FR2554308A1 - AGRICULTURAL TRACTOR PROVIDED WITH IMPROVED CONTROL MEANS OF THE LIFTING DEVICE - Google Patents

Abstract

AGRICULTURAL TRACTOR WITH AT LEAST ONE LIFTING DEVICE. THE CONTROL UNIT 51, 52, 53, 54 OF THE LIFTING DEVICE 17, 13, 43, 44 IS PLACED ON A CONTROL UNIT OF THE TRACTOR, SUCH AS THE FEED SPEED ADJUSTMENT LEVER OR THE FLYWHEEL MANAGEMENT 35.

Description

1l 2554308 The invention relates to a tractor, preferably a

  agricultural tractor with at least one lifting device.

  In known tractors, which often have two or more lifting devices, carrying machine-drawn tools, to turn 180 after working a strip of land or when reaching the end of the field or plot , the lifting devices must be raised by the driver in a sequence and with a delay which depends on the forward speed. Then, to start the work of a new strip of soil, the lifting devices must be lowered in sequence and with a certain time difference in order to put the machine or tools again in or on the ground. These maneuvers are very complicated for the driver and this results in

  errors, improper handling or accidents

  teeth. In order to remedy these drawbacks, according to the invention, the control member of the lifting device is placed on the control member of the tractor, such as the lever for adjusting the forward speed or the steering wheel. During the maneuvers, the driver can therefore control with the same hand, the tractor control member and the control device of the lifting device without removing his hand from the

steering wheel or lever.

  According to the invention two lifting devices, or

  more, can be controlled by pushers,

  rockers or feeler switches.

  According to one aspect of the invention, it is possible to order auto-

  matically using the control member in a

  certain succession of time first a lifting device

then the other.

  Other objects and characteristics of the invention

  will emerge from the description below, with reference

  to the accompanying drawings, which show, by way of examples

  non-limiting, some embodiments of the provision

  sitive according to the invention. In these drawings: FIG. 1 is a side view of the tractor according to the invention. Figure 2 is a plan view of the tractor according to

Figure 1.

  Figure 3 is a front view of the tractor according to

Figures 1 and 2.

  Figure 4 is a side view of the tractor with coupled to one end of the tractor two machines which

  can move relative to each other.

  FIG. 5 is a plan view of the combination according to

  Figure 4 at the end of a plot.

  Figure 6 is a side view of a tractor according

  the invention with a machine coupled to the front and to the rear

  and two machines, which can be moved one

  compared to each other by the driver.

  FIG. 7 is a partial view of a change lever

  speed control, provided with control members for

lifting devices.

  Figure 8 is a partial view of a steering wheel, provided

  control elements for lifting devices.

  Figure 9 is a simplified diagram of a circuit

  automatic or manual control of lifting devices.

  The tractor according to the invention shown in the figures

  1, 2 and 3, has a chassis 1, supported by rear wheels

  rière 2 et avant 3. The rear part of the chassis 1 extends below the axes of rotation of the rear wheels 2 and its front part, seen in profile according to FIG. 1, near the rear of the front wheels 3 is bent upwards and forwards so that it is above the front wheels 3. The tractor further comprises a drive motor 4, placed between the axes of rotation of the rear wheels 2 and front 3, in side view, near the front

rear wheels 2.

  The rear wheels 2 of the tractor can be driven,

  as well as the front wheels 3 from the drive motor-

  ment 4, by corresponding hydraulic motors, powered by a hydraulic pump which is driven by the

  motor 4 and whose efficiency and thus the forward speed

  tractor cement can be adjusted from the seat of the

  driver. The shaft emerging from the motor 4 causes a trans-

  gear mission, not shown, which has a

  outgoing shaft 6, perpendicular to the plane of symmetry

  vertical dinal 7 of the tractor which projects on one side of the tractor. A second shaft emerging from this transmission by

  gears is guided backwards and protrudes at the rear

  the tractor to form a PTO shaft 8.

  The shaft 6, which comes out laterally and which is propor-

  At the speed of rotation of the engine, on the side of the tractor has a bevel gear transmission 9, the outgoing shaft 10 of which extends forwards horizontally and parallel to the plane of symmetry 7. The shaft O10 rests in a tubular support 11 which surrounds it and which is fixed to the

  bevel gearbox 9.

  The front end of the shaft 10 forms a front PTO shaft 12. Seen in plan view (FIG. 2), the gear transmission 9, the shaft O10, the support il and the PTO shaft 12 are located in the corresponding rear wheel track 2. The coupling point of the plug shaft

  of force 12 is found, seen in profile, near the delimitation

  rear and upper front wheel 3.

  The tractor has a rear lifting device

  13, which in known manner has lower lifting arms

  laughers 14, arranged symmetrically on either side of the plane of symmetry 7, and an upper connecting rod 15, located

  in the plane of symmetry 7. Each of the lower lifting arms

  laughers 14 can move up and down by means of a double-acting hydraulic cylinder 16, which can be controlled from cabin 5 in a manner that will

described in more detail.

  The tractor has a front lifting device

  17, which extends above and in front of the front wheels 3.

  This lifting device 17 is produced symmetrically with respect to the plane of symmetry 7. On either side of the frame 1 are fixed two pivots 18 and 19, located one above the other, and directed perpendicular to the plane of symmetry 7. Seen in profile, the pivots 18 and 19 are located above the rear half of the front wheels 3. From each of these pivots, a support arm 20, 21 respectively extends forwards, said arms carrying their front end of the respective pivots 22 and 23, parallel to the pivots 18 and 19. In the central position, shown in FIG. 1, the pivots 22 and 23 lie in front of a vertical transverse plane, which comprises the front end front wheels 3. The pivots 18, 19, 22 and 23 are

  are found in the profile view on the vertices of a

  drastic. In their arrangement (see Figure 1), the pivots 22 and 23, for the central position of the lifting device 17, are located vertically one above the other while the pivot 19 is obliquely

  in front of and above the pivot 18. The pivots 18, 19, 22 -

  and 23 may however also be arranged at the apexes of a parallelogram. The lifting device 17 comprises a rectangular support frame, seen in profile, which comprises lateral uprights 24 and 25 (see also FIG. 3),

  the bases of which are rigidly connected by means of a tra

  pours in the shape of a sheath 27. The support frame 24 to 27 is parallel to a plane perpendicular to the plane of symmetry 7. At its upper part, the support frame is fixed, using pairs of pivots 22, 23 to the pairs of arms

  carriers 20, 21, located on either side of the chassis 1.

  The pivots 23 are fixed near the upper ends of the uprights 24 and 25. The support frame 24 to 27 carries at the lower ends of the uprights 24 and 25 points

  28 and 29 for a tool or a machine.

  In the profile view, approximately halfway between the pivot 22 and the lower end of the upright 24 (FIG. 1) is fixed a horizontal connecting bar 30, which rigidly connects the uprights 24 and 25. In the middle of the connecting bar 30 is fixed a coupling point 31 which forms the third coupling point of the lifting device

three-point 17.

  At each of the two front ends of a lateral side of the chassis 1 is fixed an ear 32, around which one end of a double-acting hydraulic cylinder 33 can rotate. Each cylinder 33 can rotate relative to

  the corresponding ear around an axis 34, perpendicular to

  laire in the plane of symmetry 7. Each cylinder 33 is directed, in a central position, from the axis 34 forward and obliquely upward and the end of the corresponding piston rod is rotatably mounted around the upper pivot 23 of the pair of pivots 22, 23. The two cylinders 33 are hydraulically connected, move at the same time and can be controlled from the cab 5 in a manner which will be described in more detail. cylinders 33, the carrier frame 24 is moved to

  27 up or down with or without machine or or-

  til coupled, whereas -as for the rear lifting device 13- a machine for working the soil can

  possibly be forcefully pressed into the ground.

  When the hydraulic circuit is operated in the opposite direction, the support frame 24 to 27 is lifted upwards and swings slightly backwards. In the case where the pivots 18, 19, 22, 23 are placed at the vertices of a parallelogram, the support frame 24 to 27 will move parallel to itself. The rotation of the steering wheel 35, placed in the cabin 5, rotates the two front wheels 3 together, starting from

  the central position, around a substantially vertical axis

  cal36, located in the plane of symmetry 7 (Figure 3), at an angle of about 60 to 80 in both directions, via a hydraulic transmission. The front wheels 3 rest on a horizontal axle 37, which includes

  the front wheel hydraulic drive motor

  3. The axle 37 is in the central position, symmetrical with respect to the plane of symmetry 7 and is rigidly fixed to a steering column 38, coaxial with the axis 36 and which,

  on its upper side, can rotate in a rotating bearing-

  which is supported by the front part of the chassis 1.

  Wheels 2 and 3 are fitted with low pressure tires

  and have a width of about 40 centimeters or more.

  The distance between the two front wheels 3 is smaller than the width of each of the wheels. The outside planes of the pair of front wheels 3 are at a short distance inside the inside planes of each of the rear wheels 2, so that the tracks of the front wheels 3

  are located inside those of the rear wheels 2.

  In this way, the weight of the tractor is distributed over a large width, so that the aggression

  soil structure is avoided as much as possible.

  As shown in FIG. 4, the tractor is provided at its rear with two coupled machines. The front lifting device 17 has been removed. The rear three-point lifting device 13 carries a working machine

  soil 39, of the rotary harrow type, which extends transversely

  badly in the direction of travel A and is provided with a row of pairs of teeth, which can be driven around

  substantially vertical axes from a gearbox

  swims 40, belonging to the machine and the input shaft of which is driven by means of a deflection shaft 41, coupled to the rear PTO shaft 8 of the tractor. The rotary harrow 39 carries at its rear a roller 42, which can be adjusted relative to the rest of the machine and which determines during the operation of the machine 39 the depth to which the teeth sink into the ground. Harrow 39 preferably corresponds to the width of the tractor. The machine 39 is furthermore provided with coupling points, around which lower lifting arms 43, which extend rearward, can rotate.

  and which can pivot up and down,

  said lifting arms being arranged symmetrically with respect to the plane of symmetry 7. The coupling points of the

  machine 39 also have a coupling point on the

  around which an upper connecting rod 44 can pivot up and down. The lower lifting arms 43 and the upper connecting rod 44 form a second three-point lifting device of the machine 39. In the embodiment according to the figure 4, this lifting device carries a seed drill 45, the drive mechanism of which can

  be driven by the wheels 46, which belong to the seed drill.

  The seed drill 45 extends in width over a distance, sensitive-

  ment equal to that of the harrow 39. On the top of the harrow 39 is also placed an axis around which a double-acting hydraulic cylinder 47 can pivot up and down. The end of the piston rod of the cylinder 47 is rotatably mounted on the upper connecting rod 44 of the

  three-point lifting device 43, 44.

  In the plan view of FIG. 5, the situation of the combination of the tractor and the machines of FIG. 4 has been represented during the execution of a turn at the end of the field or plot. By turning the front wheels 3 to an angle of about 60 to 80, the assembly pivots around

  a center of rotation 48, which is located in the prolum-

  position of the axis of rotation of the rear wheels 2 and in a lateral plane close to the tractor; then, after a rotation of the assembly on an angle of 180, the latter is ready without further maneuvers to start working the next strip of earth, which is connected laterally to the

  previous strip of land already worked.

  In order to get all the work on the ground to stop at the same place (or at the same transverse line at the end of the worked strip), the work of the

  rotary harrow 39 must stop near this line

  nale (reference 26 in FIG. 5), as well as, the

  starting with the seed drill 45. This means that the harrow 39 must be lifted earlier than the seed drill 45. This also applies when the front lifting device 17 is present and carries a machine for working the soil 49, as shown in Figure 6. In this case, the machine 49 must be lifted long enough (depending on the forward speed) before the harrow 39, coupled to the rear, so that the three machines are lifted from the ground to level of the end line 26. In the embodiment according to FIG. 6, it is also a rotary harrow 49 which is coupled to the front lifting device 17, which is necessary in heavy soils and soils with clods hard, on which one cannot be satisfied with harrowing only once, but where one must carry out harrowing work twice to obtain a good structure of the scattered soil. In such a case, the tractor should be passed twice, fitted with a harrow, on the field, which not only causes a loss of time, but also disadvantages the

  soil structure. In the case of the example of realization

  tion according to Figure 6, can be achieved in a single pass

  twice the harrowing work and direct seeding

behind.

  The maneuvers indicated above must be carried out by the tractor operator. When approaching the end line 26, the front lifting device 17 with the coupled harrow 49 must be lifted, but some time later, when the harrow 39 reaches the end line 26, the latter must in turn be lifted and then a little later the seed drill. In addition, it is necessary to start practically simultaneously the turn according to the arc of a circle 50 of FIG. 5. The fact of having to carry out at the same time several maneuvers by the control of organs of different nature, spaced from each other, in the cabin leads to inaccuracies, errors or accidents. Immediately after completing the turn, the front harrow 49 again approaches line 26, which is the start line for the new strip of land to be worked. The front harrow 49 must be put in the ground on this line and the harrow 39, coupled to the rear of the tractor, must be put in the ground some time after that and shortly after that the seed drill 45 must be lowered into the working position . This succession of maneuvers

is very complicated.

  To avoid these difficulties, the control members of the two, three or more lifting devices, are concentrated on a single control member of the tractor, such as, for example, the flywheel 35. Thus, while acting on the flywheel, the driver has the other controls within reach of a finger or a thumb of the hand on the steering wheel. In another way, the control members of the lifting devices can be assembled on, for example, the control lever for adjusting the speed of the tractor, especially if the latter is placed near the steering wheel and is provided with switches for the control of the lifting devices arranged one next to the other. It is further possible to automate the lifting of the two, three or more lifting devices, in sequence, so that when executing the turn and exiting the turn, the driver does not have to worry about maneuvering the control devices. lifting

  according to a certain chronology one behind the other.

  As already indicated, the time between the control of the first lifting device and that of the second is often greater than between the control of the second device

  and the next one. If these operations are self-

  and can be triggered by acting on a

  switch arranged for example on the steering wheel, the

  can focus on execution

correct turn.

  FIG. 7 shows a portion of a lever disposed near the flywheel, such as the speed adjustment lever (the pump flow) of the tractor, on which

  four switches are arranged. By operating the commu-

  51, which on the drawing bears the number "1", we raise

  or the lifting device 17 is lowered exclusively.

  By operating switch 52, which bears the number "2",

  the device is raised or lowered exclusively

  vage 13 and by operating the switch 53, which carries the

  number "3), the device is raised or lowered exclusively

  positive lifting 43, 44. By operating the switch 54, which bears the indication "AUTO", the lifting devices are automatically raised or lowered successively

  17, 13 and the lifting device 43, 44 with inter-

  time slots, which are set in advance. These intervals are matched with the forward speed and with the distances between the lifting devices 17, 13 and 43, 44, measured in the forward direction of the tractor. In FIG. 8 is drawn a portion of the steering wheel 35, between

  two spokes from which is fixed a plate carrying the commu-

  supports 51 to 54, near the outer circumference of the steering wheel. The switches 51 to 54 can be pushers,

  rockers or feeler switches.

  Each of the hydraulic cylinders or pairs of cylinders

  hydraulic 33, 16, 47 of the respective lifting devices

  17, 13 and 43, 44 are controlled by a special drawer to send the hydraulic fluid under pressure from one side

  either of the piston of the corresponding cylinder or cylinders.

  Each of these drawers has a neutral position, in the-

  which the supply and evacuation of the fluid to the corresponding cylinder or cylinders is blocked, a switching position

  on one side of the neutral position, in which the

  is sent to one side of the piston of the cylinder and a switching position to the other side of the neutral position, in which the fluid is sent to the other side of the piston

  or cylinders. Moving the drawer from the posi-

  neutral to one of the switching positions is controlled by an electromagnetic coil. One of the two switching positions is obtained by passing an electric current through the coil in one direction or the other using a control circuit. When the drawer is in one of the switching positions and the excitation of the electromagnetic coil ceases, the drawer

  returns from each of the two switching positions

  tion, under the effect of a spring, in the neutral position.

  The adjustment slide of the cylinder 47 of the lifting device

  43.44 is preferably housed in the tractor, like the other drawers, but it is also conceivable that it

  is on one of the coupled machines.

  The fact that the hydraulic cylinders 33, 16 and 47 are double acting is not essential. In one of the switching positions described, the slide can provide free passage for the hydraulic fluid, so that a coupled machine can move downwards by its own

  weight and can take a "floating" position.

  The control circuit indicated above for the hydraulic drawers is shown diagrammatically in FIG. 9, certain auxiliary elements being omitted. The

  control circuit according to FIG. 9 is of the electro-

  nique and is built around three "timers" or gener-

  pulse sensors constituted by integrated circuits (IC) of type 555. Each of these pulse generators is monostable. The pulse generator 55 in this exemplary embodiment is assigned to the control of the jacks 33 of the lifting device 17, the generator 56 to the control of the jack 16 of the lifting device 13 and the generator

  57 controls the cylinder 47 of the lifting device 43, 44.

  Each of the generators 55 to 57 can independently actuate the cylinder concerned or each pair of cylinders via the switches 51 to 53 (FIGS. 7, 8, 9), but the three generators 55 to 57 can be coupled together by means of switch 54, which constitutes a three-stage pulse generator which actuates the

  drawers of the three lifting devices pre-

  programmed. The duration of the high pulse H at output n. 3

  of each generator 55 to 57 is determined by the dimen-

  of the components, namely resistor 58 and capacitor 59. The duration of the pulse H can be

  set in intervals between micro-

  seconds and hours. For setting the duration, the

  resistance 58 of each generator is a varia-

corn.

  A low signal B can be brought to input n 2 of the

  generator 55, by pressing or activating the switch

  tator 51, already described in relation to FIGS. 7 and 8.

  In the same way, the input signal of the generator 56 and that of the generator 57 are obtained by actuation of the switch 52, respectively 53. If for example the switch 51 of the generator 55 is pressed, a pulse H appears at the output n 3 of this generator, pulse which reaches an open multiple switch 54, by a line 60, and has no other effect, but which at the same time is brought by a line 61 to the coil of a relay 62, this which causes the relay to close for the duration determined by the resistor 58 and the capacitor 59. For clarity, under each relay 62, 76 and 73 associated with each drawer, a block diagram is shown showing the path of the main current passing by

  relay and corresponding coil 63 of the drawer.

  As an auxiliary circuit, a simple counter 75 is used (in this example of embodiment of the type 7490), which by its output QA n 12 sends alternately a signal H and a signal B to a line 64, when it receives pulses at its input n 14 (precisely during the falling edge of the pulse). By acting on the switch 65 (which can be placed indifferently on the control lever according to

  Figure 7 or on the steering wheel according to Figure 8) the conduct-

  can determine at will that the signal on the line

  64 either an H signal or a B signal. If an H signal is pre-

  feels on line 64, this can correspond for example to the lifting of the lifting device (s), while in

  in the case of a signal B, this can correspond to the lowering

  lifting device (s) or vice versa. The

  signal on line 64 causes the opening

  turing and closing of pairs of transistors 66, 67, mounted in Darlington, which are used as switches; it follows that if a relay 62, 76, 73 is closed by the corresponding pulse generator, or if a current

  goes one way or the other in the coil 63 corres-

  laying, there will be an H signal or a B signal on line 64, as the case may be. Depending on the direction of the current in the coil 63, the corresponding drawer will move to the position of

  lifting or lowering of the lifting device concerned.

  This applies to all three coils 63 indicated in the diagram which are each assigned to a drawer and a jack. The three drawers all move when actuated either in the direction of lifting or in the direction

  lowering of the lifting devices concerned.

  Transistors 66 and 67- form a pair, one being a

  NPN transistor and the other a PNP transistor.

  By actuating one of the switches 51, 52 or 53, the corresponding pulse generator 55, 56 or 57 is therefore separately controlled, which moves the drawer concerned from the neutral position to the desired position according to the

level H or B on line 64.

  The other way of operating is obtained, namely the case where the pulse generators automatically cause a preprogrammed movement up or down of all the lifting devices enclosing

  the multiple switch 54. A pair of switch contacts

  tator 54 triggers the start of the process automatically by sending a negative pulse to input 2 of generator 55, this pulse being brought to this input without passing through switch 51. A second pair of contacts of switch 54 generates from the output pulse of the generator 55 (by lines 60 and 68) a negative pulse on the input n 2 of the generator 56, when the pulse of the generator 55 ceases, so that at the same time at the output n 3 of generator 56 is produced

  an output pulse, which is sent to the corresponding relay

  laying 67 by a line 69 and arrives by a link at the switch 54 then closed, and from there to the entry

  n 2 of generator 57 by a line 71. At the end of the

  pulse delivered by the generator 56, a negative pulse is sent to this last input, pulse which causes an output pulse at the output n 3 of the generator 57 which closes the relay 73 by a line 72 to excite the coil 63 of the corresponding drawer, and which sends by a line 74 a signal to the input 14 of the counter when the outgoing pulse from the generator 57 ceases. As the output pulse of each generator 56 and 57 begins, when the output pulse of each of the preceding generators ends, the lifting or lowering of the lifting device concerned begins only at the end of the generator pulse corresponding to the previous lifting device. The end of the pulse from the last generator 57 converts a signal H at output n 12 of the counter into a signal B or vice versa. After the

  automatic lifting of the lifting devices at the

  mite of a strip of earth, when the switch 54 is again opened then after the turn again closed, are. the lifting devices / operated in the opposite direction, because at the end of the previous lifting movements of the lifting device, the level on line 64 is automatically reversed and the transistors 66 and 67 switch, so that the direction of the current in the coils 63 is also reversed. When the output signal of each generator stops, the corresponding relay 62, 76 or 73 opens at

  again, so that the current falls in the cor-

  respondante 63. The slide therefore returns to the neutral position under the effect of the aforementioned spring, so that the movement of the lifting device stops. This applies to both individual generator control and automatic sequential control. The duration of the output pulse from each of the generators thus determines the

  when the next lifting device is activated.

  However, it may happen that the lifting device concerned reaches its final position (high or low) before the end of the output pulse from the generator concerned. In this case, it is desirable that an arm of each of the lifting devices actuates a hydraulic stop switch, both for lifting and lowering, which, for example, by raising the pressure at the end of travel, releases the fluid

hydraulic to a tank.

  According to another embodiment, pressure limiters can be placed in the hydraulic circuit, which limit the pressure to the extreme positions as long as it is a relatively high limit pressure. It is obviously possible to use more than three pulse generators for individual or automatic control, not only of lifting devices, but also of the other components of the tractor or of the coupled machines.

  for example for clutching or disengaging transmissions-

  PTO. If the number of pulse generator is greater than the number of organs

  to order (e.g. two lifting devices when

  that the assembly is used according to FIG. 9), the duration of the output pulse of the unused generator can be adjusted to a very short duration, for example a few microseconds; the unused drawer concerned will not react

or barely.

  The invention is not limited to the claims

  described in the previous embodiments with at least one rotary harrow and a drill. It can also be applied to other combinations of machines coupled for example a plow at the front and a harrow at the rear of the tractor, or the combination of a mower and a tedder or a mower front and baler at the rear of the tractor, or others

combinations of this kind.

Claims (31)

CLAIMS.   1. Agricultural tractor having at least one lifting device, characterized in that the control member (51, 52, 53, 64) of the lifting device (17; 13; 43, 44) is placed on a control member tractor, such as the travel speed control lever or steering wheel (35).   2. Tractor according to claim 1, from which at least two lifting devices can be controlled,   characterized in that the control members of the devices   lifting devices (13; 17; 43, 44) are switches (51, 52, 53, 54) arranged one beside the other on a tractor control unit.   3. Tractor according to claim 1 or 2, charac-   characterized in that the control member of the lifting device (13; 17; 43, 44) is placed on a lever   advance speed adjustment.   4. Tractor according to claim 1 or 2, charac-   characterized in that the control member of the lifting device (13; 17; 43, 44) is fixed to the steering wheel (35) of the tractor.   5. Tractor according to claim 4, characterized in that the control member of the lifting device (13;   17; 43, 44) is fixed to a radius of the steering wheel (35).   6. Tractor according to claim 4 or 5, charac-   terized in that the control member is fixed near the steering wheel circumference (35).   7. Tractor according to any one of the claims   1 to 6, characterized in that the movement of the device   lifting (13; 17; 43, 44) can be controlled by a push-button   evening, a rocker or a sensor switch.   8. Tractor according to any one of claims   -2 to 7, characterized in that at least one of the lifting devices (43, 44) belongs to a machine (39), which is coupled to the tractor.   9. Tractor according to any one of the claims   previous, characterized in that the lifting devices   (13; 17; 43, 44) are manoeuvrable by hydraulic means   liques. 10. Tractor according to claim 9, characterized in that at least one of the lifting devices (13; 17; 43, 44) is controlled by a drawer which, in at least one   positionactive, activates the lifting device and pos-   sedes a neutral position, reached from an active position under the effect of a spring force. 11. Tractor according to claim 10, characterized   in that in the neutral position the drawer blocks the movement cement of hydraulic fluid.   12. Tractor according to claim 10 or 11, characterized in that in one of the active positions, the slide provides free passage of the hydraulic fluid,   which corresponds with a downward displacement of the dispo-   lifting device (13; 17; 43, 44) under the influence of   own weight of a coupled machine (39; 45; 49).   13. tractor according to any one of the claims   above, characterized in that at least one of the   lifting devices (13; 17; 43, 44) can be operated   by double-acting hydraulic cylinders.   14. Tractor according to any one of the claims   2 to 13, characterized in that one of the lifting devices   (17) is mounted at the front of the tractor.   15. Tractor according to any one of the claims   2 to 14, characterized in that one of the lifting devices   (13) is mounted on the rear of the tractor.   16. Tractor according to any one of the claims.   tions 2 to 15, characterized in that the lifting devices (13; 17; 43, 44) can be actuated each   separately using the corresponding control elements dants (51, 52, 53).   17. Tractor according to any one of the claims   2 to 16, characterized in that, using a control member (54), a first lifting device can be controlled automatically and sequentially first   (17) then another lifting device (13).   18. Tractor according to claim 17, characterized in that the tractor comprises a control circuit comprising a plurality of pulse generators (55, 56, 57) in number equal to or greater than the number of   lifting devices (13; 17; 43, 44) to be controlled.   19. Tractor according to claim 18, characterized in that the control circuit can be actuated using a switch (54) placed on a control member (35) of the tractor.   20. Tractor according to claim 19, characterized in that the switch (54) is arranged next to the switches (51, 52, 53) intended for the separate control   lifting devices (13; 17; 43, 44).   21. Tractor according to any one of the claims   18 to 20, characterized in that each pulse generator   sions (55,56, 57) gives an electrical pulse, the duration of which determines the interval between the start of movement of the first lifting device and the start of movement from the other lifting device.   22. Tractor according to claim 21, characterized   in that the pulse duration is adjustable.   23.Tractor according to claim 21 or 22, characterized in that during the duration of the pulse the   hydraulic drawer is in working position.   24. Tractor according to one of claims 18 to 23,   characterized in that the end of an impulse on a genera-   pulse counter (55, 56, 57) causes the start of the next generator pulse.   25. tractor according to one of claims 18 to 24,   characterized in that the end of the pulse of the last active pulse generator (57) causes a signal which determines the direction of movement of the lifting device   during a next pulse cycle.   26. Tractor according to one of claims 9 to 25,   characterized in that each of the lifting devices (13; 17; 43, 44) is controlled by a hydraulic slide   which moves under the effect of an electromagnetic coil.   27. Tractor according to claim 26, characterized in that the coil is actuated by a relay (62, 73, 76) excited by an impulse.   28. Tractor according to any one of the claims.   above, characterized in that the adjustment of the   tractor forward speed is hydraulic.   29. Tractor according to any one of claims   previous, characterized in that all the wheels (2, 3) of the tractor are driven.   30. Tractor according to any one of the claims   previous, characterized in that the steered wheels (3) of the tractor can rotate at an angle such that the strips of soil worked by the coupled machines are connected to each other before or after a turn of 180.   31. Tractor according to any one of the claims   previous, characterized in that the tracks of its wheels   are located next to each other.