  permit individually setting the valve lift at each cylinder.  
         [0055]     The completed control shaft segment sub-assemblies  300  ( FIG. 9   c ) are bolted together (see  FIGS. 10   b  and  11 ). The arched flange  51  of the first unit-control shaft segment sub-assembly  300  is placed into the arched pocket  50  of the completed drive end control shaft segment  34 . A special, flanged head, clamping cap screw  56  feeds through a shaped washer  57  and the machined slot  55  of the drive end control shaft segment  34 , engaging the blind, threaded hole  52  in the notched control arm  40  of first unit-control shaft segment  35 . On the lower side of the clamping cap screw  56  head is a convex, spherical surface  58  that mates with a concave, spherical socket  59  ground into the top of each shaped washer  57 . These spherical surfaces (see  FIG. 10   a ) accommodate the upper flat  48  of the drive end control shaft segment  34  as it tilts relative to the axis of the clamping cap screw  56 , during cylinder-to-cylinder valve lift adjustments.  
         [0056]      FIG. 12  details a cross-section at the first joint of control shaft rocker pivot pin  9  to the notched control arm  40 . The hex head, adjuster cap screw  60  is threaded through a standard, thin series, hex head jam nut  61  and the threaded, adjustment hole  54  in the arm boss  53 . This adjuster cap screw  60  includes a convex, spherical tip  62  that rests against the machined flat  49  on the side of the drive end control shaft segment  34 . Whenever the flanged head, clamping cap screw  56  is loosened for cylinder-to-cylinder valve lift adjustments, clockwise rotation of the adjuster cap screw  60  causes the spherical tip  62  to push the machined side flat  49  of the drive end control shaft rocker pivot pin  9  away from the arm boss  53  of the first unit-control shaft segment  35 , resulting in a slight angular shift between these adjacent control arm segments.  
         [0057]     After lift adjustment, the clamping cap screw  56  and jam nut  61  are tightened to lock the control shaft rocker pivot pin  9  of the drive end control shaft segment  34  to the first unit-control shaft segment  35 , and the adjuster cap screw  60  in its arm boss  53 , respectively. Connections between the next two, control shaft rocker pivot pins  9  and notched control arms  40  are similar.  
         [0058]     The cross-section in  FIG. 13  illustrates the last connection of the control shaft rocker pivot pin  9  to a notched control arm  40  between the third unit-control shaft segment  37  and the actuator control shaft segment  38 . Since this connection does not require valve lift adjustments, it is different from the others. Here, an ordinary, flanged head cap screw  63  passes through a round clearance hole  64  in the free end of the cylinder  4  control shaft rocker pivot pin  9  and anchors into the blind threaded hole  52  of the last notched control arm  40 . This is followed up with a second short flanged head cap screw  65  that feeds through another clearance bolt hole  66  centered in the final arm boss  53  and engages a threaded hole  67  in the side flat  49  of the last control shaft rocker pivot pin  9 .  
         [0059]     A novel feature of a VVA system in accordance with the invention is that the control shaft assembly  1  is inherently biased toward the idle, or low load, position by the return springs  23 . This can best be seen in  FIGS. 2   a  and  2   b . Regardless of control shaft  1  load position or cylinder number, each helical torsion return spring  23  is always forcing the rocker subassembly  8  to maintain vital contact between each rocker roller  7  and its cam lobe  4  on the input camshaft  2 . Likewise, since return springs  23  are grounded through their end hooks  42  to the control shaft assembly  1 , instead of into the cylinder head as in the prior art, they also tend to rotate the control shaft arms  3 , 40  in a clockwise direction relative to the locations of their line-bored shank pins  25 , 27  in the cylinder head. As a result, at low engine speeds where inertia forces are not a concern, the control shaft electromechanical actuator (not shown) needs only to provide torque at the actuator end shank pin  27  in the counterclockwise direction to maintain a desired valve lift.  
         [0060]     System  200  utilizes this inherent control shaft biasing to facilitate minute valve lift adjustments that are required to equalize low engine speed, light load, cylinder-to-cylinder gas flows in gasoline or Diesel applications.  FIGS. 14   a - d  convey a unique lift adjustment scheme that system  200  provides for such applications, as follows.  
         [0061]     After a cylinder head has been assembled with system  200 , the engine manufacturer has several options to balance the cylinder-to-cylinder gas flow. The system flow balancing scheme provides the engine manufacturer a unique flexibility to choose the best method to fit its needs. Gas flow can be adjusted either on an individual cylinder head in a flow chamber environment, or on a completed running engine.  
         [0062]     Assembly line calibration can be carried out on an automated test stand, with either a precision air flow rate meter for calibrating individual completed cylinder heads or with a bench type combustion gas analyzer for calibrating fully assembled engines. For balancing individual cylinder heads, lift can be adjusted either statically to match a desired steady-state, steady flow rate target with the camshaft fixed, or dynamically with the camshaft spinning, by measuring the time-averaged flow rate for each cylinder. However, system  200  can also be adjusted dynamically in a repair garage with a running engine, using cylinder-to-cylinder exhaust gas analysis techniques with a portable fuel/air ratio analyzer.  
         [0063]     In the following adjustment procedure, it is assumed that a common, in-line  4  cylinder head (as shown in  FIG. 4  or  14   a - d ) requires cylinder-to-cylinder intake air flow calibration. In either of the above scenarios, the balancing would start at cylinder  4  ( FIG. 14   a ) and proceed sequentially down through cylinder  1  ( FIG. 14   d ). At cylinder  4 , under closed-loop control, the actuator voltage is varied until the angular position of the entire control shaft assembly  1  causes either the airflow or the Fuel/Air (F/A) ratio at cylinder  4  to match a target value. Once the flow rate or F/A ratio falls within a desired bandwidth at cylinder  4 , the actuator position is recorded through a system position sensor (not shown) and maintained steadily from that point on. Note that while adjusting cylinder  4 , all five control shaft segments  34 - 38  will rotate together, and that the actuator effectively “sees” the combined holding torque for all four cylinders.  
         [0064]     Next, at cylinder  3  (see  FIG. 14   b ), the adjuster jam nut  61  at the adjuster cap screw  60  and the clamping cap screw  56  between cylinders  3  and  4  are loosened slightly. While maintaining the same actuator position previously identified at cylinder  4 , the adjuster cap screw  60  between cylinders  3  and  4  is rotated either clockwise or counter-clockwise, as required, to adjust the intake valve  5  flow rate for cylinder  3 . Rotating the adjuster cap screw  60  will cause the drive end control shaft segment  34  for cylinder  1  and the unit-control shaft segments  35 , 36  for cylinders  2  and  3  to rotate relative to the unit-control shaft segment  37  for cylinder  4  by pushing against the ground side flat  49  at the free end of the cylinder  3  control shaft rocker pivot pin  9  and the resistance presented by the return springs  23  for cylinders  1 ,  2  and  3 . When cylinder  3 &#39;s airflow or F/A ratio falls within the desired bandwidth for the target, the clamping cap screw  56  and adjuster jam nut  61  are tightened to lock in the cylinder  3  adjustment.  
         [0065]     In a similar fashion, the above adjustment procedure is repeated at cylinders  2  and  1  (see  FIGS. 14   c  and  14   d , respectively), in that order, by first loosening the appropriate adjuster jam nut  61  and clamping cap screw  56 , turning the adjuster cap screw  60  to meet the flow rate bandwidth and then, tightening the adjuster jam nut  61  and clamping cap screw  56 .  
         [0066]     The flow adjustment resolution of the system is fine enough to balance the cylinder-cylinder airflow at an engine idle condition. One revolution of the adjuster cap screw  60  produces approximately a 0.2 mm change in valve lift. Preferably, a total adjustment range of about ±0.3 mm is provided at each joint.  
         [0067]     The beauty of this adjustment scheme is the way in which the control shaft assembly  1  continues to reflect the total torque applied by the return springs  23  at each cylinder, at all times during the adjustment procedure. In other words, the adjustment procedure inherently compensates for any natural twisting or deflection of the control shaft assembly  1  due to the load applied by the return springs  23 .  
         [0068]     After the adjustments are completed at cylinder  1 , then the automated stand can check to see that all cylinders are meeting their targeted flows. If any cylinder is off the target, a portion or all of the procedure can be repeated.  
         [0069]     Referring now to  FIG. 15 , a complete improved valvetrain assembly  300  is shown for an inline bank of four cylinders having an intake camshaft and an exhaust camshaft, and having two intake valves and two intake roller finger followers for each cylinder, and having two exhaust valves and two exhaust roller finger followers for each cylinder, wherein a first VVA system  200   a  is incorporated in the intake valvetrain  400   a  and a second VVA system  200   b  in incorporated in the exhaust valvetrain  400   b.    
         [0070]     While the invention has been described by reference to various specific embodiments, it should be understood that numerous changes may be made within the spirit and scope of the inventive concepts described. Accordingly, it is intended that the invention not be limited to the described embodiments, but will have full scope defined by the language of the following claims.