Abstract:
A suspension system with an oscillating, rigid axle, particularly for tractors, is described; the axle is supported on a sub-frame with oscillating arms which in turn can be mounted for oscillating on a load-bearing structure of the tractor by suspension means interposed between the axle and the load-bearing structure, the sub-frame comprising at least two pairs of arms arranged so as to form a so-called pantograph-like kinematic linkage.

Description:
BACKGROUND OF THE INVENTION 
     The subject of the present invention is a suspension system with an oscillating, rigid axle, particularly for tractors. 
     The current tendency to build fast agricultural tractors makes it necessary to provide suspension systems, particularly for the front axles, which ensure the stability of the vehicle together with adequate comfort even when travelling at the relatively fast speeds which are developed nowadays. 
     There are currently many suspension systems available on the market. A typical example, in the field of which the present invention also lies, is that of systems with oscillating, rigid axles supported by the load-bearing structure of the tractor by means of a sub-frame. 
     The sub-frame normally defines an articulation point about which the axle can move along a substantially vertical path. 
     A disadvantage encountered with these devices lies in the fact that they require specific provisions of the load-bearing structure—the so-called “carriage” of the tractor—and are unsuitable for fitting on vehicles which do not have such provision, that is, which are arranged for receiving either conventional oscillating axles or axles provided with suspension. 
     Another disadvantage lies in the fact that current structural configurations of the sub-frame, particularly with regard to the positioning of the articulation point, define a path of the axle which is not rectilinear but is generally arcuate about the articulation point. This leads to variations in the wheel base or spacing between the axles of the tractor and/or to movements of the axle transverse its vertical axis, which may adversely affect the correct behaviour of the vehicle in motion. 
     SUMMARY OF THE INVENTION 
     The main aim of the present invention is to provide a suspension system which is devised particularly but not exclusively for agricultural tractors and which is designed structurally and functionally so as to prevent all of the disadvantages complained of with reference to the prior art mentioned. 
     A further object of the invention is to provide a suspension system which can be fitted on tractors without requiring substantial structural modification thereof. 
     Another object of the invention is to render the suspension system optionally adaptable to agricultural tractors to replace conventional oscillating rigid axles. 
     This aim and these objects are achieved by the invention by means of a suspension system including the characteristics illustrated in the following claims. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The characteristics and the advantages of the invention will become clearer from the detailed description of a preferred embodiment thereof, described by way of non-limiting example with reference to the appended drawings, in which: 
     FIGS. 1 and 2 are front perspective views of the suspension system of the invention at two different operative stages, 
     FIG. 3 is a rear perspective view of the suspension system of the preceding drawings, and 
     FIG. 4 is an exploded, perspective view of the suspension system of the invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In the drawings, a suspension system, generally indicated  1 , includes a rigid axle  2  having a predominant longitudinal dimension and having, at its opposite ends, wheel hubs  3  the pivoting of which about respective steering axes is brought about by a steering cylinder  4 . The axle may be a driving axle and, in this case, contains transmission members such as a differential, half-shafts, reduction gears and other conventional components. 
     The axle  2  is in turn mounted on a carriage  5  forming part of the load-bearing structure of an agricultural tractor, by means of a sub-frame, generally indicated  6 . 
     The frame  6  comprises two pairs of first and second arms, the arms of the first pair being indicated  10  and  11 , respectively, and the arms of the second pair being indicated  10   a  and  11   a , respectively. 
     The pair of arms  10 ,  11  is disposed in a symmetrically opposed arrangement relative to the pair of arms  10   a ,  11   a , in an arrangement typical of the kinematic mechanism known as a scissor jack. 
     In each of the above-mentioned arms it is possible to identify two connecting-rod-like elements fixed together by respective transverse elements and having, at their opposite ends, through-holes constituting seats for bushes  13  and pins  14 . 
     The holes  15 ,  15   a  of respective first ends of the first arms  10 ,  10   a  are elements for the articulation of the first arms to the axle by means of the above-mentioned bushes  13  and pins  14  in respective sleeves  16 ,  16   a  which are fixed to the lower portion of the axle  2  on either side of the differential housing. 
     The holes  17 ,  17   a  and  18 ,  18   a  of respective second ends of the first arms  10 ,  10   a  and of respective first ends of the second arms  11 ,  11   a , respectively, are elements for the articulation of the first and second arms to one another by means of the bushes  13  and pins  14 . 
     The holes  19 ,  19   a  of respective second ends of the second arms  11 ,  11   a  are elements for the articulation of the second arms to one another and to the carriage  5  by means of a pin  20  belonging to the carriage  5 . 
     The second arms are thus articulated at their second ends about a single axis coinciding with the oscillation axis of the axle. 
     Suspension means constituted by a single, double-acting hydraulic jack, generally indicated  22 , are interposed between the axle  2  and the carriage  5 . The jack  22  is connected, in known manner, to gas accumulators and/or to other resilient suspension elements to provide the springing and shock-absorbing effect required thereof. 
     The jack  22  comprises a piston  23  slidable in a cylinder  24  articulated on the pin  20  by an end eye  25  of the cylinder  24  and guided for sliding, by means of its outer cylindrical surface, in a tubular seat  26  of the axle  2 . The engagement between the cylinder  24  and the seat  26  constitutes a linear guide by which the axle is restrained and guided along an axis substantially perpendicular to its own longitudinal axis and perpendicular to the axis of the pin  20  during the movement away from and towards the oscillation axis, which coincides with the axis of the pin  20 . 
     Correct operation of the suspension is thus maintained, regardless of the extent of the oscillation of the axle about the axis of the pin  20 . 
     The suspension system of the invention operates as follows. The hydraulic or hydropneumatic jack  22  constitutes a resilient and shock-absorbing member for absorbing the stresses brought about on the axle and for the adjustment of its height above the ground as desired. The jack can be locked, in conventional manner, in order to transform the system  1  into a rigid system with an oscillating axle, should this be required owing to the presence of certain tools associated with the tractor. 
     The jack  22  also constitutes a guide member for limiting the freedom of the arms  10 ,  10   a ,  11 ,  11   a  to oscillate. Instead of acting between the axle and the pin  20 , the jack is arranged so as to act between corresponding arms or even between the corresponding articulations of the arms of each pair. Under stress, or for a different adjustment of the height of the axle  2  above the ground, the piston of the jack  22  is extended further or is retracted further into the cylinder, moving from the position of FIG. 1 to that of FIG. 2 or vice versa, with every possible intermediate position. 
     The suspension system of the invention can therefore be fitted on tractors which are arranged for receiving an oscillating axle with suspended mounting; the suspension system can be adapted to tractors of different types, possibly with replacement of the carriage  5 .