GB2075325A - A traction load sensing mechanism for a tractor - Google Patents

Abstract

The mechanism 1 comprises a torsionally rigid shaft 7 which is rotatably mounted in the side walls 4 of a gearbox casing 15. At its ends the shaft 7 carries respective crank arms 2 and 12 which are rotationally fast with the shaft and which are respectively connected to one end of bottom links (draft arms) 3 and 13 attached at their other ends to the working implement. A torsion tube 6 coaxially surrounds the shaft 7 and at one end is connected rotationally fast via splines 16 in a bearing bore 5 of one casing side wall 4. At its other end the torsion tube 6 is rotatably supported in a bearing bore in the opposite side wall 4 of the casing 15 and is connected rotationally fast to the adjacent end of the shaft 7 via splines 14. An element 8 fast on the torsion tube 6 serves to transmit, to a control device to a power lift on the tractor, variations in the traction force acting on the crank arms 2 and 12 to maintain substantially constant the working depth of the implement. <IMAGE>

Description

SPECIFICATION An arrangement for controlling the working depth of a soil-cultivating implement articulated to a trac tor This invention relates to an arrangement in a trac ;tor for controlling the working depth (ploughing work in hilly country) or the level of traction force (a tractor travelling at its power limit) of a soilcultivating implement, for example a plough articu lated to the tractor, wherein, in order to achieve a substantially constant working depth, changes in the traction force values are sensed via a measured value transmitter and passed on to a control system of a power lift on the tractor, the forces being intro duced via bottom links on crank arms connected thereto and being summated via a torsionally rigid summation shaft and acting against a torsion means supported in the gearbox casing of the tractor, the summation shaft being so mounted inside said cas ing that at least one of the shaft ends extends out wards through a casing side wall and each shaft end carried rotationally and displaceably fast one of said crank arms.

In agricultural tractors, bottom link (draft arms) measured value transmitters act as force-measuring members between the tractor and a soil cultivating implement such as, for example, a plough, pulled by the tractor. The values measured by the transmitter are transmitted either via a mechanical linkage or electric or hydraulic signal transmission to control a control valve. The valve controls a lifting mechanism which, in dependence on the signal from the meas ured value transmitter, influences the depth of penetration of the plough and thereby keeps the traction force of the implement constant or ensures that it follows the unevennes of the terrain in a suit able manner.

German Auslegeschrift 28 55 544 discloses a bottom link measured value transmitter which consists of a solid shaft made up of three main portions, namely a central, torsion-resistant portion and two outer shaft portions of tapering diameter which act as torsion rods. The shaft is so disposed that it extends through the gearbox casing, a crank arm of a bottom link being disposed rotationally fast at each of the ends of the torsion-resistant shaft portion emerging from the casing, while each free end of the torsion rod portions of the shaft is indirectly con nected rotationally fast to the casing.Via the two crank arms, the tensile and compressive forces pro duced by the working implement (plough) so act on the solid shaft that the torque produced by them twists the two torsion portions of the solid shaft and rotates the torsion-resistant shaft central portion in accordance with the additive twisting paths. Via an entraining member disposed on the shaft central portion, the twisting path is passed on by means of suitable devices to a control device. It is true that this known bottom link measured value transmitter is relatively cheap to manufacture, but due to the two relatively long torsion shaft portions it occupies a lot of space, and moreover the rotationally fast attach ment of the two outer torsion rod ends requires a special bearing connected to the casing.If the sealing elements on the crank arms have to be exchanged, the corresponding external bearing of the torsion rod portions must be removed every time, and this reduces the serviceability of this known measured value transmitter.

US Patent Specification 37 22 598 also discloses a bottom link (draft arm) measured value transmitter which has a torsion rod and a torsion-resistant summation hollow shaft which carries crank arms or ears and is disposed concentric with the torsion rod, the summation hollow shaft being so disposed between two bearing blocks extending out of a rear axle casing that the torsion rod is connected rotationally fast by one end via splines to the rear axle casing, while at the other end of the torsion rod is connected rotationally fast via splines to the hollow shaft which encloses the torsiorf rod and is pivotably mounted in the bearing biocks.

Other bottom link measured value transmitters are also known (inter alia, for example, the driving mechanism T 6600 made by Zahnradfabrik Friedrichshafen) in which the crank arms are attached positively to a torsion-resistant hollow shaft. The hollow shaft is mounted through the rear axle casing, through which the hollow shaft extends, the crank arms being disposed outside the casing. Disposed inside the hollow shaft and concentric therewith is a torsion rod which is positively connected at one end to the hollow shaft, while its other end extends out of the hollow shaft and is positively connected via a support to the rear axle casing, as a result resiliently supporting the torque taken over by the hollow shaft.The twisting of the hollow shaft, as a measure of the forces operative in the bottom links, is picked up by a lever connected to the hollow shaft and passed on for further signal processing.

In these prior art measured value transmitters the relatively long hollow shaft has three entraining sections whose positions depend upon one another, including an inner section, lying substantially in the centre between the two outer sections, and this makes manufacture very expensive. Moreover, at its end projecting out of the hollow shaft the torsion rod is unprotected from the surrounding influences, and the locking part (support) is disposed externally and unprotected. The selected arrangement of the locking part is difficult to control, in relation to the stressing, and moreover a relatively expensive screwed connection is needed. Moreover, access is rendered difficult to the locking-part side sealing elements, which are highly subject to wear, and this has a negative effect on the serviceability of the prior art bottom link measured value transmitters.In these known measured value transmitters (including those disclosed in the aforementioned US Patent Specification), the two splines, torsion rod hollow shaft, torsion rod locking part, are not oil lubricated, and this causes the risk of fretting corrosion, leading to frictional losses and corresponding reduction in the sensitivity of the measured value transmitters.

It is an object of the invention to provide a bottom link measured value transmitter which is compactly constructed and is very reliable in operation, is protected to the maximum extent against surrounding influences (dirt, impacts) and is readily serviceable and has a very small number of parts. Fretting corrosion is also avoided, and the attainment of minimum frictional losses achieves as high a measuring accuracy as possible.

Accordingly, the present invention provides in a tractor an arrangement for controlling the working depth and level oftraction force of a soil-cultivating implement articulated to the tractor, for example a plough, wherein, in orderto achieve a substantially constant working depth, changes in the traction force values are sensed via a measured value transmitter and passed on to a control system of a power lift on the tractor, the forces being introduced via bottom links on crank arms connected thereto and being sum mated via a torsionally rigid summation shaft and acting against a torsion means supported in the gearbox casing of the tractor, the summation shaft being so mounted inside said casing that at least one of the shaft ends extends outwards through a casing side wall and each shaft end carries rotationally and displaceably fast one of said crank arms, characterised in that the torsion means is a torsion tube coaxially surrounding the summation shaft, the torsion tube being connected rotationally fast to the summation shaft at one end and to said casing at the other end.

Thus the torsion tube and summation shaft are disposed inside the casing and extend to and through correspondingly opposite casing bearing bores; at each of the two ends of the comparatively long summation shaft a crank arm is disposed rotationally fast, the shaft being supported via lowfriction plain bearings disposed between the crank arm and the casing bearing bore. This arrangement avoids the direct bearing of the torsion tube in the casing bearing bore and therefore undesirable frictional losses and corresponding phenomena of abrasive wear.The placing of the torsion tube inside an oil-filled casing allows the optimum lubrication of the contact surfaces, for example, between the summation shaft and the torsion tube, so that no frictional losses influencing the measured values can occur, and moreover the satisfactory oil lubrication of the splines of the measured value transmitter according to the invention prevents any possible fretting corrosion. Conveniently, the torsion tube is directly connected to the casing side wall via splines in the casing bearing bore. Preferably, the torsion tube is connected rotationally fast to a bearing flange via splines; the flange can be centred in the casing bearing bore of the side wall and be attached in known mannervia pins or screws, in accordance with assembly possibilities, to the casing inner wall or the casing side wall.

Advantageously, that end of the summation shaft which is not connected to the torsion tube is connected at the end face by friction welding to the corresponding bottom link crank arm, while the other end of the summation shaft is connected in known manner via an entraining section rotationally fast to the second crank arm. The friction welding of one shaft end to the first crank arm affords the advantage of saving a number of elements, such as a sealing element, nut screwed connection and nut lock and also expensive machining operations for producing the splines, resulting on the one hand in a saving of parts and on the other in the combination of individual parts into structural groups and therefore an assembly cheap and easy to assemble.

In order that the invention may be more readily understood, reference is made to the accompanying drawing which illustrates diagrammatically and by.

way of example one embodiment of the invention in partial axial section.

Referring to the drawing, which is a diagrammatt cal axial section, a bottom link measured value transmitter 1 mainly comprises a torsion-resistant summation shaft 7 which is so disposed in a casing 15, mounted on a tractor, that the shaft 7 extends through appropriate bearing bores 5 in the casing side walls 4 to the outside on at least one side. A crank arm 2, in which a bottom link 3 engages, is rigidly connected by end face friction welding to the left-hand (as viewed in the drawing) end of the shaft 7, while at the other (right-hand) end of the shaft 7 splines 14 are provided via which a further crank arm 12, with which a bottom link 13 engages, is mounted on the shaft 7. A screwed connection 11 secures the crank arm 12 against displacement axially outwards.

Arranged on the inwardly facing ends of each of the crank arms 2 and 12 is a sealing element 9, while a sealing element 10 is located between the crank arm 12 and the shaft 7, the result being a reliable sealing of the shaft assembly. A comparatively thin-walled torsion tube 6 is so arranged coaxially to the summation shaft 7 that the thickened ends of the tube 6 extend in a radially supporting manner into the appropriate casing bearing bores 5, the left-hand end of the torsion tube 6 having outer splines 16 via which it engages in complementary splines of the corresponding left-hand casing bearing bore 5. The right-hand end of the torsion tube 6 has internal splines which engage complementary splines of the summation shaft 7, so as to connect the two parts rotatably fast to one another.Mounted at the righthand end ofthe tube 6, adiacent the right-hand casing bearing bore 5, is an entraining member 8 in the form of a shrunk-on ring orthe like with an entraining pin orthe like.

The lower link measured value transmitter according to the invention operates as follows: The tensile or compressive forces generated whiten the working implements are used engage via the bottom links 3 and 13 the crank arms 2 and 12 respectively, and produce a torque which rotates the summation shaft 7 around its axis. In this rotary movement the right-hand end ofthetorsion tube 6, which is connected rotatably fast to the summation shaft 7, is co-rotated by the same amount, so that the torsion tube, which is retained at its left-hand end by the splines 16 fast in the casing bearing bore 5, is twisted against the resilient force of the torsion tube 6. At the same time the entraining member 8 will share in the same rotary movement and transmit via suitable devices signals to a control system on the tractor, which system controls the depth of ploughing accordingly.

Claims (6)

1. In a tractor an arrangement for controlling the working depth and level of traction force of a soil cultivating implement articulated to the tractor, for example a plough, wherein, in order to achieve a substantially constant working depth, changes in the traction force values are sensed via a measured value transmitter and passed on to a control system of a power lift on the tractor, the forces being intro 'duced via bottom links on crank arms connected thereto and being summated via a torsionally rigid summation shaft and acting against a torsion means supported in the gearbox casing of the tractor, the summation shaft being so mounted inside said cas ing that at least one of the shaft ends extends out wards through a casing side wall and each shaft end carries rotationally and displaceably fast one of said crank arms, characterised in that the torsion means is a torsion tube coaxially surrounding the summa tion shaft, the torsion tube being connected rota tionally fast to the summation shaft at one end and to said casing at the other end.

2. In a tractor an arrangement as claimed in claim 1, wherein the torsion tube is connected directly by means of splines in a casing bearing bore to the cas ing side wall.

3. In a tractor an arrangement as claimed in claim 1, wherein the torsion tube is connected rotationally fast to a bearing flange via splines, the bearing flange being centred in the casing bearing bore and being attached to the casing inner wall.

4. In a tractor an arrangement as claimed in claim 1, wherein the torsion tube is connected rotationally fast via splines to a supporting flange which is centred in the casing bearing bore and is attached to the casing side wall.

5. In a tractor an arrangement as claimed in claim 1, wherein that end of the summation shaft which is not connected to the torsion tube is connected at the end face by friction welding to the adjacent one of the crank arms, while the other end of the summa tion shaft extends through the other crank arm and is connected rotatably fast thereto via splines.

6. In a tractor an arrangement for controlling the working depth and level of traction force of a soil cultivating implement articulated to the tractor, sub stantially as herein described with reference to the accompanying drawing.