CIRCULAR HARROW

Abstract: Circular harrow comprising a supporting frame (1) which can be hitched to a traction machine, a working frame (2) rotatable in a horizontal plane about a vertical shaft by means of a power unit and having a width larger than that of the traction machine, and working elements (3) mounted on the working frame. The working elements (3) consist of S-shaped flexible prongs mounted near the outer edge of the working frame (2).

Description: CIRCULAR HARROW The present invention relates to a circular harrow consisting of a supporting frame, a working frame rotatable in a horizontal plane about a vertical shaft by means of a power unit and having a width lar¬ ger than that of the traction machine, and working elements mounted on the working frame. In soil cultivation, owing to the diversity of work to be done and to the need to adapt to diffe¬ rent soil conditions, generally a large number of dif¬ ferent soil cultivators are used. These include e.g. various types of ploughs, rototillers and harrows, such as spading harrows, flexible prong harrows and disk harrows. Ploughs are fundamental means of soil culti¬ vation for which there is no viable alternative. There has been some talk about cultivation without ploughing, but soil that has not been ploughed cannot readily be tilled with other cultivation means cur¬ rently used. Therefore, at least large fields are first ploughed and subsequently tilled with finer soil cultivators. Rototillers are efficient tillers but they have the drawback of high working costs due to the wear of expensive blades. Besides, they cannot be used on rocky soils. Moreover, their vigorously rotating blades chop up couch grass roots, causing increased proliferation of couch. Harrows are based on various elements dragged along the soil surface and penetrating into the soil, cultivating it. For example, the spading harrow is suited for the tillage of mineral soil with little rockiness, but the best use for it is on turfy soil. The flexible prong harrow again is an effective tool for most soil types, it loosens the soil and destroys couch grass efficiently as it brings couch grass roots to the surface. For effective operation of harrows, a relati¬ vely high driving speed is required and therefore also a relatively large and powerful tractor. Since effec- tive harrowing also requires that the soil be harrowed several times, harrowing involves pronounced compacti¬ on of the soil. Moreover, in small and irregular field land areas, maintaining a sufficient harrowing speed is difficult and often it is necessary to drive back and forth and perform many reversals to harrow the whole area, thus causing further compaction of the soil. From patent specifications DE 947 654 and DE 1 048 059, circular harrows are known which have a rotating frame with prongs or vanes mounted on it to cultivate the soil. However, these are only applicable in very light and easy working conditions. The object of the invention is to eliminate the drawbacks referred to above. A specific object of the invention is to produce a new type of harrow which is light in construction and does not require a high traction power or a large and heavy tractor causing soil compaction, which is capable of effective culti¬ vation at different driving speeds, which never gets clogged and works effectively even in rocky fields with tree stumps and in other kinds of difficult and heavy conditions without being damaged. In other words, the object of the invention is to present a harrow that harrows the soil to a large depth and al- lows cultivation of soils that are too rocky, stumpy and uneven to be tilled with known implements. As for the features characteristic of the in¬ vention, reference is made to the claims. The harrow of the invention is based on the use of flexible prongs which work best at a relatively high speed and on moving the flexible prongs in the soil at a speed higher than that of the traction ma- chine. Thus, the circular harrow of the invention com¬ prises a supporting frame to be hithced to a tractor, a working frame rotatable in a horizontal plane about a vertical shaft by means of a power unit, and working elements mounted on the working frame. The working frame has a width larger than that of the vehicle used as a traction engine, so that the harrow covers and tills the soil under the wheel tracks of the vehicle. According to the invention, the working elements con- sist of S-shaped flexible prongs mounted near the ou¬ ter edge of the working frame, extending downwards from the working frame. Thus, when the working frame is lowered substantially to the level of the ground surface, the flexible prongs penetrate into the soil. By rotating the working frame at a suitable speed and simultaneously pulling or pushing the harrow along the ground surface, the flexible prongs work the soil to the desired looseness during a single harrowing pass. In a preferred embodiment, the substantially horizontal portion of the flexible prongs, curved backwards towards the blades, lies clearly below the working frame, providing a surface that carries the circular harrow on the ground. Thus, the working frame does not touch the ground and the device needs no se- parate supporting wheels or corresponding elements. In a preferred embodiment, the blades of the S-shaped flexible prongs or at least their front edges are so inclined that their outer edge leads the inner edge in the working direction, so that the blade acts as an element that ploughs the soil inwards. Thus, the harrow does not heap a side ridge on the edges of the working track, but instead produces an even ground surface. In a preferred embodiment, the underside of the working frame is provided with a closed cover or shield, such as a metal plate, attached to the working frame to keep stumps, twigs and rocks away from the rotating frame. If the shield extends over the whole area of the working frame, it is provided with sui¬ table cut-outs through which the flexible prongs pro¬ ject downwards. It is also possible to provide the top side of the working frame with a suitable shield, such as a protecting net, attached to the supporting frame and serving to prevent objects or persons from falling onto the working frame. In a preferred embodiment, the device has a relatively small number of flexible S-shaped prongs, and these are mounted on the same circle in the area of the outer edge of the working frame. The number of prongs may be only two, but preferably 4 - 10, e.g. 6 - 8 prongs placed at equal distances on the same cir- cle. The flexible prong harrow of the invention has significant advantages over known technology. The degree of cultivation obtained by the harrow can be easily adjusted by varying the driving speed, rotatio- nal speed and number of prongs, allowing the soil to be worked to the desired condition with a single pass of the harrow. Moreover, since the harrow requires on¬ ly a very low traction power, i.e. allows the use of light traction vehicles, soil compaction is minimized. A further advantage is that the harrow will not get clogged as the prongs can be placed at a very large distance from each other; the harrow will work even if it has only two flexible prongs placed on opposite si¬ des of a circular frame with a diameter of about 2.5 m. Furthermore, while the prongs of a conventional spring harrow work only in the driving direction, the prongs in the harrow of the invention move in two di¬ rections relative to a given point, which means that they effectively cultivate the soil e.g. around rocks. Further advantages of the harrow of the invention over known circular harrows are that it works the soil uni¬ formly and that it works well in all circumstances. The flexible prong harrow of the invention works excellently in the cultivation of problematic cultures. On rocky fields with steep slopes and on soft, squashy fields, the required soil cultivation can be completed in one operation and using light ma¬ chinery as the harrow has an insignificant tractive resistance and a clog-proof construction. In addition, as the device works the soil uniformly regardless of the direction of advance, it allows easy harrowing of difficult field corners and ditch banks as well as small and narrow places that are inaccessible to cur¬ rently used harrows. In the following, the invention is described in detail by referring to the attached drawings, in which Fig. 1 presents a harrow according to the invention, provided with S-shaped flexible prongs. Fig. 2 presents a bottom shield plate used in the har¬ row in Fig. 1, Fig. 3 presents an S-shaped flexible prong used in the harrow in Fig. 1, and Fig. 4 presents a cross-section of the blade of the S- shaped flexible prong in Fig. 3. The flexible prong harrow presented in Fig. 1 comprises a supporting frame 1 provided with a three- point hitch 9 allowing the harrow to be hitched to a tractor or other traction engine. Attached to the sup¬ porting frame is a herringbone gear 10, which is coup¬ led to the tractor's power take off by means of a shaft 11. The supporting frame carries a circular wor¬ king frame 2 which is horizontally rotatable about a vertical shaft by the application of a force transmit¬ ted via the herringbone gear 10 and shaft 11. This embodiment has six working elements 3, S-shaped flexible prongs, mounted on the rigid outer ring 12 of the working frame 2. The prongs are suppor¬ ted by the working frame 2 and extend mainly below it. In the embodiment presented, the harrow receives its driving power from the power take off shaft of a tractor, but it is also possible to use a hydraulic system to transmit the driving power from the traction engine, in which case the flexible prong harrow is provided with a hydraulic motor. Another possibility is to use a separate power unit. In the embodiment presented, the working fra¬ me 2 is a circular structure consisting of flat-iron rings 12 of sufficient strength and radial supports 13 connecting them, forming a rigid and substantially planar round-shaped ring or circle, to whose outer ed¬ ge the flexible prongs are attached. It is also possi¬ ble to use other kinds of frame structures, e.g. sepa- rate radial supports, the flexible prongs being at¬ tached to their ends or at a suitable distance. The flexible prongs used in the harrow are S- shaped prongs, which have a very effective spring ac¬ tion and yield when necessary, e.g. when they hit rocks. The flexible prongs as illustrated in Fig. 3 have a horizontal portion 4 below the working frame 2, and this portion 4 forms a part that carries the whole device on the ground. Therefore, the harrow need not be provided with separate supporting wheels or other carriers. The blades 5 of the S-shaped flexible prongs have a cross-section as illustrated by Fig. 4, in ot ¬ her words, their outer edge 6 leads the inner edge in the direction A of rotation so that the blade forms an inwards-ploughing edge of the circular supporting fra¬ me. Therefore, soil surface worked by the harrow beco¬ mes very even and no side ridges are formed at the ed¬ ges of the harrowed track. Fig. 2 presents a shield 7 or bottom plate preferably used in the device. The bottom plate can be attached to the rings 12 and lower radial supports 13 e.g. by welding. The working elements 3 project below the bottom plate through cut-outs 8 in the edge of the plate, which are large enough to allow the working elements to bend and turn as required. On uneven terrain, the bottom plate prevents stumps and rocks from getting into the spaces between the rings 12 of the working frame 2, which might dama¬ ge the device. The flexible prong harrow of the invention preferably has a diameter of about 2.5 m, but in cer- tain applications the diameter may even exceed 3 m. Especially when the device is used in forestry work, to break up the soil before seeding or planting or for patch sowing cultivation, for which purpose the device is very well suited, it will be advantageous to use a relatively small working frame, with a diameter of e.g. 2 m. In the above, the invention has been descri¬ bed by way of example with the aid of the attached drawing, but different embodiments of the invention are possible within the scope of the inventive idea defined by the claims.

Claims: CLAIMS 1. Circular harrow comprising a supporting frame (1) which can be hitched to a traction machine, a working frame (2) rotatable in a horizontal plane about a vertical shaft by means of a power unit and having a width larger than that of the traction machi¬ ne, and working elements (3) mounted on the working frame, characterized in that the working elements (3) consist of S-shaped flexible prongs mounted near the outer edge of the working frame (2). 2. Circular harrow as defined in claim 1, characterized in that the backwards bent substantially horizontal portion (4) of the flexible prongs (3) lies below the working frame (2), providing a surface that carries the circular harrow on the ground. 3. Circular harrow as defined in claim 1, characterized in that the blades (5) are so inclined that their outer edge leads the inner edge in the wor- king direction, the blade thus acting as an element that ploughs the soil inwards. 4. Circular harrow as defined in claim 1, characterized in that the bottom surface of the wor¬ king frame (2) is formed by a substantially closed shield (7). 5. Circular harrow as defined in claim 4, characterized in that the shield (7) is provided with elongated cut-outs (8), through which the flexible prongs (3) project from the working frame (2) downwards below the shield. 6. Circular harrow as defined in any one of claims 1 - 5, characterized in that the harrow is pro¬ vided with a suitable shield, such as a protecting net, attached to the supporting frame (1) and exten- ding above the working frame (2). 7. Circular harrow as defined in any one of claims 1 - 6, characterized in that the number of fie- xible prongs is 2 - 10, preferably 4 - 8, e.g. 6. 8. Circular harrow as defined in any one of claims 1 - 6, characterized in that the flexible prongs (3) are placed on the same circle in the wor- king frame (2) .

Inventors: PUKARINEN PERTTI, PUKARINEN, PERTTI
Applicants: PUKARINEN PERTTI, PUKARINEN, PERTTI
Application year: 1995
Main classification: A01B33
IPC codes: A01B33