Note: Descriptions are shown in the official language in which they were submitted.
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SAFETY DEVICE FOR HYDRAULIC HITCH ASSEMBLY
The present invention relates to a safety device for a hydraulic hitch
assembly and in
particular to a safety device that may be operated remotely from the hitch
assembly.
Background of the Invention
Large mobile machinery, such as excavators and the like, are commonly being
fitted with
various types of attachments to increase the versatility of the machine.
Examples of such
attachments include a bucket or rock hammer. Typically, these attachments are
fitted to the
articulated aim of the excavator through means of a quick change device, such
as a hitch
assembly or quick-coupler that is normally hydraulically activated.
One type of hydraulic hitch assembly is described in Australian patent 586124
and consists
of a remotely operable pair of oppositely 'directed jaws which are adapted to
move between
an engaged position and a disengaged position. In the disengaged position, the
jaws can fit
between the internal transverse hinge pins of the attachment. The jaws are
then moved
away from each other through use of a hydraulic piston or ram into the engaged
position
where they grip the transverse hinge pins of the attachment and hold it in
place for use.
Due to the risk of hydraulic failure where the hydraulic hitch assembly could
potentially
retract into the disengaged position almost immediately, hydraulic hitch
assemblies are
required to be fitted with a safety restraining device that would prevent the
hitch assembly
from disengaging from the attachment. These safety restraining devices are
typically
mechanical arrangements that require the operator of the machinery to engage
and
disengage the safety device at the site of the hitch assembly. As such, this
means that each
time the attachment is changed, the operator must descend from the cabin
operating the
machine to disengage the safety device. Thereafter,= the operator is required
to remount the
cabin to operate the hydraulics driving the hitch assembly to replace the
attachrnent of the
hitch assembly, after which he must then once again descend from the cabin to
re-engage
the safety restraining device.
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Accordingly, the present invention seeks to provide a safety device for use in
hydraulic
hitch assemblies and in particular seeks to provide a safety device that may
be operated
from the operating cabin of the machinery including the hitch assembly.
Summary of the Invention
According to one aspect the present invention provides a safety device for a
hydraulic
hitch assembly operable between an engaged and a disengaged position, the
safety device
including:
a main body portion moveable between an engaged position and a
disengaged position, whereby when the main body portion is in the engaged
position the safety device prevents the hydraulic hitch assembly from moving
to a
disengaged position;
a biasing means to bias the main body portion towards an engaged position;
and,
a hydraulic piston which when operated acts against the biasing means and
moves the main body portion to a disengaged position.
Preferably, the main body portion moves between an engaged position and a
disengaged
position about a pivot point. '
Preferably the biasing means is provided by a mechanical arrangement such as
for example
a spring.
The hydraulic hitch assembly may be operable between a disengaged position and
an
engaged position by means of a hydraulic ram or piston. In this form, the
hydraulic ram or
piston is operated by a hydraulic circuit, wherein to move the hitch assembly
into the
engaged position hydraulic fluid is pumped under pressure into one side of the
ram or
piston to effect the movement. Once in the engaged position, the hydraulic ram
or piston is
prevented from moving the hitch assembly to the disengaged position by means
of a valve
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assembly included in the hydraulic circuit. Preferably this valve assembly is
in the form of
a check valve. The valve assembly prevents movement of the ram or piston until
a positive
hydraulic pressure is applied to the valve assembly whereby the hydraulic ram
or piston is
released allowing the hitch assembly to return to the disengaged position.
Preferably the hydraulic piston of the safety device is also connected to the
hydraulic
circuit of the hitch assembly. More preferably, the positive pressure, applied
to the valve
assembly to release the hydraulic piston and/or ram to allow the hitch
assembly to return to
the disengaged position, is initially applied to the hydraulic piston of the
safety device
thereby moving the main body portion of the safety device to the disengaged
position prior
to the hitch assembly returning to a disengaged position.
According to another aspect the present invention provides a method of
disengaging a
hydraulic hitch assembly from an engaged position, the hydraulic hitch
assembly including
a safety device and wherein the method includes the following steps:
(i) providing the hydraulic piston of the safety device with a positive
pressure sufficient to overcome the biasing means and move the safety
device from the engaged to the disengaged position; and,
(ii) moving the hydraulic hitch assembly into a disengaged position.
Brief Description of the Drawings
The present invention will become better understood from the following
detailed
description of a preferred but non-limiting embodiment thereof, described in
connection
with the accompanying figures, wherein:
Figure 1 is a schematic view of a safety device in accordance with one aspect
of the
present invention,
Figure 2 is a schematic view of a hydraulic hitch assembly,
Figure 3 is a schematic view of a hydraulic hitch assembly fitted with the
safety
device in the engaged position in accordance with one aspect of the present
invention, and,
Figure 4 is a schematic view of a hydraulic hitch assembly fitted with the
safety
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device in the disengaged position in accordance with one aspect of the present
invention.
Detailed Description of the Drawings
The term "hydraulic hitch assembly" as used throughout the specification is
intended to
include quick couplers as well as any type of hydraulic assembly for attaching
and
detaching various attachments to large machinery.
Referring to Figure 1, there is shown a safety device which may be attached to
a hydraulic
hitch assembly. The safety device 10 includes a main body portion 12 which is
substantially elongate and includes an engagement tip 85 and pivoting point
15. The safety
device 10 also includes a spring 20 which in the instant diagram is biased
against retaining
block 45 which is fixed relative to the main body portion of a hydraulic hitch
assembly
(not shown in figure 1). The safety device 10 also includes a hydraulic piston
35 with
hydraulic fluid space 25 to receive hydraulic fluid under pressure in order to
operate the
hydraulic piston 35. The hydraulic piston is shown resting against retaining
block 40 which
would also be attached and fixed relative to the main body portion of the
hitch assembly
and not attached to the main body portion 12 of safety device 10. In an
alternative
embodiment the retaining block may be attached to the body portion of the
hydraulic ram
70 associated with the hydraulic hitch assembly.
Referring now to Figure 2, there is shown generally a hydraulic hitch assembly
indicated
by 51 used for attaching an attachment such as a bucket or rock hammer to
heavy
machinery such as for example an excavator. The hitch assembly 51 includes two
remotely operable oppositely directed jaws 60, 65 which are able to move
between an
engaged position (as depicted in Figure 2) and a disengaged position. In the
disengaged
position, the opposing jaws 60 and 65 are able to fit between the transverse
hinge pins 50
and 55 of a particular attachment thereby releasing the attachment. Upon
engaging with
the attachment, the jaws 60 and 65 are pushed apart by means of a hydraulic
ram 70
operable from the cabin of the machinery, which pushes apart jaws 60 and 65
until the
attachment is securely fastened to the hitch assembly 51.
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Although not shown in Figure 2, the hydraulic ram 70 is operated via a
hydraulic circuit
through which operation pumps hydraulic fluid into the hydraulic ram 70 which
in turn
pushes jaw 65 away from 60 to engage with the attachment, at which point the
hydraulic
fluid is shut off from a main hydraulic circuit by means of check valve,
thereby
maintaining jaws 65 and 60 in an engaged state. In order to release the check
valve and
thereby disengage the hydraulic hitch assembly 51, a positive pressure must be
applied to
the check valve in order to release the hydraulic ram 70 thus allowing jaw 65
to return to
the disengaged state.
Referring now to Figure 3, there is shown a safety device 10 fitted in
conjunction with a
hydraulic hitch assembly. The safety device 10 as well as the hydraulic hitch
assembly are
shown in the engaged position, whereby an attachment is securely fastened to
the hitch
assembly. In the event of a hydraulic failure, the hydraulic ram 70 would
release thereby
allowing jaw 65 to contract towards jaw 60. In this event, the engagement
point 85 of the
safety device would engage with engagement crevasse 80 of the hitch assembly
51 thereby
preventing jaws 60 and 65 from moving together beyond a distance that would
allow the
attachment to disengage from the hitch assembly.
The safety device 10 is hinged at a fixed point 15 relative to the hitch
assembly 51 where it
may rotate about point 15 between an engaged and disengaged position. Whilst
the
hydraulic hitch assembly 51 is in the engaged position, the spring 20 of the
safety device
10 is biasing the safety device into the engaged position by pushing against
retaining block
45 attached and fixed relative to the hitch assembly 51.
In order to disengage the safety device from this position it is necessary to
supply
hydraulic fluid under pressure to cavity 25 of the hydraulic piston 35 located
in the safety
device 10. Upon applying fluid with sufficient pressure, the hydraulic piston
35 pushes
down onto retaining block 40, also attached and fixed relative to the main
body portion of
the hitch assembly, and thereby pushes =the safety device against the biasing
force of the
mechanical spring 20. Once the force of the hydraulic piston 35 pushing
against retaining
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block 40 is greater than the resilient force of the spring 20, the safety
device is caused to rise and
move about hinged point 15 such that the device moves to the disengaged
position.
Referring now to Figure 4, there is shown the safety device 10 in the
disengaged position whereby
the hydraulic piston 35 of the safety device 10 has pushed against retaining
block 40 attached to
the hitch assembly thereby moving the safety device 10 to the disengaged
position. In the
disengaged position it can be seen that the engagement point 85 of the safety
device 10 is no
longer aligned with the corresponding engagement crevasse 80 of the hitch
assembly thereby
allowing jaws 60 and 65 to retract once the hydraulic ram of the hitch
assembly is allowed to
release and move the hydraulic hitch assembly 51 into the disengaged position.
A clear advantage of the safety device 10, is that in order to release the
device and allow the jaws
60 and 65 of the hitch assembly 51 to retract to the disengaged position, the
hydraulic piston 35
of the safety device 10 may be operated from a point that is remote from the
hitch assembly such
as for example from the cabin of the heavy machinery.
As an additional advantage of this arrangement, the hydraulic fluid operating
the hydraulic piston
35 may be part of the hydraulic circuit 67 (Figures 3 and 4) associated with
the hydraulic hitch
assembly 51. In this form, the reverse pressure applied to the checking valve
to release the
hydraulic ram 70 of the hitch assembly 51 is initially directed to the
hydraulic piston of the safety
device 10 thereby moving the safety device to the disengaged position just
prior to releasing the
hydraulic ram 70 of the hitch assembly 51. In this way, the safety device 10
can be manipulated
from the cabin of an excavator or the like and thereby not requiring the
operator to descend from
the cabin in order to disengage the safety device to remove and attach various
attachments to the
hydraulic hitch assembly 51.
Furthermore, this arrangement also provides the additional safety advantage
that if there is indeed
a hydraulic failure causing the hydraulic hitch assembly to retract, the
safety device cannot be
moved to the disengaged position as it would require hydraulic pressure to do
so.
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Thus, the safety device would always be in the engaged position in the event
of a hydraulic
failure.
In order to assist an operator of an excavator or the like which is equipped
with the safety
device of the present invention to determine whether the safety device 10 is
in an engaged
or a disengaged position, the safety device may also be fitted with display
means (not
shown in the figures). According to one form, the display means may be in the
form of two
flanges, one extending from the engagement end of the safety device 10 and the
other
extending from the end adjacent the pivoting point 15. When the safety device
is in the
engaged position, the flanges are arranged so as to be in a particular
configuration when
viewed from the cabin of the excavator such that the operator can be assured
the safety
device is in the engaged position. Once the safety device is moved to the
disengaged
position, the flanges are no longer aligned in said particular configuration,
indicating that
the safety device is no longer in the engaged position. In an alternative
embodiment, a
display means may be located in the actual cabin of the excavator or the like
and be in the
form of a light for example which when operated provides the operator with an
indication
of whether the safety device is in the engaged or disengaged state.
An example of an embodiment of the invention is described as follows:
A check valve associated with a hydraulic ram of a typical hydraulic hitch
assembly
operates at a 3:1 ratio, that is the check valve can provide a captive
pressure of 3000 PSI,
which will maintain the hydraulic hitch assembly in an engaged position. As
the check
valve operates at a 3:1 ratio, it requires a reverse pressure of 1000 PSI to
release after
which the hydraulic hitch assembly will retract into the disengaged position.
In this
example the 1000 PSI of reverse pressure is provided to the hydraulic piston
of the safety
device before being applied to the check valve and this pressure is sufficient
to operate the
hydraulic piston to overcome the force of the biasing means thereby moving the
safety
device into the disengaged state and allowing the hitch assembly to move into
the
disengaged position.
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The captive pressure holding the hydraulic ram of the hitch assembly may drop
due to a number
of reasons such as for example, there is a bypass of hydraulic pressure, the
seals of the hydraulic
ram are damaged, or there is contamination in the hydraulic fluid. In this
instance, the required
pressure to release the check valve will also fall according to the 3:1 ratio
whereby the pressure
required to release the check valve will not be sufficient to for the
hydraulic piston of the safety
device to overcome the force of the biasing means (eg a spring). This means
that the safety device
cannot be moved into the disengaged position, and thereby constantly monitors
the safe working
condition of the hydraulic hitch assembly.
The scope of the claims should not be limited by the embodiments set forth in
the examples, but
should be given the broadest interpretation consistent with the description as
a whole.
