Coupling hook for a three-point connection on a tractor

A coupling hook for lockingly engaging a coupling pin on an implement or the like has a pocket within which is pivoted an operating lever and a latch has one end pivotally connected to the operating lever and its other end projecting toward the jaw opening in which is received the coupling pin. The latch is pivotable and slidable upon a supporting pin such that when a coupling pin acts upon an unlocking surface on the latch during the coupling operation the latch will slide back into the pocket to permit the coupling pin to be received within the hook jaw. When the coupling pin is locked within the jaw the pin will bear against the locking surface of the latch to urge the supporting surface of the latch against an edge of an opening in the pocket through which the latch protrudes so that a moment is produced acting upon the latch and operating lever which urges the latch into the jaw opening.

The present invention relates to a coupling hook for a three-point 
connection on a tractor for lockingly receiving a coupling pin on an 
implement or the like, more particularly, to structure for locking the 
coupling pin in the jaw of the coupling hook. 
The coupling hooks which have been employed on three-point hitches of 
agricultural tractors have been provided with various forms of locking 
arrangements for securing a coupling pin associated with a trailer, 
agricultural implement or the like in the jaw of the hook. Such a locking 
arrangement generally comprised a spring-loaded latch and an operating 
linkage connected to the latch. 
One form of such a snap closure is disclosed in the German Pat. No. 
1,273,890 and comprises a blocking element held in its closed position by 
a compression spring and releasable through a linkage which is operated 
from the seat on the tractor. However, this closure had the disadvantage 
that the arcuately shaped blocking element was mounted in a guide passage 
having substantially the same shape and the blocking element was acted 
upon by a compression spring to be urged toward the jaw of the coupling 
hook. The blocking element could not be operated linearly by applying 
traction without tilting or jamming in its guide passage unless the 
blocking element was displaced by a complicated mechanism located in the 
line of the curved blocking element in order to open the lock of the 
coupling hook. Further, this closure was not provided with any safety 
structure for preventing accidental opening during any turning movements 
of the implement pin. Any self-locking feature which might be provided so 
as to act through the shape of the blocking element, for example, would 
strongly hinder intentional opening of the coupling hook. A further 
disclosed embodiment of a straight spring-loaded blocking element has the 
same disadvantage with respect to securing the locking arrangement against 
accidental opening. 
A further snap closure is shown in British Pat. No. 1,226,501 and comprises 
a coupling hook whose frame is connected to ball joints provided on the 
lower guide rods of a tractor through a bore in the lower portion of the 
vertical supports. While this arrangement provides for required freedom 
for relative mobility of the coupled implement with respect to the 
tractor, the disadvantage exists that the pivot connection for the pins of 
the coupled implement is shifted away from the tractor and this results in 
a considerable loss of lifting force. 
The locking arrangement of this coupling hook is incorporated in the 
coupling frame and thus access to the locking arrangement is difficult. 
Further, the locking arrangement is connected by a rod to a release lever 
which is locked during the release operation. In addition, the driver must 
step down and pivot the release lever toward the tractor. The locked lower 
crank lever is then pulled up from the dead position through the 
connecting rod on its center connection. The arm of the lower crank lever 
connected to the blocking lever pulls the locking element tangentially 
over and beyond the coupling pin into the opening position. At the same 
time, the upper crank lever is pivoted such that it is locked in the dead 
point position and retains the locking device open. The driver must again 
mount the seat, lower the lower guide rods until separated from the 
coupling pins, drive the tractor away from the uncoupled implement and 
again step down from the seat in order to move the locked upper crank 
lever from the dead position. The lower crank lever under the action of 
its torsion spring then again brings the locking arrangement into a 
position of operational readiness for the next coupling operation. This 
coupling hook is unsatisfactory in view of its discontinuous or 
interrupted sequence of operating steps. Further, this locking arrangement 
comprises a number of separate components and thus the cost of manufacture 
of this coupling hook was significantly increased. 
It is therefore the principal object of the present invention to provide a 
novel and improved locking arrangement for a coupling hook employed on a 
three-point connection on agricultural tractors and the like. 
It is another object of the present invention to provide such a coupling 
hook having a locking arrangement wherein the hook is fully operational 
when covered with dirt and other foreign matter and can be operated from 
the driver's seat of the tractor without the use of force. 
It is a further object of the present invention to provide such a coupling 
hook having a locking arrangement wherein the unlocked coupling hook moves 
automatically into position ready for coupling and the hook is reliably 
retained in a locked position. 
It is an additional object of the present invention to provide such a 
coupling hook having a locking arrangement which is structurally strong, 
is simple and reliable in operation and inexpensive to manufacture and 
maintain. 
In the present invention there is provided a coupling hook having a latch 
pivotally connected to an operating lever which in turn is pivotally 
mounted in the hook pocket and the latch extends through an opening in the 
pocket toward the hook jaw. The hook pocket, the latch and a supporting 
pin are provided with co-acting supporting surfaces such that during the 
coupling operation the latch and operating lever are displaced into the 
opening or release position by the action of the implement coupling pin 
acting upon an unlocking surface on the latch. When the implement coupling 
pin is locked in the jaw of the coupling hook the pin acts upon a locking 
surface of the latch in such a manner so as to produce a moment acting on 
the latch and operating lever which will urge the latch into the coupling 
hook jaw. 
According to one aspect of the present invention there is a supporting pin 
within the hook pocket and the latch has a first supporting surface which 
is pivotable and slidable on the supporting pin. The latch is also 
provided with a second supporting surface engagable with an edge of the 
pocket opening and the other end of the latch is provided with an 
unlocking surface and a locking surface. During the coupling operation the 
implement coupling pin will act upon the latch unlocking surface to 
displace the latch upon the supporting pin into the pocket. When the 
implement coupling pin is locked within the jaw opening the pin acts upon 
the latch locking surface to urge the latch second supporting surface 
against the edge of the pocket opening to produce a moment acting upon the 
latch and operating lever to urge the latch into the jaw opening. 
The present invention has the advantage that a coupling pin when locked 
within the coupling hook will produce a moment of force directed against 
any opening movement because of the arrangement of the latch in the pocket 
and thus prevents accidental or undesirable opening of the coupling hook.

Proceeding next to the drawings wherein like reference symbols indicate the 
same parts throughout the various views a specific embodiment and 
modifications of the present invention will be described in detail. 
In FIG. 1 there is shown a coupling hook within which is formed a pocket 25 
and having a jaw 1. In the jaw opening there is pivotably mounted an 
insert 21 having a hook jaw 27 in which is received an implement coupling 
pin 11. 
The closure mechanism for the coupling hook comprises a latch 2 whose inner 
end is pivotally connected at 6 within the pocket 25 to an operating lever 
3 which in turn in pivotally mounted at 7. The operating lever is provided 
with an eye 18 to which can be attached a suitable chain or cable so as to 
exert traction force against the operating lever. The latch 2 is provided 
with a notch having a guide surface 15 which is slidable and pivotable 
upon a supporting pin 4 within the pocket 25. The notch is also provided 
with end surfaces 16 and 17. 
The free end of the latch 2 is provided with a locking projection 19 which 
extends into the jaw opening 27 through an opening 26 of the pocket 25. 
The upper surface of the locking projection 19 is provided with a curved 
releasing or unlocking surface 12 and the lower portion is provided with a 
curved locking surface 20. On the upper surface of the latch 2 immediately 
behind the release surface 12 there is a curved locking surface 14 which 
is positioned opposite a curved supporting surface 13 formed on the edge 
of the pocket opening 26 and on an abutment or wall 5 of the hook. 
The central portion of the latch 22 located between the bearing pin 6 and 
latch projection 19 has a smaller cross-section and has formed thereon an 
upper spring bearing 9 in which is received one end of a tension spring 8 
with the other end of this spring being mounted on a pin 10 located within 
the pocket 25. 
The latch 2 is mounted within the pocket 25 in such a manner that after the 
latch contacts the outer surface of supporting pin 4 the latch is tilted 
by the spring 8 about the pin 4 to cause the latch to slide in the notch 
15, 16, 17 so that the curved lock surface 14 on the latch contacts the 
support surface 13. As a result of this construction, the spring 8 
constantly moves the latch 2 into a position in readiness for coupling. In 
this position, the latch 2 in the pocket opening 26 is pressed upwardly 
against the abutment support surface 13 while being tilted about the 
supporting pin 4 and sliding in the notch 15, 16, 17 of the latch. 
In addition, in the position ready for coupling, a gap or space is formed 
between the latch locking surface 20 and the abutment 23 on the lower edge 
of the pocket opening 26. The presence of this gap is advantageous in that 
latches which may become stuck and rusty after prolonged non-use of the 
coupling device can be immediately released under the pressure of an 
implement pin 11 which is dropped in the jaw opening for the purpose of 
coupling. The presence of this gap thus assures the reliability of the 
coupling operation. 
A further advantage is that the spring 8 simultaneously moves the operating 
lever 3 into an opening of the pocket 25 which thus closes the pocket 25 
in its upper portion and prevents entry of dirt and other foreign matter. 
The unlocking surface 20 of the latch and the latch lock surface 14 have 
such a curvature that a radius projected through the point of contact of 
the unlocking surface 20 and the surface of the pin 11 and a radius 
projected through the contact between the lock surface 14 and supporting 
surface 13 will pass through the same center and that these radii will 
form an angle which is smaller than 7.degree.. This relationship 
automatically inhibits undesirable or accidental opening of the coupling 
hook. The locking structure of the coupling hook will thus not 
automatically open under working conditions. The lock surface 14 and the 
unlocking surface 20 have such curve configurations that the friction 
produced between the two surfaces remains at the optimum effectiveness 
throughout the duration of contact of the surfaces. 
OPERATION 
In order to couple an implement, trailer or other apparatus having a 
three-point connection to a tractor provided with the coupling hook of the 
present invention, the tractor is set in reverse so as to back up toward 
the implement and the guide rods are shifted under the coupling pins on 
the implement. When a guide rod is lifted, implement pin 11 will be 
pressed into the jaw opening 27 of the hook 1 and will engage unlocking 
surface 12 on the latch to tilt the latch 2 about the supporting pin 4. As 
the latch 2 is tilted about the supporting pin 4 it will also slide on its 
curved guide surface 15 in the direction of the operating lever 3 as a 
resultant of the force acting on the latch locking surface 12. 
This upward movement of the latch 2 will cause the bearing pin 6 to be 
pivoted upwardly by operating lever 3 along a circular path around the 
pivot connection 7. Because of the curvature of the guide surface 15 and 
the circular movement of the pivot pin 6 around the pivot mound 7, the 
latch projection 19 of latch 2 will describe a curve which unblocks the 
jaw opening 27 which then receives the coupling pin 11 which is sliding 
downwardly on the locking surface 12. 
The rear edge 17 of the notch 15, 16, 17 abuts supporting pin 4 so that 
both the rear wall of the hook and also the catch hook insert 21 are not 
subjected to a load. 
After the coupling pin 11 is received within the jaw opening, the latch 2 
will turn about its pivot pin 6 and its lock surface 14 will slide upon 
supporting surface 13 so that the latch returns to its initial or starting 
position and locks the coupling hook. The spring 8 will produce a moment 
about the pivot pin 6 so that on locking of the latch 2 there will be an 
abutting engagement between the supporting and lock surfaces 13, 14. This 
will reduce friction forces during the locking phase and will also 
increase the restoring forces for the locking sequence. 
In the locked position, as shown in FIG. 2, implement pin 11 will exert 
forces and moments on latch locking surface 20 which urge the lock surface 
14 of latch 2 against support surface 13 on the edge of the pocket opening 
26. The latch will also act on supporting pin 4 at the point of contact 
with guide surface 15 and end surface 16. The forces acting at these 
points will produce a self-locking of the latch. 
This locking effect can be increased by increasing the angle formed by a 
line projected through the pivot axes of the pins 6 and 7 and a line 
passing through pivot point 6 and the contact point between the support 
surface 13 and lock surface 14. This increase can be brought about by the 
force exerted by the pin 11, the contact of the lock surface 14 on the 
abutment surface 13 and the bearing pin 6 as a pivot. The increased angle 
will thus approximate 180.degree.. The increase in this angle will produce 
a moment which urges the latch into the jaw opening into its locked 
position and will thus prevent any automatic opening of the coupling hook. 
To unlock the coupling hook, the tractor operator pulls on the line 
connected to the eye 18 of the operating lever 3 to pull the lever 3 
upwardly as viewed in the drawings so that the latch pivot connection 6 
will be moved upwardly about the pivot mount 7. The force exerted on the 
operating lever is perpendicular to or at an angle up to about 60.degree. 
on either side of a line passing through pivot mount 7 and the traction 
eye 18. 
The latch 2 because of its connection to the operating lever 3 will be 
moved in a direction away from the jaw opening 27 and the surfaces 13 and 
14 will be in frictional engagement because of the force produced on the 
bearing connection 6 by the tension spring 8. As the latch 2 is guided 
upwardly by means of the operating lever 3 and the curved surfaces 13, 14 
the latch projection 19 will unblock and release the jaw opening 27 to 
permit unlocking and release of the implement pin 11. It is to be noted 
that the supporting pin 4 is not contacted by the latch 2 during this 
sequence which reduces friction during the unlocking phase. 
A further advantage of utilizing the supporting surface 13 as a stop for 
locking surface 14 during the unlocking operation is that when the 
operating lever 3 pivots about its connection 7, the latch 2 bearing 
against support surface 13 as an abutment forms a long lever through its 
pivot connection at 6 which facilitates the release of the implement pin 
11. At the same time, during the opening operation, the latch moves 
radially and tangentially with respect to the implement pin 11 which, in 
comparison with the near tangential unlocking movement of known prior art 
arrangements, significantly facilitates release of the latch even from 
jammed implement pins. 
It is to be further noted that the locking arrangement as described above 
remains operational both for locking and unlocking of the implement pin in 
the event the spring 8 should break. 
If desired, forces required for unlocking may be reduced by extending the 
lever arm 7, 18. 
Thus it can be seen that the present invention has disclosed a locking 
arrangement for a coupling hook which is simple in construction, reliable 
in operation and required a minimum of moving components. 
It will be understood that this invention is susceptible to modification in 
order to adapt it to different usages and conditions, and accordingly, it 
is desired to comprehend such modifications within this invention as may 
fall within the scope of appended claims.