The present invention relates to a steering axle for vehicles, particularly for agricultural tractors, being of a type which comprises a beam bearing at least one journal formation for pivotally mounting the axle on a load-bearing structure of a vehicle and a steering actuator including a case which is fixed to the beam.
Steering axles including such features are known from the present production of the same applicant. In such known axles, the beam has in its central portion two juxtaposed and coaxial journal formations adapted to be received pivotally in corresponding seats of the load-bearing structure of the vehicle, so that the axle, in its entirety, can swing in a plane extending substantially transverse to the vehicle, about the axle of the journal formations.
A drawback of these known axles is that the steering actuator, although leaning against the axle beam, is still undesirably cumbersome thereby hindering the mounting of the axle on tractors of a different kind. Furthermore, this actuator is in some cases not well protected against shocks and against the entrance of contaminants such as dust, clods, mud etc.
Another example of a steering axle relevant to this invention is disclosed in the Japanese Patent Publication n. 60-1075(A).
In that document, an axle is disclosed which is provided with a gear-type steering system operated through a steering actuator for pivoting the road wheel hubs fitted to the opposite ends of the beam.
That actuator is attached to the load-bearing structure of the vehicle and has an output shaft which carries, keyed to its free end, one gear of the steering system. The shaft extends through a bore in the load-bearing structure of the vehicle and a corresponding tubular passageway formed in the respective journal formation on the beam.
A steering axle according to that design has a number of drawbacks.
First, the actuator is mounted at a location where it is subject to shocks and may come to harm. This is more likely to occur when the axle is used on such all-terrain vehicles as agricultural tractors, where the probability of shocks is relatively high.
Secondly, with the above construction, relative rotation is allowed to take place both between the actuator shaft and the corresponding journal formation, as well as between the latter and the load-bearing structure of the tractor whereto said actuator is, in turn, attached. The corresponding journal formation of the beam intervenes, therefore, between the actuator shaft and the load-bearing structure of the vehicle, while being mounted to swing with respect to either. Accordingly, the machining tolerances for the different component parts add algebraically to one another, to establish operating conditions that make the required oil-tight fits between the axle beam and the actuator shaft difficult to achieve. This problem is made the more serious since the standard admissible tolerances for journal formations in the agricultural tractor industry are comparatively large. Further, with that design, the axle tends to steer, even with the steering wheel held still, every time that it is caused to perform swinging movements relatively to the vehicle structure, and this on account of the steering system gears being forced to roll about the actuator gear whenever such a situation of relative oscillation is encountered. Thus, the structure proposed in said document is unsuited to such applications.