Abstract:
A variable valve actuation system having a crank-based eccentric transmission driven by an electric motor to control valve lift, duration, and phasing in the cylinder head of an internal combustion engine. A rocker sub-assembly for each valve is pivotably disposed on a pivot shaft between the camshaft and the roller finger follower roller. A primary control crankshaft includes the pivot shaft and is itself rotated about its axis by a connecting rod driven by a motorized secondary crank mechanism to displace the rocker sub-assembly pivot shaft along an arcuate path to change the angular relationship of the rocker sub-assembly to the camshaft, thus changing the valve opening and closing timing and valve lift.

Description:
RELATIONSHIP TO OTHER APPLICATIONS AND PATENTS 
       [0001]    The present application is a Continuation-In-Part of a pending U.S. patent application Ser. No. 11/294,223, filed Dec. 5, 2005, and published as US Patent Application Publication, No. US 2007/0125329 A1. 
     
    
     TECHNICAL FIELD 
       [0002]    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 (SVVA) interposed between the engine camshaft and the valve train cam followers to vary the timing and amplitude of follower response to cam rotation, wherein the SVVA is variably positioned by a crank mechanism, preferably an electromechanical eccentric variable valve actuation transmission (EVVAT). 
       BACKGROUND OF THE INVENTION 
       [0003]    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 one or both of the intake and exhaust 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. 
         [0004]    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 countries dependent on a gasoline-based transportation economy. 
         [0005]    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 as 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, thereby reducing turbo lag. Exhaust VVA can also be used to expand the range of engine operation wherein 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. 
         [0006]    VVA devices for controlling the timing of poppet valves in the cylinder head of an internal combustion engine are well known. 
         [0007]    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. 
         [0008]    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 is 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. 
         [0009]    A shortcoming of these two 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. 
         [0010]    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 provide a return spring stiff enough for high-speed engine operation that can still fit in the available packaging space. 
         [0011]    Still another shortcoming is that assembly and large-scale manufacture of such an SSCR device would be difficult at best with its large number of parts and required critical interfaces. 
         [0012]    U.S. Pat. No. 6,997,153 discloses a drive system for continuously changing lift characteristics of the charge-cycle valves while the engine is in operation. The drive consists of a housing, a cam, an intermediate element, and a valve-actuating output element. The cam is mounted in the housing, for example, in the cylinder head, in a turning joint and actuates the intermediate element which also is mounted in a turning joint in the housing. The intermediate element is connected to the output element via a cam joint formed at the contact point of the intermediate element, having a base circle portion (stop notch) and a control section, and the output element which may include a follower roller. The output element is also mounted in a turning joint in the housing and transmits motion to a valve stem. A change in valve lift characteristics is effected by changing the position of the cam joint or the output element turning joint via an eccentric element in the housing for both the intermediate element and the output element. 
         [0013]    No indication is provided of a practical structure for implementing this arrangement. However, significant manufacturing and control complexity would exist in providing for, and controlling the action of, eccentric control shafts for both the intermediate and output elements. 
         [0014]    Several prior art VVA innovations, such as is disclosed in U.S. Pat. No. 7,252,058, employ a movable control arm or carrier assembly to vary valve lift, duration, and phasing in a dependent manner at one or more banks of engine valves. 
         [0015]    U.S. Pat. No. 5,937,809 discloses carrier frame links pivoted via pairs of teeth between the carrier frames and a control shaft, running parallel to the camshaft. While this concept affects a nice linear relationship between the actuator control shaft and the carrier rotational positions, the gears are costly to make and present a backlash concern, given the oscillating nature of the mechanisms&#39; torque loads. 
         [0016]    In the variable valve timing mechanism disclosed in U.S. Pat. No. 6,019,076, the carrier frame elements are rotated through a pin, sliding bushing, and slotted fork arrangement. The slots are machined into the frame elements, slightly offset from the frame element pivot centers. The sliding bushings are pivoted on pins offset and parallel to the camshaft and control shaft. This arrangement requires careful grinding of the carrier slots to limit backlash, and the alignment of the control shaft pins is critical to ensure ease of assembly. Finally, inherent to any sliding bushings is a loss of actuation efficiency to compete with the fuel economy savings potential of the variable valve train mechanism itself. 
         [0017]    U.S. Pat. No. 7,252,058 discloses inclusion of a slotted fork into the drive control shaft and replacement of the sliding bushing with a roller connected to the armed frame carrier. While this approach eliminates the parasitic friction of the previous forked design, the apparatus still requires a costly grind of the slot to limit lash to an acceptable level. 
         [0018]    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, requires only a single angular control element, and requires minimal packaging space in an engine envelope. 
         [0019]    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 and/or exhaust valves. 
         [0020]    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. 
         [0021]    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 
       [0022]    Briefly described, the present invention provides a simple crank mechanism for transferring the rotary motion of an electric motor or similar actuator into useful motion to control the poppet valve lift profiles produced by a mechanical VVA system 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. Two such systems are required to accommodate both the exhaust and intake banks of valves. 
         [0023]    The SVVA comprises a hardened steel rocker subassembly for each valve (or valve pair) pivotably disposed in needle roller bearings on a pivot shaft disposed between the engine camshaft and the engine roller finger follower. A primary control crankshaft supports the pivot shaft for controlling a plurality of valve trains for a plurality of cylinders in an engine bank. The primary control crankshaft is itself rotated about its axis by a secondary crank mechanism having an eccentric motion to displace the rocker subassembly pivot shaft along an arcuate path and hence to change the angular relationship of the rocker subassembly to the camshaft, thus changing the valve opening, closing, and lift. Valve actuation energy still comes from a mechanical camshaft that is driven from the engine by a belt or chain, and the electrical eccentric actuator receives its energy from the engine&#39;s alternator. 
         [0024]    The present invention improves on the SVVA system disclosed in the pending parent U.S. patent application Ser. No. 11/294,223, filed Dec. 5, 2005 in the following way. 
         [0025]    In the parent invention, the rocker sub-assembly positioning primary crankshaft is rotated directly by attachment to an electric motor with or without an intervening transmission. Prevention of lash requires an inefficient worm gear transmission. 
         [0026]    In the present invention, the primary crankshaft is rotated by a secondary crank mechanism, preferably in the form of an eccentric transmission attached to the SVVA&#39;s control shaft arms. The eccentric actuator positively rotates the primary control crankshaft without lash and eliminates torque loads transferred back to the actuator at the two end states (highest and lowest valve lift) of the VVA system&#39;s operation by placing those states at the top dead center and bottom dead center positions of crank eccentricity where virtually no actuation force is required to maintain the position of the rocker sub-assembly. 
         [0027]    Compared to prior art devices, an important advantage of the SVVA is its simplicity. The input and output oscillators of prior art continuously variable valvetrain devices, such as the SSCR and the DCDVVT, have been combined into one moving part. Due to its inherent simplicity, the SVVA differs significantly from the original SSCR device in its assembly procedure for mass production. With only one oscillating member per cylinder, 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 is the case with these other mechanisms, but rather is supported on an engine head by its own arbors and journals, and therefore is not parasitic on the camshaft. Because there are fewer mechanical 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. 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 
         [0028]    The present invention will now be described, by way of example, with reference to the accompanying drawings, in which: 
           [0029]      FIG. 1   a  is an elevational drawing of a valvetrain equipped with the variable valve actuation system described in the parent application, showing the variable valve actuation system in maximum lift position and the valve in the fully closed position; 
           [0030]      FIG. 1   b  is a drawing like that shown in  FIG. 1   a , showing the variable valve actuation system in maximum lift position and the valve in the fully open position; 
           [0031]      FIG. 2   a  is a drawing like that shown in  FIG. 1   a , showing the variable valve actuation system in minimum lift position and the valve in the fully closed position; 
           [0032]      FIG. 2   b  drawing like that shown in  FIG. 2   a , showing the variable valve actuation system in minimum lift position and the valve in the fully open position; 
           [0033]      FIG. 3  is an isometric drawing of four valvetrains for a four-cylinder engine bank, each of the valvetrains being equipped with the variable valve actuation system described in the parent application linked together; 
           [0034]      FIG. 4  is a graph showing a family of lift curves for a valvetrain equipped with the variable valve actuation system as shown in  FIG. 3 , the curves being bounded by maximum lift of the apparatus shown in  FIGS. 1   a  and  1   b , and by minimum lift of the apparatus shown in  FIGS. 2   a  and  2   b;    
           [0035]      FIG. 5  is an isometric view of a module of a variable valve actuation system having a crank-based actuation transmission in accordance with the present invention, arranged for parallel operation of dual valves for a single engine cylinder; 
           [0036]      FIG. 6   a  is a schematic cross-sectional view of the system shown in  FIG. 5  with the system at full valve lift; and 
           [0037]      FIG. 6   b  is a schematic cross-sectional view of the system shown in  FIG. 5  with the system at minimum valve lift. 
       
    
    
       [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]    Referring to  FIGS. 1   a  through  3 , an exemplary prior art mechanical system for variable valvetrain actuation (SVVA), substantially as disclosed in pending U.S. patent application Ser. No. 11/294,223, filed Dec. 5, 2005 is shown. In  FIGS. 1   a , 1   b , 2   a , 2   b , 5 , 6   a , and  6   b , only the components required for one cylinder&#39;s worth (one module) of an internal combustion engine are depicted. As shown in  FIG. 3 , for adjacent cylinders within an engine&#39;s cylinder head, additional modules  200  are placed and connected end-to-end by a carrier shaft primary crank assembly to provide variable valve timing control for all cylinders within the head. 
         [0040]    High lift valve events with full duration are produced by the prior art SVVA mechanism  100  whenever its carrier shaft rocker pivot pins  1  are positioned as far as possible away from the input camshaft  2 , as indicated in  FIGS. 1   a  and  1   b.    
         [0041]    In operation, as the input camshaft  2  rotates clockwise, the opening flank  3  of the cam lobe  4  pushes the rocker roller  5  away, causing the rocker subassembly  6  to rotate in a clockwise direction. As the rocker subassembly  6  rotates, it turns about one of the carrier shaft rocker pivot pins  1  of the lift carrier shaft assembly  7 , which are located at each of the engine&#39;s cylinders (not shown). A mating babbit or needle pivot bearing insert  8  facilitates the rotation of rocker subassembly  6 . 
         [0042]    Clockwise rotation of rocker subassembly  6  advances the output cam profiles  9 , 10  ground onto rocker flanges  11 , 12  to where the radius of the output cam opening flank  13  increases beyond that of the base circle portion  14  of the cam profile. The further that rocker subassembly  6  is rotated clockwise about the carrier shaft rocker pivot pin  1 , the greater the lift imparted through the finger follower rollers  15 . The left end of each finger follower  16  pivots about the ball shaped tip  17  of a conventional hydraulic valve lash adjuster  18  mounted in the engine head. Pushing downward on the centrally located finger follower roller  15  imparts lift to an engine valve  19  via the curved pallet surface  20  at the right end of finger follower  16 . 
         [0043]    When the carrier shaft assembly  7  is in the full lift position, as shown in  FIGS. 1   a , and  1   b , maximum lift of engine valves  19  is reached whenever the rocker roller  5  reaches the nose portion  21  of the input cam  2 . At this point, the rocker subassembly  6  ceases movement in the clockwise direction. As the input cam lobe  4  rotates still further in the clockwise direction, the nose portion  21  of the camshaft  2  slips past the rocker roller  5 , and a helical torsion return spring  22  forces the rocker subassembly  6  to rotate counter-clockwise. This counter-clockwise rotation, in turn, reduces valve lift produced by the output cam profiles  9 , 10  and the finger follower rollers  15 . 
         [0044]    Eventually, as camshaft  2  continues to rotate clockwise, the rocker roller  5  reaches the constant radius portion  23  of the input cam lobe, where lift remains at zero until the next engine event occurs for that cylinder. The motion described above produces a peak lift profile  102  ( FIG. 4 ) to maximize gas flow to the engine. 
         [0045]    Short shank pins  24  of the carrier shaft assembly  7  ride in matching holes (not shown) bored through the engine&#39;s camshaft bearing towers which are integral to the cylinder head. Rotation of the carrier shaft assembly  7  about the center of these holes will vary engine load. Note that the carrier shaft shank pin axes  25  coincide with the finger follower roller axes  26  whenever they are on the base circle portions  14  of the output cam profiles  9 , 10 , as shown in  FIGS. 1   a  and  2   a.    
         [0046]    Note further that carrier shaft assembly  7  defines, and is synonymously referred to herein as, a primary crank mechanism (PCM)  7  for varying the position of rocker sub-assembly  6 . 
         [0047]    Referring to  FIGS. 1   a ,  1   b ,  2   a  and  2   b , if the PCM  7  is rotated clockwise through about 20° from its full load position, the mechanism produces progressively lower lift events with reduced duration (see  FIG. 4 ). In the full 20° rotation position ( FIGS. 2   a  and  2   b ), the carrier shaft rocker pivot pins  1  are in their closest proximity to the input camshaft  2 . 
         [0048]    Likewise, when the PCM  7  is in the light load position ( FIGS. 2   a  and  2   b ), the finger follower roller  15  spends most of its time on the base circle portion  14  of the output cam profiles  9 , 10 , just barely reaching the opening flank  13  of the profile, whenever the rocker roller  5  is aligned with the nose portion  21  of the input camshaft  2 . Thus, the SVVA mechanism produces progressively shorter and shallower lift events, which minimize gas flow to the engine, culminating in lowest-lift profile  104  ( FIG. 4 ). Varying the PCM  7  between the full load position first illustrated and the minimum load position described above produces the remaining lift curves within the family, as depicted in  FIG. 4 . 
         [0049]    Referring to  FIGS. 5 ,  6   a , and  6   b , a secondary crank mechanism (SCM)  27  is shown for actuating the SVVA mechanism  300 . A presently preferred SCM  27 , also referred to synonymously herein as an EVVAT, comprises a pair of connecting rods  29  pivotably linked to each pair of SVVA control shaft arms  31  by a connecting rod pin  28 . Each connecting rod  29  is provided with a circular opening at the outer end  40  thereof defining a bearing journal for a circular lobe  32  integral to an actuator control shaft  33  eccentrically attached to lobe  32  and driven preferably and conventionally by an electric motor (not shown). Large diameter section  36  separates each pair of lobes  32  axially along actuator control shaft  33 . Smaller diameter sections  34  ride in bearing journals also bored into the cylinder head&#39;s camshaft towers  35 , and the larger diameter sections  36  serve to separate the lobe pairs  32 . Preferably, babbit or needle bearing inserts  37 , 38  are provided at each end of each connecting rod  29  to facilitate rotating motion at the smaller connecting rod pin ends  39  and at the larger outer ends  40 . 
         [0050]    It will be seen that a lobe  32  and eccentrically-positioned actuator control shaft  33  define SCM  27 , and that any analogous crank mechanism is comprehended by the present invention. The EVVAT crank mechanism just described is the presently preferred embodiment of a generic crank-based SCM  27  wherein the actuator control shaft  33  is a crank shaft and the lobe  32  is a crank throw. EVVAT  27  is a specialized case wherein the crankshaft axis of rotation  43  lies within the cross-sectional area of the crank throw. This arrangement provides a desirably large bearing surface between the crank throw and the connecting rod for absorbing torque reversal forces emanating from the engine&#39;s camshaft. 
         [0051]    By optimizing the offset radius  41  of the actuator control shaft eccentrics  32 , the position of the connecting rod pin  28  and the length of the connecting rods  29 , an actuator shaft rotation of between about 160° and 175° can be provided to increase the limited rotational capability (˜20°) inherent in the prior art SVVA carrier shaft arms  31 . 
         [0052]    Moreover, the end positions of the eccentrics&#39; motion can be designed to coincide with the points where the axes  42 , 43 , 44  of the connecting rod pin, actuator control shaft, and center of the eccentric radius, respectively, are collinear. Furthermore, when the two end states of the eccentrics&#39; motion are arranged to correspond to full and minimum valve lifts, unwanted torque pulses cannot be transferred back to the actuator. 
         [0053]    For example, as shown in  FIG. 6   a , the center of an EVVAT eccentric radius  44  is collinear with the connecting rod pin axis  42  and the actuator control shaft axes  43 , but farthest away in its motion (SCM  27  Top Dead Center, or TDC) from the input camshaft  2 , yielding highest lift in the SVVA system, since the carrier shaft rocker pivot pin  1  is also in its farthest position from the camshaft  2 . As the actuator control shaft  33  is rotated clockwise from this position, the connecting rods  29  apply forces to push the SVVA&#39;s carrier shaft arms  31  closer to the camshaft  2 . In  FIG. 6   b , rotation of actuator control shaft  33  has continued until the axes  42 , 43  of the connecting rod pin and the actuator control shaft are collinear with the eccentric center  44  (SCM  27  Bottom Dead Center, or BDC), but now the eccentric center  44  lies between them, and the carrier shaft rocker pivot pin  1  is closest to the camshaft  2 , in its lowest lift position. 
         [0054]    As shown in the end states of the eccentrics&#39; motion ( FIGS. 6   a  and  6   b ), with the important centers aligned as described above, the effective gear ratios are infinite. Careful optimization of the EVVAT arrangement can yield a useful range of effective gear ratios looking forward from the actuator control shaft ( 33 ) to the SVVA mechanism  100 . Given today&#39;s internal combustion engine&#39;s packaging constraints, and a proper design, approximately mid-stroke through the eccentrics&#39; travel can correspond to a minimum gear ratio as high as 7:1. Typically, the camshaft torque reversal forces encountered within the SVVA mechanism are their highest when it is in its full lift position. With the centers aligned as described above in the full lift end state of the SCM EVVAT crank system (as in  FIG. 6   a ), resulting forces transmitted through the connecting rods  29  are perpendicular to the actuator control shaft  33  and are directed through the actuator control shaft axis  43 ; thus, virtually no actuator torque is required to maintain this position. This is highly desirable from the standpoint of electric motor size and power consumption, and is an important and novel benefit of the present invention. 
         [0055]    Although the SVVA mechanism forces are typically at their lowest when in the BDC minimum lift position ( FIGS. 2   a ,  2   b , and  6   b ), having an infinite gear ratio is desirable for yielding the highest possible actuator/lift resolution. 
         [0056]    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.