Abstract:
A combination is made up of a tractor and a seeder suitable for direct drilling mounted on a three-point hitch of the tractor. The seeder has a crossbeam that is connected to the three-point hitch and on which a plurality of sowing units are arranged laterally in succession. The sowing units, each equipped with at least one furrow opener, are respectively prestressed downward in relation to the crossbeam by an actuator, and the three-point hitch can be self-locked in relation to a chassis of the tractor. During the sowing operation, the pressing forces for the furrow openers are therefore introduced via the sowing units, the actuator, the crossbeam and the three-point hitch into the chassis of the tractor.

Description:
FIELD 
     The disclosure relates to a combination of a tractor and a seeder appropriate for direct drilling attached to a three-point hitch of the tractor. 
     BACKGROUND 
     Seeders suitable for direct drilling, which are designed for sowing on fields that have not first been prepared by cultivating implements, and on which plant stubble remaining from previous harvesting process and other impurities are present, require sufficient pressing forces for their furrow openers. These pressing forces are necessary in order to produce a sufficiently deep seed furrow and possibly a fertilizer furrow and to push aside or cut through the plant parts and other materials still present on the field. 
     In the prior art (cf. EP 2 517 545 A1, for example), such seeders suitable for direct drilling are generally equipped with a frame of their own, which is supported on wheels and pulled across the field by a towing vehicle (generally a tractor). A seed container, which supplies the individual sowing units supported on the frame, is mounted on the frame. The seed is transported pneumatically from the seed container to the sowing units. The seeder itself has a sufficiently high weight that it causes no problems to provide the forces necessary for introducing the furrow into the ground by means of springs and/or hydraulic or pneumatic actuators, which are arranged between the furrow opener (or a sowing unit, on which the furrow opener is mounted), and the frame. The force necessary for opening the furrow is transmitted by the spring or the actuator onto the frame of the seeder. 
     DD 204 827 A1 describes a seeder with spring-loaded sowing colters mounted on the three-point hitch of the tractor. The weight of the seeder is borne by wheels of the seeder during the sowing process. To increase the load on the front wheels of the tractor during the turning process or to adjust the pressing force of the sowing colter, the seeder can be pivoted forward and upward relative to the three-point hitch by means of a hydraulic cylinder. The pressing force for the sowing colter (not expressly suitable for direct drilling) is likewise provided by the of the seeder&#39;s own weight. 
     It is therefore considered undesirable that a high weight of the seeder itself was required in the prior art in order to provide the pressing force for the furrow opener. It would be desirable, however to provide a lighter-weight seeder, which is nevertheless suitable for direct drilling. 
     SUMMARY OF THE DISCLOSURE 
     This problem is solved by the teaching of Claim  1 , while features that further develop the solution in an advantageous manner are specified in the additional claims. 
     A combination is made up of a tractor and a seeder suitable for direct drilling mounted on a three-point hitch of the tractor. The seeder has a crossbeam on which a plurality of sowing units are arranged laterally, one alongside another, and which is connected to the three-point hitch. The sowing units, each equipped with at least one furrow opener, are prestressed downward in relation to the cross beam by associated prestressing means. The three-point hitch is locked in relation to a chassis of the tractor. 
     This has the effect that when sowing, the pressing forces of the furrow opener are introduced via the sowing units, the prestressing means, the cross beam and the three-point hitch into the chassis of the tractor during the sowing operation. The seeder suitable for direct drilling, i.e. sowing on fields not previously prepared by cultivating equipment, thus uses the weight of the tractor for providing the pressing force of the furrow openers, so that the weight of the sowing machine itself can remain relatively low. 
     Said pretensioning means can be a spring and/or an actuator operated by a pressure medium, and can be, in particular, a hydraulic or pneumatic cylinder to which a predeterminable pressure can be applied, or a pneumatic (bellows) cylinder. 
     The three-point hitch can comprise a lower link that can be adjusted in height, i.e. raised and lowered, by means of a double-acting hydraulic cylinder, and the hydraulic cylinder can be locked by a valve during the sowing operation. 
     The seeder is preferably supported only on the three point hitch and optionally on depth-adjusting wheels of the seeder, but not on support wheels on the ground that are associated with the seeder. 
     The sowing units can each comprise a frame, on which a seed material container, the furrow opener, a depth adjusting wheel, a seed delivery device and a metering device are arranged, wherein the metering device is designed to successively remove seed material from the seed material container and supply it to the seed delivery device, which discharges the seed into a furrow produced by the furrow opener, the depth of which is determined by the depth-adjusting wheel. 
     The frame can be fastened to the cross beam by an parallelogram linkage comprising two links, and the prestressing means can be coupled to the linkage and the cross member. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a side view of a tractor with a seeder; and 
         FIG. 2  shows an enlarged view of the seeder. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  shows a tractor  10 , which is constructed on a chassis  12  and is supported on the ground by front wheels  14  and rear wheels  16 . An operator work station is situated in a cab  18 . A three-point hitch  20 , which is composed of two lower links  22  arranged one alongside another and an upper link  28  mounted thereabove, is arranged at the rear end of the chassis  12 . The lower links  22  are height-adjustable by means of associated double-acting hydraulic cylinders  26  that pivot the lower links  22  at their articulation points on the chassis  12  about horizontal axes extending approximately perpendicular to the forward direction. The upper link  28  is designed as a hydraulic cylinder  24  and is accordingly variable in length. By displacing the hydraulic cylinders  26 , rear coupling points  30  of the lower links  22  can be brought into a position suitable for attaching the seeder  36 . A rear coupling point  32  of the upper link  28  can be moved into a position suitable for attaching the seeder  36  by adjusting the length of the upper link  28 , which can be done purely manually by means of a suitable threaded spindle instead of by the hydraulic cylinder  24 . Lower link coupling points  30  in the form of upward-extending catch hooks (or any other desired coupling points such as coupling eyes as described in DIN ISO 730-1 Agricultural machines and tractors—Rear three-point attachment—Part 1: Categories 1, 2, 3 and 4) are arranged at the rear end of the lower link  22 , while a likewise conventional upper link coupling point  32  is provided at the rear end of the upper link  28 . 
     The double-acting hydraulic cylinders  26  of the lower links  22  are connected to a valve  46 , which is in turn coupled to a hydraulic pump  48  driven by the engine of the tractor  10  and to a tank  50  for hydraulic fluid. The valve  46  can be connected to both hydraulic cylinders  26 , or a separate valve  46  can be assigned to each hydraulic cylinder. The valve  46  can be brought into a closed position as shown, into a hitch-lowering position, if it is displaced upward as in  FIG. 1 , and into a hitch-raising position if it is displaced downward as in  FIG. 1 . The valve  46  can be actuated manually by the operator in the cab  18  or by suitable electromagnetic actuators  52 , which are in turn operated by switches arranged in the cab  18  or by a headland automation unit (not shown). In the position of the valve  46  shown in  FIG. 1 , the oil flow in and out of the cylinder  26  is blocked and the three-point hitch is thus locked in position. The hydraulic cylinder  24  of the upper link  28  is used only for one-time initial adjustment of the position of the coupling point  32  and is not adjusted during field operation, but is instead locked (like the hydraulic cylinders  26  of the lower link  22 , as shown in  FIG. 1 , by the valve  46 ). At the end of the field, the seeder  36  can be raised by bringing the valve  46  into the hitch-raising position by the operator or the headland automation unit, and before working the next track, can be analogously lowered by bringing the valve  46  into the hitch-lowering position by means of the operator or the headland automation unit. Thereby the lower links  22  are raised and again lowered by the hydraulic cylinders  26 , whereby the seeder  36  is also raised and lowered. 
     The seeder  36  comprises a holding frame  54  that is fastened by lower bars  40  and bolts  42  to the lower link coupling points  30  of the lower links  22 , and by an upper mounting element  56  and a bolt  44  to the upper link coupling point  32 . A crossbeam  58 , which extends over the entire length of the seeder  36  and on which a number of sowing units  60  are mounted, arranged one alongside another laterally, is fastened to the holding frame  54 . The sowing units  60  are fastened to the cross beam  58  via U-shaped bolts  62 , which are connected to a bracket  64  that extends vertically on the rear side of the crossbeam  58  and on which two links  66 ,  68  are pivotally mounted, one above another, which are also each pivotally mounted to a frame  70  of the sowing unit  60 . Together with the bracket  64  and the frame  70 , the links  66 ,  68  form a pivotal mounting of the frame relative to the crossbeam  58 . A pneumatic actuator  72 , which serves as a pretensioning means and is designed in the illustrated embodiment as a pneumatic bellows cylinder, engages at the top with the bracket  64  and at the bottom with the lower link  66  (at point  74 ) and defines the position of the frame  70  and the pressing force with which the furrow openers  78 ,  80  supported on the frame  70  interact with the ground. The pressure in the pneumatic actuator  72  is specified by a pneumatic control device  92 , which can comprise a compressor and a pressure regulation valve. A hydraulic cylinder (not shown) could also be used in place of the pneumatic actuator  72  as well as one or more mechanical springs. 
     The frame  70  supports, in a conventionally known manner, a seed material container  84 , a seed delivery device  86 , which can be in the form of a gravity drop seed tube (as shown) or a mechanical delivery system, and a metering device  88  (such as, but not limited to, a vacuum seed meter shown), which discharges individual seeds one after another from the seed stored in container  84  into the sowing seed delivery device  86 , which deposits it into a furrow that is produced by the furrow opener  80 , the working depth of which is specified by a depth-adjusting wheel  82 . The furrow is closed by a closing wheel  90 . Another furrow can be produced by a furrow opener  78 , the working depth of which is specified by a depth-adjusting wheel  76 . This additional furrow can be used for depositing fertilizer into the soil, and can be likewise closed by the closing wheel  90 . With regard to further details of the sowing units  60 , the reader is referred to the disclosure of U.S. Pat. No. 8,850,997 B2 the disclosure of which is hereby incorporated by reference into the present documents. 
     The seeder  36  is supported only on the three-point hitch  20  and on the depth-adjusting wheels  80  of the sowing units  60 , but not on the associated support wheels on the ground. As already mentioned, the seeder  36  is suitable for direct drilling, i.e. for working on fields not cultivated by cultivating machines after the previous harvest or only cultivated slightly. The furrow opener  80  therefore requires a sufficiently high pressing force in order to be able to cut through materials such as plant stems and stubble that may be present as well as to penetrate hardened soil. Since the actual seeder  36  is constructed relatively lightly, and has only a few and light elements, the furrow opener  80  is supported during operation on the chassis  12  of the tractor  10  via the frame  70 , on which it is rotatably suspended, the lower link  66 , the pneumatic actuator  72 , the bracket  64 , the mountings  62 , the crossbeam  58 , the holding frame  54 , the upper and lower links  22 ,  28  and the hydraulic cylinders  26  of the lower links  22 . The rear axle of the tractor  10  is therefore relieved and the front axle is loaded. As a result, there is no need for separate ballast weights, which otherwise (i.e. without the rigid connection according to the invention of the seeder  36  to the tractor  10 ) are necessary in order to ballast the seeder  36  to provide a pressing force required for direct drilling operation. 
     The pressing force of the furrow opener  80  is specified by the pneumatic actuator  72  and could be changed by means of a controllable pneumatic control device  92  that can be controlled by the operator from the cabin  18  via an interface (e.g. a virtual terminal, not shown), and a bus line (not shown) or by an automatic mechanism for adjustment to the respective conditions on the field. The pneumatic actuator  72  could also be replaced or supplemented by a spring (not shown) connected in parallel thereto. 
     It should be noted that further refinements of the seeder  36  are conceivable. Thus the crossbeam  58  could be composed of multiple sections, which makes it possible to move outer sections with sowing units  70  attached thereto into a non-operating position, offset upward and inward, for road travel. A fertilizer tank, the contents of which would be introduced by suitable known pneumatic conveyance means successively into the above-mentioned additional furrow, could be mounted at the front side of the tractor  10 .