Patent Publication Number: US-2006016609-A1

Title: Implement control systems

Description:
BACKGROUND OF THE INVENTION  
      This invention relates to implement control systems for controlling a ground engaging implement mounted and a tractor via a linkage having a pair of lower links and at least one top link. The invention is primarily concerned with control systems for front linkages but is also applicable to the control of rear linkages for mounting an implement on the rear of a tractor.  
      Whilst front such linkages are well known, problems arise with the control of implements mounted on such front linkages, since, contrary to implements mounted on the rear of a tractor which are inherently stable in their operation, front mounted implements exhibit instability and the forces applied to the top link can give misleading indications as to the actual forces applied to the implements by the ground.  
      It is an object of the present invention to provide an implement control system which is particularly suitable for use with a front linkage and which at least reduces the above problems.  
     BRIEF SUMMARY OF THE INVENTION  
      Thus according to the present invention there is provided a system for controlling a ground engaging implement mounted on a tractor via a mounting linkage, the system comprising: 
          a sensing system for providing a signal representative of only the horizontal component of the forces applied to the implement by the ground thereby eliminating the effect of the weight of the implement from the sensed signal,     a positioning means for controlling the height of the mounting linkage relative to the tractor,     a control means which receives signals from the sensing system and from the tractor operator as to the desired operating condition of the implement and which compares these signals to provide an output signal to the positioning means to adjust the working position of the implement to meet the desired operating condition of the implement.        

      Such a system provides for a more stable control of front mounted implements since the instability inherent due to the effect of the weight of the implement on the upper link forces is eliminated.  
      The mounting linkage may comprise a pair of lower links and at least one upper link for supporting the implement from the tractor, the sensing means comprising a first linkage for connecting the lower links with a force sensor to transmit to the sensor only the horizontal component of the forces applied to the lower links by the implement and a second linkage connecting the (or each) upper link with the force sensor to transmit to the sensor only the horizontal component of the forces applied to the upper link (or links) by the implement.  
      The first linkage may include a first bell crank pivoted about a first generally horizontal and transverse axis relative to the tractor, the first bell crank having a first arm or arms connected with the lower links and a second arm of arms connected with an intermediate link to load the intermediate link with the horizontal component of the forces applied to the lower links and the second linkage includes a second bell crank pivoted about a second generally horizontal and transverse axis relative to the tractor, the second bell crank having a first arm or arms connected with the or each upper link and a second arm or arms connected with the intermediate link to load the intermediate link with the horizontal components of the forces applied to the upper link(s), the intermediate link being connected with the force sensor. The force sensor may comprise an electrical force sensing pin, a hydraulic ram or any other suitable sensor.  
      In a further form of the system the mounting linkage comprises a pair of lower links and at least one upper link for supporting the implement from the tractor, the sensing means comprising electronic force sensing means to sense only the horizontal component of the forces applied to the upper and lower links by the implement, the control means receives these signals from the sensing means, compares the signals with the desired operating condition signal set by the tractor operator and generates an electrical output signal which controls the operation of the positioning means accordingly.  
      As will be appreciated, the positioning means preferably comprises hydraulic ram means connected with the mounting linkage so as to apply only a vertical force to the mounting linkage when the system is in use to control the implement and hence avoid any effect on the sensing system signal.  
      Other features of the invention are set out in the sub-claims.  
      One embodiment of the present invention will now be described, by way of example only, with reference to the accompanying drawings which: 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is a perspective view of an implement control system for use with an implement mounted on the front of an agricultural tractor;  
       FIG. 2  is a diagrammatic view of the system of  FIG. 1 ;  
       FIG. 3  shows the forces applied to the linkage of the system of  FIGS. 1 and 2 , and  
       FIG. 4  shows the forces applied to the linkage of the system when mounting a rear implement.  
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
      Referring to  FIG. 1  this shows an implement control system for use with an implement  10  (shown diagrammatically) mounted on the front of an agricultural tractor. The implement is mounted on the tractor via a frame  11  which is bolted to the tractor chassis (not shown). An upper link  12  and the pair of lower links  13  connect the implement with the frame  11 . The lower links are connected via a bracing piece  14  which is in turn connected with a lower bell crank member  15  which is pivoted on frame  11  about a pin  16 . Bell crank member  15  has two pairs of lower arms  17 , 18  within which the bracing piece  14  is connected by pins  19  and a pair of upper arms  20  within which a link  21  is connected via a pin  22 .  
      The upper link  12  is connected with an upper bell crank member  23  which is pivoted on frame  11  via a pin  11   a  which extends through frame flanges  11   b . Bell crank  23  has an upper pair of arms  24  which receive between them one end of the upper link  12  via a pin  25  and a lower pair of arms  26  which are connected with the other end of link  21  via a pin  27 . Lower arms  26  are also connected via pin  27  with links  28  which are attached to a tube  29  within which an electrical draft force sensing pin  30  is mounted. Pin  30  mounts the tube  29  to the frame  11  via pillars  31 .  
      A hydraulic cylinder, not shown in  FIG. 1  but visible diagrammatically as  32  in  FIG. 2 , acts between the frame  11  and each of the lower links  13  to raise/lower the links and hence the implement  10  relative to the frame. The line of action of cylinder  32  passes through pivot pin  11   a  and is arranged to be vertical when the linkage is in its so-called “neutral” position when the system is being used to control implement  10 . This ensures that cylinder  32  does not apply any turning movement to either of the bell cranks  15  and  23  and hence any vertical adjustment of the position of the implement of the position of the implement has no effect on the forces sensed by sensing pin  30 . In the “neutral” position bell crank arms  17 ,  18  and  24  are also arranged to be vertical.  
      The geometry of the bell crank linkage arrangement described above which connects the lower links  13  and the upper link  12  to the frame  11  is such that in the “neutral” position the effect on the top link  12  of the weight of the implement  10  is eliminated from the forces sensed by the sensing pin. This can be shown by an analysis of the forces acting in the linkage as follows.  
      Referring to  FIG. 3 , when the lower links  13  are raised to position the implement  10  clear of the ground so that only the weight of the implement is loading the linkage.  
      In this condition it can be seen that linkage applies a force L with a horizontal component Lx to the implement  10  via lower links  13  and a force T with a horizontal component Tx to the implement via the upper link  12 .  
      These forces act in opposite directions and are equal to each other thus Lx=Tx.  
      Now, considering the forces acting on link  21 , with the linkage in its so-called “neutral” position (i.e. with the bell crank arm  17 ,  18  and  24  vertical) and assuming that the lengths of the bell crank arms are in the ratio 24/26=(17,18)/20 it can be seen that bell crank  15  applies a force equal to Lx to link  21 .  
      Similarly, bell crank  23  applies a force equal to Tx to link  21 .  
      The only other force acting on link  21  is the reaction force R applied to link  21  by links  28  which is in effect the force which the sensing pin  30  will measure.  
      Thus we can say, considering the forces acting on link  21  that 
 
 Tx+Lx+R= 0 
 
      Since we know that Tx and Lx are equal and opposite  
      therefore 
 
 Tx−Tx+R= 0 
 
 therefore 
 
R=0 
 
      Thus the senor  30  sees no force in links  28  due to the weight of implement  10 .  
      If one now considers the implement in a ground engaging condition in which the ground applies a force D to the implement with a horizontal component Dx it can be seen, taking moments about a point A of the implement, that 
 
 Tx·L 1 =Dx·L 2 
 
 (where L 1  and L 2  are the dimensions of the implement marked in  FIG. 3 ). 
 
      Similarly, taking moments about point B then 
 
 Lx·L 1= Dx· ( L 1+ L 2) 
 
      Since R=Lx−Tx from above  
         Then   ⁢           ⁢   R     =         Dx   ·       (     L1   +   L2     )     L1       -     Dx   ·     L2   L1         ⁢     
     ⁢           =         Dx   ·   L1     L1     +       Dx   ·   L2     L1     -       Dx   ·   L2     L1             
 
 therefore 
 
R=Dx 
 
      Thus, the force R applied to the sensing pin  30  equals the horizontal component of the force applied to the implement by the ground for all values of L 1  and L 2 .  
      Thus the linkage eliminates the significance of the point at which the ground force is applied by the implement.  
      Typically the signal output from pin sensor  30  is passed to a cab mounted electronic control unit  33  via line  34 . Unit  33  has various driver input devices, for example, control dials  35 , 36  for setting levels of draft force or implement position etc and the draft force levels set by the driver are compared with the signals received from pin sensor  30  and a control signal output is sent to solenoid control valve  37  of a hydraulic positioning unit  38  which supplies or exhausts pressurized hydraulic fluid to or from hydraulic cylinders  32  to raise or lower the implement as necessary to achieve the control settings set by the driver.  
      In a variation of the system described above, links  28  and pin sensor  30  could be replaced by a hydraulic cylinder which connects pin  27  to frame  11  with the level of pressure in this cylinder being used as the indication of the forces applied to link  21  by the upper link  12  and the lower links  13 .  
      In a still further variation, lower links  13  and upper links  12  could be connected to frame  11  by electronic draft force sensors (e.g. pin sensors similar to sensor  30  described above). The three sensors would be designed to measure only the horizontal forces applied to implement  10  by the ground and this signals would be processed by an electronic control unit in which they are compared with the values set by the tractor driver to produce the appropriate control signal for use by hydraulic positioning unit  38 .  
      With the sensing system of the present invention a more constant working depth of the implement can be achieved with resulting more constant power requirement to push the implement and less adjustment of the implement required by the driver. Also, no depth control wheel is required which means that more weight is taken on the front wheels of the tractor thus reducing wheel spin. It also means that the implement is shorter in length which make road travel easier.  
      Although the invention has been described above in relation to a front mounted implement it is also useful for use on rear mounted implements since the use of only the horizontal component of the forces acting on the implement as the control signal for the system again promotes greater system stability and enables the use of a hydraulic top link to vary ground reaction of the tractor and implement without affecting the draft force measured.  
      For example,  FIG. 4  shows diagrammatically a tractor  40  having a long implement  41  connected to the rear thereof by a pair of lower links  42  and a hydraulic top link  43 . Implement  41  has a support wheel  47  and top link  43  includes a hydraulic cylinder  44  which can be pressurized by the hydraulic system of the tractor. The top link  43  is connected to the implement post  45  via an elongated slot  46  in which a pin  48  on the end of the top link slides.  
      Considering a static analysis of the forces acting on the implement  41 .  
      Resolving vertically then: 
 
 Cy+Dy+P 2 +Ey= 0  (equation 1) 
 
 where 
          Cy=the vertical effect of the ground on the wheel  47  at contact point C     Dy=the vertical component of the force applied by draft links  42  to the implement  41  at point D     P 2 =the weight of the implement  41  acting through its centre of gravity     Ey=the vertical component of the forces applied to the implement  41  by the top link  43  at point E.        

      Resolving horizontally then: 
 
Dx=Ex=0  (equation 2) 
 
 where 
          Dx=the horizontal component of the force applied by draft links  42  to the implement  41  at point D.     Ex=the horizontal component of the force applied to the implement  41  by the top link  43  at point E.        

      Taking movements about point D then: 
 
 Ex·L 4 +P 2 ·L 5 +Cy·L 2=0  (equation 3) 
 
 Where 
          L 5 =the distance of the centre of gravity of the implement from point D     L 2 =the distance of the point of contact of wheel  47  from point D.        

      Also the horizontal component Ex of the force E in top link  43  is equal to E.cos x where x is the angle of inclination of the top link to the horizontal. 
 
Therefore Ex=E.cos x  (equation 4) 
 
      Now considering the static analysis of the forces acting on the tractor then resolving vertically 
 
 Ay=By=Pi−Ey−Dy= 0  (equation 5) 
 
 Where 
          Ay=the vertical effect of the ground on the tractor at contact point A     By=the vertical effect of the ground on the tractor at contact point B     P 1 =the weight of the tractor  40  acting through its centre of gravity. 
 
 Taking movements about point A then: 
 
 Ex ( L 4+ L 7)+ Dy·L 3 +Ey·L 3 +By·L 1+ P 1· L 6=0  (equation 6) 
 
 Where 
    L 4 =the distance between points D and E     L 6 =the distance of the centre of gravity of the tractor from point A     L 7 =the distance point D and the ground.        

      If the top link has no strain since pin  48  is in the mid region of the slot  46  then:  
      The force E in top link  43 =0  
      Therefore Ex=0 and Ey=0  
      Thus from equation 2 we can say that Dx=−Ex=0  
         From   ⁢           ⁢   equation   ⁢           ⁢   3   ⁢     :       ⁢     
     ⁢     Cy   =       -     (       Ex   ·   L4     =     Pz   ·   L5       )       /   L2       ⁢     
     ⁢       And   ⁢           ⁢   since   ⁢           ⁢   Ex     =       E   ·   cos     ⁢           ⁢   x   ⁢           ⁢   from   ⁢           ⁢   equation   ⁢           ⁢   4   ⁢           ⁢   then   ⁢     :         ⁢     
     ⁢     Cy   =       (         -   L4     ·     (     E   ⁢           ⁢   cos   ⁢           ⁢   x     )       -     L5   ·   P2       )     /   L2       ⁢     
     ⁢     From   ⁢           ⁢   equation   ⁢           ⁢   1   ⁢     :       ⁢     
     ⁢     Dy   =       -   Cy     -   Pz   -   Ey       ⁢     
     ⁢       therefore   ⁢           ⁢   Dy     =         (       Ex   ·   L4     =     P2   ·   L5       )     L2     -   P2   -   Ey       ⁢     
     ⁢     From   ⁢           ⁢   equation   ⁢           ⁢   5   ⁢     :       ⁢     
     ⁢     Ay   =       -     (     By   +   P1   -   Dy   -   Ey     )       ⁢     
     ⁢           =       -   By     -   P1   +   Dy   +   Ey         ⁢     
     ⁢       And   ⁢           ⁢   since   ⁢           ⁢   Ey     =     sin   ⁢           ⁢     x   ·   E     ⁢           ⁢   therefore       ⁢     
     ⁢     Ay   =       -   By     -   P1   +   Dy   +     Sin   ⁢           ⁢     X   ·   E               
       From   ⁢           ⁢   equation   ⁢           ⁢   6   ⁢     :         
       By   =           -   P1     ·   L6     -     Ey   ·   L3     ⁢           -     Dy   ·   L3     -     Ex   ⁡     (     L4   +   L7     )         L1         
     therefore     
       By   =       [         -   P1     ·   L6     -     L3   ⁡     (     Ey   +   Dy     )       -       E   ·   cos     ⁢           ⁢     x   ⁡     (     L4   +   L7     )           ]     /   L1         
 
      It can therefore be seen from the above equations for Cy, Ay and By that if the top link is pressurized to increase the force E in the top link then: 
          Cy decreases (since the negative value of the term containing E in the equation for Cy increases).     Ay increases (since the positive value of the term containing E in the equation for Ay increases), and     By decreases (since the negative value of the terms containing E in the equation for By increases.        

      Thus since Cy and By both decrease as the pressure in the top link is increased and Ay increases the rear wheel ground reaction can be varied by adjusting the pressure in the top link cylinder  44  to reduce rear wheel slip when ploughing. The objective is to have Ay=2By when ploughing and when the implement is raised (and Cy=0) then By should be greater than say 1 Ton to retain a good steering capability.  
      Since, as demonstrated above, the implement control system of the present invention eliminates the effect of the weight of the implement from the draft forces sensed, the pressure in top link  44  can be varied between zero and its maximum (when the implement is raised with the support wheel  47  clear of the ground) without affecting the draft forces sensed.  
      The present invention thus also has significant benefits when used on a rear mounted implement.