Abstract:
A direct drive seed metering device for a row crop sowing machine with a seed metering disc rotatable about a central shaft having a plurality of seed capturing and retaining holes for capturing and retaining the seeds and laying them in a controlled manner in a furrow. The seed disc has a flexible sealing member attached to an inner wall of the housing and sealingly pressed against a face of the metering disc thereby forming a vacuum chamber by a the vacuum generator that lowers the air pressure on a face of the metering disc so as to capture and retain the seeds. The vacuum chamber is created by the vacuum generator being fluidly connected to the chamber through a hollow shaft of a drive motor and through a perforated hollow hub.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a Divisional of co-pending application Ser. No. 14/611,659, filed on 2 Feb. 2015, for which priority is claimed under 35 U.S.C. §120; and this application claims priority of U.S. Provisional Application No. 62/001,867 filed on 22 May 2014 under 35 U.S.C. §119(e), the entire contents of all of which are hereby incorporated by reference. 
    
    
     FIELD OF THE INVENTION 
     The present invention refers to a direct drive seed metering device and more specifically to a seed metering device for sowing machines, driven by an coaxial electric motor, comprising a seed metering disc for capturing seeds from a reservoir and laying them in a controlled manner in a furrow in the soil, where in the coaxial electrical motor couples directly to the metering disc without the need for intermediate transmission elements, redactors, gears or timing belts, thus increasing the efficiency of the device. 
     In preferred embodiments of the present invention, the means for capturing and releasing the seeds operate by vacuum or high pressure. 
     Additionally, preferred embodiments of the present invention comprise a toroidal electric motor with a hollow rotor shaft, through which the seed capturing means is fluidly connected to vacuum or pressure generating means 
     BACKGROUND OF THE INVENTION 
     Row crop sowing machines or seed planters for single seed sowing have been widely used for decades. Usually, said machines comprise at least one rotating disc for holding and supplying the seeds to be planted and means for releasing and conducting the seeds to the furrows on the ground at determined depths and spacing. 
     The rotating discs usually comprise holes, pockets, cradles or teeth for retaining the seeds with the help of vacuum or positive air pressure that is interrupted at a desired point in order to let the seeds drop into conducting means to the ground. 
     Most known sowing machines comprising a plurality of metering discs rely on only one driving assembly for simultaneously rotating all discs. In case of machines comprising a large number of metering discs, e.g. 20 or more, said driving assembly is bulky, complicated and expensive, not allowing the individual adjustment of the rotation of each metering disc, necessary in occasions when the sowing machine is not supposed to follow a rectilinear path, wherein the more external sowing devices run for a longer distance than the more internal ones. 
     Such drawbacks were addressed by the use of hydraulic systems for driving individually each disc, comprising sophisticated electronic control means, requiring both expensive and continuous maintenance. 
     Some late developments in sowing machines, replaced said hydraulic systems by individual electric motors, leading to much simpler and economic equipment, as particularly disclosed in patent application WO 2012/142607 A1 where the motors are connected to the axles of the metering discs. 
     Nevertheless, there is still a need for simpler metering devices, with reduced power requirements, and less expensive building and maintenance. 
     BRIEF DESCRIPTION OF THE INVENTION 
     The above mentioned drawbacks can be overcome and said needs fulfilled by the use of a seed distributing or metering device driven by a direct drive DC motor of the brushless type, high torque, and annular or toroidal shape comprising a hollow shaft or annular rotor and coaxially coupled to the metering disc. 
     The application of a high torque motor directly coupled to the rotational working elements of the seed metering device of the invention reduces the need for reductions, gear transmissions, belt transmission and other auxiliary transmission components found in seed metering devices known in the art. This reduction or complete elimination of mechanical transmissions elements between the power source and the load implies a substantial reduction in power loss, which in turn results in improvement in power output, reduced noise and vibrations, and all around greater efficiency. 
     Additionally, the reduction or elimination of auxiliary transmission elements greatly reduces maintenance costs and complexity, while also improving the device operational life. 
     Furthermore, the slim design of the high torque, annular motor allows for the motor to be arranged partially or completely within the seed meter housing, reducing the overall size of the device and partially or completely protecting the motor from outside elements. 
     Therefore, it is an object of the present invention to provide a seed metering device for row crop sowing machines, also called seed planters, comprising:
         a seed metering disc rotatable about a central shaft, having a plurality of seed capturing and retaining means for capturing and retaining the seeds,   a motor, which drives the seed metering disc,   releasing means for releasing the seeds from the seed capturing and retaining means,   conducting means for conducting the released seeds onto the ground, and   a housing for containing and protecting the metering disc,
           wherein the motor is of the hollow-shaft type, toroidally shaped and coaxially coupled to the metering disc.   
               

     In a preferred embodiment of the present invention, the hollow-shaft motor is a direct drive DC motor of the brushless type. 
     In a preferred embodiment of the present invention, the seed capturing and retaining means are selected from the group comprising holes, cells or cradles located near the outer perimeter of the metering disc. 
     In a preferred embodiment of the present invention, the seed capturing and retaining means consist of holes located near the outer perimeter of the metering disc and the hole size is determined by the type of seed to be sown, so as to be able to retain the seeds in place until reaching the releasing means. 
     In a preferred embodiment of the present invention, the metering disc is a cogwheel or gear, the teeth of which are the seed capturing and retaining means, where the teeth shape and the size of the gap between the teeth being determined by the type of seed to be sown, so as to be able to retain the seeds in place until reaching the releasing means. 
     In a more preferred embodiment of the present invention, the housing containing the metering disc forms a vacuum chamber together with one of the faces of the metering disc, the device being provided with vacuum generating means for lowering the air pressure on said face of the metering disc so as to capture and retain the seeds within the seed capturing and retaining means arranged on the face of the metering disc opposite the vacuum chamber. 
     In a more preferred embodiment of the present invention, the housing containing the metering disc forms a high pressure chamber together with one of the faces of the metering disc, the device being provided with blowing means for increasing air pressure on said face of the metering disc so as to capture and retain the seeds within the seed capturing and retaining means arranged on the same face of the metering disc. 
     In a more preferred embodiment of the present invention, the device further comprises a flexible sealing member contained within the housing, which is sealingly attached to the inner wall of the housing and which is sealingly pressed against one face of the metering disc, thus defining a vacuum chamber, the device being provided with vacuum generating means for lowering the air pressure on said vacuum chamber so as to capture and retain the seeds within the seed capturing and retaining means arranged on the face of the metering disc opposite the vacuum chamber. 
     In a more preferred embodiment of the present invention, the device further comprises
         a concave plate within the housing, sealingly attached to one face of the seed metering disc, and coupled to the hollow shaft of the motor, thus defining a rotatable vacuum chamber,   vacuum generating means,   a non-rotatable tube or conduit, non-rotatably attached to the housing, which passes through the housing and the hollow shaft of the motor into the rotatable vacuum chamber, fluidly connecting the vacuum means to the rotatable vacuum chamber.       

     In a most preferred embodiment of the present invention, the motor is coupled to the seed metering disc by means of a hollow hub or other suitable coupling means comprising a hollow shaft or tube, and wherein the hollow hub is perforated, fluidly connecting the high pressure chamber or the vacuum chamber, where appropriate, to the hollow motor shaft of the motor coupled to said hollow hub. 
     In a most preferred embodiment of the present invention, the vacuum generating means or the blowing means are fluidly connected to the vacuum chamber or the high pressure chamber, where appropriate, through the hollow motor shaft of the motor and through the perforated hollow hub. 
     In a preferred embodiment of the present invention, the vacuum generating means or the blowing means are fluidly connected to said vacuum chamber or high pressure chamber, where appropriate, through an opening or orifice in the housing in a position other than the hollow shaft—eccentrically regarding the metering disc—and wherein the coupling means coupling the motor to the seed metering disk does not allow fluid connection between the vacuum chamber or high pressure chamber, where appropriate, and the hollow shaft of the motor. 
     In a preferred embodiment of the present invention, the releasing means comprises a plate, fixed to the non-rotatable tube or conduit and located within the rotatable vacuum chamber, which makes contact with a region of the face of the metering disc inside the rotatable vacuum chamber, blocking the orifices of the seed capturing and retaining means and therefore interrupting the vacuum applied to the seeds retained on the other face of the metering disk, making them drop into the conducting means towards the ground. 
     In a more preferred embodiment of the present invention, the vacuum chamber does not simultaneously overlap with all the seed capturing and retaining means of the metering disc and wherein the release of the seeds from the holes of the seed capturing and retaining means occurs when a particular hole of the seed retaining means no longer overlaps with the vacuum chamber. 
     In a preferred embodiment of the present invention, the seed releasing means comprises a rotatable wheel contacting the metering disc on the face opposite the seeds capturing and retaining means, the wheel blocking the holes of the seed capturing and retaining means and therefore interrupting the vacuum or pressure applied to the retained seeds, making them drop into the conducting means towards the ground. 
     In a most preferred embodiment of the present invention, the motor is housed within the housing, fixed to the inner surface of the housing wall. 
     In a preferred embodiment of the present invention, the motor is fixed to the outer surface of the housing wall. 
     In a preferred embodiment of the present invention, the seed releasing means comprise stationary or mobile brushes that physically remove the seeds from the seed capturing and retaining means. 
     In a preferred embodiment of the present invention, the device further comprises singulating means for allowing only one seed to be retained in each capturing and retaining means. 
     In a preferred embodiment of the present invention, the singulating means comprise a plate, parallel to the metering disc and spaced apart so as to allow only one seed to be retained in each capturing and retaining means. 
     In a preferred embodiment of the present invention, the conducting means for conducting the released seeds onto the ground comprises a conveyor belt provided with bristles for guiding the seeds to an outlet close to the soil and into an opened furrow in the soil. 
     In a preferred embodiment of the present invention, the conducting means for conducting the released seeds onto the ground comprises a tube for allowing the seeds to freely reach the soil by gravity, into an opened furrow in the soil. 
     In a preferred embodiment of the present invention, the seed capturing and retaining means of the seed metering disc comprises holes and the housing comprises a rotatable toothed wheel with a plurality of teeth or projections, that engage with said holes of the seed capturing and retaining means as the disc rotates, removing obstructions and releasing seeds stuck in said holes. 
     In a most preferred embodiment of the present invention, the motor is a large diameter annular torque motor with an annular rotor. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an exploded perspective view of a vacuum seed metering device wherein the vacuum generating means are connected to the housing through the hollow motor shaft, according to a first embodiment of the present invention; 
         FIG. 2  is a schematic cross-section side view of the vacuum seed metering device of  FIG. 1 ; 
         FIG. 3  is an exploded perspective view of a pressure seed metering device wherein the blowing means are connected to the housing through the hollow motor shaft, according to a second embodiment of the present invention; 
         FIG. 4  is a schematic cross-section side view of the pressure seed metering device of  FIG. 3 ; 
         FIG. 5  is an exploded perspective view of a vacuum seed metering device wherein the vacuum generating means are connected to the housing through an air extraction conduit, according to a third embodiment of the present invention; 
         FIG. 6  is a schematic cross-section side view of the vacuum seed metering device of  FIG. 5 ; 
         FIG. 7  is an exploded perspective view of a pressure seed metering device wherein the blowing means are connected to the housing through an air intake conduit, according to a fourth embodiment of the present invention; 
         FIG. 8  is a schematic cross-section side view of the vacuum seed metering device of  FIG. 7 ; 
         FIG. 9  is an exploded perspective view of a vacuum seed metering device comprising a vacuum chamber, according to a fifth embodiment of the present invention; 
         FIG. 10  is a schematic cross-section side view of the vacuum seed metering device of  FIG. 9 ; 
         FIG. 11  is an exploded perspective view of a vacuum seed metering device comprising a rotating vacuum chamber, according to a sixth embodiment of the present invention; 
         FIG. 12  is a schematic cross-section side view of the vacuum seed metering device of  FIG. 11 ; 
         FIG. 13  is an exploded perspective view of a vacuum seed metering device comprising a vacuum chamber connected to the vacuum generating means through the hollow motor shaft, according to a seventh embodiment of the present invention; 
         FIG. 14  is a schematic cross-section side view of the vacuum seed metering device of  FIG. 13 ; 
         FIG. 15  is an exploded perspective view of a pressure seed metering device comprising a large diameter torque motor with an annular rotor, wherein the pressure generating means are connected to the housing through the annular rotor of the torque motor, according to an eighth embodiment of the present invention; 
         FIG. 16  is a schematic cross-section side view of the pressure seed metering device of  FIG. 15 ; 
         FIG. 17  is an exploded perspective view of a vacuum seed metering device comprising a large diameter torque motor with an annular rotor, wherein the vacuum generating means are connected to the housing through the annular rotor of the torque motor, according to a ninth embodiment of the present invention; 
         FIG. 18  is a schematic cross-section side view of the vacuum seed metering device of  FIG. 17 ; 
     
    
    
     DEFINITIONS 
     To the effects of the present invention, the terms “fluid connection”, “fluidly connected”, “fluidly coupled” and variations of the same are meant to be understood as connection or couplings that allow or maintain the flow of fluids, and more particularly air, between the connected elements. 
     For all of the embodiments described in the present invention, and any other embodiment within the scope of the present invention, the term “atmospheric pressure chamber” is meant to the be understood as making reference to a chamber that is neither the high pressure chamber nor the vacuum chamber. In some embodiments of the present invention, the “atmospheric pressure chamber” may be fluidly connected to the exterior of the device through suitable fluid connection means, such as holes or conduits. Regardless of the above, the “atmospheric pressure chamber” may not be actually be at atmospheric pressure, but instead is used to identify said chamber from the vacuum chamber or high-pressure chamber respectively. More specifically, it refers to the chamber that is at a higher pressure than the vacuum chamber in vacuum seed metering devices, or the chamber that is at lower pressure than the high pressure chamber in high pressure seed metering devices. 
     Likewise, the term “vacuum” is meant to be understood as a pressure that is lower than the pressure in the atmospheric pressure chamber, and the term “high pressure” is meant to be understood as a pressure that is higher than the pressure in the 
     The terms “toroidal motor”, “annular rotor” and “torque motor” refer to electrical motors whose rotor comprises a passing hole or orifice about its central axis. 
     DETAILED DESCRIPTION OF THE INVENTION 
     The invention will be described in more detail below, with reference to the accompanying drawings that illustrate different exemplary embodiments of the present invention. 
     For all of the following embodiments, while the hollow shaft electric motor of embodiments 1 to 7 and the large diameter torque motor of claims  8  to  9  can be of any type of suitable electric motor with a hollow motor shaft, preferred embodiments of the present invention utilize brushless DC electric motors. 
     Embodiment 1 
       FIGS. 1 and 2  show a vacuum seed metering device according to a first embodiment of the present invention. Said vacuum seed metering device comprises a cylindrical housing  01 , which houses a rotating metering disc  02  coupled about its central axis to a hollow rotor shaft  03 . 1  of a coaxially arranged motor  03  by means of a hollow hub  13  or other suitable coupling means which allow the passage of air through it. The stator  03 . 2  of the motor  03  is fixed to the interior of the housing  01  by suitable fastening means (not shown). The hollow hub  13  is coupled to the hollow motor shaft  03 . 1  by rods or pins  14  or other suitable fastening means. The metering disc  02  is coupled to the hollow hub  13  by a cotter pin  12  or other suitable securing means. 
     The metering disc  02  divides the housing  01  into two chambers; a vacuum chamber, fluidly connected to a vacuum generation means (not shown), and an atmospheric pressure chamber. Seeds  07  are loaded into a reservoir  21  within the atmospheric pressure chamber through a seed inlet  06 , which may or may not comprise a hopper and/or closure means (not shown). Vacuum is created in the vacuum chamber by the extraction of air in said chamber by means of a vacuum generating means (not shown) through an air extraction outlet  05 . Fluid connection between the vacuum generating means and the vacuum chamber in the housing  01  is achieved through a plurality of orifices or holes  18  in the hollow hub  13  which connects the hollow motor shaft  03 . 1  of the motor  03  to the metering disc  02 . In turn, the hollow motor shaft  03 . 1  is fluidly connected to the air extraction outlet  05 , which is connected to the vacuum generating means (not shown). 
     The metering disc  02  comprises a plurality of radially spaced holes  19  or other suitable seed retaining means on its outer region. The holes  19  utilize the vacuum generated in the vacuum chamber by the vacuum generating means to capture seeds  07  from the seed reservoir  21  and retain them until the vacuum is interrupted by a wheel  09  or other suitable seed releasing means, releasing the seed  07  from the holes  19  of the metering disc  02 , preferably into a seed outlet  10 . 
     In a preferred embodiment the wheel  09  comprises a device arranged to block or isolate the affected holes  19  from the vacuum generated by the vacuum generating means, causing the seed to be released from said affected hole  19 . Preferably, the wheel  09  is made from a flexible material, like rubber or other polymeric material, and located on the side of the metering disc  02  opposite to the seeds  07 , which can isolate a particular hole  19  from the vacuum source. 
     The embodiment further comprises a suitable curved plate  08  or other singulating means to prevent the simultaneous retention and discharge of two or more seeds  07  from a single hole  19 , by removing excess seeds and returning them to the seed reservoir  21 . Additionally, the embodiment further comprises a toothed wheel  11  with a plurality of teeth or projections, or other suitable auxiliary ejector means, arranged in a cavity  17  within the housing  01 , which doubles both as a cleaning device for cleaning and removing obstructions in the holes  19  and as an auxiliary means for releasing seeds  07  not properly released by the seed releasing wheel  09 . Preferably, the toothed wheel  11  is made from flexible material, like rubber or other polymeric material. 
     In operation, seeds  07  captured by the metering disc  02 , and not removed by the curved plate  08 , are carried over to the wheel  09 , which in turn releases the seeds  07  from the metering disc  02  and allows them to freely fall through a seed outlet  10 , through a conducting means to an opened furrow on the soil or another section of the seeding equipment. 
     Embodiment 2 
       FIGS. 3 and 4  show a pressure seed metering device according to a second embodiment of the present invention. Said pressure seed metering device comprises a cylindrical housing  01 , which houses a rotating metering disc  02  coupled about its central axis to a hollow rotor shaft  03 . 1  of a coaxially arranged motor  03  by means of a hollow hub  13  or other suitable coupling means which allow the passage of air through it. The stator  03 . 2  of the motor  03  is fixed to the interior of the housing  01  by suitable fastening means (not shown). The hollow hub  13  is coupled to the hollow motor shaft  03 . 1  by rods or pins  14  or other suitable fastening means. The metering disc  02  is coupled to the hollow hub  13  by a cotter pin  12  or other suitable securing means. 
     The metering disc  02  divides the housing  01  into two chambers; a positive pressure chamber, fluidly connected to a blowing means (not shown), and an atmospheric pressure chamber. Seeds  07  are loaded into a reservoir  21  within the positive pressure chamber through a seed inlet  06 , which may or may not comprise a hopper and comprises sealing means (not shown). Pressure is created in the positive pressure chamber by the pressurization of air in said chamber by means of a blowing means (not shown), such as an air compressor, through a pressurized air inlet  05 . Fluid connection between the blowing means and the positive pressure chamber in the housing  01  is achieved through a plurality of orifices or holes  18  in the hollow hub  13  which connects the hollow motor shaft  03 . 1  of the motor  03  to the metering disc  02 . In turn, the hollow motor shaft  03 . 1  is fluidly connected to the pressurized air inlet  05 , which is connected to the blowing means (not shown). 
     The metering disc  02  comprises a plurality of radially spaced holes  19  or other suitable seed retaining means on its outer region. The holes  19  utilize the pressure generated in the positive pressure chamber by the blowing means to capture seeds  07  from the seed reservoir  21  and retain them until the pressure is interrupted by a wheel  09  or other suitable seed releasing means, releasing the seed  07  from the holes  19  of the metering disc  02 , preferably into a seed outlet  10 . 
     In a preferred embodiment the wheel  09  comprises a device arranged to block or isolate the affected holes  19  from the pressure generated by the blowing means, causing the seed to be released from said affected hole  19 . Preferably, the wheel  09  is made from a flexible material, like rubber or other polymeric material, and located on the side of the metering disc  02  opposite to the seeds  07 , which can isolate a particular hole  19  from the pressure source. 
     The embodiment further comprises a suitable curved plate  08  or other singulating means to prevent the simultaneous retention and discharge of two or more seeds  07  from a single hole  19 , by removing excess seeds and returning them to the seed reservoir  21 . Additionally, the embodiment further comprises a toothed wheel  11  with a plurality of teeth or projections, or other suitable auxiliary ejector means, arranged in a cavity (not shown) within the housing  01 , which doubles both as a cleaning device for cleaning and removing obstructions in the holes  19  and as an auxiliary means for releasing seeds  07  not properly released by the seed releasing wheel  09 . Preferably, the toothed wheel  11  is made from flexible material, like rubber or other polymeric material. 
     In operation, seeds  07  captured by the metering disc  02 , and not removed by the curved plate  08 , are carried over to the wheel  09 , which in turn releases the seeds  07  from the metering disc  02  and allows them to freely fall through a seed outlet  10 , through a conducting means to an opened furrow on the soil or another section of the seeding equipment. 
     Embodiment 3 
       FIGS. 5 and 6  show a vacuum seed metering device according to a third embodiment of the present invention. Said vacuum seed metering device comprises a cylindrical housing  01 , which houses a rotating metering disc  02  coupled about its central axis to a hollow rotor shaft  03 . 1  of a coaxially arranged motor  03  by means of a hub  13  or other suitable coupling means. The stator  03 . 2  of the motor  03  is fixed to the interior of the housing  01  by suitable fastening means (not shown). The hub  13  is coupled to the hollow motor shaft  03 . 1  by rods or pins  14  or other suitable fastening means. The metering disc  02  is coupled to the hub  13  by a cotter pin  12  or other suitable securing means. 
     The metering disc  02  divides the housing  01  into two chambers; a vacuum chamber, fluidly connected to a vacuum generation means (not shown), and an atmospheric pressure chamber. Seeds  07  are loaded into a reservoir  21  within the atmospheric pressure chamber through a seed inlet  06 , which may or may not comprise a hopper and/or closure means (not shown). Vacuum is created in the vacuum chamber by the extraction of air in said chamber by means of a vacuum generating means (not shown) coupled to an air extraction outlet  05  formed on or attached to the housing  01 , fluidly connecting the vacuum generating means to said vacuum chamber. The hub  13  further provides a fluid seal over the hollow motor shaft  03 . 1  of the motor  03 , preventing fluid circulation of air through the hollow shaft  03 . 1  from and to the housing  01 . 
     The metering disc  02  comprises a plurality of radially spaced holes  19  or other suitable seed retaining means on its outer region. The holes  19  utilize the vacuum generated in the vacuum chamber by the vacuum generating means to capture seeds  07  from the seed reservoir  21  and retain them until the vacuum is interrupted by a wheel  09  or other suitable seed releasing means, releasing the seed  07  from the holes  19  of the metering disc  02 , preferably into a seed outlet  10 . 
     In a preferred embodiment the wheel  09  comprises a device arranged to block or isolate the affected holes  19  from the vacuum generated by the vacuum generating means, causing the seed to be released from said affected hole  19 . Preferably, the wheel  09  is made from a flexible material, like rubber or other polymeric material, and located on the side of the metering disc  02  opposite to the seeds  07 , which can isolate a particular hole  19  from the vacuum source. 
     The embodiment further comprises a suitable curved plate  08  or other singulating means to prevent the simultaneous retention and discharge of two or more seeds  07  from a single hole  19 , by removing excess seeds and returning them to the seed reservoir  21 . Additionally, the embodiment further comprises a toothed wheel  11  with a plurality of teeth or projections, or other suitable auxiliary ejector means, arranged in a cavity  17  within the housing  01 , which doubles both as a cleaning device for cleaning and removing obstructions in the holes  19  and as an auxiliary means for releasing seeds  07  not properly released by the seed releasing wheel  09 . Preferably, the toothed wheel  11  is made from flexible material, like rubber or other polymeric material. 
     In operation, seeds  07  captured by the metering disc  02 , and not removed by the curved plate  08 , are carried over to the wheel  09 , which in turn releases the seeds  07  from the metering disc  02  and allows them to freely fall through a seed outlet  10 , through a conducting means to an opened furrow on the soil or another section of the seeding equipment. 
     Embodiment 4 
       FIGS. 7 and 8  show a pressure seed metering device according to a fourth embodiment of the present invention. Said pressure seed metering device comprises a cylindrical housing  01 , which houses a rotating metering disc  02  coupled about its central axis to a hollow rotor shaft  03 . 1  of a coaxially arranged motor  03  by means of a hub  13  or other suitable coupling means. The stator  03 . 2  of the motor  03  is fixed to the interior of the housing  01  by suitable fastening means (not shown). The hub  13  is coupled to the hollow motor shaft  03 . 1  by rods or pins  14  or other suitable fastening means. The metering disc  02  is coupled to the hub  13  by a cotter pin  12  or other suitable securing means. 
     The metering disc  02  divides the housing  01  into two chambers; a positive pressure chamber, fluidly connected to a blowing means (not shown), and an atmospheric pressure chamber. Seeds  07  are loaded into a reservoir  21  within the positive pressure chamber through a seed inlet  06 , which may or may not comprise a hopper and comprises sealing means (not shown). Pressure is created in the positive pressure chamber by the pressurization of air in said chamber by means of a blowing means (not shown), such as an air compressor, through a pressurized air inlet  05  formed on or attached to the housing  01 , fluidly connecting the blowing means to said positive pressure chamber. The hub  13  further provides a fluid seal over the hollow motor shaft  03 . 1  of the motor  03 , preventing fluid circulation of air through the hollow shaft  03 . 1  from and to the housing  01 . 
     The metering disc  02  comprises a plurality of radially spaced holes  19  or other suitable seed retaining means on its outer region. The holes  19  utilize the pressure generated in the positive pressure chamber by the blowing means to capture seeds  07  from the seed reservoir  21  and retain them until the pressure is interrupted by a wheel  09  or other suitable seed releasing means, releasing the seed  07  from the holes  19  of the metering disc  02 , preferably into a seed outlet  10 . 
     In a preferred embodiment the wheel  09  comprises a device arranged to block or isolate the affected holes  19  from the pressure generated by the blowing means, causing the seed to be released from said affected hole  19 . Preferably, the wheel  09  is made from a flexible material, like rubber or other polymeric material, and located on the side of the metering disc  02  opposite to the seeds  07 , which can isolate a particular hole  19  from the pressure source. 
     The embodiment further comprises a suitable curved plate  08  or other singulating means to prevent the simultaneous retention and discharge of two or more seeds  07  from a single hole  19 , by removing excess seeds and returning them to the seed reservoir  21 . Additionally, the embodiment further comprises a toothed wheel  11  with a plurality of teeth or projections, or other suitable auxiliary ejector means, arranged in a cavity (not shown) within the housing  01 , which doubles both as a cleaning device for cleaning and removing obstructions in the holes  19  and as an auxiliary means for releasing seeds  07  not properly released by the seed releasing wheel  09 . Preferably, the toothed wheel  11  is made from flexible material, like rubber or other polymeric material. 
     In operation, seeds  07  captured by the metering disc  02 , and not removed by the curved plate  08 , are carried over to the wheel  09 , which in turn releases the seeds  07  from the metering disc  02  and allows them to freely fall through a seed outlet  10 , through a conducting means to an opened furrow on the soil or another section of the seeding equipment. 
     Embodiment 5 
       FIGS. 9 and 10  show a vacuum seed metering device according to a fifth embodiment of the present invention. Said vacuum seed metering device comprises a cylindrical housing  01 , which houses a rotating metering disc  02  coupled about its central axis to a hollow rotor shaft  03 . 1  of a coaxially arranged motor  03  by means of a hub  13  or other suitable coupling means. The stator  03 . 2  of the motor  03  is fixed to the interior of the housing  01  by suitable fastening means (not shown). The hub  13  is coupled to the hollow motor shaft  03 . 1  by rods or pins  14  or other suitable fastening means. The metering disc  02  is coupled to the hub  13  by a cotter pin  12  or other suitable securing means. 
     A sealing member  15  is sealingly attached to the interior wall of the housing  01  and is sealingly pressed against a face of the metering disc  02 , thus defining a vacuum chamber, while the remaining volume of the housing  01  defines an atmospheric pressure chamber. The sealing member  15  is made from a flexible material, like rubber or other polymeric material. The vacuum chamber is fluidly connected to a vacuum generation means (not shown), through an air extraction outlet  05  formed on or attached to the housing  01 . The hub  13  further provides a fluid seal over the hollow motor shaft  03 . 1  of the motor  03 , preventing fluid circulation of air through the hollow shaft  03 . 1  from and to the housing  01 . 
     Seeds  07  are loaded into a reservoir  21  within the atmospheric pressure chamber through a seed inlet  06 , which may or may not comprise a hopper and/or closure means (not shown). 
     The metering disc  02  comprises a plurality of radially spaced holes  19  or other suitable seed retaining means on its outer region. The sealing member  15  is arranged over the face of the metering disc  02  so as to overlap the vacuum chamber over some, but not all, the radially spaced holes  19 . 
     The holes  19  utilize the vacuum in the overlapping vacuum chamber generated by the vacuum generating means to capture seeds  07  from the seed reservoir  21  and retain them until the vacuum is interrupted, releasing the seed  07  from the holes  19  of the metering disc  02 , preferably into a seed outlet  10 . Interruption of the vacuum affecting a specific hole  19  is achieved by rotating the metering disc  02  until said specific hole no longer overlaps with the vacuum chamber, thus releasing the captured seed. 
     The embodiment further comprises a suitable curved plate  08  or other singulating means to prevent the simultaneous retention and discharge of two or more seeds  07  from a single hole  19 , by removing excess seeds and returning them to the seed reservoir  21 . Additionally, the embodiment further comprises a toothed wheel  11  with a plurality of teeth or projections, or other suitable auxiliary ejector means, arranged in a cavity  17  within the housing  01 , which doubles both as a cleaning device for cleaning and removing obstructions in the holes  19  and as an auxiliary means for releasing seeds  07  not properly released by the seed releasing mechanism. Preferably, the toothed wheel  11  is made from flexible material, like rubber or other polymeric material. 
     In operation, seeds  07  captured by the seed holes  19  in the metering disc  02 , and not removed by the curved plate  08 , are carried over by the rotating metering disc  02  until their respective seed holes  19  no longer overlaps with the vacuum chamber, thus releasing the seeds  07  from the metering disc  02  and allowing them to freely fall through a seed outlet  10 , through a conducting means to an opened furrow on the soil or another section of the seeding equipment. 
     Embodiment 6 
       FIGS. 11 and 12  show a vacuum seed metering device according to a sixth embodiment of the present invention. Said vacuum seed metering device comprises a cylindrical housing  01 , which houses a rotating metering disc  02  sealingly attached to an concave plate  20  coupled about its central axis to a hollow rotor shaft  03 . 1  of a coaxially arranged motor  03  by screws, bolts or other suitable fastening means  14 . The stator  03 . 2  of the motor  03  is fixed to the interior of the housing  01  by suitable fastening means (not shown). 
     The metering disc  02  and the concave plate  20  define a rotating vacuum chamber, fluidly connected to a vacuum generation means (not shown) through a vacuum conduit  22 . The remaining volume of the housing  01  defines an atmospheric pressure chamber. Seeds  07  are loaded into a reservoir  21  within the atmospheric pressure chamber through a seed inlet  06 , which may or may not comprise a hopper and/or closure means (not shown). 
     The vacuum conduit  22 , having a protruding hollow member  22 . 1 , a flange  22 . 2  and an air extraction outlet  05 , is sealingly attached by its flange  22 . 2  to the exterior of the housing  01  by means of screws  14 , bolts or any other suitable fastening means. The protruding hollow member  22 . 1  of the vacuum conduit  22  is inserted coaxially and through the hollow motor shaft  03 . 1  of the motor  03  and into vacuum chamber defined by the metering disc  02  and the concave plate  20 , providing fluid connection between said vacuum chamber and the vacuum generating means (not shown) through the air extraction outlet  05 . It should be noted that the protruding hollow member  22 . 1  of the vacuum conduit  22  is not joined or attached to the hollow motor shaft  03 . 1  of the motor  03  and thus does not rotate. 
     The metering disc  02  comprises a plurality of radially spaced holes  19  or other suitable seed retaining means on its outer region. The holes  19  utilize the vacuum generated in the vacuum chamber by the vacuum generating means to capture seeds  07  from the seed reservoir  21  and retain them until the vacuum is interrupted by a plate  04  or other suitable seed releasing means, releasing the seed  07  from the holes  19  of the metering disc  02 , preferably into a seed outlet  10 . 
     The plate  04  is a plate made from a flexible material, like rubber or other polymeric material, located within the rotating vacuum chamber and non-rotatably attached to the protruding hollow member  22 . 1  of the vacuum conduit  22  by means of a hub  13 . The hub  13  is joined to the protruding hollow member  22 . 1  of the vacuum conduit  22  by at least one rod or pin  16  or a suitable fastening means. 
     The embodiment further comprises a suitable curved plate  08  or other singulating means to prevent the simultaneous retention and discharge of two or more seeds  07  from a single hole  19 , by removing excess seeds and returning them to the seed reservoir  21 . 
     In operation, seeds  07  captured by the metering disc  02 , and not removed by the curved plate  08 , are carried over to the plate  04 , which in turn releases the seeds  07  from the metering disc  02  and allows them to freely fall through a seed outlet  10 , through a conducting means to an opened furrow on the soil or another section of the seeding equipment. 
     Embodiment 7 
       FIGS. 13 and 14  show a vacuum seed metering device according to a seventh embodiment of the present invention. Said vacuum seed metering device comprises a cylindrical housing  01 , which houses a rotating metering disc  02  coupled about its central axis to a hollow rotor shaft  03 . 1  of a coaxially arranged motor  03  by means of a hollow hub  13  or other suitable coupling means which allow the passage of air through it. The stator  03 . 2  of the motor  03  is fixed to the interior of the housing  01  by suitable fastening means (not shown). The hollow hub  13  is coupled to the hollow motor shaft  03 . 1  by rods or pins  14  or other suitable fastening means. The metering disc  02  is coupled to the hub  13  by a cotter pin  12  or other suitable securing means. 
     A sealing member  15  is sealingly attached to the interior wall of the housing  01  and is sealingly pressed against a face of the metering disc  02 , thus defining a vacuum chamber, while the remaining volume of the housing  01  defines an atmospheric pressure chamber. The sealing member  15  is made from a flexible material, like rubber or other polymeric material and contains an opening or orifice  15 . 1  formed on its inner wall. The vacuum chamber is fluidly connected to the hollow motor shaft  03 . 1  of the motor  03  through said opening or orifice  15 . 1  formed on the inner wall of the sealing member  15  and through a plurality of orifices or holes  18  formed in the hollow hub  13 , which connects said hollow motor shaft  03 . 1  of said motor  03  to the metering disc  02 . In turn, said hollow motor shaft  03 . 1  is fluidly connected to the vacuum generating means (not shown) through an air extraction outlet  05 . Thus, fluid connection between the vacuum chamber and the vacuum generating means is achieved (not shown). 
     Seeds  07  are loaded into a reservoir  21  within the atmospheric pressure chamber through a seed inlet  06 , which may or may not comprise a hopper and/or closure means (not shown). 
     The metering disc  02  comprises a plurality of radially spaced holes  19  or other suitable seed retaining means on its outer region. The sealing member  15  is arranged over the face of the metering disc  02  so as to overlap the vacuum chamber over some, but not all, the radially spaced holes  19 . 
     The holes  19  utilize the vacuum in the overlapping vacuum chamber generated by the vacuum generating means to capture seeds  07  from the seed reservoir  21  and retain them until the vacuum is interrupted, releasing the seed  07  from the holes  19  of the metering disc  02 , preferably into a seed outlet  10 . Interruption of the vacuum affecting a specific hole  19  is achieved by rotating the metering disc  02  until said specific hole no longer overlaps with the vacuum chamber, thus releasing the captured seed. 
     The embodiment further comprises a suitable curved plate  08  or other singulating means to prevent the simultaneous retention and discharge of two or more seeds  07  from a single hole  19 , by removing excess seeds and returning them to the seed reservoir  21 . Additionally, the embodiment further comprises a toothed wheel  11  with a plurality of teeth or projections, or other suitable auxiliary ejector means, arranged in a cavity  17  within the housing  01 , which doubles both as a cleaning device for cleaning and removing obstructions in the holes  19  and as an auxiliary means for releasing seeds  07  not properly released by the seed releasing mechanism. Preferably, the toothed wheel  11  is made from flexible material, like rubber or other polymeric material. 
     In operation, seeds  07  captured by the seed holes  19  in the metering disc  02 , and not removed by the curved plate  08 , are carried over by the rotating metering disc  02  until their respective seed holes  19  no longer overlaps with the vacuum chamber, thus releasing the seeds  07  from the metering disc  02  and allowing them to freely fall through a seed outlet  10 , through a conducting means to an opened furrow on the soil or another section of the seeding equipment. 
     Embodiment 8 
       FIGS. 15 and 16  show a pressure seed metering device according to an eighth embodiment of the present invention. Said pressure seed metering device comprises a cylindrical housing  01 , which houses a rotating metering disc  02  coaxially coupled about its central axis to an annular rotor  03 . 1  of a coaxially arranged large diameter torque motor  03  by means of a hollow hub  13  or other suitable coupling means which allow the passage of air through it. The annular stator  03 . 2  of the large diameter torque motor  03  is fixed to the interior of the housing  01  by suitable fastening means (not shown). The hollow hub  13  is coupled to the annular rotor  03 . 1  by rods or pins  14  or other suitable fastening means. The metering disc  02  is coupled to the hollow hub  13  by suitable securing means. In a preferred embodiment, the metering disc  02  is secured to the hollow hub  13  by means of a cotter pin  12  secured about a main central rod of the hollow hub  13  and a plurality of radially displaced lesser pins  24  secured about secondary fastening rods on the hub  13 . 
     The metering disc  02  divides the housing  01  into two chambers; a positive pressure chamber, fluidly connected to a blowing means (not shown), and an atmospheric pressure chamber. Seeds  07  are loaded into a reservoir  21  within the positive pressure chamber through a seed inlet  06 , which may or may not comprise a hopper and comprises sealing means (not shown). Pressure is created in the positive pressure chamber by the pressurization of air in said chamber by means of a blowing means (not shown), such as an air compressor, through a pressurized air inlet  05 . Fluid connection between the blowing means and the positive pressure chamber in the housing  01  is achieved through a plurality of orifices or holes  18  in the hollow hub  13  which connects the annular rotor  03 . 1  of the large diameter torque motor  03  to the metering disc  02 . In turn, the annular rotor  03 . 1  is fluidly connected to the pressurized air inlet  05 , which is connected to the blowing means (not shown). 
     The metering disc  02  comprises a plurality of radially spaced holes  19  or other suitable seed retaining means on its outer region. The holes  19  utilize the pressure generated in the positive pressure chamber by the blowing means to capture seeds  07  from the seed reservoir  21  and retain them until the pressure is interrupted by a wheel  09  or other suitable seed releasing means, releasing the seed  07  from the holes  19  of the metering disc  02 , preferably into a seed outlet  10 . 
     In a preferred embodiment the wheel  09  comprises a device arranged to block or isolate the affected holes  19  from the pressure generated by the blowing means, causing the seed to be released from said affected hole  19 . Preferably, the wheel  09  is made from a flexible material, like rubber or other polymeric material, and located on the side of the metering disc  02  opposite to the seeds  07 , which can isolate a particular hole  19  from the pressure source. 
     The embodiment further comprises a suitable curved plate  08  or other singulating means to prevent the simultaneous retention and discharge of two or more seeds  07  from a single hole  19 , by removing excess seeds and returning them to the seed reservoir  21 . Additionally, the embodiment further comprises a toothed wheel  11  with a plurality of teeth or projections, or other suitable auxiliary ejector means, arranged in a cavity (not shown) within the housing  01 , which doubles both as a cleaning device for cleaning and removing obstructions in the holes  19  and as an auxiliary means for releasing seeds  07  not properly released by the seed releasing wheel  09 . Preferably, the toothed wheel  11  is made from flexible material, like rubber or other polymeric material. 
     In operation, seeds  07  captured by the metering disc  02 , and not removed by the curved plate  08 , are carried over to the wheel  09 , which in turn releases the seeds  07  from the metering disc  02  and allows them to freely fall through a seed outlet  10 , through a conducting means to an opened furrow on the soil or another section of the seeding equipment. 
     Embodiment 9 
       FIGS. 17 and 18  show a vacuum seed metering device according to an ninth embodiment of the present invention. Said vacuum seed metering device comprises a cylindrical housing  01 , which houses a rotating metering disc  02  coaxially coupled about its central axis to an annular rotor  03 . 1  of a coaxially arranged large diameter torque motor  03  by means of a hollow hub  13  or other suitable coupling means which allow the passage of air through it. The annular stator  03 . 2  of the large diameter torque motor  03  is fixed to the interior of the housing  01  by suitable fastening means (not shown). The hollow hub  13  is coupled to the annular rotor  03 . 1  by rods or pins  14  or other suitable fastening means. The metering disc  02  is coupled to the hollow hub  13  by suitable securing means. In a preferred embodiment, the metering disc  02  is secured to the hollow hub  13  by means of a cotter pin  12  secured about a main central rod of the hollow hub  13  and a plurality of radially displaced lesser pins  24  secured about secondary fastening rods on the hub  13 . 
     The metering disc  02  divides the housing  01  into two chambers; a vacuum chamber, fluidly connected to a vacuum generation means (not shown), and an atmospheric pressure chamber. Seeds  07  are loaded into a reservoir  21  within the atmospheric pressure chamber through a seed inlet  06 , which may or may not comprise a hopper and/or closure means (not shown). Vacuum is created in the vacuum chamber by the extraction of air in said chamber by means of a vacuum generating means (not shown) through an air extraction outlet  05 . Fluid connection between the vacuum generating means and the vacuum chamber in the housing  01  is achieved through a plurality of orifices or holes  18  in the hollow hub  13  which connects the annular rotor  03 . 1  of the large diameter torque motor  03  to the metering disc  02 . In turn, the annular rotor  03 . 1  is fluidly connected to the air extraction outlet  05 , which is connected to the vacuum generating means (not shown). 
     The metering disc  02  comprises a plurality of radially spaced holes  19  or other suitable seed retaining means on its outer region. The holes  19  utilize the vacuum generated in the vacuum chamber by the vacuum generating means to capture seeds  07  from the seed reservoir  21  and retain them until the vacuum is interrupted by a wheel  09  or other suitable seed releasing means, releasing the seed  07  from the holes  19  of the metering disc  02 , preferably into a seed outlet  10 . 
     In a preferred embodiment the wheel  09  comprises a device arranged to block or isolate the affected holes  19  from the vacuum generated by the vacuum generating means, causing the seed to be released from said affected hole  19 . Preferably, the wheel  09  is made from a flexible material, like rubber or other polymeric material, and located on the side of the metering disc  02  opposite to the seeds  07 , which can isolate a particular hole  19  from the vacuum source. 
     The embodiment further comprises a suitable curved plate  08  or other singulating means to prevent the simultaneous retention and discharge of two or more seeds  07  from a single hole  19 , by removing excess seeds and returning them to the seed reservoir  21 . Additionally, the embodiment further comprises a toothed wheel  11  with a plurality of teeth or projections, or other suitable auxiliary ejector means, arranged in a cavity  17  within the housing  01 , which doubles both as a cleaning device for cleaning and removing obstructions in the holes  19  and as an auxiliary means for releasing seeds  07  not properly released by the seed releasing wheel  09 . Preferably, the toothed wheel  11  is made from flexible material, like rubber or other polymeric material. 
     In operation, seeds  07  captured by the metering disc  02 , and not removed by the curved plate  08 , are carried over to the wheel  09 , which in turn releases the seeds  07  from the metering disc  02  and allows them to freely fall through a seed outlet  10 , through a conducting means to an opened furrow on the soil or another section of the seeding equipment. 
     The above embodiments should not to be taken as limiting examples of the invention, as the benefits of the application of a direct drive seed metering device driven by a DC brushless toroidal torque motor, as disclosed herein, in other embodiments of seed metering devices will be apparent to those skilled in the art. Thus, the invention is further suited for its application on other seed metering devices as, for example, devices without a pressure or vacuum source and which utilize other types of seed capturing, retaining and releasing means, such as teeth, cells, cradles and the like.