The present invention relates to tractors, and more specifically
to devices for attaching farm implements to an agricultural tractor. Typically,
such devices are formed by a so-called three-point hitch having two lower arms
and one top link.
Such a three-point hitch attachment is described, for example, in
US-A-3.053.552, which illustrates means for attaching a farm implement of any type,
e.g. a plough, in a carried fashion to a tractor. The hitch comprises a top link
and two lower arms which all three are connected in articulated manner to the tractor
frame. Each lower arm is connected to a respective hydraulic lifting device whereas
the length of the top link is adjustable by the operator rotating a sleeve connected
at one end to the tractor frame, and at the other end to an attachment point of
the implement. Accidental rotation of the sleeve is prevented by an elastic member
connected to the sleeve and which can be lifted and lowered. In the embodiment
described in US-A-3.053.552, when the top link is disconnected from the implement
and raised, the elastic member is used to lock the top link in an upright position.
However, since the elastic member is integral with the sleeve and thus moves in
unison therewith, the tilt of the top link, in its inoperative position, depends
on the position of the sleeve.
Excessive tilting of the top link is without any grave consequence
in the case of an implement attached to the rear of the tractor, but not in the
case of front-mounted implements. In the latter case, excessive tilting of the
top link in the rest position towards the front hood of the tractor could impede
opening and closing of the hood.
It is therefore an object of the present invention to provide a fixed
tilt angle for each possible length of the top link and to facilitate adjustment
of the length of the top link.
Further advantages will be disclosed in the preferred embodiment
According to a first aspect of the present invention, there is provided
a device for attaching a farm implements to a tractor, as claimed in Claim 1.
According to a second aspect of the present invention, an adjustable
top link is provided, as claimed in claim 5.
A non-limiting embodiment of the present invention will now be described
by way of example with reference to the accompanying drawings, in which:
- Figure 1 shows a three-dimensional assembly drawing of a device for attaching
farm implements to a tractor in accordance with the present invention;
- Figure 2 is a perspective view of a top link forming part of the Figure 1 device
and shown with the component parts in a first position;
- Figure 3 is a perspective view comparable to Figure 2 and shown with the component
parts in a second position;
- Figure 4a shows a first view of a first detail of the top link in Figures 2,
- Figure 4b shows a second side view of the first detail of the top link in Figures
- Figure 4c shows a longitudinal section along line X-X of the first detail in
- Figure 5, 6 and 7 show respective second, third and fourth details of the top
link in Figures 2, 3;
- Figure 8a shows a plan view of a fifth detail of the top link in Figures 2,
- Figure 8b shows a side view of the fifth detail in Figure 8a.
Number 10 in Figure 1 indicates a device, typically referred to as
a three-point hitch, for attaching farm implements (not shown) to a tractor (not
shown) in accordance with the present invention.
For the sake of simplicity, a number of mechanical and hydraulic
components have been omitted in Figure 1, and, for the same reason, not all the
devices shown in Figure 1 are described in detail in the present disclosure.
Attachment device 10 comprises, in conventional manner, two lower
arms 11, 12 and a top link 13 which, in Figure 1, is shown in the raised position,
i.e. disconnected from the farm implement.
As shown in Figure 1, attachment device 10 further comprises a frame
14 having two side plates 14a, 14b connected integrally to the tractor by a double
set of bolts 15. Frame 14 is reinforced by a bottom crossbar 16 and a top crossbar
17. The lower arms 11, 12 are hinged in known manner to the bottom crossbar 16
and top crossbar 17 is provided with hydraulic cylinders 18, 19 for lifting and
lowering respective arms 11, 12. The top crossbar 17 further comprises a lock device
20 for locking top link 13 in the upright position shown in Figure 1. The lock
device 20 has at least one seat 21 for the purpose explained in detail later on.
At one free end 13a, top link 13 comprises a hook 22 having a device
23 by which to attach end 13a to the farm implement whereas the other end 13b of
top link 13 is hinged to the top crossbar 17.
As shown in Figures 2 and 3, top link 13 comprises a substantially
tubular central body 24 with a circular cross section, the already mentioned hook
22 at end 13a and a spherical joint 25 at end 13b for connection to top crossbar
17. The top link 13 further comprises a square-section sleeve 26 housing central
body 24, which is fitted integrally on opposite sides with two handles 27 having
projecting ends 27a for a purpose explained in detail later on. An elastic member
28 also is part of the top link 13 for a purpose which will be explained in detail
As shown in more detail in Figures 4a, 4b, 4c, the central body 24
has two tapered ends 24a, 24b having respective internal threads 29a, 29b for receiving
corresponding ends of hook 22 and joint 25. Internal threads 29a and 29b are oppositely
threaded, i.e. while the one is right-hand threaded, the other one is lefthand
threaded. As such, the distance between the hook 22 and the joint 25 will either
increase or decrease depending on the rotation direction of central body 24 about
its central axis A.
With specific reference to Figures 4a and 4b, two metal rods 30 are
welded 180° apart to the outer surface of central body 24; the rods 30 fitting
in two diametrically opposed corners of sleeve 26, as seen in Figures 2 and 3.
This allows to operatively connect circular-section central body 24 to square-section
sleeve 26, so as to enable the operator, by means of sleeve 26, to rotate central
body 24 about axis A. It furthermore enables sleeve 26 to slide in a direction
parallel to axis A for reasons to be explained in detail later on.
With reference to Figure 5, hook 22 is integral with a threaded shank
22a which screws on to thread 29b in central body 24. Similarly, and as shown in
Figure 6, joint 25 has a threaded shank 25a which screws on to thread 29a in central
body 24. As already stated, the threads in ends 24a, 24b being counter-rotating,
top link 13 as a whole is lengthened or shortened as required when central body
24 is rotated one way or the other by means of sleeve 26. Joint 25 further comprises
a lug 25b (Figure 6) having holes 31, 32 for housing the ends of elastic member
28. As shown clearly in Figure 7, sleeve 26 comprises two handles 27 having projecting
Another fundamental feature of top link 13 according to the invention
is the elastic member 28, shown in more detail in Figures 2, 3 and 8a, 8b. With
specific reference to Figures 8a, 8b, elastic member 28 is formed by bending a
spring steel rod into a substantially rectangular shape having two bent superimposed
ends 28a, 28b, which, as shown in Figure 8b, are not coplanar, so as to fit inside
holes 31, 32 in joint 25 (Figure 6) and exert a given elastic pressure when elastic
member 28 rests on an outer face of sleeve 26.
In actual use, and as shown in Figures 2 and 3, top link 13 is lengthened
or shortened after raising elastic member 28, which, as stated, on account of the
offset position of ends 28a, 28b and holes 31, 32 in lug 25b into which they are
fitted, presses elastically on one face of sleeve 26 (Figure 2). When raised by
the operator, elastic member 28 takes up the position shown by the dashed line
in Figure 2.
Once elastic member 28 is raised and before effectively rotating
sleeve 26, the operator may have to axially slide sleeve 26 in the direction of
hook 22 to free the ends 27a of handles 27 from being obstructed by the lug 25b;
the latter condition being shown in Figure 2. Sleeve 26, and therefore central
body 24, is rotated by means of the two handles 27, so that, depending on the
direction of rotation about axis A, hook 22 is moved towards or away from joint
25 to respectively shorten or lengthen top link 13. Once top link 13 is set to
the required length, the operator simply lowers elastic member 28, which may be
positioned as shown in Figure 3, i.e. on either side of one of the two handles
27, as such preventing accidental rotational movement of the sleeve 26 which could
result in unwanted length adjustments of the top link 13.
As shown in Figure 1, when top link 13 is raised to an inoperative
position, projecting ends 27a of handles 27 can be inserted inside seats 21 on
lock device 20 by sliding sleeve 26 with respect to central body 24 in the direction
of axis A towards the joint 25. This sliding movement is assisted by the rods 30
interposed between the outer surface of central body 24 and the inner surface
of sleeve 26.
The locking of top link 13 in the rest position is thus fully independent
of the length of the link 13, which is therefore positioned substantially perpendicular
to the ground regardless of its length. This is particularly advantageous in the
case of attachment devices 10 for front-mounted farm implements whereby, when
fully raised, top link 13 in no way impedes opening or closing of the engine hood.
It will be appreciated that, although not shown in Figure 1, lock
device 20 may comprise a number of pairs of seats 21 to enable different tilt positions
of the top link 13 when disconnected from the farm implement. Further advantages
are the straightforward design of top link 13, and the ease with which it can be
adjusted in length.
As will be understood from the foregoing, the function of the sleeve
26 is threefold, namely : adjusting the length of the link 13 by rotating the
central body 24; positioning the link 13 in an inoperative position; and, in co-operation
with the elastic member 28, preventing unwanted length adjustments of link 13.