GB2120074A

GB2120074A - Draft control device

Info

Publication number: GB2120074A
Application number: GB08313541A
Authority: GB
Inventors: Gottfried Achberger; Franz Muller
Original assignee: ZF Friedrichshafen AG
Current assignee: ZF Friedrichshafen AG
Priority date: 1982-05-19
Filing date: 1983-05-17
Publication date: 1983-11-30
Also published as: GB8313541D0; IT1163295B; DE3218846A1; GB2120074B; IT8320914A0

Abstract

A draft control device for a tool connected to a tractor is such that no hysteresis, such as a bearing play, may impair the sensitivity of the measurement. The device includes a mounting plate or frame (6) for connection to the tractor which is distortion-free, but has arms (41,42) having a predetermined elasticity. Mounting bolts (39, 40) for the lower draft links 29, 30 are rigidly attached to these arms and operatively connected to a summing member, e.g. a deflectable sleeve 21 or bending rod, which deflects in dependence on draft forces on the links to contact a sensor 28 formed by a variable throttle in the tractor hydraulic circuit whereby the links are raised or lowered. <IMAGE>

Description

SPECIFICATION Pick-up for tool guide rod The invention relates to a pick-up for a lower guide rod for a tool, for example for a tractor wherein the rod acts as the dynamometer ofa control device for maintaining constant the operating height of a soil cultivation implement drawn and guided via upper and lower guide rods by the tractor, having a summing memberfordetecting a resultant physical magnitude formed from the forces of traction acting on the lower guide rods and having a sensorfor detecting and converting the magnitude produced.

German Patent Specification 2855544 discloses a pick-up for the measured values of a lower guide rod in which a resultant is formed from forces acting on lower guide rod cranks. Asolid shaft comprises a central torsionally rigid section and two externally disposed further sections supported on the gearbox housing as the torsion device. The solid shaft is mounted in friction bearings provided on the housing side. The detection of torsion paths of the solid shaft is influenced by the respective play ofthe friction bearings.

Afurther pick-up for the measured values of a lower guide rod is known from the German Patent Specification 3017735, in which a torsion tube acting as the torsion device is disposed concentricailyto a summing shaft. The torsion tube is connected in a rotationally fixed manner at one of its ends with the summing shaft and at its other end with the housing.

Although a compact construction may be achieved with this known device, a necessary bearing play is also included in this case in the measurement.

An object of the invention is to provide a pick-up for the measured values of a lower guide rod, in particular for tractors, which is free from hysteresis in a compact construction with respect to the known devices and maytherefore process very small signal values.

According to the invention, there is provided a pick-up forthe measured values of a lower guide rod foratool,forexampleforatractorwhereinthe rod acts asthedynamometerofa control device for maintaining constant the operating height of a soil cultivation implement drawn and guided via upper and lower guide rods bythetractor,the pick-up having a summing memberforthe production of a resultant physical magnitude formed from the forces of traction acting on the lower guide rods and having a sensorfor detecting and converting the magnitude provided, characterised in that a distortion-free plate is provided for fastening to a carrier body such as a tractor, which plate on one hand produces a rigid connection between the body and the sensor and, on the other hand, comprises arms of predetermined elasticity for the fastening of bolts acting as a pivotable mounting for the lower guide rods, which bolts are in operational connection with the sensor via the summing member.

With respecttothe known devices, the invention has the advantagesthat the measured value pick-up reacts to very small paths of variation and the servo hydraulic system may consequently act on the lower guide rods in the case of relatively small power modifications, as the disadvantageous bearing play of the known measured value pick-ups is completely eliminated. As a result of the possibilityof attaching an adjustable drawbarto the distortion free plate (or equivalentframe),there is no need, when the invention is used with a tractor, for additional means forthe attachment of an adjustable drawbar directlyto the tractor.

The invention is described with respect two embodi mentsthereofwith reference to the accompanying drawings, in which: Figure lisa partial diagrammatic view of the rear region of a tractor with a soil cultivation implement attached thereto together with a pick-up for the measured values of a lower guide rod in accordance with the invention, Figure 2 is a top view of an embodiment of a pick-up forthemeasuredvaluesofa lower guide rod in accordance with Figure 1, Figure 3 is a further embodiment of a measured value pick-up ofthe invention utilising a bending rod, Figure 4 is a cross section along the line IV-IV through the embodiment of Figure 3.

A soil cultivation implement 5, for example a plough, is attached to a tractor 1 by means of a three-point linkage. This implement may be raised or lowered atwill buy a lifting arm 8via a lifting rod 7. The three-point linkage comprises an upper guide rod 3 and two lower guide rods 29,30 (Figures 1,2). If the tractor 1 travels in the direction ofthe arrow 4, the soil cultivation implement 5 penetrates into the ground to a greater or lesser degree depending on the subsoil condition. In orderto maintain the force of traction on the tractor as constant as possible, the soil cultivation implement 5 is raised by the lifting arm 8 and the lifting rod 7 in the case of comparatively high forces of traction and lowered in the case of comparatively low forces of traction.

A pick-up for measured values of a lower guide rod comprises a distortion-free frame or plate 6 (Figures 1, 2), which has walls 49,66,67 projecting from the plane ofthe plate in order to increase its rigidity (Figure 2).

Bores 55,56,57, 58 are provided forthe attachment of the plate 6to the tractor 1. Arms 41,42 are provided on the plate 6, outside of the distortion-free area thereof, which arms possess a predetermined elasticity and serve forthe fastening of bolts 39,40 which are provided with ball joints 47,48 by means of which the lower guide rods 29,30 are in turn mounted on the bolts. Locking discs 45,46 attached rigidly to the bolts 39,40 prevent the ball joints 47,48 ofthe bolts from sliding off.

In this embodiment, the bolts 39,40 (Figure 2) are provided in each case with a conical section which is inserted in a hub 43,44 with a conical internal bore disposed atthe end of the arms 41,42 and is locked by a nut 53,54, so that a rigid connection is produced between the bolts 39,40 and the arms 41,42. The bolts 39,40 are respectively provided with extensions 37,38 whose free ends 35,36 are disposed in a sleeve 21 acting as a summing member. The sleeve 21 is scanned by a tappet 20 of a sensor 28. A bushing 19 of soft material, for example rubber, may be provided to surround the tapper 20 between the sleeve 21 and the sensor 28 in order to protect against fouling The sensor 28 is disposed on a mounting plate 18 which is, in turn, fastened to the wall 67 of the plate 6.

In the embodiment, the sensor 28 is formed buy a variable throttle (Figure 2) disposed in a hydraulic circuit. The circuit also comprises a cylinder 16 controlled by a way-valve 14 via a conduit 1 5 for the actuation ofthe lifting arm 8. A pump 9which supplies fluid from a tank 10 and is used as the operating pump operates on a line 13which leads to the way-valve 14 and is returned from this point, via the conduit 17, to the tank 10. A pressure reliefvalve 11 lies in parallel with the pump 9.The hydraulic circuit also comprises a further pump 12 used as a control pump which operates on a bridge circuit comprising restrictors 23, 24, a variable throttle 27 and the sensor 28 in the form ofthe variable throttle. The sensor 28 is connected to thevariablethrottle 27 bya conduit 22 and a conduit 31 leads from the sensor 28 back to the tank 10.

Control conduits 25,26 leading to both hydraulic control inputs ofthe way-valve 14 are connected to the hydraulic bridge circuit. The hydraulic bridge circuit is set bythe variable throttle 27 in such a way that identical pressure conditions are present at the control inputs ofthe way-valve. As a result of the action of two springs on the way-valve, its slide is maintained in the central position shown in Figure 2. In this condition, the pump 9 returns pressure medium to the tank 10.

As a result of actuation ofthetappet 20 ofthesensor 28, the symmetry ofthe hydraulic bridge circuit may be disturbed. If the pressure present in the control conduit 26 increases, for example with respect to that in the control conduit 25, the way-valve 14 is adjusted such thatthe conduit 13 is connected with the conduit 15via the way-valve 14 and the cylinder 16 receives pressure medium and actuates the lifting arm 8 as a result ofwhich the soil cultivation implement 5 is lifted via the lifting rod 7.

However if the pressure present in the control conduit 26 decreases below the value present in the control line 25, the slide ofthe way-valve is brought into the opposite end position, as a result of which the conduit 17 is connected with the conduit 15 and therefore to the tank 1 via the slide ofthe way-valve 14. As a result ofthis, the cylinder 16 receives the pressure medium via the conduit 15, the way-valve 14 and the conduit 17, the soil cultivation implement5 is lowered under its own weight and thereby takes with it the lifting arm 8 via the lifting rod 7.

In a chamber 50 formed in one ofthe walls 49,67, the sensor 28 and the ends of the extensions 37,38 of the bolts 39,40 are located. The extensions 37,38 penetrate into the chamber 50 through openings 51, 52.

When the tractor 1 travels in the direction of the arrow 4,forces act in the direction of the arrows 64,65 on the bolts 39,40 via lower guide rods 29,30 and the ball joints 47,48. As the bolts are rigidly connected with the arms 41,42 they are only very slightly twisted with respect to the distortion4ree plate 6. In relation to positions 61,62 (Figure 2), there is produced in each case a path 59 or 60 for elastic deformation, the free ends 35 and 36 ofthe exten sions 37,38 are correspondingly deflected and form a sum of the described movement via the sleeve 21.

The deflection of the sleeve 21 finaliy leads to a greater or lesser actuation ofthetappet 20 of the sensor 28. The actuation ofthe sensor 28 causes a reaction in the hydraulic circuit as described above and leads to raising or lowering ofthe soil cultivation implement 5.

A bolt 63 (Figures 1,2) may be fastened to the plate 6 and procided with a nut 68. By means of this fastening means, a drawbarattachmentmay be connected if this is required forthe particular soil cultivation implement. A separate facility for fasten- ing a drawbar attachment to a tractor in a direct manner is notthen required.

In accordance with a further embodiment of the invention, arms 81,82 are provided on a further disto rtion-free plate 70 (Fig ure 3), wh ich arms termi n- ate in each case in a hub 93,94. The latter act as fasteningsfor bolts 79,80 by means ofthe nuts 53,54 in the manner described above. The lower guide rods 29,30 are pivotably mounted on the bolts in the same wayvia ball hoints47,48and prevented from sliding by the discs 45,46.

On the ends ofthe bolts 79,80, opposite to the discs 45,46, bearing pieces 73,74 are provided on the bolts, these being formed either by suitable machining of the bolt ends or by fitting on the bolts. The bearing pieces 73,74 are provided with recesses in which the ends of a bending rod 71 are mounted. The bending rod 71 is pre-stressed and guided on a mounting plate 72 by means of a guide fork 83 (Figures 3,4) which plate is attached to a wall 89 ofthe plate 70 and serves to fasten the sensor 28. The wall 89 and furtherwalls 88,91,92 stiffen the plate 70.

When the tractor 1 travels in the direction ofthe arrow 4, forces act in the direction ofthe arrows 64,65 on the bolts 79,80 via the lower guide rods 29,30 of the soil cultivation implement 5 and the ball joints 47, 48. As a result there is a slight bending of the arms 81, 82 on the distortion-free plate 70. The load-dependent bending ofthe arms 81,82 with respect two positions 84 and 85 leads to paths 86 and 87, which provide a measurementforthe elastic deformation ofthe arms.

This elastic deformation leads to a modification ofthe pre-stressing, i.e. the bending ofthe bending rod 71, as a result of which the bending rod 71 forms the sum of the elastic deformations of both arms 81,82 in a direct manner. Whereas in the embodiment of Figure 2theoperationalconnection betweenthe bolts and thesensorwas provided via the sleeve acting asthe summing member,theoperational connection ofthe embodiment of Figure 3 is provided directly by means of the bending rod 71. Bores 75,76,77,78 are provided for the fastening of the plate 70 to thetractor 1. The sensor 28 and the bending rod 71 are disposed in a protected manner in a chamber 95 which is formed bythewalls 89,91,92 and the wall portion 90.

The plate 6 (Figure 2) and the plate 70 (Figure 3) may be produced as one-piece cast components.

Both plates may also be produced as weight-reducing frames with transverse reinforcements.

The pick-up forthe measu red values of a lower guide rod may also be used as a monitoring pick-up in steel construction, building machines, machine tools or crane construction. It may be used in all cases in which hydraulic monitoring, control or regulation is employed.

Claims

1. Apick-upforthe measuredvaluesofa lower guide rod fora tool, for example for a tractor wherein the rod acts as the dynamometer of a control device for maintaining constantthe operating height of a soil cultivation implement drawn and guidedvia upper and lower guide rods by the tractor, the pick-up having a summing memberforthe production of a resultant physical magnitude formed from the forces oftraction acting onthe lowerguide rods and having a sensorfor detecting and converting the magnitude provided, characterised in that a distortion-free plate is provided for fastening to a carrier body such as a tractor, which plate on one hand produces a rigid connection between the body andthe sensorand, on the other hand, comprises arms of predetermined elasticityforthefastening of bolts acting as a pivotable mounting forthe lower guide rods, which bolts are in operational connection with the sensor via the summing member.

2. A pick-up as claimed in claim 1, characterised in thatthe said arms form a one-piece component with the plate.

3. Apick-upasclaimedineitherofclaims 1 or2, characterised in thatthe bolts are rigidly mounted on the arms ofthe plate.

4. A pick-up as claimed in any one of claims 1 to 3, characterised in thatthe bolts are provided with extensions whose free ends are in operational connection with the sensor via the summing member.

5. A pick-up as claimed in any one of claims 1 to 3, characterised in thatthe bolts are in operational connection with the sensor via a bending rod clamped between them and acting asthesumming member.

6. A pick-up as claimed in any one of claims 1 to 5, characterised in that the sensor is a variable throttle located in a hydraulic circuit.

7. A pick-up as claimed in claim 6, characterised in that the sensor forms a bridge element in a hydraulic bridge circuit.

8. Apick-up as claimed in any one of claims 1 to 7, characterised in that means for pivoting an adjustable drawbarfor a soil cultivation implement are provided on the distortion-free plate.

9. A pick-up as claimed in claimS, characterised in thatthe bending rod is mounted in bearing pieces which are fixed to the bolts.

10. A pick-up as claimed in claims, characterised in thatthe bending rod is mounted in bearing pieces which form the one-piece components with the bolts.

11. Apick-up as claimed in any one of claims 1 to 10, characterised in that the distortion4ree plate is constructed as a frame.

12. A pick-upforthe measuredvaluesofa lower guide rod for a tool, substantially as hereinbefore described with reference to the accompanying drawings.