GB2272352A

GB2272352A - Reversible plough

Info

Publication number: GB2272352A
Application number: GB9224060A
Authority: GB
Inventors: Peter Douglas Temple Topham
Original assignee: Individual
Current assignee: Individual
Priority date: 1992-11-17
Filing date: 1992-11-17
Publication date: 1994-05-18
Also published as: AU4728493A; EP0725561A1; CA2149113A1; WO1994010826A1; GB9224060D0

Abstract

A reversible plough is disclosed in which a plurality of plough bodies 12 are pivotally supported from a beam 8 which itself is pivotable about main pivot P, so as to permit the plough to produce right-hand or left-hand turning of the soil as required, to enable the plough to go back and forth producing similar furrows across a field. A parallelogram linkage is provided, connecting the plough bodies, to a link 26 extending parallel to the beam, a second pivot A connecting the link and the frame 2 with pivot A being spaced towards the front of the frame 2 in relation to pivot P. <IMAGE>

Description

"REVERSIBLE PLOUGH" This invention relates to an improved reversible plough and, in its preferred form, relates to a plough having rotary discs or inversion wheels as the means for turning the soil.

With a reversible plough where a beam from which the various plough bodies depend is swingable about a headstock pivot between oppositely inclined positions depending upon whether a left-hand or a right-hand furrow is required, there is a requirement to maintain the various plough bodies parallel, one with the other, during beam reversal as it is swung from one ploughing position to the other and there is a further problem that the body angle of the plough bodies should be so-controllable that when the plough is in work, the angle is such as to enable the plough.to counteract the forces due to the opposite angle of pull from the tractor to the plough.

The present invention is directed at providing a reversible plough having a linkage capable of providing this control of plough body direction.

According to the present invention, there is provided a reversible plough comprising a headstock for attachment at one end to a tractor and provided with a substantially vertical axis main pivot at its other end, a beam connected by a rigid support to said main pivot whereby the beam is spaced from said axis and is pivotable thereabout in a substantially horizontal plane so as to be inclinable to either side of the direction of movement of the plough, a plurality of plough bodies pivotally supported by said beam for pivoted movement about substantially vertical axes whereby the plough bodies can pivot upon pivotal movement of the beam to maintain their trailing position substantially parallel with the direction of movement of the plough during pivotal movement of the beam, a parallelogram linkage having arms fixed to said plough bodies and to a link extending parallel to the beam, and a secondary pivot connecting said link and the headstock, the secondary pivot being spaced from the main pivot towards the front of the headstock and the length of the parallelogram linkage arms being such that in all pivotal positions of the beam, the line of the link between the points of connection to the arms is located between the main pivot axis and the beam, whereby as the beam is pivoted relative to the headstock, the plough bodies are controlledly pivoted relative to the beam.

Preferably, the secondary pivot is so-located or locatable that the plough bodies are inclined to the centre line of the headstock in a position to counteract the tendency of the beam to swing due to the resultant line of pull from the plough bodies being offset from the centre line of the headstock. Thus, means may be provided for controllably varying the distance between the secondary pivot and the line of the link connecting the ends of the arms while the secondary pivot itself may be positionable relative to the headstock. Such positioning may be along a locus extending along the length or at an angle to the length of the headstock or, in another embodiment, may be along an arc centred on a fixed axis of the headstock.

In a preferred, simple, construction, the link is in the form of an isosceles triangle frame with the ends of its base being pivotally connected to the arms and its apex being connected to the headstock at said secondary pivot.

Preferably, the plough has rotary inversion wheels as the soil turning members, with these members comprising a flat, or substantially flat, central disc, provided with a frustoconical working flange at its periphery. In the illustrated embodiment, this flange is provided by a number of teeth, individually detachably secured to the periphery of the central disc.

According to a further aspect of the invention, there is provided a plough comprising a frame and, supported by said frame, tilling apparatus comprising a primary concave ploughing disc rotatable by reaction with the ground to be tilled and inclined in the direction of forward movement to provide a soil tilling and ploughing action and a secondary, smaller, ploughing disc mounted within the concavity of the primary ploughing disc and more greatly inclined to the direction of forward movement, in order to displace a sliver of soil together with stubble and straw off the surface of the ground, the primary ploughing disc being operative in use of the plough to roll the clean soil from the underside of the sliver over to cover the sliver of soil, stubble and straw initially displaced, the secondary ploughing disc being rotatable about its axis, a point depending from the frame to penetrate the ground in front of the forward edge of the primary ploughing disc, the secondary ploughing disc also having its forward edge substantially aligned with the point.

The invention will be further described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a plan view of a plough embodying the present invention; Figure 2 is a diagrammatic view illustrating the construction for controlling the direction of operation of ploughing bodies; Figure 3 is a diagram further illustrating the operation of the plough; Figure 4 is a view similar to Figure 3 but illustrating a modified construction; Figure 5 is a plan view of the beam of the plough of Figure 1; Figure 6 is a plan view of the headstock of the plough; Figure 7 is an elevational view of the headstock; Figure 8 is an end view of the headstock;; Figure 9 is a part fragmentary view illustrating a plough body provided with a rotary disc from the front with the rotary disc arranged in a non-ploughing condition at right-angles to the direction of extent of the plough body; Figure 10 is a side elevational view of the plough body of Figure 9; Figure 11 is a sectional view illustrating the mounting for the rotary disc; Figure 12 is a top view of the plough body with the rotary disc removed; Figure 13 is a diagrammatic view illustrating an alternative form of link for use in the plough; and Figure 14 is a diagrammatic view explaining the theoretical basis for the control linkage used in the plough.

Referring to the drawings, Figure 1 illustrates a plough in accordance with the present invention which comprises a headstock 2 provided with outwardly extending retaining brackets 4 which are engageable with brackets 6 on a beam 8 for retaining the beam in either of two limiting positions inclined to the centre line of the headstock. While, in this embodiment, two working positions only are shown, by appropriate redesigning of the brackets 4 and 6 more than one working position may be provided on each side of the centre line, the plough bodies being correctly aligned by the linkage to be described regardless of the degree of inclination of the beam adopted. The beam itself comprises a rigid support 9 comprising a bearing 11 for mounting to a vertical axis main pivot P at the rear end of the headstock 2. Wheels 10 are provided for supporting the plough beam in its ploughing position with these wheels being mounted on struts rotatable about pivots 18 at the end of the beam, these pivots also supporting outermost plough bodies 12 which are rotatable with the wheel supports about the pivot axis 18. Rotation of the beam 8 about the pivot P is controlled by a hydraulic cylinder 20 having a piston connected at 22 to an arm projecting to the side of the rigid support 9.

The construction of the individual plough bodies 12 will be described later, with reference to Figures 9, 10, 11 and 12.

With the plough as illustrated in Figure 1, in the position shown, upon forward movement of the plough, the rotary plough discs or inversion wheels will turn soil to the left to form the required furrows. However, due to the fact that the resultant force required to pull the plough bodies is displaced to one side of the centre line of the main pivot P, there would be a tendency, where the plough bodies are parallel with the line of extent of the ploughing for them to pull sideways on the tractor with resultant traction difficulties. In order to overcome this problem, the plough bodies as shown in the embodiment of Figure 1 are inclined slightly to the longitudinal centre line of the headstock and the direction of ploughing so as to apply a sideways force which counteracts the effect of their being to one side of the centre line.When the beam is rotated so as to be oppositely inclined to the direction of ploughing, the plough bodies are arranged to be inclined themselves appropriately to provide the opposite correcting force with the oppositely inclined beam.

Accordingly, with the plough of the present invention, there has been designed a linkage to maintain the plough bodies parallel to one another during beam reversal and to have the body angle variable when the plough is in work. The variable angle is to counteract the forces due to the offset angle of pull from tractor to plough. In the particular case of the plough shown, designed to run out of the furrow, the bodies must be biased to pull away from the centre line of the tractor to maintain stability.

Figure 2 diagrammatically illustrates a linkage arrangement for controlling the angle of the plough bodies responsive to pivotal movement of the beam. Thus, referring to this Figure, the beam 8 can be seen as pivoting about the point P on the headstock with EB and FC being two arms controlling the angle of the plough bodies with the length of EB being equal to FC. These arms are shown in Figure 1 by reference numeral 25.

EB and FC are constrained to remain parallel one with the other by the link BC which is the same length as EF. In the form illustrated BDC is the base of a rigid triangular link frame ABC with the triangular link being an isosceles triangle so-formed that AD equals PG, where G is the mid-point of EF, and D is the mid-point of BC with AB equal to AC and BD equal to DC. With these constraints, AP must equal BE and CF, and AP, BE and CF will remain parallel when the beam rotates about pivot point P.

This system can be considered as representing a pair of parallelogram linkages APFC and APEB linked by a third parallelogram linkage BCFE and allows the parallelogram linkage APFC to go over-centre when the beam is rotated anticlockwise while the linkage parallelogram APEB maintains control.

This linkage can be considered mathematically by visualising a phantom link connected between the mid-point of EF (which by definition is G) and point D on the triangular linkage. DG is the same length as BE and CF and always remains parallel with them. Also, instead of using the triangular link, the line AD may be considered instead as being perpendicular to the original connecting link BC, and also the line EF. Thus although for structural reasons we have shown the link as being triangular, it can be of any convenient form, provided that it defines the locations of the points B, C and A.

With the above explanation, one obtains the geometric diagram illustrated in Figure 3. Where APGD becomes a new parallel linkage, it is clear that because of the rigid nature of the triangular link, the projection of AD onto the line EGF will always be perpendicular since by construction the beam assembly PG is perpendicular to the line EF.

While, in the above explanation, the point A has been considered as being a fixed pivot point on the centre line of the frame, position A could be visualised as being able to slide along the line AP, i.e. that there is no fixed link between A and P. The point A would still, however, remain in a fixed position relative to P because DG is a fixed length and AD and PG must remain parallel to each other, as defined as the visualised linkage was described. Having adopted the possibility of having a slide at A then the possibility exists to alter the dimensions of the link AD, still maintaining AD parallel to PG. Lengthening or shortening the length AD will rotate DG so that it is not parallel to AP.

This idea can be taken one stage further in that the point A need not necessarily slide along the line AP.

Thus, as shown in Figure 4, the concept is introduced of point A being allowed to slide along a locus JK. The position of A and length AD do not necessarily constrain DG parallel to JPH and the variation from parallel will be a function of the position of point A along the locus AK and the relative lengths of AD, DG and PG and the angle HH subtended by the beam. The constraint that AD is parallel to PG still exists.

The plough illustrated in Figure 1 utilises a fixed triangular linkage with the secondary pivot A being received within a slipper pad having a variable degree of angular movement. However, as will be discussed later, either with this arrangement or with a slipper fixed to the centre line of the plough headstock advantages can be appreciated by having what is effectively a triangular link with a variable geometry. Such a triangular link could be made as shown in Figure 13 where the triangular link is shown as comprising a base 26 connecting the pivots B and C, two sides 27 and 28 welded to an outer box section 30 and an inner box section 32 slidable within the outer box section 34 along the centre line of the triangular link. The position of the inner box section along the length of the outer box section is controllable by a threaded member 34.The box section 32 carries a bearing 36 for engagement with the pivot A. It will be appreciated that in Figure 13 the beam is shown in its mid-position, between its normal ploughing positions extending transversely of the direction of ploughing.

We will explain later, in connection with Figure 14, the mathematical background to the embodiments illustrated.

Reverting to the particular construction of the plough shown in Figure 1, the headstock is illustrated in Figures 6, 7 and 8. The headstock comprises a triangular base frame having the pivot P at its rearward end and provided with lower connecting members 40 at its forward end. An upper pivot connection 44 is connected by a central sloping member 46 and two lateral sloping members 42 to the base frame. Forward of the pivot point P there is provided a mounting for the apex of the triangular link which comprises a platform 52 having an upstanding member 50 defining a rearwardly opening recess with diverging sides. A hole 54 is provided in this mounting plate 52 to provide a fixed vertical axis for receiving a bolt 54' which pivotally retains a pivot supporting member 56 which carries the secondary pivot A.The pivot supporting member 56 is thus pivotal between limiting positions in engagement with the diverging walls of the member 50, the secondary pivot A being displaceable about a radius centred on the axis of the hole 54.

With this arrangement, as shown in Figure 1, the pivot point A is offset to one side of the centre of the headstock 46 with the result that with the beam in its inclined ploughing position shown in this Figure, the plough bodies will be inclined to the centre line of the headstock to the required extent, to provide the corrected bias. When the direction of the plough is reversed so that the beam is swung round to the other side of the headstock, the pivotable member 56 will itself rock to engage the opposite side of the recess provided by the member 50 with the pivot point A then being on the opposite side of the centre line of the headstock with the result that the appropriate alignment of the plough bodies is achieved.

Figures 9 to 12 illustrate the construction of the plough bodies themselves. As shown in these Figures, the rotary disc is not shown in its operative position but is shown arranged to extend with its plane perpendicular to the line of extent of the plough body.

The plough body is illustrated detached from the remainder of the plough and comprises an upper L-shaped frame member 60 having a lower extension 62 welded thereto with the extension 62 being connected by bolts 63 to a downwardly depending leg 64 provided at its front edge with a soil penetrating or cutting member 66. As shown, the member 66 is bolted into position and is reversible so that as the point 67 wears, it can simply be adjusted down using a plurality of bolt holes provided on the leg 64 to permit adjusting of the position of the soil penetrating element 66 to take up for shortening of the member in use.

Once the limit of adjustment has been reached, the member 66 can simply be removed and reversed to use the other point 67.

Extending rearwardly from the leg 64 is a landslide 68 which extends beneath a rotary soil inversion wheel 90. Rearwardly of the soil inversion wheel 90 a post 70 is upstanding from the landslide and secured by bolt 73 to a member 72 which has an upper flange providing a support 74 for the lower end of a shaft 76.

The frame member 60 is adapted to be secured to bodies pivotally mounted on the pivots E,F and 18 by members 80 and 81 (Figure 1) extending rearwardly from the bodies mounted on the pivots. Carried by the rearwardly extending portion of the frame 60 is a body 82 which carries at its rearward end a support 86 for the upper end of the shaft 76. The shaft 76 rotatably mounts a sleeve 84provided with grease nipples 85. Also carried by the frame member 82 are a pair of adjustable stops 88 which limit rotation of the sleeve 84 by cooperating with a stop 92 rotatable with the sleeve 84. Secured to the sleeve 84 is a plate 94 which extends forwardly and has a laterally projecting portion to which is secured a pivot 96 for attachment to the end of a piston cooperable with a hydraulic cylinder 97. At the lower end of the sleeve, there is provided a bearing 100 for mounting a rotatable hub 98.Secured to the forward end of the hub 98 is an inversion wheel mounting plate 102 to which is secured by bolts 103 the central planar plate 104 of inversion wheel 90. The working portion of the inversion wheel 90 can be considered as being constituted by an annular frustoconical flange secured to the periphery of the central disc portion 104 by bolts 105. In the embodiment shown, the working flange is constituted by a plurality of separate teeth 106 bolted to the periphery of the central disc portion although other forms of flange are possible, for example a continuous flange which may have a smooth edge, a toothed edge, an undulating edge or any other edge formation as considered desirable, depending upon the environment in which the plough is to be used.

To the forward end of the plate 94 there is provided a downwardly extending scraper 108 which is cooperable with the inversion wheel during use of the plough.

To the top of the body 82, there is provided a pivot shaft 110 for receipt within a bore at the end of a connecting bar 112. As can be seen in Figure 1, the connecting bar 112 extends between the rods 110 extending upwardly from two neighbouring plough bodies in order to ensure that the plough bodies remain parallel one with the other.

Also shown in Figure 10 is a support 150 for use in detachably mounting a secondary ploughing disc operative as disclosed in my earlier GB-A-2 254 232.

Support 150 depends from a plate 154 which is rotatable about the shaft 86 independently of the sleeve 84. A pair of stops 152 project upward from the plate 94 so that upon operation of the hydraulic cylinder 97 to reverse the angle of inclination of the inversion wheel 90, the plate 94 will rotate until such time as a stop 152 engages the plate 154 to displace the plate 154 through the remainder of the rotational movement of the plate 94 with the result that the plate 154 is swung through a smaller angle than the angle through which the plate 94 is turned.

Conversely, upon return movement of the plate 94, stop 152 is only engageable with the plate 154 for the latter part of the movement of the plate 94 with the result that the required smaller degree of pivoting movement of the plate 154 is required.

Although not shown in Figure 10, the box 150 serves as a support for a detachable secondary ploughing disc which will be mounted in front of the main ploughing disc or inversion wheel 90 with its leading edge substantially aligned with the leg 64. With the secondary ploughing disc in position with its support mounted depending from the box section 150, the tilling apparatus can be seen to comprise the primary concave ploughing disc 90 rotatable by reaction with the ground to be tilled and inclined to the direction of forward movement to provide a soil tilling and ploughing action and the secondary, smaller, ploughing disc mounted within the concavity of the primary ploughing disc and more greatly inclined to the direction of forward movement in order to displace a sliver of soil, together with stubble and straw off the surface of the ground, the primary ploughing disc being operative in use of the plough to roll the clean soil from the underside of the sliver over to cover the sliver of soil, stubble and straw initially displaced, the secondary ploughing disc being rotatable about its axis. The forward edges of both the secondary and the primary ploughing discs are substantially aligned with the point 66 and leg 64. The secondary ploughing disc may be a soil inversion wheel construction with a flat central disc as for the main ploughing disc although in some circumstances a simple concave disc may be utilised. A small scraper may be provided associated with the secondary ploughing disc to operate in a manner similar to that in which the scraper 108 operates with the main soil inversion wheel 90.

In use of the plough, it can be seen that in one normal working position for producing left-hand furrows, the plough will be in the position as shown in Figure 1 with the beam having been inclined about the main pivot P until the left-hand retainers 4 and 6 have engaged. In that position, the linkage comprising the main triangular link 26,27,28 controls the position of the two innermost plough bodies so that they are slightly out of parallel with the direction of movement of the plough, in order to provide a correcting bias, assisting straight traction by the tractor. The outermost plough bodies are maintained parallel with the two inner controlled plough bodies by the connecting bars 112.

When it is desired to reverse the direction of the plough, the cylinder 25 can be actuated to rotate the beam 8 about the main pivot P until the right-hand retainers 4 and 6 are engaged. During this rotation, the plough bodies will automatically be, themselves, rotated relative to the beam so as to reach the desired orientation, slightly non-parallel, in the opposite sense, with the direction of motion of the plough. At the same time, the inversion wheels are, themselves, moved from the working position shown in Figure 1 to an oppositely inclined working position relative to the plough body by operation of the cylinders 97. The limiting rotating positions of the inversion wheel relative to the plough body are controlled by the adjustable stops 88.

As further explanation, there will now be described in connection with Figure 14, the mathematical explanation of the linkage used for controlling the angular position of the plough bodies. This can be expressed as having a problem to show the body steering angle GG in terms of the slider angle JJ, the beam angle HH and the link length AD. The lengths PG (beam offset), DG (lever arm), JP (slider pivot position), can be considered as the required data since, due to the constraints imposed in the practical linkage, AD must always be parallel to PG. In Figure 14, JA and GP have been produced to meet at K and GL has been drawn parallel to JA to meet AD produced at M.

The method that is applied is to use the parallelogram AKGN to determine the length of DM and by applying the sine rule to triangle DGX to find the angle DG.

First, find KP by applying the sine rule to triangle JKP.

KP ~ JP = SinJJ Sin(#/2+HH-JJ) Therefore KP = JP Sin JJ Cos(HH-JJ) clearly DM = KP + PG - AD 2 from 1 and 2 DN - sin JJ + PG - AD Cos(HH-JJ) now, applying the sine rule to triangle DNG DN = DG Sin (JJ-GG) Sin(#/2+HH-JJ) hence Sin(JJ-GG) = DM Cos (HH-JJ)' DG and

and eliminating DM from 3 and 4

Equation 5 is the general expression relating angle GG in terms of angles JJ and GG and length AD with given lengths JP, DG, PG and AD.

If the more particular case where the slider angle is always zero, as in the embodiment of Figure 13, and GG is controlled by varying AD, then equation 5 reduces to

Claims

1. A reversible plough comprising a headstock for attachment at one end to a tractor and provided with a substantially vertical axis main pivot at its other end, a beam connected by a rigid support to said main pivot whereby the beam is spaced from said axis and is pivotable thereabout in a substantially horizontal plane so as to be inclinable to either side of the direction of movement of the plough, a plurality of plough bodies pivotally supported by said beam for pivoted movement about substantially vertical axes whereby the plough bodies can pivot upon pivotal movement of the beam to maintain their trailing position substantially parallel with the direction of movement of the plough during pivotal movement of the beam, a parallelogram linkage having arms fixed to said plough bodies and to a link extending parallel to the beam, and a secondary pivot connecting said link and the headstock, the secondary pivot being spaced from the main pivot towards the front of the headstock and the length of the parallelogram linkage arms being such that in all pivotal positions of the beam, the line of the link between the points of connection to the arms is located between the main pivot axis and the beam, whereby as the beam is pivoted relative to the headstock, the plough bodies are controlledly pivoted relative to the beam.

2. A plough according to claim 1, wherein the secondary pivot is so-located or locatable that the plough bodies are inclined to the centre line of the headstock in a position to counteract the tendency of the beam to swing due to the resultant line of pull from the plough bodies being offset from the centre line of the headstock.

3. A plough according to claim 1 or 2, wherein means are provided for controllably varying the distance between the secondary pivot and the line of the link connecting the ends of the arms.

4. A plough according to claim 3, wherein the link is in the form of an isosceles triangle frame with the ends of its base being pivotally connected to the arms and its apex being connected to the headstock at said secondary pivot.

5. A plough according to claim 4, wherein at the apex of the triangular frame, an adjustable connection is provided to said secondary pivot

6. A plough according to claim 5, wherein the adjustable connection comprises a member controllably movable relative to the triangular frame in a direction perpendicular to said base, said member being pivoted to said secondary pivot.

7. A plough according to claim 6, wherein the member is comprised by an inner box section slidably movable within an outer box section fixed to the sides of said triangular frame and means for adjusting the position of the inner box section comprises a screw cooperating with both said box sections.

8. A plough according to any preceding claim, wherein the secondary pivot is;itself positionable relative to the headstock.

9. A plough according to claim 8, wherein the secondary pivot is itself positionable relative to the headstock along a locus extending at an angle to the length of the headstock.

10. A plough according to claim 9, wherein the angle of said locus is variable.

11. A plough according to claim 8, wherein the secondary pivot is displaceable about a radius centred on a fixed axis on said headstock.

12. A plough according to claim 11, wherein a pivot supporting member is mounted for movement about said fixed axis between limiting positions in which it is inclined to opposite sides of the headstock centre line, said secondary pivot being carried by said pivot supporting member.

13. A plough according to any one of the preceding claims, wherein said headstock is provided with means for holding said beam in required working positions inclined to the direction of movement of the plough.

14. A plough according to claim 13, wherein the means for holding the beam is adapted to hold the beam in either of two oppositely inclined limiting positions.

15. A plough according to any one of the preceding claims, wherein the link is secured to two plough bodies, said two plough bodies each being connected to at least one other plough body to ensure that the plough bodies are movable together and in parallelism one with the other.

16. A plough according to any one of the preceding claims, wherein each plough body comprises a point on a depending leg adapted to penetrate the soil in front of a rearwardly extending landslide which passes below and to the rear of a rotary ploughing disc.

17. A plough comprising a frame and, supported by said frame, tilling apparatus comprising a primary concave ploughing disc rotatable by reaction with the ground to be tilled and inclined in the direction of forward movement to provide a soil tilling and ploughing action and a secondary, smaller, ploughing disc mounted within the concavity of the primary ploughing disc and more greatly inclined to the direction of forward movement, in order to displace a sliver of soil together with stubble and straw off the surface of the ground, the primary ploughing disc being operative in use of the plough to roll the clean soil from the underside of the sliver over to cover the sliver of soil, stubble and straw initially displaced, the secondary ploughing disc being rotatable about its axis, a point depending from the frame to penetrate the ground in front of the forward edge of the primary ploughing disc, the secondary ploughing disc also having its forward edge substantially aligned with the point.

18. A plough according to claim 17, wherein a landslide extends rearwardly from the point below and to the rear of both said primary and secondary ploughing discs.

19. A plough according to claim 16, wherein each plough body comprises a secondary, smaller, ploughing disc mounted within the concavity of the first ploughing disc and being more greatly inclined to the direction of forward movement of the plough in order to displace a sliver of soil, together with stubble and straw, off the surface of the ground, the primary ploughing disc being operative in use of the plough to roll the clean soil from the underside of the sliver over to cover the sliver of soil, stubble and straw initially displaced, the secondary ploughing disc being rotatable about its axis.

20. A plough according to claim 17, 18 or 19, wherein the primary rotary ploughing disc and preferably also the secondary ploughing disc comprises a substantially flat central member having a frustoconical ploughing flange extending from its periphery.

21. A plough according to claim 20, wherein the ploughing flange comprises a plurality of teeth detachably secured to the periphery of the flat disc.

22. A plough according to any one of claims 16 to 21, wherein means are provided for pivoting the rotary ploughing disc about a substantially vertical axis between positions in which it is oppositely inclined to the direction of movement of the plough.

23. A plough according to claim 22, wherein means are provided for pivoting a or the secondary tilling member through an angle small than the angle of pivotal movement of the main rotary ploughing disc.

24. A plough according to claim 23, wherein the means for pivoting the secondary ploughing disc are operative responsive to operation of the means for pivoting the main rotary ploughing disc.

25. A plough constructed and arranged to operate substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.