GB2147186A - An agricultural tractor - Google Patents

Abstract

A tractor has front wheels (38) and a lifting device (44) which is wider than the overall distance between the outer faces of the front wheels (38). The lifting device (44) comprises a quadrilateral linkage defined by pivot axes (47,50,57,58). The rear pivot axes (47,58) are connected to the tractor to the rear of the front wheels (38). The lower lifting arms (45) are longer than the upper arms (46) and are at or below the level of the wheel axes. A control system is provided for maintaining the engine speed constant by raising or lowering the lifting device (44), so adjusting the resistance to travel. <IMAGE>

Description

SPECIFICATION An agricultural tractor This invention relates to an agricultural tractor.

According to one aspect ofthe present invention there is provided an agricultural tractor having one or more front wheels and a lifting device disposed atthe front of the tractor, the width of the lifting device, with respect to the normal direction of travel ofthe tractor, being greaterthan the distance between the outer mostboundarvfacesofthefrontwheel orwheels.

With a tractor constructed in this manner a very stable support of broad machines or implements, more particularly soil cultivating machines, coupled with the lifting device can be obtained. Such machines can exertconsiderablyvarying forces in the longitudinal direction on the tractor.

According to a second aspect ofthe present invention there is provided an agricultural tractor comprising a frame, front and rear wheels rotatable about respective axes, and a lifting device which is pivotally connected to the frame at a pivotal axis which is approximately at the same heightas or lower than thefront wheel axis and between the front and rear wheel axes.

According to a third aspect ofthe present invention there is provided an agricultural tractor having a lifting device atthefront end ofthe tractor, with respect to the normal travel of the tractor, lifting device having at its front end at least one ground wheel.

According to afourth aspect ofthe present invention there is provided an agricultural tractor comprising a driving engine and a lifting device, a control system forthe lifting device being provided which is responsive to the engine whereby a decrease in the speed of the engine results in lifting of the lifting device.

For a better understanding ofthe present invention and to show how it may be carried into effect, reference will now be made, by way of example, to the accompanying drawings, in which: Figure 1 is a side view of a tractor provided with a lifting device carrying a cultivator; Figure 2 is a plan view ofthe tractor and cultivator of Figure 1; and Figure 3 is a schematic circuit diagram representing acontrol circuitforthe lifting device.

The tractor comprises a frame 1, which is disposed symmetrically with respect to the vertical central longitudinal plane 2 ofthetractor (Figures 1 and 2).

The frame 1 comprises two substantially horizontal, parallel beams 3which extend forwardly from the rear oftheframeand meet, attheirfrontends, supporting beams 4which slope upwardly and forwardly with respect to the normal direction A of operative travel of the tractor. The beams 4, like the beams 3, are parallel to the plane 2.

A horizontal tie beam 5 is fastened across the top ends ofthe two supporting beams 4 and extends at right anglesto the plane 2. Two horizontal L-shaped profiles 6 are fastened to the tie beam 5 and extend forwardly from the beam 5.

The L-profiles 6 are spaced apart but converge slightly in the forward direction.

The front ends of the two L-profiles 6 are rigidly interconnected by a vertical end plate 7 which is at right angles to the plane 2. The horizontal flanges of the profiles 6 face each other and are covered on their top sides across their common width by a cover plate 8. The sloping supporting beams 4 and the profiles 6 constitute a gooseneck front portion ofthe frame 1, below which are situated frontwheelswhich will be described in more detail later. The beams 3 are disposed at a height above the ground which is substantially equal to half the diameter of the tractor wheels, and are rigidly interconnected at their rear ends by a horizontal tie beam which is at right angles to the plane 2.The tie beam 9 is provided on its rear face with rearwardlyextending lugsholding horizontal pins which are normal to the plane 2, about which are pivotable the lower lifting arms 10 of a rear three-point lifting device 11. The tie beam 9 also has lugs receiving further pins which are normal to the plane 2 and about which are pivotablethe lower ends of hydraulic rams 12. As shown in Figure 2, the lower lifting arms 10 are inclined slightly outwardly to the rear away from the frame 1 and the hydraulic ram 12 associated with each lifting arm 10 is pivotally connected to the tie beam 9 at a position slightly outboard ofthe pivotal axis by which the associated lower lifting arm 10 is fastened to the frame.

Figures 1 and 2 show support plates 13 welded to the top faces ofthe rear ends of the two beams 3, these plates 13 extending upwardly and being initiallyfairly strongly inclined inwardlytowards the plane 2, after which they are bent upwardlyto extend parallel to the plane 2, the upper parts ofthe supports 13 being close to the plane 2. Atube 14 is supported in these upper parts ofthe support plates 13 and extends at right angles to the plane 2.

A shaft isjournalled in the tube 14, about which rearwardly extending arms 15 are pivotable. The end of each arm 15 awayfrom the tube 14 is respectively pivotally connected by a lifting arm 1 6to one ofthe lower lifting arms 10. At a position between the free end of each arm 15 and the tube 14there is a pivotal shaftwhich extends at right angles to the plane 2, aboutwhich is pivotable the free end of the piston rod ofthe associated hydraulic ram 12.The upper parts of the support plates 13 also carry a pivotal shaft at right angles to the plane 2, about which an upper lifting arm 17 is pivotable, this lifting arfl17 also extending to the rearawayfrom its pivotal shaft.Acoupling member 18 in the form of an upwardly open hook is fastened to the free end of each lower lifting arm 10. In a similar manner a downwardly open hook 19 is fastened to the free end ofthe upper lifting arm 17. The hooks 18 and 19 each have a quick-action fastener in the form of a locking bolt 20 which is pivotable about an axis at right angles to the plane 2, which bolt can retain in place a stub shaft or length of pipe of a machine attached to the lifting device 11 located in the hooks 18 or 19 respectively during operation.

The lifting device 11 can be hydraulically actuated from a driver's seat 25 in a cab 24 of the tractor.

Near the front side of the beams 3 there is a driving engine 26 which is supported on and fastened to the beams 3. The engine is slightly offset with respect to the plane 2 so that its crank shaft emerging from the rear is disposed to one side of the plane 2. The crankshaft ofthe engine 26, which has a power output of about 60 to 100KW, constitutes an input shaft of a gearbox 27, which is fastened to the rear ofthe engine 26 and extends laterally beyond the beam 3 nearerthe crankshaftand beyond the outermost boundary planes ofthe front wheels of the tractor on that side.

To the rear of the gearbox 27 is fastened achange- speed gearbox 28 which is controllable from the driver's seat 25, the input shaft of which coincides with the output shaft of the gearbox 27. The output shaft 29 ofthe gearbox 28 projects rearwardly. The shaft 29 is in line with the crank shaft ofthe engine 26 and, as viewed on plan, it lies between the frame beams 3 on one side ofthe plane 2. To the rearface ofthe end of the gearbox 27 projecting beyond the frame 1 are fastened two pumps 30 and 31. The pumps 30 and 31 are driven by output shafts ofthe gear-box 27 and their fluid displacement can be controlled bythe driver from his seat 25. The pump 30 serves to drive the rear wheels ofthe tractor and the pump 31 to drive the front wheels.To thefrontface of the gearbox 27 is fastened a gearwheel transmission 32 having an output shaft 33, which projects from the gear wheel transmission in the direction Ato constitute a front power take-off shaft. Figures 2 and 3 showthethe power take-off shaft 33 lies to one side ofthe plane 2 and is outboard ofthe outer surface of the neighbouring front wheel and, as viewed on plan, in the track of the rear wheels.

The output shaft 29 of the change-speed gear box 28 is coupled by an auxiliary shaft34 having two universal joints with a rear power take-off shaft 36 supported in a bearing 35, the horizontal centre line of which lies in the plane 2. The bearing 35 is supported on the top ofthetie beam 9.

The tractor has in total two rearwheels 37, one each side ofthe plane 2. Each ofthe rearwheels 37 can be driven by an associated hydraulic motor (not shown), thefluid displacementof which can be controlled by the driverfrom his seat 25. The hydraulic motors ofthe rearwheels 37 are supplied from the hydraulic pump 30.

The tractor has in total two front wheels 38, one on each side of the plane 2. The track width ofthe front wheels 38 is about 90 cms and the track width of the rear wheels 37 is about 240 cms. The diameter of all of the wheels 37,38 is the same, and is about 135 cms. All of the wheels are provided with pneumatictyres, preferably low-pressuretyres, having a width of about 60 cms. With the frontwheels 38 and the rearwheels 37 disposed as described above, the front wheels 38 are situated within the track width of the rearwheels 37 so thatthe tractor bears on the ground over an overall width of about 240 cms. This results in a very low ground pressure so that deterioration of the soil structure is avoided for the subsequent growth of plants. The overall width ofthe tractor is about 300 cms.

As seen in the side view of Figure 1 the cab 24 extends forwardlyfor about 200 cms from a vertical plane containing the rotary axis of the rear wheels 37.

The largest dimension of the cab 24 measured at right angles to the plane 2 is 200 cms so thatthe rear ofthe cab (Figure 2) lies partly above the rear wheels 37. The front of the cab is positioned as viewed from the side, centrally above the driving engine 25.

At the front, the tractor has a steering shaft 39. The steering shaft 39 is pivotable about a pivotal axis 40 which lies in the plane 2 and is substantially vertical in the illustrated embodiment. The steering shaft 39 may be provided at its lower end with only one steerable wheel, but in the illustrated case the steering shaft provides a central pivotability for the two front wheels 38,which are disposed symmetricallyaboutthe plane 2. The steering shaft 39 comprises a beam and is constituted in the illustrated embodiment by a circular tube, the centre line of which constitutes the pivotal axis 40.

The steering shaft and the wheels 38 are situated in the space below the interconnected profiles 6 and in front of the sloping supporting beams 4.

The front wheels 38 are each provided with a hydraulic motor supplied from the pump 31. The two front wheels 38 are rotatablyjournalled on a tubular, substantially horizontal front axle 41, in which the hydraulic motors may be accommodated. The front axle 41 is pivotable with respect to the steering shaft 39 aboutthe axis of a horizontal pivotal shaft 42 lying in the plane 2.

The tubular steering shaft 39 togetherwith the front wheels 38 can beturned from the seat 25 by means of a hydraulic ram 43.

The tractor has a front lifting device 44 intended to provide a stable, broad supportfor machines or implements attached to it, where such machines or implements exert relatively heavy tractive orthrusting forces on the tractor during operation and/ortransport. The lifting device 44 comprises two lower lifting arms 45 and two upper lifting arms46, disposed symmetricallyaboutthe plane 2. The box-shaped lower lifting arms 45 are parallel to each other and are pivotally connected to the rest of the tractor by pivotal shafts 47 which are normal to the plane 2.Forthis purpose a hollow beam 48, lying at right anglestothe plane 2 iswelded tothe underside ofthetwo beams 3 oftheframe 1 ,the length of the beam 48 being such thatthe beam projects beyond the outer side ofthe frame 1 (Figure 2), the two ends lying in the respective paths ofthe rear wheels 37. Lugs 49 are welded to the front of each of the two ends of the beam 48, these lugs protrudingforwardlyand holding thetwo aligned pivotal shafts 47 located one on each side ofthe plane 2.

In the side view of Figure 1 the two pivotal shafts 47 are shown substantially midway between the rotary axes of the rearwheels 37 and the frontwheels 38 and at approximatelythe same height as or lowerthan the axes of the wheels 37 and 38.

The two lower lifting arms 45 extend, in a medium position, from the pivotal shafts 47 substantially horizontally to the front. Attheirfront ends, the two lower lifting arms 45 terminate a short distance in front ofthe foremost points ofthe front wheels 38. At these front ends each of the lower lifting arms 45 carries a pivotal shaft 50 lying at right angles to the plane 2, the two pivotal shafts 50 being aligned with each other. The pivotal shafts 50 pivotally connectthe lifting arms 45 with a substantially vertical frame 51 fabricated from beams. The height of the frame 51 is about75 to 85% ofthe diameter of the front or rear wheels and is preferably about 80% of that diameter.

The width ofthe frame 51 is substantially equal to the distance between the two outboard faces of the lower lifting arms 45. The frame 51 comprises a lower beam 52 which is at right angles to the plane 2 and extends over the width oftheframe. Attwo places disposed symmetrically about the plane 2 and midway between the plane 2 and the ends ofthe beam 52, box-section posts 53 are welded to the top of the beam 52,these posts 53 being substantially vertical in the medium position of the lifting device. The top ends of the two posts 53 are interconnected by a box-section beam 54which is welded to the top ends of the posts 53 and is parallel to the beam 52. The beam 54 extends solely in the region between the outer faces ofthe posts 53.Moreover, the beam 54 is connected with the beam 52 by a third, box-section post 55, the centre line of which lies in the plane of symmetry 2, the post 55 being welded between the beams 52 and 54.

Pairs of lugs 56 are welded to the beam 54 nearthe top ends ofthe posts 53. The lugs 56 are directed to the rearwith respectto theframe 51. Each pair of lugs has atthe rear a pivotal shaft 57. The two pivotal shafts 57 are aligned with each other and serve to connect the front ends ofthe two upper lifting arms 46 to the frame 51. Viewed on plan (Figure 2) each of the upper lifting arms 46 is substantially midway between one ofthe lower lifting arms 45 and the plane 2. The rear end of each upper lifting arm 46 is pivotally connected by a respective pivotal shaft 58 with lugs 59 welded to the front of the tie beam 5 fastened to the top ends ofthe supporting beams4.Viewed on plan(Figure2)thetie beam 5 extends to both sides ofthe plane 2 as far as the outerfaces of the lower lifting arms 45.Downwardly inclined lugs 60, 60A are secured to the ends of the tie beam 5, each of which has a pivotal shaft 61 about which is pivotable a respective hydraulic ram 62 which is controllable from the driver's seat 25. The ends ofthe piston rods ofthe hydraulic rams 62 are connected by pivotal shafts 63 to the top faces ofthe lower lifting arms45 at places substantially midway between the ends of the lower lifting arms 45 (Figure 1). The hydraulic rams 62 slope downwardlyto the front from the pivotal shafts 61. The lower and upper lifting arms 45 and 46 constitute with the frame 51 a quadrilateral pivotal linkage comprising the pivotal shafts 47,50,57 and 58. The pivotal shafts 58 as viewed on plan, are nearthe hindmost points ofthe frontwheels and the upper lifting arms 46 are directly above the front wheels 38.The distance between the pivotal shafts 47 and 58, measured lengthwise ofthe tractor, is about half the length of each upper lifting arm 46.

The two upper lifting arms 46 slope slightly downwardly from the pivotal shafts 58 at their rear ends towards the pivotal shafts 57 at their front ends.

Viewed from the side (Figure 1),the length of each of the upper lifting arms 46 is about 60 to 70%, preferably about 65% ofthe length of each of the lower lifting arms 45. Itis noted here that the front pivotal shafts 57 ofthe upper lifting arm 46, as shown in the side view of Figure 1, appear substantially vertically above the front pivotal shaft 50 ofthe lower lifting arms 45. The two upper lifting arms 46 are interconnected neartheir front ends by a box-section tie beam 64 to improve their lateral stability. The tie beam 64 is at right angles to the plane 2 and its ends are welded to the inner faces ofthe lifting arms 46.

Thefrontface of each ofthe posts 53 of the frame 51 is provided with a pivotal shaft 65 in the form of a removable pin,thetwo pivotal shafts 65 being aligned with each other and at right anglesto the plane 2. The distance ofthe pivotal shafts 65 above the top of the beam 52 is about30 to 40% of the vertical distance between the top of the beam 52 and the bottom of the beam 54.A carrier 66 is pivotable about each of the two pivotal shafts 65 and extends from the pivotal shafts 65to the front. Each carrier 66 has a first portion extending horizontallyfrom the associated pivotal shaft 65 in the working position towards the front and a second portion which meets the first portion art a bend 67 and slopes downwardly to the front at an angle of about 45". At its lower end each carrier 66 carries a wheel axle 68 of an auxiliary wheel 69. The two carriers 66 are disposed symmetrically about the plane 2 (Figure 2) and nearthe bend 67 they are rigidly interconnected by a tube 70 at right angles to the plane 2.The two carriers 66 together with their auxiliary wheels 69 are pivotable upwardly and downwardly with respectto the frame 51 ofthe front lifting device 44. The assembly comprising the box-section carriers 66, the tube 70 and the wheels 69 is releasable from the lifting device 44 by means of the removable pins which form the pivotal shafts 65, and it constitutes an auxiliaryframe ofthe lifting device 44.

At the top end ofthethird post 55 the front face of the upper beam 54 is provided with a pair of lugs 71 which receive a pivotal shaft 72 extending at right anglestotheplane2,aboutwhich is pivotablea hydraulic ram 73 actuablefrom the driver's seat 25.

The end ofthe piston rod ofthe ram 73 is pivotally connected tothe middle ofthe tube 70 buy a pivotal shaft 74 extending parallel to the pivotal shaft 72. The hydraulic ram 73, like the two hydraulic rams 62, is preferably double-acting so that the lifting device 44 and the carriers 66 can be pressed both upwardly and downwardly. However, the rams 62 and 73 may, as an alternative, be single-acting so that the lifting device 44 can be forced upwards, and can float, and the rigid combination of the carriers 66 with the auxiliary wheels 69 can be forced downwards with respect to the lifting device 44 and can float, so thatthe assembly can movefreely up and down with respect to the lifting device44when driving across uneven ground.At each ofthe posts 53thefrontface ofthe beam 52 and thefrontface of the post have welded to them a pair of parallel forwardly projecting, lugs 75 in the form of upwardly open hooks. The two pairs of lugs 75 constitute the lowercoupling points of the three-point lifting device 44. Nearthetop ofthe cavity in each lug 75 there is a lock bolt 76 which is pivotable under control from the drivers cab for preventing upward escape of coupling pins provided at the coupling points of an attached machine or implement during operation. Near the top end ofthe post 55 there is another pair of lugs 77 (Figure 1) which are identical to the lugs 75 and which are also provided with a pivotable lock bolt 76, which is controllable from the driver's seat nearthe top ofthe upwardly open recess.

in the embodiment shown a power-driven cultivator 78 is fastened to the coupling members 75 and 77 of the lifting device 44 and is disposed ahead ofthe front of the frame 51 of the lifting device. The cultivator78 is bridged by the forwardly projecting carriers 66 ofthe auxiliaryframe. Itwill be appreciated that, instead of a cultivator, other implements may be attached to the lifting device 44, for example rotary harrows, weeders, cultivating machines, ploughs and the like. If high machines are to be coupled, the auxiliaryframe66,70 can be removed by removing the pins 65 and 72. This particularly applies to hay-making machines, mowers and the like, in which the use of the auxiliary frame 66, 70 may be less necessary.

The soil cultivator 78 comprises a frame having two parallel hollowframe beams 79 which are parallel to each otherabovethe ground, these beams being at right angles to the direction A. The two frame beams 79 are interconnected at their ends by downwardly directed plates 80 in which a drive shaft 81 of a cultivating body 82 isjournalled.The drive shaft 81 is provided with outwardly directed cultivating tines 83, which are driven in the direction of rotation B (Figure 1), which corresponds with the direction of rotation of thetractorwheels during forward travel.The drive shaft 81 is driven at one outer end of the frame through a drive casing 84comprising a chainorgearwheel transmission that receives drive from a drive shaft 85 extending parallel to the frame beam 79. The drive shaft 85 itself can be driven through a pair of bevel gearwheels 87 in a gearbox86 (Figure 2).The driving gearwheel 87 is mounted on an input shaft 88, which, when the cultivator 78 is coupled with the lifting device 44, is drivably connected by an auxiliary shaft 89 provided with universal joints to the powertake-off shaft 33 ofthe tractor, said power take-off shaft being arranged on the same side ofthe tractor as the input shaft 88.Viewed on plan, the auxiliary shaft 89 as well as the powertake-offshaft 33 are displaced sideways with respect to the frame and are located in the track of the rearwheels37.

Between the two carriers 66 ofthe auxiliaryframe, the top faces of the two frame beams 79 are provided with two upwardly and inwardly directed plates 90, which are provided neartheirtop and rear edges with coupling pin 91 forattaching the cultivatortothetop point ofthe lifting device. The plates 90, which are rigidly secured to the frame 79, constitute a coupling trestle ofthe cultivator. The two plates extend downwardlyfromthe pin 91 to below and behind the hindmostframe beam 79, wherethey are provided with coupling pins 92, which are received in the lugs 75 during operation, the lugs 75 forming the two lower coupling points ofthe lifting device 44.

To hitch the cultivator to the tractor, the tractor is driven towards the cultivator in a direction normal to the length of the beams 79, and by means ofthe hydraulic ram 73, the driver controlsthe auxiliary frame 66,70 provided with the two auxiliary wheels 69 so that this assembly moves over and across the cultivator until the position is reached in which the pins 91 and 92 can engagethe coupling members of the three-point lifting device 44. Then the auxiliary frame 66,70 is lowered by means of the lifting device 73 until the wheels 79 rest on the ground.

A lifting device similar to the device 44 with oF without the auxiliary frame 66,70,69 may also be arranged atthe rear ofthe tractor, in which case however, assuming the maximum permissible width of the tractor to be determined bytheouterfacesofthe rearwheels 37, the distance between the lower lifting arms 45 has to be smallerto enable them to pass between the rearwheeis 37. If this is not possible, the lower lifting arms 45 can be disposed along the outer faces ofthe rear wheels.

In operation, the engine 26 drives the gear wheels of the gearbox 27 which in turn drives the change-speed gearbox 28, whose output shaft 29 drives the auxiliary shaft 34 and hence the powertake-offshaft 36. The speed of rotation of the powertake-off shaft 36 can be adjusted to be substantially proportional to the travelling speed ofthe tractor, with the aid ofthe change-speed gearbox. In the same manner not only a seed drill, but, for example, also a drivable roller attached to the rear lifting device 11 can be driven so that the circumferential speed of the rollerissubstan- tially equal to the travelling speed ofthetractor and the roller can provide part of the tractive force of the tractor.The pumps 30 and 31 driven bythe gear wheels ofthe gearbox 27 hydraulicallydrivethe rear wheels and the front wheels respectively, these wheels being provided with hydraulic motors (not shown) which are controllable from the driver's seat 25. The gearwheels ofthe gearbox 27 also drive the powertake-off shaft 33 arranged to one side ofthe tractor. In this embodiment the powertake-off shaft 33 is used to drive the soil cultivator78 in the manner described above.

The three-point lifting device 44 is pivotally connected bythe pivotal shafts 47 and 58 to the rest ofthe tractor. As stated above the pivotal shaft 47 of the lower lifting arms is atthe same height as or below the plane containing the rotary axes of the wheels 37 and 38 so that a very low point of application is obtained on the tractor. Viewed from the side, the pivotal shaft 47 is approximately midway between the rotary axes ofthe wheels 37 and 38. The pivotal shafts 58, as viewed vertically, are approximately midway between the front wheel axle and the centre line ofthe pivotal shafts 47 but at the level ofthe engine 25. The engine 25, viewed from the side, is disposed between the pivotal shafts 47 and 58 (Figure 1).

The centre of gravity of the whole tractor lies near the line of connection between the pivotal shafts 47 and 58, as viewed from the side. When running on uneven ground, the tractorwill perform pitching movements about an axis at right angles to the plane 2 and going through the centre of gravity of the tractor or about a transverse axis below the centre of gravity.

Since the lifting device 44 is connected to the tractor near the centre of gravity, as viewed from the side, the orientation of the frame 51, which determines the orientation of the attached implement, as well as the upward and downward movements oftheframe 51 during operation, which frame imparts these move ments to the attached implement, will vary considerably lessthan they would if the lifting device were fastened to the front end of the tractor in front ofthe centre of gravity, which is the case with known lifting devices. Therefore not only the orientation but also the depth at which an attached implement works in the soil may be said to be very constant.

The proportioning ofthe lifting device 44 as described above also means that, during lifting or forcibly lowering the frame 51 within its normal range of movement, the orientation of the frame, viewed from the side, hardly changes, if at all. The abovedescribed lifting device 44, therefore, ensures a uniform movementofthe attached implementwith respectto the ground. This also applies to machines otherthan soil cultivating machines.

Owing to the broad base ofthe connection ofthe lifting device 44 with the tractor, a very stable support is obtained for implements exerting relatively heavy, varying forces on the tractor.

Because the connection of the lower lifting arms 45 with the tractor is approximately midway between the front and rear wheels, forces applied to the attached implement along lines of action displaced from the plane 2 are resisted by both the front and the rear wheels to avoid turning.

If the hydraulic rams 62 are double-acting, an implement can not only be lifted from or out ofthe ground, but also where the implement is a soil cultivating machine it can be pressed to the desired depth into the ground. When the auxiliaryframe 66,70 provided with the wheels 69 is coupled with the lifting device 44, the working depth ofthe coupled soil cultivating machine can be very accurately set when, for example, the hydraulic rams 62 exert a downwardly directed force on the frame 51 and the hydraulic ram 73 ofthe auxiliary frame 66,70 is hydraulically blocked. In this case the auxiliarywheels 69 together with the tractor wheels 37 and 38 accurately determine the working depth.By energizing the hydraulic ram 73 the frame 66,70 moves downwards and the wheels 69 take a considerable part of the weight of the implement and also part ofthe tractorweight so that the pressure ofthe front wheels 38, which may adversely affect the soil structure, is reduced. Forthis purpose the auxiliary wheels 69 are disposed between the tracks ofthe rear wheels 37 and the front wheels 38, as is shown in the plan view of Figure 2. In this way the supporting area for the overall weight is enlarged so that the ground pressure of the tractorwheels is reduced, thus avoiding deterioration of the soil structure. The provision of the auxiliary frame 66,70 is important particularly when soil cultivating machines are used.

In particular when the tractor is working with a soil cultivating implement, for example a plough, it is important to minimize the specific fuel consumption orthefuel consumption based ontheworked area as well as the overall costs of the tractor per unit of area worked. The engine setting isrelatedtothecombina- tion of the driving torque exerted on the drivable wheels and the number of revolutions of the engine at different rates offuel injection. It has been found that minimum overall costs for using a tractor are frequently attatined nearthe setting in which the driver drives atfull speed or maximum power, which depends to some extent on the factwhether light or heavy soil is being ploughed.In order to achieve both an engine setting in which the specific fuel consumption is minimized and a setting in which the overall costs are minimized it appears to be very importantto maintain a given engine speed. The value of this given speed depends on the characteristics of the engine and it will vary with engines of different makes. To solve this problem the tractor is provided with a control system for maintaining a predetermined engine speed (which, therefore, depends on the properties ofthe engine type concerned). When a plough isworking in a partofafieldwherethesoil is heavier, the engine speed tends to drop below the desired value, whereas in a part ofthe field with lighter soil the engine speed tends to increase.In view of the desired optimalisation of the costs the control system now to be described, by use ofthe operating mechanism ofthe lifting device, maintains the engine speed constant by automatically lifting the lifting device slightlywhenthe plough digs into heavy soil and the engine speed drops below the desired value and by automatically moving the lifting device downwards when the plough gets into lighter soil and the engine speed would otherwise rise above the desired value. With this control system the fuel injection rate can be kept substantially constant. Furthermore the transmission ratio between engine and the wheels is, at least in principle, also kept constant.

A schematic diagram of this control system is shown in Figure 3. The surface of the output shaft of the engine 26 of the tractor is provided in a manner not shown with a steel extension which rotates with the shaft. In the vicinity ofthe path described by the extension there is an electro-magnetic pick-up which is fixed with respect to the tractorframe. In a known manner, an electric pulse is produced in the pick-up when the extension passes it. These pulses are fed to a shaping circuit which converts the pulses into rectangular pulses which can be processed bythe electronic circuit of Figure 3. These rectangular pulses are applied to an input 93 (Figure 3).

In the following example it is assumed that the desired engine speed to be maintained is 1620 rev/min, which corresponds with 27 rev/sec. On the basis of the number of revolutions per second it is readily possible to control the hydraulic lifting device in dependence on the engine speed, whilst approximately every alternate second correcting or noncorrecting reading takes place.

In this embodimentthe control system of Figure 3 comprises integrated circuitsoftheTTLtype or units compatible therewith, the types of which are indicated in Figure 3. The circuit is fed by a d.c. voltage of 5 V obtainedfromthetractoraccumulatorthrough a voltage regulator. This feed voltage is indicated by V5.

Earth conductors are indicated by G. The circuitry of Figure 3 requires costs which are negligible compared with the overall tractor cost.

Clock pulses of 1 second duration are obtained from a 555-lC 94, whose characteristics with respect to the duration ofthe produced pulses are known to be very stable and highly independent of ambienttemperature. The IC 94 is connected in known manner as an a-stable multivibrator and the values of the surrounding resistors and capacitors are chosen so that output pulses of a duration of accurately one second are produced in a connection 95.

Both the pulses applied to the input 93 and the second pulse from the IC 94 are fed to the inputs of an AND gate 96 so thatthe output of the gate 96 emits the pulses emanating from the input 93 during each one second period, through a connection 97. The interval between each two successive pulses emanating from the IC 94 may also be about one second, but it may be shorter. The pulses from the gate 96 are fed to the input oftwo cascade-connected counters 98 and 99, which countthe number of pulses fed to the input 93 in each second. This counted number of pulses per second is available at the outputs ofthe counters 98 and 99 in the form of, in total, eight bits in a BCD code.

The counter 98 has at its outputsthe unitsofthe numberofcounted pulses per second in a binaryform and the counter 99 hasthetens. These output pulses ofthe counters 98 and 99 are applied to the inputs of two cascade-connected latches 100 and 101, which pass the counted pulses directlyto the output while the voltage at the control-inputs (inputs 4 and 13) is high (H), but when the voltage at the control-inputs is low (L), the number applied last to the inputs and present prior to the change-overfrom H to L remains.

The predetermined engine speed desired by the driver is set by the driver by means of a sequence of eight switches 102, 103. In the case of the embodiment concerned in which the number"27" has to be set, the switches S1-S4, adding "7" are set in the order of succession S1 to S4, that isto say: H H H Land the switches S5-S8, adding "2", thus in the order of succession S5 to S8: L H L L. This setting is carried out beforethetractor is put into use by closing or opening the switches. When the switch is connected to the voltage conductorV, the Signal is atthe output concerned of a switch, but when the switch is connected with the ground conductor G the Lsignal is at the output concerned ofthe switch.The outputs of the switches 102,103 are applied to the B inputs and the outputs ofthe latches 100,101 are applied to the A inputs (Figure 3) of two cascade-connected comparators 104 and 105. The comparator 105 has three outputs (5,6,7). Output (5) becomes H when the number applied to theAside exceeds the number set on the B side, whilstthetwofurtheroutputs remain L.

Output (7) becomes H, when the numberappliedto theA side is lowerthan the number set on the B side, whilstthetwo further outputs remain L. The third output (6) only becomes H when the numbers applied to both sides are equal. This output is not of importance.

When the signal produced bythe IC94 becomes low at the end of a time period of 1 second,the application of pulses to the counters 98 and 99 and to the latches 100 and 101 stops owing to the nature ofthe gate 96.

This L signal (connection 95) also stops counting ofthe outputs of these IC's so that atthese outputs remains the highest number counted, which is also applied to the Aside of the comparators. Atthis instant the counter 98 and 99 are resetfrom the connection 95 and an inverter 106 sothatthe counters return to zero so asto be ready to count again during the nextfollowing second pulse. The output 5 ofthe comparator 105 is connected through an inverter 107 to the control input of a Darlington transistor 111, which can actuate a relay 112. The relay 112 actuates the same electromagnetic solenoid as mentioned above of the same hydraulic valve of the rams 62 and/or73 of the lifting device, but in a direction opposite to that achieved by the relay 109.The relays 109 and 112 can be operated by the 12 V supply voltage directly obtained from the tractor accumulator (V12).

If during each 1-second period determined by the IC 94the counters 98,99 add from zero to,forexample, 26 (i.e. lowerthanthe predetermined numberof revolutions), the final number applied to the A side of the comparators 104, 105 at the end of the 1-second pulse is lowerthan that on the B side set by means of the switches 102, 103. This means that the output 5 of the comparator 105 (Figure 3) was and remains Lso that a continuous H signal occurs at the control input ofthetransistor 108 owing to the inverter 107. The transistor 108 is thus conductive and the relay 109 is closed. The solenoid of the hydraulic valve displaces the valve in the direction requiredto causethe rams 62 to liftthe lifting device.This reduced the working depth ofthe soil cultivating implement and consequentlythe resistance to be overcome by the tractor, and the speed (27 revs/sec) ofthe engine increases towards the predetermined speed. Subsequently when this predetermined speed is exceeded, the number applied to the A side of the comparators 104, 105 atthe end of the second pulse is higher, (for example, 28) than the number (27) set by the switches 102,103 on the B side. The output 7 ofthe comparator 105then becomes Lduring the interval between two second pulses and the output 5 becomes H. Owing to the inverter 110, the transistor 111 becomes conductive and relay 112 is closed.The solenoid ofthe hydraulicvalveofthe rams 62 is energized sothatthe valve is displaced in the opposite direction and the hydraulic rams 62 press the lifting device 44 downwards. As a result,theworking depth of the soil cultivating machine increases as does the resistance encountered by the tractor, so that the speed of the engine decreases. At the same time the factthatthe output 5 of the comparator 105 has a H signal means that, owing to the presence ofthe inverter 107, L voltage is applied to the base of the transistor 108 and the relay 109 thus remains open.

In this way it is ensured thatthe control illustrated in Figure 3 is maintained within fairly narrow limits around the predetermined speed setbythe driver, since a fall in the speed ofthe engine results in lifting ofthe lifting device and vice versa. In the case of reduction in engine speed the control prefers lifting of the lifting device (forthetime the counters are filling up) overthe inverse situation, since lower speeds decrease the surface worked per unit time. It will be obviousthatthe control system shown in Figure 3 can be used notonlyforthe lifting cylinders 62ofthe three-point lifting device 44 (for example, in the absence ofthe auxiliaryframe 66,70) but also forthe hydraulic ram 73 of the auxiliary frame 66,70 when the hydraulic valve of the rams 62 is set by the driver in a position in which the lifting device 44 is freely movable upwardly and downwardly. By maintaining the predetermined desired standard engine speed it is possible to ensure that the tractor with the attached implement can be driven nearthe minimum of the required overall operating costs ofthetractor.

It is advisableto provide a (preferably controllable) choke valve in the two hydraulic ducts connecting the control valve with the two ends ofthe rams. The choking ofthe hydraulic fluid flowing to the ends of the cylinders corresponding to lifting may, if desired, be chosen to exceed the choking resulting in a downward movementofthe lifting device, if there is no preferenceforthe lifting movement.

However,the choke valves ensure in the first place a quiet adaptation oftheworking depth ofthe imple mentasafunction of the speed of the engine.

Claims (1)

1. An agricultural tractor having one or more front wheels and a lifting device disposed at the front ofthe tractor, with respectto the normal direction of travel of the tractor, the width of the lifting device, being greaterthan the distance between the outermost boundary faces ofthe front wheel or wheels.

2. An agricultural tractor as claimed in Claim 1, in which, as viewed from the side, the lifting device comprises a quadrilateral pivotable linkage.

3. An agricultural tractor as claimed in Claim 2, which, as viewed from the side, two pivotal axes of the quadrilateral linkage arefixed with respectto aframe of the tractor and are disposed one on each side of and nearthe centre of gravity ofthetractor.

4. An agriculturaltractoras claimed in Claim 3, in which, as viewed from the side, a line of connection between the othertwo pivotal axes ofthe quadrilateral linkage is substantially vertical.

5. An agricultural tractor as claimed in Claim 4, in which that the lifting device is proportioned so that the said line of connection moves substantially parallel to itself within its normal range of movement for displacing attached equipment.

6. An agricultural tractor as claimed in any one of the preceding Claims, in which the lifting device comprises lower lifting arms which arefastenedto a frame of the tractor, as viewed from the side, approximately midway between the rotary axes ofthe front wheel orwheels, and rearwheels of the tractor.

7. An agricultural tractor as claimed in any one of the preceding Claims, in which the lifting device comprises lower lifting arms which extend, as viewed from the side, beyond the foremost point or points of thefrontwheel or wheels.

8. An agricultural tractor as claimed in Claim 6 or7, in which the lower lifting arms are disposed outwardly beyond the outer sides of the tractor frame and extend substantially parallel to the longitudinal vertical central plane ofthe tractor.

9. An agricultural tractor as claimed in any one of the preceding Claims, in which the lifting device comprises two upper lifting arms.

10. An agricultural tractor as claimed in Claim 9, when appendantto any one of claims 6to 8, in which at least one of the upper lifting arms is shorterthan a lower lifting arm.

11. An agricultural tractor as claimed in Claim 10, in which the pivotal axis connecting an upper lifting arm with thetractorframe is substantiallyvertically above the rearmost point of a frontwheel.

12. An agricultural tractor as claimed in any one of Claims 9 to 11, in which an upper lifting arm slopes downwardly away from its connection with the frame.

13. An agricultural tractor as claimed in any one of Claims 9 to 12, in which an upper lifting arm ofthe lifting device is disposed substantially above a front wheel.

14. An agricultural tractor as claimed in any one of Claims 9to 13 when appendantto any one of claims 6 to 8, in which the horizontal distance between the upper lifting arms is approximately halfthe distance between the lower lifting arms.

15. An agricultural tractor as claimed in any one of Claims 9 to 14when appendantto any one of Claims 6 to 8, in which the connection of the lower lifting arms with the frame is located furtherto the rearthan that of the upper lifting arms.

16. An agricultural tractor as claimed in Claim 15, in which, as viewed on plan, the distance between the pivotal axes atwhich the upper and lower lifting arms are respectively fastened to the frame is substantially half the length of the upper lifting arm.

17. An agricultural tractor as claimed in any one of Claims 9to 16 when appendantto any one of Claims 6 to 8, in which, as viewed on plan, the front pivotal axes ofthe upper and lower lifting arms respectively substantially coincide.

18. An agricultural tractor as claimed in Claim 2 or in any one of Claims 3 to 17 when appendantto Claim 2, in which a pivotal axis of the quadrilateral linkage is at aboutthe same height as, or lowerthan, the wheel axle of the front wheel of wheels and between the front and rear axles ofthe tractor.

19. An agricultural tractor comprising a frame, front and rearwheels rotatable about respective axes, and a lifting device which is pivotally connected to the frame at a pivotal axis which is approximately at the same height as or lowerthan the front wheel axis and between the front and rearwheel axes.

20. An agricultural tractor as claimed in Claim 18 or 19, in which the said pivotal axis is below the tractor frame.

21. An agricultural tractor as claimed in any one of the preceding Claims in which the foremost pivotal axes ofthe lifting device carry a coupling frame for receiving attached equipment.

22. An agricultural tractor as claimed in Claim 21, in which the coupling frame is provided with two lower coupling members and one upper coupling member.

23. An agricultural tractor as claimed in any one of the preceding Claims, in which the lifting device is provided with at least one hydraulic lifting cylinder which is controllable from a driver's seat and is pivotally connected to a carrying beam which is also pivotally connected to an upper lifting arm of the lifting device.

24. An agricultural tractor as claimed in any one of the preceding Claims, in which the lifting device has at the front end one or more ground wheels.

25. An agricultural tractor having a lifting device at the front end of the tractor, with respect to the normal direction of travel of the tractor, the lifting device having at its front end at least one ground wheel.

26. An agricultural tractor as claimed in any one of Claims 24to 26 in which each ground wheel is adjustable upwardly and downwardly by means of a hydraulic ram controllablefrom the driver's seat.

28. An agricultural tractor as claimed in any one of Claims 24to 27, in which two ground wheels are provided.

29. An agricultural tractor as clamed in any one of Claims 24to 28, in which the or each ground wheel is pivotally connected with the lifting device by means of an auxiliaryframe.

30. An agriculturaltractoras claimed in Claim 29, in which the auxilliaryframe is connected to theframe of the lifting device.

31. An agricultural tractor as claimed in any one of Claims 24to 30, in which the diameter of the or each ground wheel isabout60cms.

32. An agricultural tractor as claimed in any one of Claims 29to 31, in which the or each ground wheel and the auxiliaryframe are releasable from the lifting device.

33. An agricultural tractor as claimed in any one of the preceding Claims, in which a control system for the lifting device is provided which is responsive to a driving engine of the tractor whereby a decrease in the speed ofthe engine results in lifting ofthe lifting device.

34. An agricultural tractor comprising a driving engine and a lifting device, a control system forthe lifting device being provided which is responsive to the engine whereby a decrease in the speed of the engine results in lifting ofthe lifting device.

35. An agricultural tractor as claimed in Claim 33 or34, in which an increase in the speed ofthe engine causes downward movement of the lifting device.

36. An agricultural tractor as claimed in any one of Claims 33 to 35, in which the control system operates to maintain a predetermined speed ofthe engine.

37. An agricultural tractor as claimed in Claim 36, in which the predetermined speed is adjustable.

38. An agricultural tractor as claimed in any one of Claims 33 to 37, in which the tractor comprises a pick-up responsive to the speed of the engine said pick-up co-operating with a shaping circuit to obtain pulses offixed duration.

39. An agricultural tractor as claimed in Claim 38, in which the control system comprises at least one comparatorforcomparingthe number of engine revolutionsina predeterminedtimewith a number representing a required number of revolutions, in that time.

40. An agricultural tractor as claimed in Claim 39, in which means is provided for controlling the lifting devicewhen the counted number of engine revolu tionsdiffersfromthe number representing the required number of revolutions.

41. An agricultural tractor as claimed in Claim 40, in which the controlling means comprises at least one comparator-controlled relay which co-operates with a hydraulic valve of at least one hydraulic ram ofthe lifting deviceand/ora hydraulic ram ofthe auxiliary frame of the lifting device.

42. An agricultural tractor as claimed in any one of the preceding claims in which the hydraulic supply to the lifting device includes one or more choke valves.

43. An agricultural tractor substantially as described herein with reference to, and as shown in, Figures 1 and 2 of the accompanying drawings.

43. A control system for an agricultural tractor, substantially as described herein with reference to, and as shown in, Figure 3 ofthe accompanying drawings.