Abstract:
Method and apparatus for controlling the attitude of an agricultural implement drawn by an agricultural tractor, the device including a lift; two deflection sensors located at the attachment points of the bottom arms of the lift to the frame of the agricultural tractor; and an electronic central control unit for processing data received from the sensors and controlling lifting and lowering of the implement by the lift as a function of the data detected by the two sensors; the device being characterised in that each of the sensors has a locking device for adjusting the position of each of the sensors with respect to the frame so that each of the sensors assumes a predetermined tilt with respect to the ground.

Description:
FIELD OF THE INVENTION 
     The present invention relates generally to a method and apparatus for controlling the attitude of an implement drawn by an agricultural tractor, and more spectifically to improved method and apparatus for such purpose that do not rely on measurement of the working resistances of the implement. 
     BACKGROUND OF THE INVENTION 
     Many agricultural tractors are equipped with devices for automatically controlling the attitude of the implement by detecting the force exerted on the lift attachment arms, so as to optimise tractor performance by lifting the implement as a function of its working resistance. In particular, devices applied to a hydraulic lift are known in which ground action on the implement is determined by two sensors fitted to two pins about which the bottom lift arms pivot with respect to the tractor frame; and the implement is lifted by two top arms pivoting with respect to the frame, powered by a hydraulic system, and also connected mechanically to the bottom arms. In other words, the two top arms and respective bottom arms and connecting rods together define the lift. The sensors on the bottom arm pins provide for measuring deflection of the pins under the load exerted by the implement. Such a device is described, for example, in European patent application no. 95203063.3 (in the name of New Holland Italia S.p.A.) in which the agricultural tractor described employs two Hall-effect deflection sensors located at the attachment points of the lift arms to the frame. 
     The neutral plane of the sensors remains substantially perpendicular at all times to the ground being worked, so that the apparatus shown in the European application identified above, and similar apparatus, do not allow for the deflection sensor being rotated a given angle with respect to the ground. For this reason, since the deflection sensor detects stress substantially perpendicular to the neutral plane, the arrangement shown in the above-identified European application only provides for measuring the pulling force of the implement, which results in poor measurement and control when the pulling force is affected by the configuration as opposed to the working depth of the implement. 
     With an implement such as a ripper, in which the pulling force is mainly exerted by the ends, and which provides for producing drainage holes of more or less constant depth, on encountering ground areas of different consistency, pull-controlled lifting is only effective in the presence of considerable undesired variations in working depth. Lifting also produces an increase in vertical load due to the geometry of the ends, which results in increased lift pressure in the hydraulic circuit and in a chain reaction which may even result in the implement being withdrawn completely from the ground. At which point, the system commands a rapid downstroke, thus resulting in jerky operation with the implement being continually withdrawn and lowered rapidly. 
     SUMMARY OF THE INVENTION 
     Accordingly, it is an object of the present invention to provide novel and improved method and apparatus for controlling the attitude of an implement drawn by an agricultural tractor, and which enables the operator to selectively adjust the tilt of the deflection sensors with respect to the ground plane. More particularly, these novel method and apparatus provide for tilting the neutral plane of the sensor with respect to the substantially horizontal ground plane for different working conditions of the implement and different ground consistencies and properties. 
     Another object of the invention is to provide method and apparatus wherein the deflection sensor detects not only the pulling force of the implement but also a sustaining and lifting force component indicating, instant by instant, the way in which the pulling force is actually affected by the lifting force. The lifting force produces a component on the read axis of the sensor but oppositely oriented with respect to the pulling force projection, so that the electronic central control unit receives a lower reading which slows down, and eventually arrests, the lift operation in proportion to the ground penetration force of the implement. The lift operation can therefore be arrested long before the implement is withdrawn completely from the ground, thus eliminating any jerkiness and enabling smooth operation more in keeping with conditions external to the automatic implement lift system. 
     These and other objects, features and advantages are accomplished according to the instant invention by providing method and apparatus for controlling the attitude of an implement drawn by an agricultural tractor, the device comprising a lift; two deflection sensors located at the attachment points of the bottom arms of the lift to the frame of the agricultural tractor; and an electronic central control unit for processing data received from the sensors and controlling lifting and lowering of the implement by the lift as a function of the data detected by the two sensors. The device is further characterised in that each of the sensors comprises locking means for adjusting the position of the sensor with respect to the frame so that the sensor assumes a predetermined tilt with respect to the ground. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of the rear of an agricultural tractor equipped with a device in accordance with the instant invention; 
     FIG. 2 is a side elevational view of the of the sensor arrangement of the instant invention; 
     FIG. 3 is a cross-sectional view, taken along lines III—III of FIG. 2.; 
     FIG. 4 is a dynamic diagram relative to a deflection sensor in the prior-art position with respect to the frame; and 
     FIG. 5 is a dynamic diagram relative to a sensor positionable with respect to the frame according to the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now to FIG. 1, reference number  10  indicates the rear of an agricultural tractor comprising a frame  11  for supporting a seat  12  and a rear axle  13  fitted in known manner with two rear wheels  10   a  (only one shown). Frame  11  is fitted mechanically with a device  14  for controlling the attitude of an agricultural implement A (not shown in FIG.  1 ), and which is the main object of the present invention. 
     Device  14  comprises two bottom arms  15 , by which respective members  16  (only one shown in FIG. 1) projecting from frame  11  (see also FIGS. 2 and 3) are connected mechanically to the agricultural implement A drawn by agricultural tractor  10 . Device  14  also comprises two top arms  17  corresponding with and connected to bottom arms  15  by respective articulated rods  18 , i.e., as shown in FIG. 1, each bottom arm  15  is connected mechanically to the corresponding top arm  17  by a corresponding rod  18  pivoting with respect to arms  15  and  17 . 
     One end of each top arm  17  is integral with a shaft  19 , which is rotated in known manner (not shown) by an electronic central control unit  20  for processing a number of signals from two deflection sensors  21  fitted to members  16  projecting from frame  11 . 
     Bottom arms  15 , top arms  17 , rods  18 , and shaft  19  together form part of a lift S powered, for example, by a hydraulic circuit (not shown) and for lifting and lowering with respect to ground T any implement A attached by known mechanical means to bottom arms  15 . Lifting and lowering of implement A with respect to ground T may obviously be controlled by electronic central control unit  20 , which may activate a hydraulic system (not shown) to rotate shaft  19  one way or the other. 
     As shown in FIG. 3, each sensor  21  is inserted inside two coaxial through holes  22  and  23 , between which cavity  24  houses a spherical joint  25  interposed between sensor  21  and the corresponding bottom arm  15 . 
     When pull F (FIG. 3) is exerted by implement A, sensor  21  deflects by an amount depending on the value of force F. That is, the greater the pull F exerted by implement A via arm  15 , the greater the deflection of corresponding sensor  21 ; and the amount of deflection is convertible into an electrical signal transmitted over a cable  26  to central control unit  20  which, as stated, controls lift S. 
     Consequently, when an anomalous increase in force F occurs during the working of ground T by implement A, central control unit  20  raises implement A from ground T in known manner, and, once the cause of the anomalous increase in F is removed, lowers implement A back down to ground T. 
     As shown in FIGS. 2,  4 , and  5 , the cross section of sensor  21  comprises three straight sides  21   a - 21   c  perpendicular to one another, and a curved side  21   d  connecting straight sides  21   a  and  21   c . The cross section of sensor  21  is so shaped to enable sensor  21  to be positioned correctly with respect to a locating plate  27  (FIGS. 2 and 3) which may be fixed by two bolts  28 ,  29  to member  16  integral with frame  11 . More specifically, curved face  21   d  of sensor  21  must be positioned facing implement A, so that, in the prior-art embodiment shown in FIG. 4, the neutral axis N of sensor  21  is substantially perpendicular to the surface of ground T. 
     It should be pointed out that neutral axis N is the line left in the drawing plane by the neutral plane N of the deflected beam defined by sensor  21  C, (see also FIG.  3 ). If the neutral plane N is not positioned correctly, the F values detected by sensor  21  are unreliable and result in malfunctioning of the system as a whole. 
     To position sensor  21  correctly with respect to locating plate  27 , a foolproof seat  30  need simply be formed in known manner in the face  27   a  of plate  27  facing implement A. Seat  30  has three flat perpendicular faces to house sides  21   a - 21   c  of sensor  21 , so that curved face  21   d  of sensor  21  is positioned correctly facing implement A. 
     FIG. 4 shows a conventional position of sensor  21 , in which neutral axis N is coincident with the axis P perpendicular to ground T, and, as stated, axis N is perpendicular to the force F exerted by implement A on one of bottom arms  15 . H indicates the force produced by rod  18  to lift implement A off the ground upon force F exceeding a predetermined threshold. As can be seen, in this case, force H is not detected by sensor  21  by lying along neutral axis N and therefore being unable to exert either tensile or compressive stress on the fibers of sensor  21  on either side of neutral plane N. 
     On the other hand, if, as shown in FIG. 5, sensor  21  is tilted a given angle α as explained in detail below, sensor  21  is able to detect not only component F 1  of F along an axis C perpendicular to neutral axis N, but also component H 1  of force H along the same axis C. F 1  will obviously be equal in absolute value to (F cos α), and H 1  equal in absolute value to (H sin α). 
     From a different point of view, angle α may be considered the angle formed by neutral axis N and axis P perpendicular to ground T. Obviously, in the prior-art situation shown in FIG. 4, angle α=0°. 
     In the FIG. 5 case, central control unit  20  is able to determine force F 1  perpendicular to neutral axis N, which is actually less than F. By means of appropriate processing by central control unit  20 , however, it is possible to correct this false reading to work out the real value of F from the detected F 1  value. 
     Only being able to read a force lying along axis C, sensor  21  determines the value R of the vector sum of F 1  and H 1 . In other words, sensor  21  can also “see” the force H, in the form of H 1 , produced by arms  17  via rods  18 , and can therefore read the instantaneous value of R=(F 1 −H 1 ). 
     Consequently, when rod  18  lifts bottom arm  15 , and hence H is other than zero, not only is the resultant force R reduced on account of the increase in H 1 , but there is also a simultaneous reduction in force F 1  by implement A being raised by arms  15 . Arms  15  stop lifting as soon as value R falls within a predetermined acceptance range. If force R increases again, central control unit  20  commands rods  18  to produce new forces H to lift implement A, and so on. 
     Off-ground lifting of implement A is thus broken up into several parts to prevent implement A from being withdrawn completely from ground T to no purpose. In other words, in the presence of an exceptional force F 1 , and hence F, lift S begins lifting bottom arms  15  by just enough to restore the values of R to a predetermined acceptance range, so that in many cases implement A is allowed to continue working ground T as opposed to being withdrawn completely by lift S. 
     By correctly coordinating forces H and F, the present invention therefore provides for preventing jerky operation caused by implement A being withdrawn completely from ground T, being plunged straight back into ground T upon central control unit  20  determining a zero force F, and then being withdrawn completely once more upon force F again exceeding the threshold value. For example, when working fairly soft ground T beneath a very hard layer, as in the case of grassland, using sensor  21  tilted at a given angle α (FIG.  5 ), central control unit  20  stops implement A from being lifted once R falls once more within an acceptable range. Using a conventionally positioned sensor  21  (FIG.  4 ), on the other hand, once the hard outer layer is detected, implement A is withdrawn completely, thus giving rise to undesired jerking. As stated, positioning sensor  21  with respect to frame  11  according to the present invention prevents implement A from being withdrawn completely to no purpose, thus keeping the implement longer in the work position. 
     Tilt α depends on the desired sensitivity of the system. More specifically, the further sensor  21  is tilted, i.e. the greater angle α, the greater the value of H 1  and hence system sensitivity with respect to H. 
     Tilt α is also user selected on the basis of mean penetration of implement A, the type of ground, and desired system sensitivity. The system may therefore be sold, for example, together with maker&#39;s tables indicating recommended tilt angles α for different ground consistencies and implements; and the system may be in-field calibrated by the user on a trial and error basis using values in the region of the α angles recommended by the maker. 
     If implement A is a ripper, for example, ground penetration is deep, so that lift action is preferably broken up considerably, and a tilt angle α ranging between 20° and 25° preferably selected to obtain substantial H 1  components and increase lift action break-up. 
     Conversely, in the case of soft ground and an implement A in the form of a disk harrow or cultivator, tilt angles α of close to zero and nearing the FIG. 4 (prior-art) position may be used. In this case, in fact, a high degree of break-up is not required. 
     Tests have shown that angles α ranging between 0° and 40° cover a wide range of agricultural implements A and different types of ground. 
     Sensor  21  can be tilted using the system shown in FIG. 2. A substantially C-shaped groove  31  is formed in the outer face  16   a  (FIG. 3) of member  16 , so that by means of bolts  28  and  29 , plate  27  can be fitted in a position other than that shown by the continuous line in FIG.  2 . For example, plate  27  can be fitted in a first position defined by a tilt angle α1 of 15°, or in a second position defined by a tilt angle α2 of 25°; α1 and α2 both being within an angle β of 40° for the reason explained above. In the FIG. 2 embodiment, groove  31  is therefore in the form of a 130° sector (90°+40°). 
     To adjust the system to the conditions of a new implement A or different ground T, or both, the user simply unscrews bolts  28  and  29  from groove  31 , rotates plate  27 , e.g. clockwise, to set the approximate tilt angle α recommended, for example, in a table supplied by the maker of agricultural tractor  10 , and then fixes plate  27  back on to member  16 . The user then proceeds by trial and error to determine the best tilt angle α for the implement A and ground T involved. 
     To anyone skilled in the art, the above-described system with particular reference to FIG. 2 may obviously be replaced with a similar mechanical system for rotating plate  27  by the desired angle α without, however, departing from the scope of the present invention. For example, in a further embodiment not shown, plate  27  is rotated by a lever connected to plate  27  itself. Plate  27  may also be rotated by remote-control systems, in particular, operated by the user from seat  12 .