Abstract:
The epicyclical drive incorporates a dual flywheel carrying a pinion in a balanced axially compact assembly. The assembly includes a counterweight for the pinion nested between the flywheels, which also connects the flywheels and transfers loading conditions therebetween, to reduce and distribute torsional and eccentric loading conditions and reduce vibrations. The use of a second flywheel also provides an improved rotary seal capability for keeping out dust, debris and moisture. The drive is adapted for incorporation into a floor of a header of an agricultural harvesting machine for reciprocatingly driving a sickle thereof, advantageously jointly with a mirror image companion drive in a side by side relationship and timed such that forces generated by the reciprocating actions are cancelled.

Description:
TECHNICAL FIELD 
     This invention relates generally to an epicyclical drive incorporating a dual flywheel and pinion assembly in a counterbalanced axially compact arrangement, which reduces torsional and eccentric loading and vibrations during operation and provides an improved seal, and which is particularly well adapted for incorporation into a floor of a header of an agricultural harvesting machine for driving the sickle thereof. 
     BACKGROUND ART 
     Epicyclical drives are noted for their utility for converting rotary motion to reciprocating linear motion, in a variety of applications, notably, sickles. Sickles are commonly used on agricultural plant cutting machines, particularly on the headers of combines, windrowers and other harvesting machines. Such sickles typically include cutter bars supporting a row of knives, have been used to cut plants, including, but not limited to, hay, grasses, small grains and the like. 
     The knives are composed of a plurality of knife or sickle sections which are mounted in side by side relation forming an elongate metal knife assembly. The elongate knife assembly is normally supported so as to slide longitudinally along an elongate stationary bar that has forwardly projecting, spaced apart guards bolted to a structural beam. The knife assembly moves back and forth in a reciprocating movement to move the knives relative to the guards so that the leading knife edges of the knives cross over the guards or through slots in the guards. This produces a shearing or cutting action which severs plant stems and stalks or other material captured between the knives and the guards. 
     In a harvesting machine, such as a combine or windrower, the knife assembly and stationary bar are typically supported in connection with a cutting head or header and are oriented so as to extend sidewardly along a forward edge portion of structure such as a floor or pan of the header, hereinafter sometimes referred to generally as the floor. The floor or pan defines the lower periphery of a cut crop or plant flow area, which can include conveying apparatus, such as one or more augers or belts, operable in cooperation with a reel in machines so equipped, for conveying the cut plant material and crops, for instance, to a feeder inlet of a combine or windrow forming apparatus of a windrower. 
     The knife assembly is driven reciprocatingly longitudinally by an oscillating drive, which can include, but is not limited to, an eccentric shaft on a rotating hub, a wobble drive, an epicyclical drive, or a similar well known commercially available device. Reference in regard to known epicyclical drives, Regier et al., U.S. Pat. No. 7,121,074, issued Oct. 17, 2006 and entitled Balanced Epicyclic Sickle Drive. Such drives typically have a large axial extent, which in this context is vertical, and thus by necessity are located at the sides of the header, and drive the knife assembly from the end. This location is advantageous as it allows the driving point for the knife assembly to be in line with the stationary bar, provides clearances for removal of the knife assembly, and provides space for assembly of the drive. Disadvantages of the side location include that the header must include significant frame structure for supporting the drive and to withstand forces and vibrations generated thereby. The end structure or crop divider at the end of the header must also be relatively wide, to accommodate the drive and to direct adjacent standing crops therepast, and increasing the possibility of unavoidably pushing over adjacent standing crops. Additionally, for headers utilizing two drives located on opposite sides of the header, it is usually desired to time the operation of the drives such that the forces and vibrations generated by the respective drives and reciprocating knife assemblies cancel one another. This typically involves relatively long mechanical drive lines connecting the two drives together, which is disadvantageous as it adds weight, cost and complexity. 
     The vertical axis epicyclical drive of U.S. Pat. No. 7,121,074 referenced above uses a large rotating counterweight in an attempt to counterbalance the knife assembly driven thereby, but the knife assembly travels in only the side to side direction, and thus requires only counterbalancing in those directions, whereas the large counterweight rotates eccentrically through a circular swing arc, and thus introduces eccentric loads in the other directions, most notably the fore and aft directions. Additionally, as the weight of the knife assembly is increased, e.g., for a longer sickle, the counterbalance must be correspondingly increased, which increases the fore and aft eccentric loading condition. 
     To illustrate the magnitude of the vibrational challenges associated with eccentric loading conditions generated by sickle drives, a knife assembly will weigh at least 30 pounds for a typical 20 foot wide header, and typically must accelerate and decelerate two times per cycle as a result of the reciprocating movement. A typical speed for the knife assembly is up to about 16 hertz or cycles per second. Thus, it can be seen, the reciprocating motion at a high cycle per second generates high acceleration values and high deceleration values that in turn generate high forces on the structural components. These high forces can have at least two negative effects, vibration at and within the drive system that may be transmitted to other components of the machine, and torsional and vibration related failure of the structural components of the drive itself, and also the seals thereof. To compound the seal failure problem, operation of plant cutting machines typically generates substantial dust and plant fragments that can rapidly damage seals and infiltrate the drive to cause failure thereof. 
     Driving a knife assembly or assemblies of a header from a more central location, such as the center of the header, would provide several advantages compared to a side location. Notably among these advantages, the header structure, typically supported at the center, would not be required to support heavy drive units on one or both sides, such that the structure of the header could be lighter. Long timing apparatus extending between the ends could also be eliminated. If the drive mechanism is incorporated into a location that would not interrupt or require dividing crop or plant material flow through the crop flow area of the header, the normal crop flow of the header is not be significantly impacted. And, since the drives are not located in the ends, the end dividers can be made significantly thinner, such that the header can have a shorter overall width, would be more easily maneuverable in relation to adjacent standing crop, and danger of downing the adjacent standing crop would be reduced. Additionally, it has been found that by driving two knife assemblies in opposite directions from a location between the two assemblies, the forces generated by the opposite reciprocating movements of the assemblies translated to the frame of the header can be largely cancelled, essentially leaving only the vibrational loads generated by the drives themselves to be dealt with. 
     Thus, what is sought is an epicyclical drive adapted for a sickle of a header of an agricultural cutting machine, such as a combine or windrower, which provides at least one of the advantages, namely, a compact axial extent and low eccentric loading and vibrations, and which overcomes one or more of the problems, negative effects, and disadvantages, referenced above. 
     SUMMARY OF THE INVENTION 
     What is disclosed is an epicyclical drive adapted for a sickle of a header of an agricultural cutting machine, such as a combine or windrower, which provides at least one of the advantages, namely, a compact axial extent and low eccentric loading and vibrations, and which overcomes one or more of the problems, negative effects, and disadvantages, referenced above. 
     According to a preferred aspect of the invention, the epicyclical drive includes a generally flat housing or frame including a ring gear extending around a passage through the frame and defining a central axis through the passage, the passage having a first axial end and a second axial end opposite the first axial end. The drive is configured to be axially compact, and includes a dual flywheel and pinion assembly including a first flywheel supported on the housing or frame adjacent to the first axial end of the passage for rotation about the central axis, and a second flywheel supported on the frame adjacent to the second axial end of the passage for rotation about the central axis in coaxial relation to the first flywheel. The drive includes a pinion shaft extending through the passage and supported by the first flywheel and the second flywheel eccentric to the central axis for rotation about an eccentric axis parallel to the central axis, the pinion shaft carrying a pinion gear for rotation therewith enmeshed with the ring gear such that rotation of the flywheels about the central axis will cause the pinion gear to rotate about the eccentric axis. And, the drive includes a counterweight carried by and between the flywheels in the passage for eccentric rotation about the central axis in a manner to at least partially counterbalance the pinion shaft and the pinion gear when rotating. 
     To facilitate the axial compactness, the flywheels are preferably relatively flat, disk shaped members located just above and below the flat frame. And because the flywheels are both supported by the frame, and, in turn, support the pinion therebetween for eccentric rotation, counterbalanced by the counterweight, any significant eccentric and torsional loading conditions generated by these components are eliminated or reduced to a non-consequential level. 
     According to another preferred aspect of the invention, to drive a sickle, the pinion shaft is connected in reciprocatingly driving relation to a knife assembly of the sickle, by a drive assembly configured and operable for translating the eccentric rotation of the pinion shaft to a reciprocating back and forth motion of the knife assembly. 
     According to another preferred aspect of the invention, the second flywheel is disposed and configured so as to provide a sealed condition about the second axial end of the passage, to prevent entry of dust and debris such as plant fragments, and also moisture, into the inner workings, such as the ring and pinion gear mechanism. As another feature, the counterweight is connected to the flywheels by fasteners such as pressed fit pins, screws or bolts, or the like, to enable easy assembly and disassembly. 
     According to another preferred aspect of the invention, a second epicyclical drive constructed as a mirror image is provided in driving relation to a second knife assembly of the sickle, in oppositely timed relation to the first, such that vibrations generated by the reciprocating actions of the respective drives are cancelled by one another. According to still another preferred aspect of the invention, the first and second epicyclical drives are jointly driven by a drive element connected in driving relation to the flywheels for rotating the pinion shafts in the timed relation. This drive element can comprise, but is not limited to, input gears disposed about the radial outer peripheries of one of the flywheels of each of the respective drives, and a bevel gear arrangement including a gear enmeshed in driving relation with the input gears. 
     As still another preferred aspect of the invention, the epicyclical drive is adapted to be located beneath, or incorporated into, a floor or pan of a header of a plant cutting machine such as a combine or windrower, at a location spaced from the sides or ends of the header, such that cut crops or other plant material can flow over and around the drive and not be obstructed thereby. 
     As an advantage of the invention, the dual flywheel and pinion assembly substantially eliminates eccentric and torsional loading conditions emanating from the internal mechanism of the drive to the header, and the vibrations and damage that can result. This feature, when combined with the use of dual drives timed to oppositely reciprocate the knife assemblies of the sickle, provides a greatly reduced vibrational output overall for smoother operation and reduced failure. In this regard, the dual flywheels are preferably connected together for joint rotation, e.g., using pinned connections, preferably through the counterweight, which enables side and torsional loads to be transferred or distributed through and between the flywheels, to reduce load concentrations on the flywheels individually and on the pinion. For instance, at least a portion of the drive forces exerted as side and torsional loads against the driven one of the flywheels are transferred through the connection directly to the other flywheel. And, portions of loads exerted by the reciprocating action of the knife assembly on the more proximal flywheel are transferred to the other flywheel through the connection, such that, overall, the dual flywheel and pinion assembly is robust and resistant to damage. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a forward end view of a combine including a header having an axially compact epicyclical sickle drive mechanism according to the present invention; 
         FIG. 2  is an enlarged fragmentary perspective view of the header of  FIG. 1 , showing the drive mechanism of the invention and aspects of the sickle; 
         FIG. 3  is an enlarged fragmentary top view of the header of  FIG. 1 , showing the drive mechanism and aspects of the sickle; 
         FIG. 4  is an enlarged perspective view of a dual flywheel and pinion assembly of a drive of the drive mechanism; 
         FIG. 5  is an enlarged top view of the dual flywheel and pinion assembly of  FIG. 4 ; 
         FIG. 6  is a sectional view of the drive mechanism, showing aspects of an epicyclical drive thereof, including the dual flywheel and pinion assembly thereof; 
         FIG. 6   a  is another sectional view of the drive mechanism, showing a pin connecting the dual flywheels and counterweight thereof; 
         FIG. 6   b  is another sectional view of the drive mechanism, showing a screw connecting the dual flywheels and counterweight thereof as an alternative to the pin; 
         FIG. 7  is another sectional view of the drive mechanism, showing aspects of a drive element thereof for simultaneously driving the epicyclical drives thereof; 
         FIG. 8  is an exploded view showing aspects of an epicyclical drive of the drive mechanism; 
         FIG. 9  is a perspective view showing aspects of one of the dual flywheel and pinion assemblies of the drive mechanism, showing installation of the pinion thereof; 
         FIG. 10  is a forward end view of a combine including a header having multiple axially compact epicyclical sickle drives according to the present invention; and 
         FIG. 11  is a fragmentary top view of a combine, with a portion of a draper belt of a header of the combine removed to reveal one of the epicyclical sickle drive mechanisms of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Turning now to the drawings wherein several preferred embodiments of the invention are shown, in  FIG. 1 , a conventional, well known agricultural cutting machine, which is a combine  20 , is shown including a header  22 . Header  22  is shown supported in the conventional, well-known manner on a forward end  24  of combine  20 , and is operable for cutting or severing crops such as, but not limited to, small grains such as wheat and soybeans, and inducting the severed crops into a feeder  26  for conveyance into combine  20  for threshing and cleaning, in the well known manner, as combine  20  moves forwardly over a field. Header  22  includes a pan or floor  28  which is supported in desired proximity to the surface of the field during the harvesting operation, and an elongate, sidewardly extending sickle  30  along a forward edge portion  32  of floor  28 , sickle  30  being operable for severing the crop for induction into header  22 , as will be explained. Header  22  additionally includes an elongate, sidewardly extending reel  34  disposed above sickle  30  and rotatable in a direction for facilitating induction of the severed crops into header  22 . An elongate, rotatable auger  36  (shown in outline form in  FIG. 1 ) that extends in close proximity to a top surface  38  of floor  28  and has helical flights therearound (not illustrated) is operable in cooperation with reel  34  for conveying the severed crops toward an inlet opening of feeder  26  for induction into combine  20 , in the well-known manner. 
     Sickle  30  extends in a sideward direction along the width of floor  28 , between a first side edge portion  40  of the floor, and an opposite second side edge portion  42 . Sickle  30  includes an elongate, sidewardly extending first cutter bar assembly  44 , and an elongate, sidewardly extending second cutter bar assembly  46  extending in end to end relation to cutter bar assembly  44 , cutter bar assemblies  44  and  46  being supported in substantially longitudinally aligned relation adjacent to forward edge portion  32  of floor  28 . 
     Referring also to  FIGS. 2 and 3 , each of cutter bar assemblies  44  and  46  supports and restrains an elongate knife assembly  48  for reciprocating longitudinal movement, each knife assembly  48  including a row of knife sections including oppositely facing, angularly related knife edges  50 , which, in conjunction with adjacent guards  52 , effects a shearing or cutting action which severs plant stems and stalks or other material captured between the knives and the guards as the knife sections are reciprocatingly moved sidewardly, as denoted by arrows A, all in the well known manner. 
     As noted above under the Background Art heading, it is desirable to reduce negative effects of the reciprocating sideward motion of knife assemblies  48 , including, but not limited to, vibration, fatigue failure, and the like, and also the disadvantages of known structures for effecting the motion, including the need for substantial structure for supporting drives on the sides of headers, the increased width of side dividers containing the drives, and apparatus for timing drives located on opposite sides of a header. It is also desirable to eliminate or substantially reduce eccentric and torsional loading conditions generated within the drives themselves which can be damaging to the drives and supporting structure, and transmit vibrations to the header and supporting machine, e.g., combine. 
     Reduction of the above discussed negative effects and disadvantages is achieved according to the present invention by utilizing an improved compact epicyclical drive mechanism  54  constructed and operable according to the teachings of the present invention for reciprocatingly driving knife assemblies  48 . 
     Epicyclical drive mechanism  54  is illustrated in  FIG. 1  at a location on header  22  between side edge portions  40  and  42  which is at about the center of header  22 , although it should be noted that it is contemplated that drive mechanism  54  could alternatively be utilized at other locations on a header such as header  22 , and that multiple drive mechanisms  54  could be used on a header, as described hereinafter and illustrated in  FIGS. 10 and 11 . 
     As shown in  FIGS. 2 and 3 , compact epicyclical drive mechanism  54  includes a first knife head driver element  56  in connection with the knife assembly  48  of first cutter bar assembly  44 , and a second knife head driver element  58  in connection with the knife assembly  48  of second cutter bar assembly  46 , knife head driver elements  56  and  58  being simultaneously operable by drive mechanism  54  for reciprocatingly driving the knife head assemblies  48  of respective cutter bar assemblies  44  and  46  sidewardly, as illustrated by arrows A, in timed relation so as to move in opposite sideward directions. That is, as knife assembly  48  of first cutter bar assembly  44  is moved in one sideward direction, knife assembly  48  of second cutter bar assembly  46  will be moved in the opposite sideward direction. The length of the sideward movements, or strokes, will be sufficient for providing the desired cutting action, which will typically be equal to about the sideward extent of a knife edge  50  of a typical knife section. First and second knife head driver elements  56  and  58  are preferably constructed of a sheet or cast metal bent or formed to a sectional shape about as shown, and are connected to knife assemblies  48  of the respective cutter bar assemblies  44  and  46  in a suitable manner, here using sidewardly extending elongate bars  60  on the forward ends of driver elements  56  and  58 , which connect to the knife assemblies  48  with suitable fasteners such as screws or the like. Here, it should be noted that it is desired for the knife assemblies  48  to move only in the sideward directions relative to guards  52 , and not forwardly, rearwardly, upwardly or downwardly to any significant extent relative thereto. Because driver elements  56  and  58  are rigidly connected with knife head assemblies  48 , respectively, driver elements  56  and  58  are also restricted to sideward movements only. 
     Compact drive mechanism  54  includes a first epicyclical drive  62  connected in driving relation to first knife head driver element  56 , and a second epicyclical drive  64  connected in driving relation to second knife head driver element  58 , epicyclical drives  62  and  64  being contained in a compact common housing  66  of drive mechanism  54 . 
     It is contemplated and preferred that compact drive mechanism  54  be incorporated in or beneath floor  28  of header  22 , in a manner such that cut plant material, particularly crops, cut by those portions of cutter bar assemblies  44  and  46  forwardly of drive mechanism  54  will be able to relatively smoothly and uninterruptedly flow over and around drive mechanism  54  onto floor  28 , and so as to subsequently be conveyed, for instance, by reel  34  and auger  36 , to the inlet of feeder  26  of combine  20 . To facilitate this, drive mechanism  54  is vertically compact, preferably having a vertical extent of no more than about six inches. It is also contemplated that drive mechanism  54  can be supported so as to float upwardly and downwardly with the cutterbar assemblies  44  and  46  as typical when harvesting grains, such as soybeans. Additionally, the apparatus of the invention can be configured for use with flexible sickles or cutter bars assemblies, as well as variable floor headers wherein the cutter bar assembly and possibly a leading edge of the floor is fore and aft movable relative to the more rearward region of the floor. 
     Knife assemblies  48  are preferably reciprocatingly driven in timed relation by the respective epicyclical drives  62  and  64  of mechanism  54  so as to move in opposite sideward directions, such that forces generated by the moving masses of the knife assemblies are at least substantially contained within the structure of the invention, thereby substantially reducing or eliminating transfer of vibrations to the structure of header  22 , and, from there to combine  20 . 
     Preferably, drives  62  and  64  are commonly driven, by, but not limited to, a fluid motor  68 . Fluid motor  68  is illustrated as being mounted to a rear end  70  of housing  66 . Fluid motor  68  is connected to a source of pressurized fluid and a fluid reservoir (not shown) on combine  20  in the conventional, well-known manner, via fluid lines  72  and  74  ( FIG. 3 ). This provides the power to first and second epicyclical drives  62  and  64 , which are configured to translate the power into the sideward reciprocating movements of first and second knife head driver elements  56  and  58 , and thus of knife assemblies  48 , as will be explained. Alternatively, drive mechanism  54  can be driven by an alternative power source, which can include, but is not limited to, a PTO shaft, or an electric motor, or other common driver such as a belt or chain or a combination of such drives. In either of the illustrated instances, the alternative power source can be connected in rotatably driving relation to drive mechanism  54  via an input shaft or other suitable manner of connection. Representative contemplated configurations of header  22 , sickle  30 , support apparatus for drive mechanism  54 , and alternative power sources, are disclosed and illustrated in detail in Priepke U.S. Pat. No. 7,520,118 B1, issued Apr. 21, 2009, hereby incorporated herein by reference in its entirety. 
     Referring also to  FIGS. 4 ,  5 ,  6 ,  6   a ,  7 ,  8  and  9 , aspects of drive mechanism  54  and drives  62  and  64  are shown to illustrate the features of the invention, namely, the vertical or axial compactness of the drives, as well as reduced eccentric and torsional loads and vibrations generated by operation of the drives, and an improved seal capability. In particular in this regard,  FIGS. 4 and 5  illustrate a balanced dual flywheel and pinion assembly  76  common to each of drives  62  and  64 . Each balanced dual flywheel and pinion assembly  76  includes a generally flat, disk shaped first flywheel  78 , and a similarly generally flat, disk shaped second flywheel  80 , connected together for coaxial, joint rotation about a central rotational axis  82  of the respective drive  62  or  64 . Here, it can be observed that flywheel  78  is larger than flywheel  80 , but assembly  76  is not limited to this configuration. Flywheels  78  and  80  carry a pinion shaft  84  therebetween for rotation eccentrically relative thereto, about an eccentric axis EA parallel to axis  82 . Flywheels  78  and  80  additionally carry a crescent shaped counterweight  86  therebetween, in eccentric offset and counterbalancing relation to pinion shaft  84  and a pinion gear  88  thereof ( FIGS. 6 ,  8  and  9 ). 
     Counterweight  86  of each dual flywheel pinion assembly  76  connects flywheels  78  and  80  of the assembly together for joint rotation about axis  82 , e.g., using fasteners  156  ( FIGS. 6   a ,  6   b ,  8  and  9 ) in a manner for also advantageously transmitting eccentric and torsional loads therebetween, including the driving or motive force for rotating the flywheel pinion assembly; the driving force of pinion shaft  84 ; and also eccentric loads generated by the translation of the rotational forces to the reciprocating action of the associated knife assembly, as will be explained. Also shown, is a puck bearing assembly in connection with pinion shaft  84  above dual flywheel assembly  76 , operable in connection with knife head driver element  56  or  58  ( FIGS. 2 and 3 ) for translating the eccentric rotations of the pinion shaft into the reciprocating actions of the associated knife assembly connected to driver element  56  or  58 . 
     Referring also more particularly to  FIGS. 6 ,  7 ,  8  and  9 , to power the drives  62  and  64 , first flywheel  78  of each of the drives  62  and  64  has a radial outer periphery comprising a flange  92  including an input gear  94  thereabout, enmeshed with a spur gear  96  of a compact common drive element  98 , preferably disposed between flywheels  78  and operable for simultaneously rotating them in opposite directions about their respective rotational axis  32 . Drive element  98  additionally includes a bevel gear  100  combined for joint rotation with a spur gear  96  on a common shaft, and which is enmeshed with a bevel gear  102  also of drive element  98 , providing a  90  degree drive capability. Bevel gear  102 , in turn, is located on an input shaft  104  connected to fluid motor  68  ( FIGS. 2 and 3 ), or other rotary power source for rotation thereby, e.g., PTO shaft, electric motor, etc. As a result, in operation, rotation of motor  68  (or other input) will rotate shaft  104  and gear  102 , to rotate gear  96 , which will rotate input gears  94  and flywheels  78 , and thus drives  62  and  64  in opposite directions. 
     Dual flywheel pinion assemblies  76  of drives  62  and  64 , as well as drive element  98 , are compactly contained within or on housing  66 . Housing  66  is a generally flat structure of unitary construction, preferably of cast or welded metal, and includes mounting lugs  106  positioned for attachment to a suitable structural element of header  22 . Here, such structure is a support arm  108  supporting a section of sickle  30 , and housing is mounted thereto by fasteners  110 , as shown in  FIGS. 2 and 3 , although it should be understood that other manners of support and attachment to the header could be used. 
     Within housing  66 , first flywheel  78  of each drive  62  and  64  is mounted for rotation about central rotational axis  82  of the drive, to a downwardly extending annular bearing flange  112  of housing  66 , which defines a downwardly facing round cavity. Flange  112  includes an inner circumferential bearing seat  114  into which a lower flywheel bearing  116  is suitably mounted and retained, for instance, using a snap ring  118 . Flywheel  78  includes an inner hub  120  disposed radially inwardly of outer flange  92  sized to be received in the downwardly open cavity and having an outer circumferential surface around which lower flywheel bearing  116  is retained, for instance, by a press fit, snap ring, or other suitable manner of mounting. Thus, lower flywheel bearing  116  is received in an annular space between outer flange  92  and hub  120 , such that outer flange  92 , bearing  116 , and inner hub  120  are concentric about rotational axis  82 . Installation of ring  118  can be accomplished, for instance, using one or more holes that can be provided through flywheel  78 , or in any other suitable manner. Hub  120  of flywheel  78  includes a hole  122  therein at a location offset from central rotational axis  82 , and through which eccentric axis EA extends, parallel to, but offset from rotational axis  82 . A bearing seat  124  extends around a portion of hole  122  and receives a lower pinion bearing  126  which is suitably retained in position by a retainer ring  128 , a press fit, or like. 
     The lower end of pinion shaft  84  is received in and supported by lower pinion bearing  126  for rotation relative to flywheel  78 , and extends upwardly through a central passage  130  extending through housing  66  and concentric about central rotational axis  82 , such that hub  120 , and thus flywheel  78 , serve as a carrier for the lower end of pinion shaft  84  disposed in or closely adjacent to a lower end of passage  130 . Flywheels  78  of the respective drives are disposed in timed relation to each other, such that eccentric axes EA, and thus pinion shafts  84 , will be in about 180 degree offset relation, essentially in the manner disclosed and illustrated in detail in Priepke U.S. Pat. No. 7,520,118 B1 incorporated herein by reference. This timed relationship facilitates the desired opposite reciprocating movements of the knife assemblies, in the manner as also illustrated and explained in U.S. Pat. No. 7,520,118 B1. 
     To translate the rotational movements of the drives into reciprocating movements of the knife assemblies, each of drives  62  and  64  includes a ring gear  132  fixedly mounted on or incorporated into housing  66  about the respective passage  130 , for instance, using pins  134 , press fit, or other fasteners. Pinion gear  88  of each drive is enmeshed with the ring gear  132  thereof, such that when flywheel  78  is rotated about central rotational axis  82 , pinion gear  88  will cause pinion shaft  84  to rotate therewith about eccentric axis EA, while circling or orbiting about central rotational axis  82 . Here, to facilitate and effect the timed relationship between pinion shafts  84 , the internal pitch diameter of ring gear  132  is preferably selected to be equal to twice the pitch diameter of pinion gear  88 , such that for each revolution of flywheel  78 , pinion shaft  84  and pinion gear  88  about central rotational axis  82 , pinion shaft  84  and gear  88  will be rotated two revolutions about eccentric axis EA, which will be translated into back and forth movements of the associated puck bearing assembly  90 , and thus the knife head driver element  56  or  58  connected thereto. 
     The upper end of pinion shaft  84  is supported for rotation about eccentric axis EA on second flywheel  80  by an upper pinion bearing  136  mounted in a bearing seat  138  in second flywheel  80 . Second flywheel  80 , in turn, is supported for rotation about rotational axis  82  by an upper flywheel bearing  140  mounted in a bearing seat  142  on housing  66  adjacent an upper end of passage  130 . The upper end of pinion shaft  84  extends a short distance above second flywheel  80  and fixedly connects to puck bearing assembly  90  in an eccentric relationship. A puck  144  of puck bearing assembly  90  is carried and rotatable within a bearing  146  thereof, which, in turn, is carried in a bearing seat  148  of the associated knife head driver element  56  or  58 . Each knife head driver element  56  and  58  includes a connecting arm  150  which extends forwardly therefrom to connect with the respective knife assembly  48 , and a torque arm  152  extending sidewardly therefrom and between a pair of rollers  154  mounted externally on the top surface of housing  66 . As a result, driver elements  56  and  58  are restrained for side to side movement only, and the eccentric rotations of pinion shafts  84  will translate to oscillations of pucks  146  within the respective driver element, to cause side to side reciprocating movements of the drivers and knife assemblies connected thereto, respectively, as more thoroughly explained in U.S. Pat. No. 7,520,118 B1. 
     As noted above, the eccentric motion of pinion shaft  84  about axis creates a side force or loading condition within each drive  62  or  64 . This is substantially countered or offset by counterweight  86  which is sized and shaped, e.g., crescent shaped, for this purpose, such that operation of the respective dual flywheel pinion assemblies  76  alone will generate only a low or no net side load. As explained above, the lower flywheel  78  is the driving input, and the driven load is connected to assembly  76  at the upper end of pinion shaft  84 , above flywheel  80 , such that both external side and torsional loads are distributed to and between both flywheels of assembly  76 . Counterweight  86  is preferably connected to both of the flywheels  78  and  80 , e.g., by fasteners  156  which pass through holes  158  in counterweight  86  and both flywheels, such as press fit pins as shown in  FIG. 6   a , or threaded bolts or screws as shown in  FIG. 6   b , for connecting those members together. This enables counterweight  86  to be supported by both flywheels (as is pinion shaft  84 ) for better counterbalancing effect, and it more positively transfers the driving force from flywheel  78  to flywheel  80  for joint rotation, and distributes the loading condition generated by the reciprocating action of the knife head drivers and knife assemblies through both flywheels. This also serves to reduce the loading conditions exerted on the pinion shaft and bearings, thus increasing the strength and robustness of the dual flywheel and pinion assemblies for better longevity and reliability, and allows easy assembly and disassembly. 
     As another advantage of the invention, pinion shafts  84  can be relatively short, and the drive mechanism  54  thus axially or vertically compact, for instance, on the order of a vertical dimension of about 100 millimeters or less. Another advantage is that the pinion shafts  84  are supported by bearings at their lower and upper ends, axially closely about ring gear  132 , such that bending loads and axial moments resulting from offset and eccentric loads about the ring and gear arrangement are minimized. Additionally, the flywheel bearings are about axially coextensive with the pinion bearings, such that forces are transmitted along generally straight, radial paths from the pinion bearings through the flywheel bearings to the housing, thereby avoiding complex and oblique or offset loading conditions that could lead to failures. 
     As another feature of drive mechanism  54  of the invention, second flywheels  80  enclose the upper ends of passages  130  of housing  66 , and upper pinion bearing  136  and upper flywheel bearing  140  are preferably sealed bearings, forming a completely sealed condition about the upper end of the passage, for preventing entry of dust, debris and moisture into the inner regions and workings of mechanism  54 . Additionally, sealed bearings  136  and  140  utilize annular rotary seal mechanisms which typically form a better sealed condition and are more reliable and longer lasting than alternative wiper type seals. The lower end of housing  66  can be enclosed and sealed in any desired suitable manner, such as using a generally planar bottom cover  160  of cast or sheet metal or the like. 
     Combined spur and bevel gears  96  and  100  of compact drive element  98  can be supported for rotation using any suitable bushing or bearing arrangement, such as compact bushing in the bottom of gear  96  that receives a pin  164  carried on cover  160 , and a shaft extending upwardly from the gears and received in a bushing  166  in the body or frame of housing  66 , to facilitate placement between flywheels  78 . Gear  102  can also be suitably supported, for instance, by bearings  168  retained in a horizontal bore in housing  66  by snap rings or the like, such that the overall fore and aft extend of mechanism  54  can be only marginally larger than the diameters of flywheels  78 . 
     In  FIGS. 10 and 11 , combine  20  is shown including an alternative header  198  which is a representative draper type header, including two compact sickle drive mechanisms  54  constructed and operable according to the teachings of the present invention, like parts of header  198  and header  22  being identified by like numerals. Draper header  198  includes a sickle  30  extending across a forward edge portion  32  of a floor  28 , between first and second side edge portions  40  and  42  of the floor. Sickle  30  is composed of a first cutter bar assembly  44  in end to end relation with a second cutter bar assembly  46 . A reel  34  is disposed above sickle  30 . A pair of elongate draper belts  200  and  202  extended sidewardly along and form a portion of floor  28 , and are movable toward the center of the header for conveying cut crops through a crop conveying area to a center belt  204  operable for conveying the crop rearwardly into a mouth or inlet opening of a feeder of combine  20 . Compact sickle drive mechanisms  54  of header  198  are constructed and operable in the above-described manner, and provide all of the features and advantages of sickle drive mechanism  54  of header  22 . 
     Here, sickle  30  of draper header  198  is comprised of four cutter bar assemblies  206 ,  208 ,  210  and  212  extending in end to end relation between edge portions  40  and  42  of a floor  28  of the header. Cutter bar assemblies  206  and  208  are connected in reciprocating sideward driven relation to compact sickle drive  54  on the left side of the machine as viewed in the drawing, and cutter bar assemblies  210  and  212  are connected in reciprocating sideward driven relation to drive  54  on the right side. Here, it can be observed in reference to  FIG. 11  that drives  54  are supported beneath draper belts  200  and  202 . The location of reel  34  above sickle  30  is also illustrated in  FIG. 11 . Thus, it should be apparent that compact sickle drive mechanisms of the invention can be used with a wide variety of header constructions. 
     It will be understood that changes in the details, materials, steps, and arrangements of parts which have been described and illustrated to explain the nature of the invention will occur to and may be made by those skilled in the art upon a reading of this disclosure within the principles and scope of the invention. The foregoing description illustrates the preferred embodiment of the invention; however, concepts, as based upon the description, may be employed in other embodiments without departing from the scope of the invention. Accordingly, the following claims are intended to protect the invention broadly as well as in the specific form shown.