GB2172486A

GB2172486A - Reversible plough

Info

Publication number: GB2172486A
Application number: GB08504424A
Authority: GB
Inventors: Richard John Hawes
Original assignee: Ransomes Sims and Jefferies PLC
Current assignee: Ransomes Sims and Jefferies PLC
Priority date: 1985-02-21
Filing date: 1985-02-21
Publication date: 1986-09-24
Also published as: GB8504424D0

Abstract

A reversible plough has a headstock for connection with a tractor three point linkage and a reversing spindle rotably mounted in the headstock. A main link extending between the reversing spindle and the plough frame carried the main bending, torsion and draft loads between the headstock and frame. Two further links of adjustable length extend between the reversing spindle and the plough frame. One of the adjustable links is so inclined relative to the main link as to define an imaginary intersection point which is spaced rearwardly of the plough frame. <IMAGE>

Description

SPECIFICATION Reversible plough This invention relates to reversible ploughs and is particularly concerned with means for adjusting the position of the plough frame relative to the headstock.

The width of the front furrow is determined by the lateral spacing between the front plough body and the tractor tyre. If it is desired to adjust the front furrow width,forexample because of a change in tractortyre size or wheel track or because of an adjustment made to the width of cut ofthe other bodies, the plough frame must be shifted laterally relative to the tractor. It is a disadvantage with certain known ploughs that such an adjustment of the frontfurrow width introduces a yawing moment on the tractor and necessitates a continuous steering correction. This is referred to as "crabbing". The criterion that must be satisfied if tractor crab is to be avoided is that the line of draft, that is to say the line of action of the force transmitted between the plough and tractor, must pass centrally through the tractor rear axle.The line of draft passes through the imaginary intersection point ofthe tractor lower links and the centre of pressure of the plough.

Means have been suggested forcarrying outthe necessaryadjustmentto remove or minimize tractor crab butthis adjustment is cross-coupled with the frontfurrowwidth adjustment so thatto change either parameter, at least two adjustments are necessary.

It is suggested in British patent No.203371 9B that the plough frame be connected to the reversing spindle by a main link which carries the main traction, flexure and torsional forces and a second link extends from the reversing spindle to the main link and is again adjustable in position. By adjusting the length ofthe second link it is possible to rotate the plough frame aboutthe pivotal connection between the frame and the main link. This effects the required change in front furrow width, the undesired change in attitude of each body being corrected automatically as ploughing begins by swinging of the headstock aboutthe lower links.However, this adjustment of the front furrow width will usually result in the line draft no longer passing centrally through the rear axle and a further adjustmenthasto be made byvaryingthe length of the third link to restore the balanced condition.

It is an object of one form of this invention to provide an improved reversible plough in which adjustment of the front furrow width and adjustmentofthe intersection between the line of draft and the tractor rear axle can be effected independenly, without one adjustment necessitating a compensating change in the other.

Accordingly, the present invention consists in a reversible plough comprising a headstock adapted for mounting on a tractorthree point linkage; a reversing spindle mounted in the headstockfor rotation about a generally longitudinally reversing axis; a plough frame carrying left-handed and right-handed plough bodies; a main link pivotally connected at one end to the reversing spindle and at the other end to the plough frame, the main link serving in use to transmit the main bending, torsion and draft loads between the headstock and the frame; a second link, of adjustable length, pivotally connected at one end to the reversing spindle and at the other end to the plough frame, the main link and second link lying in respective straight lines which intersect at a point rearward of the plough frame; and a third link, adjustable in length, pivotally connected at one end to the reversing spindle at a location spaced from the connection to the reversing spindle of at least one ofthe main and second links and pivotally connected at its other end to the plough frame at a location spaced from the connection to the plough frame of at least the other one ofthe main and second links.

It will be understood that by adjustment of the length of the third link, a rotation ofthe plough frame is effected aboutthe rearward point of virtual intersection ofthe main and second links. The change in attitude ofthe plough bodies is corrected automatical ly as ploughing commences by swinging movement ofthetractorlowerlinks. Sincethe pointaboutwhich the frame is rotated is rearward ofthe plough frame, the result is achievedthatthe movement in one lateral sense ofthe centre of pressure is accompanied by a movement in the opposite lateral sense ofthe imaginary intersection point between the tractor lower links such that the intersection between the line of draft and the tractor rear axle is substantially unaltered.The optimum location ofthevirtual in- tersection between the main and second links can be calculated in the manner hereinafter described so that tractor crab is avoided entirely.

Preferably, the main link and third link lie in respective straight lines which intersect at substantiallythe same distance forwardly ofthe headstock asthe imaginary point of intersection of the tractor lower links. In this way, adjustment in length of the second link effects a lateral shift in the intersection ofthe line of action and the rear axle, without change in the front furrow width. This adjustment may be necessary for example, if the centre of pressure is altered through changing soil conditions orthe addition of bodies.

In anotherform, the present invention consists in a reversible plough comprising a headstock adapted for mounting on a tractor three point linkage; a reversing spindle mounted in the headstockfor rotation about a generally longitudinal reversing axis; a plough frame carrying left-handed and right-handed plough bodies; two links each extending between the reversing spindle and the plough frame, the two links being mutually inclined in a horizontal plane so asto define an imaginary intersection rearwardly ofthe plough frame; and means for adjusting the position of the frame relative to the headstockto alter the frontfurrow width, said imaginary intersection point being selected so that, with the plough bodies in the working attitude, the intersection of the line of draft with the The drawings originally filed were informal and the print here reproduced is taken from a later filed formal copy.

The claims were filed later than the filing date within the period prescribed by Rule 25(1) of the Patents Rules 1982.

tractor reara,cle is unchanged by said adjustment of frontfurrowwidth.

The invention will now be described by way of example with reference to the accompanying draw ings in which: Figure lisa plan schematic view of a reversible plough according to this invention mounted on a tractorthree point linkage, Figures 2 and 3 are views similarto Figure 1 showing the resultoftwo separate adjustments, and Figure 4 is a viewsimilarto Figure 1 with identification of relevant dimensions for use in a calculation.

Referring to Figure 1, a tractor 1 is shown in partial outline with lower links 2 of a conventional three point linkage. The centre line ofthe rear axle is shown at 3 with tractor reartyres 4. The plough comprises a headstock 5, to opposite lateral extremities of which are pinned the tractor lower links 2. A reversing spindle 6 is mounted in the headstockfor rotation about a longitudinal axis and carries a rigid transverse arm 7.

The plough frame 8 carries sets of right-handed and left-handed plough bodies 9 arranged in conventional manner so as to be brought selectively into operation through rotation ofthe reversing spindle 6. Atransverse arm 10 is rigidly secured to the plough frame and a main link 11 connectsthis arm 10with the arm7 ofthe reversing spindle. The main link 11 is a substantial structurewhich carries the main bending, torsion and draft loads.

An adjustable length link 12 is pivotally connected at one end to the arm 7 and atthe other end to the arm 10.

Itwill be apparent to the skilled man that the adjustable length link can take a great variety of formes including a turn buckle and a hydraulic cylinder. The link 10 is inclined relative to the link 11 such thatthe lines in which the respective links lie, intersect at a point 15 which is a substantial distance rearwardly of the plough frame. Athird link 13 is pivotally connected to the arm 7 at the same location of the connection thereto ofthe arm 12 and is pivotally connected at its other end to the arm 10 ata location spaced from the connections thereto of the link 12 and the main link 11.

The adjustable length link 13 is inclined to the main link 11 such thatthe lines in which they lie intersect at a forward point 14 which is at approximatelythe same distance forward ofthe headstock5 as the imaginary lower link intersection point 16.

The line of draft, orthe line of action ofthe resultant force transmitted between the tractor and plough, is shown in Figure 1 at Rand passesthroughthe imaginary intersection point 16 of the tractor lower links and through the centre of pressure 18. In order forthereto be zero lateral force reaction on the front axle, the line of action R should pass centrallythrough the rear axle; that isto say the perpendicular separation of the line Rand the axle mid-point 17 as shown as X in the drawing, should be zero.

In orderto alterthefrontfurrowwidth shown atY, without altering the lateral force reaction on the front axle, it is necessary to maintain the dimension X constant and, usually, zero. If the length of link 13 is altered, the effect isto rotate the plough frame 8 about the intersection point 15 relativetothe headstock5.

Because the working plough bodies will tend to return totheiroriginalforeandaftrunning angles, once ploughing recommences, the tractor lower links will shift laterallyto rotate the plough frame through the same angle but in the opposite sense. The combined effect of these movements is to alter the furrow width Ywithoutchanging the distance X as shown in Figure 2. The optimum position ofthe intersection point 15 can be determined by testing or calculated in the manner hereinafter described.

In orderto alterthe distance X without adjusting the furrow width Y, the length ofthe link 12 is altered. This moves the frame 8 laterally and rotates it about a vertical axis relative to the headstock 5. However, because the lower link intersection point 16 is at sensiblythesameforward distancefromthe headstock as the point 14, and because the plough bodies tend to re-establish their previous for and aft running angles, the headstock5 moves laterally and rotates about a vertical axis an amount equal to the original adjustment but in an opposition sense. In this way the furrowwidth is returned to its original value but the intersection point 16 of the lower links is shifted thus altering the distance X as desired.This adjustment is illustrated in Figure 3 where the distance X has been reduced to zero by adjusting the length of link 12 an appropriate amount.

The manner in which the optimum position is calculated forthe imaginary intersection ofthe main and second links will now be described. Reference will be made to Figure 4 in which the relevant dimensions are identified.

It has been explained that in an ideal situation,the line of draft passesthrough the centre ofthetractor rear axle (when viewed from above).This produces a zero yawing moment on the tractor and therefore requires no steering correction. Ifthefrontfurrow width Y has to be adjusted for whatever reason, the position of the lower links and headstock must move laterally to enable the line of draft R to continue to pass through the centre ofthe back axle.

Thus if the frontfurrowwidth Y is reduced by a small amountAYthen the distanced ofthe centre of pressure from thefurrowwall decreases by Ad. If R is tocontinueto pass through the centre of the back axle:

Forsmall positional changes the headstock lateral movement A e is given by:

and rotates an amountn8(8 in radians) where: :--

Forthese conditions to be satisfied, the adjustment between theframeand the the headstock must make up the difference between the intended frontfu rrow width change A Y and the movement ofthe headstock A e, and rotate an amount in the opposite sense to the headstock rotation so as to maintain the alignment ofthe bodies.

The distance Z to the instantaneous centre of rotation ofthe adjustment between the frame and the headstock is therefore given by:

where A Y is positive when Y increases and A e is positive when the headstock is moving towards the front plough body.

Using equation (3) and the expansion

it can be seen that

In orderto calculate A dye e it can be seen from equation (7j that:

substituting in equation (2) gives-

and by substituting forA e in equation (3) and rearranging itcan be seen that

In orderto calculte A d/E Y, that is to saythe lateral shift in the centre of pressure consequent upon a change ofthe frontfurrowwidth, it is necessary to derive an expression for the position of the centre of pressure.From field measurements, it has been found thatthe centre of pressure of an individual body is approximately 0.8 x furrow width F from the furrowwall and a constant distance h rearward of the point Thus for a multi-furrow plough with N bodies and afrontfurrowwidth of Y, and a general furrow width F, the distance d ofthe centre of pressure from thefurrowwall is

This equation applies only to ploughs having three or more bodies; the expression for less than three bodies is:

It can be observed thatthe distance ofthecentre of pressure from the instantaneous centre ofthe lower links, which is required in equation (8) above, is given buy a = c + m + h + (N-1)q/2.Equation (10) can be s differentiated with respectto Y giving:

In the case where the frontfurrowwidth Y is adjusted to be equal to the general furrow width F, this reduces to :-

Therefore by substituting from equations (8) and (12) in equation (5) it can be seen that

Example In a multi-furrow plough having the dimensions (shown in Figure 4) as follows::- b = 1.398 m c=2.412m h = 0.508 m m = 0.250 m q=0.801 m p=0.914m when = F = 0.356 m the value of the dimension Z can be calculated from the expressions given above for various numbers of furrows as follows:- Numberoffurrows ZMeters 3 9.7 4 12.2 5 14.6 6 17.0 7 19.3 8 21.6 It should be understood thatthis invention has been described by example only and a variety of modifications are possible without departing from the scope of the invention. Thus, for example, whilst the arrangement has been described of a reversing spindle having a rigid lateral arm, other means could be employedforsecuring the linktothe reversing spindle. Whilstthe arrangement of a main link and two adjustable links is advantageous in providing separate adjustments as described, there may in certain cases be advantage in having an arrangement oftwo linkswith some means for adjusting the position ofthe frame relative to the headstock. This arrangement would permit adjustment ofthe front furrowwidth without change in intersection of the line of draft with the tractor rear axle but would not of itself allowfor alteration of that intersection pointfor other purposes. The means for adjusting the position oftheframe relative to the headstock might be a further link but could take other forms.

Claims

1. A reversible plough comprising a headstock adapted for mounting on a tractor three point linkage; a reversing spindle mounted in the headstockfor rotation about a generally longitudinal reversing axis; a plough frame carrying left-handed and righthanded plough bodies; amain link pivotally connected at one end to the reversing spindle and at the other end to the plough frame, the main link serving in use to transmitthe main bending,torsion and draft loads between the headstock and the frame; a second link, of adjustable length, pivotally connected at one end to the reversing spindleandattheotherendto theploughframe,the main link and second linklying in respective straight lines which intersect at a point rearward ofthe plough frame; and a third link adjustable in length, pivotallyconnected at one end to the reversing spindle at a location spaced from the connection to the reversing spindle of at least one of the main and second links and pivotally connected at its other end to the plough frame at a location spaced from the connection to the plough frame of at least the other one ofthe main and second links.

2. A reversible plough according to Claim (1), wherein the main link and third link lie in respective straight lines which intersect substantially the same distance forwardly of the headstock as the imaginary point of intersection of the tractor lower links.

3. A reversible plough comprising a headstock adapted for mounting on a tractorthree point linkage; a reversing spindle mounted in the headstockfor rotation about a generally longitudinal reversing axis; a plough frame carrying left-handed and righthanded plough bodies; two links each extending between the reversing spindle and the plough frame, the two links being mutually inclined in a horizontal plane so asto define an imaginary intersection rearwardlyofthe plough frame; and meansfor adjusting the position ofthe frame relative to the headstockto a Iterthe front fu rrowwidth, said imaginary intersection point being selected so that, with the plough bodies in the working attitude, the intersection ofthe line of draftwith the tractor rear axle is unchanged by said adjustmentoffrontfurrow width.

4. A reversible plough substantially as hereinbefore described with reference to and as shown in the accompanying drawings.