Note: Descriptions are shown in the official language in which they were submitted.
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Method In A Pressure Medium System For Employing And Controlling A Lifting
Boom Unit Particularly In Connection With A Work Machine
The invention relates to a method which is particularly intended for use in
combination with a system using pressurized medium for employing and
controlling
a hoisting boom assembly, the hoisting boom assembly comprising a
substantially
vertical main boom, whose first end is connected to the working machine, an
intermediate boom, whose first end is connected with an articulated joint to
the
second end of the main boom, and a terminal boom, whose first end is connected
with an articulated joint to the second end of the intermediate boom and whose
second end is provided with means for fixing the equipment required in working
operations of the hoisting boom assembly, wherein the system using pressurized
medium comprises: a first cylinder-piston mechanism using pressurized medium
and being effective between the main boom and the intermediate boom, for
producing substantially vertical movements of the second end of the terminal
boom,
a second cylinder-piston mechanism using pressurized medium and being
effective
befirveen the intermediate boom and the terminal boom, for producing
substantially
horizontal movements of the second end of the terminal boom in connection with
the
first cylinder-piston mechanism using pressurized medium, a pressurizing unit
for
pressurizing the medium to be pressurized, and a control unit comprising a
first and
a second operating valve for conveying the pressurized medium to and from the
pressure chambers of the first and second cylinder-piston mechanisms for
achieving
the desired movement of the second end of the terminal boom, wherein upon
application of the method: A) the flow of the pressurized medium is led via
the first
operating valve to the first cylinder-piston mechanism for achieving
substantially
vertical movements of the second end of the terminal boom.
A lifting or hoisting boom assembly for applying the method of the invention
typically
comprises a substantially vertical main boom and an intermediate boom
pivotally
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mounted on the main boom. Further, a terminal boom is pivotally mounted on
this
intermediate boom, whereby a load, a working machine or the like can be fixed
to
the intermediate boom to be moved by the hoisting boom assembly. Such a
hydraulic hoisting boom assembly is operated with two cylinder-piston
mechanisms
wherein the first cylinder-piston mechanism connecting the main boom to the
intermediate boom is used for effecting a movement substantially in the
vertical
direction, and a substantially horizontal movement is effected in a
corresponding
manner by using the second cylinder-piston mechanism connecting the
intermediate
boom to the terminal boom in association with the first cylinder-piston
mechanism. In
conventional hoisting boom assemblies, a cylinder-piston mechanism is
controlled
using a control unit provided with separate operating valves via a hydraulic
medium
pressurized in a pressure unit and conveyed by independent primary and
secondary
lines connected to the operating valves.
A hoisting boom assembly of the above-mentioned type is manoeuvred in a way
that
e.g. when the load is to be moved towards the main boom, the first cylinder-
piston
mechanism is used for pivoting the intermediate boom upwards and
simultaneously
the free end of the terminal end is descended with the second cylinder-piston
mechanism correspondingly, wherein the manoeuvre is naturally made in reverse
order for moving the load away from the main boom. The weight of the load will
induce a certain amount of pressure in each cylinder-piston mechanism. For
carrying the load away from the main boom, no pressure from the pressure unit
will
be required for controlling the first cylinder-piston mechanism because of the
effect
of gravity, whereas full pressure will be required for controlling the second
cylinder-
piston mechanism. Thus, in a hydraulic system where the cylinder-piston
mechanisms are linked to the hydraulic system with fully independent flow
channels
according to the prior art, the operating pressure will always be determined
by the
maximum pressure required. Consequently, if both of the cylinder-piston
mechanisms are equal in size, half of the energy produced by the pressure unit
will
always be turned into dissipation heat. Further, the cylinders are very easily
subject
to cavitation. This is due to the fact that the pressure caused by the load
and by the
mass of the hoisting boom assembly itself directs a strong flow to the return
ports of
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the cylinder-piston mechanisms, and it is not possible to provide a
pressurized
medium replacement through the valve arrangements to the inlets at a
sufficient
rate. Moreover, it is difficult to use the hoisting boom assembly for moving a
load or
the like particularly in the horizontal direction, because simultaneous use of
both
cylinder-piston mechanisms is necessary, and these are controlled separately
but
simultaneously with two operating valves.
The purpose of the method of the invention is to provide a decisive
improvement to
the problems presented above and thus to improve the prior art substantially.
For
achieving this purpose, the method of the invention is primarily characterized
in that
the first and the second cylinder-piston mechanisms are connected in series
for
achieving substantially horizontal movements of the second end of the terminal
boom, and upon application of the method, B) the flow of the pressurized
medium is
led via the second operating valve to the first cylinder-piston mechanism, the
pressure chamber of which is being filled and used for moving pressurized
medium
from the pressure chamber of the first cylinder-piston mechanism to be emptied
to
the pressure chamber of the second cylinder-piston mechanism to be filled up,
or
vice versa, wherein a complex movement of the second end of the terminal boom,
containing substantially vertical and horizontal components of motion, is
effected by
simultaneous application of operations A) and B); and wherein the second
pressure
chamber of the second actuator is coupled with the first pressure chamber of
the
first actuator via a load lowering valve in such a manner that medium flow
created
by the movement of the second pressure chamber of the second actuator is
conveyed substantially as the same amount to the first pressure chamber of the
first
actuator.
The most important general advantages of the method of the invention include
its
simplicity, reliability and effectiveness. Using the method, it is possible to
make even
very massive constructions having pressure units and cylinder-piston
mechanisms
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with essentially smaller capacities than conventional systems. Further, it is
possible
to reduce the quantity of the pressurized medium to be circulated as much as
to the
half of the quantity used in current systems. Moreover, particularly in
hoisting boom
assemblies, the forces and moments directed from the cylinder piston
mechanisms
to the hoisting boom assembly are reduced significantly from the present ones;
consequently, it is even possible to make the construction of the hoisting
boom
assembly less complex and less massive, if necessary. Thus, the invention has
in
this respect also the advantage of significantly better efficiency and output
than
current methods. Another advantage of the method according to the invention
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is easier control of the pressurized medium system, wherein the appli
cation of the method most often does not require controlling two inde
pendent cylinder-piston mechanisms with separate operating valves.
Also, the method of the invention makes it possible to reduce substan
tially problems of cavitation.
Advantageous embodiments of the method of the invention will be pre-
sented in the dependent claims relating to the method.
In the following description, the invention will be described in detail with
reference to the appended drawings, in which
Fig. 1 shows an advantageous operational chart relating to a
pressurized medium system applying the method of the
invention, and
Fig. 2 shows an advantageous hoisting boom assembly applying
the method and pressurized medium system according to
the invention, seen from the side.
The invention relates to a method in a pressurized medium system
comprising at least two cylinder-piston mechanisms 1, 2 (later actua-
tors) using a pressurized medium; a pressure unit P, such as one or
several pumps for pressurizing the medium; and a control unit V having
a valve arrangement 4, 5 for operating said actuators 1, 2 by conveying
pressurized medium to their pressure chambers to be filled in at the
time and, in a corresponding manner, by displacing pressurized
medium from their pressure chambers to be emptied at the time. To
improve the efficiency of the pressurized medium system particularly
during simultaneous use of the actuators 1, 2, the actuators 1, 2 are
coupled to operate in a series so that pressurized medium to be dis-
placed is conveyed from the pressure chamber of one actuator 1 or 2 to
be emptied to the pressure chamber of the other actuator 2 or 1 to be
filled in. The pressurized medium is returned to the control unit V from
the pressure chamber of the second actuator 2 or 1 to be emptied.
The method of the invention is advantageously applied, according to
the operating principle shown in Figure 1, in a pressurized medium
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system having two actuators 1, 2 which are controlled by two operatin-g
valves 4, 5 of the control unit V by means of pressurized medium sup-
plied via a flow arrangement, such as primary 6a, 7a and secondary
lines 6b, 7b, connected to the operating valves 4, 5. At least during
simultaneous use of the actuators 1, 2, pressurized medium is con-
veyed by the control unit V, such as the first or second operating valves
4 or 5, to one actuator, such as the first or second pressure cylinder 1
or 2, from which the pressure medium to be displaced is further con-
veyed to the next actuator 2 or 1 and returned to the control unit V.
In a particularly advantageous embodiment, further with reference to
the principle shown in Fig. 1, during simultaneous use of actuators 1, 2
pressurized medium is conveyed by the control unit V, e.g. from the
primary port 5A of the second operating valve 5 to the second pressure
chamber C2 of the first actuator 1 to be filled up. Next, the pressurized
medium is conveyed further from the first pressure chamber C1 of the
first actuator 1 to be emptied to the second pressure chamber D2 of the
second actuator 2 to be filled up. After this, the pressurized medium is
returned from the first pressure chamber D1 of the second actuator 2 to
be emptied to the control unit V, e.g. to the secondary port 5B of the
second operating valve 5.
In a situation of reverse use of the pressurized medium system, during
simultaneous use of actuators 1, 2, pressurized medium is conveyed
via the control unit V, i.e., from the secondary port 5B of the second
operating valve 5, to the first pressure chamber D1 of the second
actuator 2 to be filled up, whereafter the pressurized medium is con-
veyed further from the second pressure chamber D2 of the second
actuator 2 to be emptied to the first pressure chamber C1 of the first
actuator 1 to be filled up. The pressurized medium is then returned from
the second pressure chamber C2 of the first actuator 1 to be emptied to
the control unit V, i.e., to the primary port 5A of the second operating
valve 5.
In a particularly advantageous embodiment of the method, reference is
made to Fig. 2 showing a pressurized medium system in connection
with a so-called hoisting boom assembly. This kind of a hydraulic
hoisting boom assembly X is to be placed in connection with a working
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machine, such as a tractor, a forest harvester or an excavator, and rn
its operating situation the hoisting boom assembly comprises a sub-
stantially vertical main boom X1 with its lower, first end connected to
the working machine and its second end its journalled to the first end of
intermediate boom X2 which is further, at its second end, journalled to
the first end of terminal boom X3, wherein the second end of the termi-
nal boom X3 is provided with means for fixing a load, working tool or
the like to be moved with the hoisting boom assembly. The hoisting
boom assembly is preferably operated with two cylinder-piston mecha-
nisms 1, 2 (later actuators), wherein the first actuator 1 connecting the
main boom X1 and the intermediate boom X2 is used for effecting a
movement of the second end of the terminal boom X3 substantially in
the vertical direction and, in a corresponding manner, the horizontal
movement of the second end of the terminal boom X3 is effected by
using the second actuator 2 connecting the intermediate boom X2 to
the terminal boom X3 in association with the said first actuator 1. In an
embodiment of this kind, the method of the invention is utilized during
simultaneous use of actuators 1, 2, i.e., for example in horizontal trans-
fers of the end of the hoisting boom assembly, by using the displace-
ment energy of the pressurized medium supplied to the actuator 1 for
operating the second actuator 2. by coupling the flow channels of the
flow arrangement entering them at least partly together as shown in the
chart of Fig. 1; the first section i I of the primary duct 7a of the second
actuator 2 to the secondary duct 6b of the first pressure cylinder 1 for
conveying pressurized medium to the pressure chamber C2, and the
second section 7II of the primary duct 7a to the primary duct 6a of the
first pressure cylinder 1 for connecting the pressure chamber C1 with
the pressure chamber D2 of the second pressure cylinder 2. Conse
quently, the changes in length of the actuators 1, 2 take place in the
same direction.
In another advantageous embodiment, pressurized medium is supplied
from the primary port 5A of the operating valve 5 to the pressure cham-
ber C2 of the first actuator 1 to be filled up. In a corresponding manner,
pressurized medium is removed from the pressure chamber C1 of the
first actuator 1 to be emptied to the pressure chamber D2 of the second
actuator 2 to be filled up, whereafter the pressurized medium is first
returned from the pressure chamber D1 of the second actuator 2 to be
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emptied to the secondary port 5b of the second operating valve 5. The
above process corresponds for example to moving a load at the end of
the hoisting boom assembly outwards, wherein the intermediate boom
X2 pivots downwards and simultaneously pushes the second end of the
terminal boom X3 away from the main boom X1. Upon application of
the method, the weight of the load induces a substantially equal pres-
sure on both actuators 1, 2. Further, in this connection it is possible to
use suitable actuator volumes for achieving their suitable movement
relations particularly in an endeavour to facilitate substantially horizon-
tal movements. Thus, when using the pressurized medium system of
the invention for moving a load, an optimally low pressure will be
needed, because the pressure of the hoisting actuator 1 itself is used
directly for operating the second actuator 2. For the same reason, also
the required oil quantity is as small as possible, because oil is now
supplied to the first actuator 1 only.
For moving the load towards the main boom X1, pressurized medium is
supplied in a corresponding manner from the secondary port 5B of the
second operating valve 5 to the pressure chamber D1 of the second
actuator 2 to be filled up. Pressurized medium is removed from the
pressure chamber D2 of the second actuator 2 to be emptied, in a cor-
responding manner, to the pressure chamber C1 of the first actuator 1
to be filled up. Following this, the hydraulic fluid is returned from the
pressure chamber C2 of the first actuator 1 to be emptied to the primary
port 5A of the second operating valve 5. Also in this case the required
operating pressure is as low as possible, because the intermediate
boom X2 induces a pressure in the actuator 2, thus tending to extend
the first actuator 1. According to what was presented above, the quan-
tity of the oil to be circulated is also in this case one half of that
required
when using conventional methods.
As shown in Figures 1 and 2, the sole hoisting movement, i.e. the pivot-
ing of the intermediate boom X2 upwards, can be conducted advanta-
geously by supplying the pressurized medium through the outlet port of
the first operating valve 4, i.e., through the primary port 4A, to the first
pressure chamber C1 of the first actuator 1, wherein the second pres-
sure chamber C2 is connected with the return port of the first operating
valve, i.e., with the secondary port 4B. When the second operating
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valve 5 is closed, also the first pressure chamber D1 of the second
actuator 2 is closed, and this second actuator 2 is prevented from
moving although the pressure is effective in its second pressure cham-
ber D2. In a corresponding manner, the sole descending motion, i.e.,
the pivoting of the intermediate boom X2 downwards, is conducted in
the reverse order by supplying the pressurized fluid through the secon-
dary port 4B of the first operating valve 4 to the second pressure
chamber C2 of the first actuator 1, wherein, in a corresponding manner,
its first pressure chamber C1 is connected with the primary port 4A of
the first operating valve. Also in this case, the second operating valve 5
is closed, and the pressure has no effect elsewhere. For balancing the
operations described above, the operation chart of Fig. 1 also includes,
as a conventional embodiment in this context, a so-called load lowering
valve 3 for preventing any unintentional movement of the second actua
for 2.
It is obvious that the operating valves 4 and 5 can also be used simul-
taneously, in which case the movement of the hoisting boom assembly
is a complex movement comprising dynamic components selected
according to the need and produced on one hand by operations of the
first operating valve 4 as described above, and on the other hand by
operations of the second operating valve 5 as described above. Con-
sequently, the method according to the invention renders it possible to
make a movement in a certain direction with easy control, as well as to
make the paths completely (freelylat random), if necessary. These ver-
satile operations can be controlled with only two operation valves 4, 5.
