Implement hitch for a tractor

An implement hitch is disclosed for a tractor, wherein the hitch is fitted with a mechanism for stabilizing lateral movement of lifting arms of the hitch. The lifting arms are raised and lower by respective hydraulic cylinders. The stabilizing mechanism has a locking pin that is automatically retracted to an unlocked position by means of a flexible linkage when the lifting arms are in a lowered position. In the invention, the opposite end of the flexible linkage from the locking pin is connected to an anchoring point provided on the hydraulic cylinder serving to raise and lower one of the lifting arms.

CROSS REFERENCE TO RELATED APPLICATIONS

This patent application claims priority from and the benefit of Italian Patent Application Serial No. MO2013A000306, entitled “IMPLEMENT HITCH FOR A TRACTOR”, filed Nov. 6, 2013, which is hereby incorporated by reference in its entirety.

FIELD OF THE INVENTION

The present invention relates to an implement hitch for a tractor, the hitch being fitted with a mechanism for stabilising lateral movement of lifting arms of the hitch.

BACKGROUND OF THE INVENTION

Tractors are commonly fitted with a three-point hitch to allow an implement, such as a plough or a harrow, to be connected to them. A three-point hitch comprises three movable arms, namely two lower lifting arms and an upper arm, that is also termed a top link, positioned centrally in relation to the lifting arms. The two lifting arms are raised and lowered by hydraulic cylinders that allow the towed implement to be raised, lowered or tilted. The top link is also movable but it is not usually hydraulically powered.

In a lowered position, the lifting arms should be allowed to move laterally from side to side. However, in a raised position, that is used for example when towing an implement on metalled roads, the lifting arms should be prevented from moving laterally in order to prevent yawing, or fish-tailing, of the implement.

To meet these needs, a stabilising mechanism is connected to the lifting arms, an example of a stabilising mechanism being shown in FIG. 1 of U.S. Pat. No. 5,462,303.

The stabilising mechanism includes a sprung telescopically collapsible strut, connected between one of the lifting arms and the tractor chassis. In the lowered position of the lifting arms, the two ends of the strut can move relative to one another against the action of the springs, so that the lifting arms are biased by the springs of the strut into the central position but are still capable of moving from side to side.

A lockable strut is connected between the other lifting arm and the tractor chassis. Though a separate strut is described in U.S. Pat. No. 5,462,303, the sprung telescopically collapsible strut may itself be lockable. The lockable strut is formed of two members that can slide, for example telescopically, relative to one another when the lifting arms are lowered but are prevented by a locking pin from moving relative to one another when the lifting arms are raised so as to lock the lifting arms of the hitch in a central position, symmetrical about the longitudinal axis of the tractor.

The locking pin of the lockable strut is biased towards its locked position and is attached by a flexible linkage, hereinafter often referred to as a chain though it may alternatively be a cable, to a point on the tractor chassis. The length of the chain is selected such that, when the lifting arms are lowered, the chain becomes taut and automatically retracts the locking pin to allow free lateral movement of the lifting arms.

In order to retract the locking pin smoothly and without risk of damage, it is desirable for the tension of the chain to act along the axis of movement of the locking pin, which is generally substantially vertical. However, as can be seen from FIG. 1 of U.S. Pat. No. 5,462,303, there is usually no convenient fixing point on the tractor chassis that is aligned with the axis of the locking pin and a compromise position needs to be adopted for anchoring the opposite end of the chain, the position being selected to be as close as possible to the line of action of the locking pin.

OBJECT OF THE INVENTION

The present invention seeks to provide a better way of anchoring the chain connected to the locking pin of a stabilising mechanism, to unlock the stabilising mechanism automatically as the lifting arms of the hitch are lowered.

SUMMARY OF THE INVENTION

According to the present invention, there is provided an implement hitch for a tractor, wherein the hitch is fitted with a mechanism for stabilising lateral movement of lifting arms of the hitch, which lifting arms are connected to be raised and lowered by respective hydraulic cylinders, and wherein the stabilising mechanism has a locking pin that is automatically retracted to an unlocked position by means of a flexible linkage when the lifting arms are in a lowered position, characterised in that the opposite end of the flexible linkage from the locking pin is connected to an anchoring point provided on the hydraulic cylinder serving to raise and lower one of the lifting arms.

The invention takes advantage of the fact the line of action of the locking pin of the stabilising mechanism, that is to say the axis movement of the locking pin, is substantially directly beneath one of the hydraulic cylinders acting to raise and lower the lifting arms of the hitch. By correctly positioning the anchoring point of the opposite end of the chain on the hydraulic cylinder, the invention ensures that the tension in the chain acts substantially in line with the axis of movement of the locking pin and thereby avoids lateral stresses on the pin that make it more difficult to move and risk it being distorted in the process.

In some embodiments, the anchoring point for the opposite end of the chain is provided by a clamp encircling and gripping the hydraulic cylinder, the clamp having an eyelet projecting from the surface of the hydraulic cylinder within which the opposite end of the chain may be engaged.

Hydraulic cylinders are usually of circular cross section and the clamp of an embodiment of the invention is therefore also of circular section. This allows the clamp to be oriented such that the eyelet lies as closely as possible to the line of action of the locking pin.

Conveniently, the clamp may comprise a first component having a part-cylindrical portion to engage the surface of the hydraulic cylinder and a radially projecting flat portion formed with a hole to serve as the eyelet for receiving the opposite end of the flexible linkage, and of at least one second component having a curved portion connectable to the curved portion of the first component to encircle the remainder of the circumference of the hydraulic cylinder and a flat portion securable to the flat portion of the first component to clamp the hydraulic cylinder between the two components.

The curved portions of the two components may be pivotably connected to one another but more simply the curved portion of one of the components may terminate in a bent tongue or hook to engage releasably within an opening in the end of the curved portion of the other component. In this way, the clamp may be formed of stamped sheet metal parts that are only interlocked with one another during assembly about the hydraulic cylinder.

If desired, additional fixing holes may be provided in the radially projecting flat portion of the at least one of the two components to receive attachments of other ancillary equipment.

DETAILED DESCRIPTION OF THE INVENTION

FIGS. 1 and 2show the rear axle10of a tractor fitted with a three-point hitch. The hitch has two lower arms12and14that can be raised and lowered by means of respective hydraulic cylinders16and18. The lifting arms12and14each form part of a parallelogram-like linkage that enables the ends of the lifting arms12and14to move through a greater distance than the stroke of their hydraulic cylinders16and18. The mounting bracket20for the top link of the hitch may be seen inFIG. 1but the top link itself has been omitted in the interest of clarity.

As more clearly shown inFIG. 2, a sprung strut22is connected to the lifting arm12and a lockable strut24is connected to the lifting arm14. Both of these struts are telescopically collapsible and together form a stabilising mechanism that controls lateral movement of the lifting arms12and14, that is to say movement from side to side as viewed inFIG. 2.

The sprung strut22serves to bias the lifting arms12and14into a central position while allowing them to move from side to side when in their lowered position.

The lockable strut24serves no purpose in the lowered position of the lifting arms12and14because in that position a locking pin of the strut24is retracted to allow the strut to change in length freely. However, in the raised position of the lifting arms12and14, the locking pin of the strut24moves to a position in which it prevents expansion and contraction of the strut24, thereby holding the lifting arms12,14rigidly in their central position and preventing their lateral movement.

In larger type of tractors often a second lockable strut24is used to control movement of lifting arm14, instead of sprung strut22.

As so far described, the three-point hitch and the stabilising mechanism are conventional and their construction and operation will be clear to the person skilled in the art without the need for more detailed explanation.

The locking pin of the lockable strut24is conventionally connected by a fixed length flexible linkage, usually a chain, to a point on the rear axle10of the tractor. Because of the position of the locking pin relative to the rear axle10, the chain is obliged to adopt a position that is inclined relative to the axis of movement of the locking pin. This makes the locking pin more difficult to move and can cause damage to the pin through wear and distortion.

The present invention seeks to overcome these problems by providing an anchoring point for the opposite end of the chain that is at least substantially in line with the line of action of the locking pin.

The anchoring point in the invention is provided by a clamp30that is fitted around the hydraulic cylinder18. The clamp30, to be described in more detail below by reference toFIGS. 3 to 6, has a radially projecting plate with an eyelet for receiving an end of the chain40which is connected to the locking pin of the lockable strut24by means of a spring42. The plate can be dimensioned and oriented so that the eyelet lies directly in line with the axis of movement of the locking pin.

The clamp30is formed of a first component shown inFIGS. 3 and 4and two identical second components shown inFIGS. 5 and 6. The first component50has a curved portion52made up of four fingers52ato52dhaving a curvature matching that of the hydraulic cylinder18and extending over an angle of about 120°. The ends of fingers52ato52dhave bent over tongues54. The first component50also has a flat portion56that projects radially from the cylinder18and includes a projecting eyelet59for engaging with the release chain40of the locking pin. Various holes are formed in the flat portion56onto which nuts58and60are welded. A notch on first component50can be used to position and orient first component50on cylinder18. Consequently a mirrored version of first component50may be used so that the notch also fits on the second, mirrored lifting cylinder. The second components60of the clamp as shown inFIGS. 5 and 6have a curved portion62and a flat portion66. The curved portion62is in the form of a narrow strap that terminates at one end in a flange64formed with two rectangular openings65. At its other end, the strap62is connected to the flat portion66which is formed with a hole68for receiving a bolt.

To fit the clamp30to the cylinder18, the four fingers52ato52dof the curved portion52of the first component50are first placed against the outside of the cylinder18. The openings65in the flange64of a second component60are then slipped over two of the tongues54and the curved strap62is positioned to encircle the cylinder18. A bolt is passed through the hole68and screwed into a nut58to hold the clamp in place. The other second component is next mounted in the same manner and after the clamp has been rotated to orient the flat portion56correctly, the bolts are tightened. The release chain may then be engaged in the eyelet59.

The spring42limits the force that can be applied to the locking pin, thereby avoiding the pin being damaged if the chain should accidentally snag an object. It also limits the force pulling down on the clamp30to prevent it from being dislodged.

The nuts60are provided on the flat portion56for other ancillary equipment or tools that may require a convenient anchoring point but are not relevant to the stabilising mechanism.

A further advantage of anchoring the locking pin release chain to a hydraulic cylinder rather than the rear axle is that the chain is moved further away from the wheels of the tractor and is therefore less likely to gather dirt that is thrown up by the tractor wheels.