Abstract:
A method and device for longitudinally balancing an agricultural vehicle, in particular a tractor, whereby at least one sensor, for detecting at least one respective stress affecting a longitudinal attitude of the agricultural vehicle, controls an actuating device of a ballast to move the ballast longitudinally along the agricultural vehicle, which at least partly compensates for the stress.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to a method and device for longitudinally balancing an agricultural vehicle, in particular a tractor. 
       BACKGROUND OF THE INVENTION 
       [0002]    As is known, one of the major hazards when operating an agricultural vehicle is the loss of longitudinal stability in the various and, often, difficult conditions in which the vehicle is operated. 
         [0003]    Commonly, the longitudinal attitude of an unloaded, stationary agricultural vehicle having a substantially horizontal barycentric longitudinal axis is altered, and may even be compromised. An altered longitudinal attitude often results in the loss of longitudinal stability and tip-up of the vehicle, whenever any static and/or dynamic force is applied having a vertical component and a point of application some distance from a barycentric plane perpendicular to the barycentric longitudinal axis. 
         [0004]    For example, the loss of longitudinal stability may occur when a very heavy projecting implement is connected to a lift member of the vehicle. In certain operating conditions the weight of the vehicle alone may not be sufficient to counterbalance the tip-up moment produced when the implement, normally resting on the ground, is lifted off the ground. 
         [0005]    The same also applies, whether or not the implement is lifted, when the vehicle is operated over very rough or steep ground. 
         [0006]    To safeguard against loss of longitudinal stability caused by a raised implement, agricultural vehicles are equipped with ballast, connected integrally in a fixed position to the end of the vehicle opposite the implement end, to produce a stabilizing moment to counterbalance the tip-up moment produced by lifting the implement. 
         [0007]    Because the stabilizing moment produced by the ballast is constant and proportional to the weight of the ballast and its distance from the end of the vehicle, the effectiveness of the above known balancing system is seriously impaired by the obvious reasons of size, and that the ballast must project as little as possible from the end of the vehicle. The ballast must also not be so heavy as to unnecessarily overload the vehicle in normal operating conditions. 
       OBJECT OF THE INVENTION 
       [0008]    It is an object of the present invention to provide an agricultural vehicle balancing method and device which are cheap and easy to implement, and designed to eliminate the aforementioned drawback. 
       SUMMARY OF THE INVENTION 
       [0009]    According to the present invention, there is provided a method of balancing an agricultural vehicle by using a sensor to detect the effects on the agricultural vehicle of stress affecting a given longitudinal attitude of the agricultural vehicle. An actuating device of a ballast that can be moved longitudinally along the agricultural vehicle in response to an output signal of the sensor is then controlled to move the ballast to at least partly compensate the effects. Since the stress can affect the longitudinal inclination of the agricultural vehicle; the sensor could be an inclinometer. 
         [0010]    The actuating device is activated in response to a signal emitted by the sensor, if the intensity of the signal is above a given threshold. The ballast is moved longitudinally by the actuating device between a fully withdrawn position and a fully extracted position, proportionately to the intensity of said signal. The actuating device may be a hydraulic actuator supplied with pressurized fluid via a valve controlled by a central control unit connected to the sensor. The sensor is configured to emit signals of an intensity proportional to the effects of the stress. 
         [0011]    The stress may comprise a load and a tip-up moment caused by raising an implement being connected to and projecting from the agricultural vehicle, off the ground by a hydraulic lifting arrangement having a hydraulic feed circuit, which may communicate with the hydraulic actuator via a valve. The internal pressure of the hydraulic feed circuit can also be detected by a sensor. 
         [0012]    The present invention, also provides for a device for balancing an agricultural vehicle, in particular a tractor, that has at least one ballast movable longitudinally along the agricultural vehicle, a sensor for detecting the stress on a given longitudinal attitude of the agricultural vehicle; and an actuating device connected to the ballast. The actuating devices moves the ballast longitudinally in to at least partly compensate for the stresses in response to a signal from the sensor. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0013]    The invention will now be described further, by way of example, with reference to the accompanying drawings, in which: 
           [0014]      FIG. 1  shows a schematic, partly sectioned side view of an agricultural vehicle featuring a preferred embodiment of the balancing device according to the present invention; 
           [0015]      FIG. 2  shows a front view of the  FIG. 1  vehicle; 
           [0016]      FIGS. 3 and 4  show partly sectioned, partly block plan views of the  FIG. 1  vehicle in respective different operating configurations; 
           [0017]      FIGS. 5 and 6  show schematic block diagrams of a first and second preferred embodiment, respectively, of a control circuit of the balancing device according to the present invention. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0018]      FIG. 1  shows a vehicle  1  in particular a crawler tractor, which has a barycentric longitudinal axis  2 , and comprises a frame  3 , a body  4 , and two known crawler traction devices  5  on opposite sides of axis  2 . 
         [0019]    Vehicle  1  has a known member  6  for attaching and lifting an implement  7  (shown by the dash line) at the rear longitudinal end. 
         [0020]    As shown in  FIGS. 1 and 3 , member  6  comprises a fork  8  hinged to frame  3  and connectable removably to implement  7 ; and a known hydraulic cylinder  9  connected to a hydraulic circuit  10  of vehicle  1  and interposed between frame  3  and fork  8  to lift and lower fork  8  and implement  7  with respect to the ground in response to control by the operator. 
         [0021]    As shown in  FIGS. 5 and 6 , hydraulic circuit  10  comprises, in known manner, a pump  11  communicating with an oil tank  12  and for feeding oil to hydraulic cylinder  9  via a valve  13 , which is activated by the operator by an external control  14 . The valve  13  and comprises an inlet  15  connected to the delivery of pump  11 , an outlet  16  connected to hydraulic cylinder  9 , and a drain  17  communicating with tank  12 . 
         [0022]    When implement  7  is resting on the ground, inlet  15  and drain  17  of valve  13  are open, and outlet  16  is closed, so that pump  11  is kept running by the engine (not shown) of vehicle  1  and keeps oil circulating, in a known manner, through valve  13  with no effect on hydraulic cylinder  9 . When activated by the operator, external control  14  closes drain  17  and opens outlet  16  in a known manner, thus feeding oil to hydraulic cylinder  9 , raising implement  7 , and exerting a longitudinal tip-up moment on vehicle  1 . 
         [0023]    As shown in the accompanying drawings, vehicle  1  is fitted with a balancing device  18  which, as explained in detail below, provides for automatically and, preferably, adjustably balancing vehicle  1  upon detection of stress affecting the longitudinal attitude of vehicle  1 . 
         [0024]    In the example shown, balancing device  18  is used to compensate disturbance stress produced by lifting implement  7  and is conveniently connected to the opposite end of vehicle  1  to that fitted with member  6 , i.e. to the front end of vehicle  1  in the example shown. Should member  6 , however, be connected to the front end of vehicle  1 , as is sometimes the case, balancing device  18  is, obviously, conveniently connected to the rear end of vehicle  1 . 
         [0025]    In the example shown, balancing device  18  comprises a bracket  19  connected rigidly to the front end of frame  3 ; and ballast  20  fitted in longitudinally sliding manner to bracket  19  by four guide rods  21 , which are integral with bracket  19 , parallel to axis  2 , and housed in sliding manner inside respective holes in ballast  20 . 
         [0026]    A known double-acting hydraulic actuator  22  is interposed between bracket  19  and ballast  20 , is connected to hydraulic circuit  10 , and is activated, as explained below, to move ballast  20  longitudinally between a withdrawn position ( FIG. 3 ) and an extracted position ( FIG. 4 ) in response to disturbance stress producing a tip-up moment capable of rotating vehicle  1  about a horizontal axis crosswise to axis  2 . 
         [0027]    In a variation not shown, hydraulic actuator  22  is a single-acting hydraulic actuator, the piston of which is connected to a return spring. 
         [0028]    As shown in  FIG. 5 , balancing device  18  comprises a sensor  23 , which, in the example shown, is a pressure sensor located between output  16  of valve  13  and hydraulic cylinder  9 , and which supplies a central control unit  24  with a signal proportional to the pressure inside hydraulic cylinder  9 . Central control unit  24  controls a slide valve  25  forming part of hydraulic circuit  10  and located between hydraulic actuator  22  and pump  11 . 
         [0029]    In actual use, when hydraulic cylinder  9  is activated to lift an implement  7 , attached to fork  8 , off the ground, sensor  23  detects an increase in oil pressure in hydraulic circuit  10 , and transmits a relative signal to central control unit  24 . If the value of the signal exceeds a given threshold, the central control unit  24  opens slide valve  25  to feed oil to hydraulic actuator  22  and so move ballast  20  along rods  21  into the extracted position to counterbalance the destabilizing moment produced by lifting implement  7 . 
         [0030]    In another embodiment shown in  FIG. 6 , in addition to sensor  23 , balancing device  18  also comprises a sensor sensitive to the effects caused by a different type of disturbance. In the example shown, the additional sensor is a longitudinal inclinometer  26  integral with vehicle  1  and sensitive to the longitudinal attitude of vehicle  1 . 
         [0031]    Like sensor  23 , inclinometer  26  transmits a signal to central control unit  24 , which, if the signal exceeds a given threshold, opens slide valve  25  to feed oil to hydraulic actuator  22  and so move ballast  20  along rods  21 . 
         [0032]    Operation of hydraulic actuator  22  in response to a signal from inclinometer  26  is made independent of whether or not a load is attached to fork  8  by a control valve  27  located between pump  11  and valve  13  to control the delivery of pump  11  and produce, in the absence of a load attached to fork  8 , a pressure allowing oil supply to hydraulic actuator  22 . 
         [0033]    In a variation not shown, balancing device  18  comprises, together with or instead of ballast  20 , further ballast similar to ballast  20  but located at the rear of vehicle  1  to compensate the effects of external stress having a tendency to tip vehicle  1  longitudinally forwards. 
         [0034]    In a further variation not shown, in addition to sensor  23  and inclinometer  26 , balancing device  18  may comprise further sensors for determining longitudinal displacement of ballast  20  upon detection of disturbance affecting the stability of vehicle  1 . 
         [0035]    In connection with the above, it should be pointed out that any stress, of whatever nature, tending to destabilize vehicle  1  longitudinally, undoubtedly affects the inclination of axis  2 . Consequently, inclinometer  26  or any sensor system, e.g. a system of load cells, sensitive to variations in load distribution on the axles of vehicle  1 , may be more than sufficient, on its own, to control longitudinal displacement of ballast  20 . 
         [0036]    It should be pointed out that the longitudinal displacement of ballast  20  may be the full travel of the ballast along guide rods  21  (control circuit open) or to a portion of its full travel, proportional to the degree of disturbance which is detected (feedback-closed control circuit). 
         [0037]    Finally, an important point to note is that maintaining a stable longitudinal attitude of vehicle  1  by movable ballast  20  also has the advantage of minimizing noise and vibration of crawler traction devices  5 .