Abstract:
A suspended axle for a tractor, the axle having a lower link mechanism selectively operable between a first configuration in which the lower links are in fixed relation to the suspended axle and a second configuration in which the lower links are isolated from the suspended axle.

Description:
BACKGROUND OF THE INVENTION 
     Field of Invention 
     The present invention relates to tractor rear links and in particular, but not exclusively, to an independent rear suspension mechanism for isolating the rear link. 
     Description of Related Art 
     Tractors are provided with a top link and lower links in order to carry implements such as ploughs and hay tools which need supporting rather than simply towing. Most link-supported implements work best when the links follow closely the profile of the soil. In a tractor with no rear suspension the links will naturally follow the line of the soil as the connection between the tyre and the plough is rigid (subject to the elasticity of the tyre). 
     In a tractor with a suspended rear axle this is not the case as the suspension between the chassis and the wheel breaks the rigid link between profile of the soil and the link position. As a result, with the lower link mounted on the suspended rear axle the link can rotate with the rear axle leading to the implement being less than ideally located with respect to the soil surface. 
     It is an objective of the present invention to at least mitigate one or more of the above problems. 
     OVERVIEW OF THE INVENTION 
     According to the invention there is provided a suspended axle for a tractor, the axle having a lower link mechanism selectively operable between a first configuration in which the lower links are in fixed relation to the suspended axle and a second configuration in which the lower links are isolated from the suspended axle. 
     Advantageously, this allows the operator to select the most appropriate configuration for the conditions. For example the lower links can be isolated from the suspended axle for field work and move with the rear axle for road work. 
     Preferably, the suspended axle is pivoted on the tractor chassis. The suspended axle may be provided as a retrofit solution which is adapted to be pivotable on a tractor chassis. 
     Preferably, the suspended axle has a rear axle arm which carries a lift arm lever pivotally attached to an upper end of a lift arm. 
     Preferably, a lower end of the lift arm is connected to the lower links. 
     Preferably, the mechanism is selectively operable by actuation of a link connected to the lift arm lever between a first position in which a first end of the link coincides with the suspended axle pivot and a second position in which the first end of the link is distal from the suspended axle pivot. 
     In one aspect, the mechanism is arranged such that there is no direct physical connection between the first end of the link and the suspended axle pivot, when the first end of the link is in the first position. In an alternative aspect, the mechanism may be arranged such that a physical connection can be made between the first end of the link and the suspended axle pivot when the first end of the link is in the first position, e.g. through use of a suitable locking pin or arm or other device arranged between the first end of the link and the suspended axle pivot, when the first end of the link is in the first position. 
     Preferably, the link is actuable by a first end of an isolation arm. 
     Preferably, a second end of the isolation arm is pivoted on the tractor chassis and is actuable by a hydraulic actuator. 
     The hydraulic actuator may be coupled with a hydraulic system provided on a tractor. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will now be described, by way of example only, and with reference to the following drawings, in which: 
         FIG. 1  is a schematic side view of the suspended axle of the present invention shown in a first position; 
         FIG. 2  is a schematic side view of the suspended axle of  FIG. 1  shown in a second position; and 
         FIG. 3  is a side view of an agricultural tractor having a suspended axle according to the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIGS. 1 and 2  show a suspended rear axle  10  for a tractor with full independent suspension. The rear axle  10  is pivoted on the tractor chassis indicated generally at  12  at pivot  14 . The rear axle arm  16  carries a rear differential centred at point A. At the rear end of the rear axle arm  16  is a flange  18  that supports rear links  20 . The opposite end of the rear links  20  are supported by rear lift arms  22  the upper end of which is attached to a lift arm lever  24  which is pivoted on an upper extension  26  of the rear axle arm  16 . The opposite end of the lift arm lever  24  is connected to a link  28  which is moveable under the action of an isolation arm  30 . The isolation arm  30  is actuated by an actuator  32  between its first position shown in  FIG. 1  and its second position shown in  FIG. 2 . 
     In  FIG. 1 , rotation of the rear axle arm  16  in an upward direction in response to changing terrain along arc B causes a consequential rotation of the rear link  20  along the same arc since the connection between the isolation arm  30  and link  28  is coincidental with the rear axle arm pivot  14 . 
     In contrast, in  FIG. 2 , rotation of the rear axle arm  16  in an upward direction along the same arc B does not lead to the same displacement of the rear link due to the establishment of a four bar linkage resulting from the movement of the link  28  to its new position. In this configuration the rear link is caused to move in an upward direction C. This direction C more closely matches the profile of the terrain (ie an upward deflection) than does the movement of the rear link in the first configuration shown in  FIG. 1 . 
     This allows the rear link, and, as a result the implement being carried on the rear linkage, to more closely match the terrain. This allows the tractor to match the rear link operation to the nature of the work being undertaken, in particular matching the requirements of the implement during on-road and on-field conditions. 
     An agricultural tractor  100  is illustrated in  FIG. 3 . The tractor  100  comprises front wheels  102 , rear wheels  104 , an engine section  106  and a cab section  108 . The engine section  106  comprises a tractor engine  110  and an engine cooling system  112  located adjacent thereto. The rear link  20  of  FIGS. 1 and 2  is provided towards the rear of the tractor  100 . The tractor  100  may comprise a chassis or frame to which components may be attached or mounted. 
     In one aspect, the suspended axle mechanism shown in  FIGS. 1 and 2  is provided as a component of a tractor  100 . In an alternative aspect, the suspended axle mechanism may be provided as a retrofit solution for an existing tractor  100 . 
     The invention is not limited to the embodiment described herein, and may be modified or adapted without departing from the scope of the present invention.