Note: Descriptions are shown in the official language in which they were submitted.
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Pressurized medium supply circuit
The invention relates to a pressurized medium supply circuit according
to the preamble of the appended claim 1.
The invention relates especially to the pressurized medium supply
circuit of a mobile machine, and it is particularly applied in mobile
hydraulics.
The publication SE-B-8001459A (Publication number 448762) dis-
closes a hydraulic circuit, in which each actuator is assigned pre-
determined pumps to which it can be connected. Characteristic to this
system is to priorize different actuators and the fact that the same
actuator can be simultaneously connected with two different pumps.
The publication also presents an auxiliary pump, the purpose of which
is only to function on the return side of hydraulic fluid to prevent cavi-
tation, and thus it does not supply power to the actuators.
In the publication DE-A-4100988 a pressurized medium system with
two pumps is presented. Each pump supplies its own block, i.e. its own
subsystem. The blocks, in other words, subsystems can be connected
with each other with a direction control valve. In addition, it is possible
that one pump supplies its own block or, together with the other pump,
both blocks.
In the publication DE-A-3139635 an auxiliary pump connected in
parallel with the feeder pump of the pressurized medium system is
presented.
Furthermore, pressurized medium supply circuits are presented in the
following publications of prior art: GB-1405724, EP-A-41686 and EP-
236750.
Especially in connection with mobile working machines, several actua-
tors are used, each of which is set to move a predetermined tool or
manipulating device. Manipulating devices also include moving means,
for example articulated swinging arms for carrying different tools.
Actuators are devices which consume the power of the pressurized
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medium system and which are connected to the pressurized medium
supply circuit, to which a feeder pump for supplying pressurized
medium is also connected in order to supply power to the actuators by
means of the pressurized medium. Forest machines, which are pro-
s vided with implements and manipulating devices for performing steps of
operation in tree harvesting and loading, provide an example of such
mobile machinery. A known forest machine type is the harvester which
by means of a felling head on the end of a mobile boom performs the
felling and possibly also delimbing and cutting to predetermined
lengths. In addition to the fact that pressurized medium is used in the
operation of different implements and manipulating devices, it can also
be utilized for moving the working machine itself and for the progres-
sive motion of the working machine.
Characteristic to many implements and manipulating devices are such
successive work stages, where at one of them the actuator moving the
implement or manipulating device is subjected to great forces due to
the work performed by the implement or the manipulating device, and at
another of them the implement or manipulating device is moved at a
higher speed and under a smaller load compared to the work stage
mentioned above.
In machines applying the so-called walking technique, swinging arms
pivotally articulated in the body are utilized, which on one hand support
the body with respect to the ground and on the other hand by means of
their movement cause the machine to advance with respect to the
ground. Such arms are usually constructed of several sections so that
the construction resembles a leg as much as possible. Characteristic to
the walking movement achieved with such a construction is the alter-
nation of two separate stages, a transfer stage and a supporting stage.
At the supporting stage a leg carries for its own part the weight of the
machine and is subjected to great forces. At the transfer stage, the !eg
is moved in the air fast compared with the supporting stage to the be-
ginning of a support stage of a new step. Except for its own weight and
friction, the leg is thus unloaded. In the category of the working
machine size, it is reasonable to carry out power transmission to the
legs with hydrostatics, due to its good power intensity, adjustability and
loading capacity. The walking technique is described for example in
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U.S. Patent 5,353,886 "Swinging Arm" and in the international applica-
tion PCT/F196/00583 "Leg Mechanism" (Publication WO 97/17250) by
the applicant; a corresponding U.S. application has been filed to the
U.S. Patent and Trademark Office under the serial number 08/886,397
on July 1, 1997. The said patent and patent application are incorpo-
rated herein by reference.
To guarantee reliability and good mobility in the 6-legged machines
made by the modern technology, presented for example in the afore-
mentioned U.S. Patent 5,353,886, which have swinging arms and a
joint which allows the leg to pivot around the longitudinal axis of the
machine (so-called extensor joint), a joint which allows the leg to pivot
in the vertical plane (so-called hip joint), and a joint which brings about
the bending of the leg (so-called knee joint), 18 servo-controlled actua-
tors (joints) are needed. With respect to the operating efficiency, it
would be most advantageous to operate each of these actuators with a
separate pump controlled servo circuit. Practical reasons, however,
place restrictions on this method. First of all, servo pumps as such are
expensive components. Second, power transmission from the prime
mover to the pumps becomes complicated and expensive to implement
and because of its size and shape it complicates the design of the
machine and the practical realization of the mechanical construction.
For simplicity and reliability, the most advantageous solution is a valve-
controlled single-pump system. Its weakness, however, lies in the poor
operating efficiency, especially for the reason that the same feeding
pressure has to be used for all actuators, regardless of the loading
situation.
As stated above, double-pump systems are known in pressurized
medium supply circuits. Double-pump systems used in connection with
forest machines are presented in international publication WO
82/04105 and in U.S. Patent 4,632,158. In these publications the
double-pump system is applied for turning a boom assembly and for
moving implements. In the publication WO 82/04105, either the first or
the second pump is utilized to bring about the pivotal movement of the
upper portion of the harvester and therewith the boom assembly. If the
first pump is used for the higher priority progressive movement of the
harvester, the second pump, with which also other. implements can be
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supplied, can then be coupled to swing in the upper portion of the har-
vester. In the publication US-4,632,158, pumps with different capacities
are coupled together to simultaneously supply hydraulic oil to actuators
effecting the movements of the gripping arms and the saws of the
forest machine. After a certain pressure level has been achieved, one
of the pumps is switched off by means of a valve, whereby volume flow
and correspondingly capacity is saved at the final stage of the
movements of said actuators, as the movements can be performed
more slowly.
As stated in the beginning, there are two discernible stages in the wal-
king, which differ in their loading and speed requirements: the transfer
stage and the supporting stage. In the supporting stage the motion
speeds of the legs are low, and the forces acting on them great, i.e. the
pressure required in their. actuators is high and the volume flow rela-
tively small. When the legs are in the transfer stage, the situation is the
opposite. High speed is required, but the need for power is small. It is
obvious that under these circumstances it is not possible to accomplish
a power transmission supply circuit with good energetic efficiency with
only one pump. The solutions presented in the aforementioned publi-
cations provide no help for this problem because they do not present ~
system intended for the advancing movement of the working machine.
The object of the invention is to present a pressurized medium supply
circuit which does not have the aforementioned drawbacks and which
can be used especially in the pressurized medium systems of mobile
vehicles and working machines. For attaining this purpose, the supply
circuit is primarily characterized in what will be presented in the charac-
terizing part of the appended claim 1.
By utilizing two pumps, either one of which can be upon choice coupled
to a selected actuator or group of actuators, a very good compromise
can be achieved with respect to reliability, simplicity, price, size and on
the other hand, efficiency. Thus, when an actuator is under a load
determined by an implement or a manipulating device, one of the
pumps and the corresponding feeder line is in operation, and cor-
respondingly when the actuator reaches the speed-requiring transfer
stage of the implement or manipulating device, the feeder line from the
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other pump is opened, thereby achieving a large volume flow at a low
pressure level. If pressurized medium were supplied with only one
pump, the situation would always be such that the large volume flow
required to move the implement or manipulating device would also be
supplied at the pressure determined by the heaviest possible load.
Applied to the walking technique the invention means that when a leg is
at the supporting stage, one of the pumps and the corresponding
feeder line are in operation, and correspondingly when the leg enters
the transfer stage, the feeder line from the other pump is opened,
wherein a large volume flow is achieved at a low pressure level. If
pressurized medium were supplied with only one pump, the situation
would always be such that the large volume flow required to move the
leg would also be supplied at the pressure determined by the heaviest
possible load.
As for other advantageous embodiments, the reference is made to the
enclosed dependent claims and the description below.
In the following, the invention will be described in more detail with refe-
rence to the following drawings, in which
Fig. 1 shows a mobile machine, in which a supply circuit according
to the invention can be used,
Fig. 2 is a diagram illustrating the supply circuit according to the
invention,
Fig. 3 shows an alternative way to make the supply circuit, and
Fig. 4 is a hydraulic diagram showing a feeder line for one leg.
The machine shown in Fig. 1 comprises a body R and the arms 1-6
pivotally articulated on the same. The construction of the arms resem-
bles a leg, i.e. the arms have two sections, articulated to each other by
means of a joint (knee joint). The whole leg is arranged to swing with
respect to the body R in the vertical plane around a hip joint, which is
arranged in a separate part, which in turn moves pivotally with respect
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to the body around the rotation axis extending longitudinally of the body
in order to incline the whole leg with respect to the body. By means of
the aforementioned movements it is possible to carry out the movement
of the body R with respect to the ground, whereby the aforementioned
transfer and supporting stages are used to move the body.
Because each joint requires a separate actuator, the machine illus-
trated in the drawing has 6 x 3 = 18 actuators.
Fig. 2 is a diagram showing a pressurized medium supply circuit. A
valve block L, where the main lines of the circuit run, is separated with
a broken line. A feeder line running from a first pump A and along the
block L branches into lines 1a - 6a which lead to different legs 1-6. The
block connectors to the legs 1-fi are indicated with the same reference
numbers as the legs. The feeder line leading from a second pump,
additional pump B, along the block L branches in a similar way into
feeder lines 1 b-6b which lead to different legs. The lines 1 a, 1 b; 2a, 2b
etc. which branch from the different pumps and lead to the same leg
are connected in parallel to the same connector, in other words, they
are connected in parallel with each other to the same actuator in the
leg. The block L is located in the body in the longitudinal direction, and
there are channels running in the transverse direction. To each of these
channels, each respective pair of feeder lines is connected in parallel in
the aforementioned way. The channels open to both sides of the block
as connectors. For the sake of simplicity of the construction, one of the
connectors is joined to the pressurized medium line leading to the leg
and the other one is closed with a plug so that in successive channels,
the connectors are provided alternately on different sides in the way
shown by numbers 1-6.
Each of the line pairs 1 a, 1 b; 2a, 2b etc. contains the following compo-
nents, which are described with reference to the lines 1 a, 1 b. In the line
1 a which branches from the feeder fine of the first pump A, there is a
controllable direction control valve 1 c, which, depending on the position
either lets pressurized medium through line 1 a or blocks the flow. In the
second line 1 b of the pair, which branches from the feeder line from the
additional pump B, there is correspondingly a check or non-return valve
1 d, which only allows the flow from the pump to the actuator. The
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direction control valve 1c is a conventional 2/2 direction control valve,
with positions 'open' and 'closed'.
The controllable direction control valves 1 c-6c are normally open. Thus
the pump A which has been set at a higher feeding pressure ensures
that the pressure level is sufficient in the feg that is at the supporting
stage. For example, the position illustrated in Fig. 2 describes precisely
the situation where all the legs are on the ground. The lower pressure
flow of the pressurized medium produced by the additional pump B
does not reach the legs at this stage because the check valves 1 d-6d
are closed due to the parallel connection because of the higher
pressure prevailing at the connector.
When one leg, for example leg 1 rises from contact with the ground, it
no longer supports the body R any more. Thus a high pressure is not
required in the moving stage. When the lifted leg is for example leg 1,
valve 1 c in the corresponding line 1 a is closed, which is illustrated with
an arrow in Fig. 2, and thus the pressure is no longer allowed from the
first pump A into this leg. The flow of the pressurized medium is allowed
from the additional pump B along the line 1 b as soon as the check
valve 1 d can open up due to the decreased pressure level of the leg.
Now the flow with a low pressure but high volume flow rate produced by
the pump B is allowed to act on the actuators of the leg to bring about a
quick transfer movement. When the controllable valve 1c in the other
line 1 a is opened, the line 1 b leading from the additional pump B is clo-
sed again as the check valve 1 d is closed and a higher pressure level
will be present in the actuators. This takes place when the leg is again
in contact with the ground.
The valves 1 c-6c, located in the lines branching from the first pump A
are spring-loaded, two-position electric valves, which are held in the
open position by means of a spring or an other constant force. The val-
ves 1 c-6c can be closed correspondingly by electric control with the
help of a solenoid, in other words, they are thus moved by means of
external control against the force of the spring or the like. These valves
may also be hydraulically pilot-operated, as presented in Fig. 2.
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A hydraulic pressure accumulator can be connected to each feeder
line, from which the lines branch in parallel to the same legs, to guaran-
tee the sufficiency of the volume flow and on the other hand to elimi-
nate harmful pressure peaks. Pressure accumulators and their control
valves are indicated jointly with the reference numbers 7a and 7b. The
return line of the pressurized medium, which runs through the block L,
is indicated with the reference number 8, and the connector to the
pressurized medium tank in block L is indicated with the letter T. In the
supply direction of pressurized medium in block L, there may be other
channels and actuators, or the feeder lines may end at the block.
Even though the function of the hydraulic circuit has been described
above with reference to moving a machine, the invention can also be
used in such pressurized medium systems which contain several power
requiring actuators, which bring about movements of different imple-
ments and manipulating devices. Reference numbers 1-6 in Fig. 2 can
thus be understood to indicate connectors to different actuators or
groups of actuators which move implements and manipulating devices
according to determined stages of operation.
A substantial saving of power input is achieved with this invention, be-
cause it is not necessary to supply large quantities of volume flow at
high pressure during the transfer stage, due to the additional pump B
having been switched on and functioning then separately under a lower
feeding pressure. The power required is directly proportional to the
clause dp x Q (Q=V/t) showing that a multiple decrease in the pressure
means a corresponding saving in power.
The connection presented in Fig. 2 gives the advantage that in every
situation it is possible to obtain at least a lower pressure level for all
legs 1-6 , because pressurized medium is always allowed to flow from
the additional pump B into the legs, unless there is higher pressure on
the other side of the check valves 1 d - 6d. The co-operation between
the controlled valve and the non-controlled check valve is rapid when
switching over from the supporting stage to the transfer stage. Thus the
legs are in no event left without the pressurized medium supply. Be-
cause the controllable direction control valves 1 c - 6c are open when
without control, the legs have always a sufficient supporting force in the
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rest position of the valves, and switching over to a lower force requires
an active control of the valve, i.e. the valve has to be in the energized
position.
The above described operating principle is analogous if pressurized
medium is directed to actuators which require a supporting force and a
transfer force at different work and transfer stages of implements and
manipulating devices.
It is also possible to use other connections to change the pumps. In Fig.
3 an alternative parallel connection has been presented, where a pair
of valves can be replaced by one, electrically controlled 3/2 direction
control valve 1 e...6e, which is urged by spring to the position of con-
necting the pump A to the corresponding leg and under external control
changes to the additional pump B so that it becomes connected with
the line running to the feg. A drawback here is the slight delay when the
valve moves between the positions, compared to the aforementioned
combination having a quick, automatically functioning check valve. The
connection of Fig. 3 can also be used for connecting the pumps alter-
nately to the corresponding actuator or group of actuators, when the
actuators are used to transfer implements and manipulating devices
and to carry the load caused by them.
In addition, externally controlled valves 1 c-6c or 1 e-6e can be con-
nected to the automatic control system of the machine in suitable ways
so that they operate automatically according to the contact of the leg. In
its simplest form, the automatic control system of the walking machine
only includes position sensors. Due to the sensor arrangement, the
automatic control system knows the momentary position of each leg.
On the basis of the position data, the automatic control system can
make an assumption whether the leg in question is at the tramsfer
stage or at the supporting stage, and select the pressurized medium
supply for that leg either from pump A or pump B. A slightly more
sophisticated automatic control system also recognizes the forces
directed to the leg. The force data can be obtained directly by means of
force sensors, which can be located e.g. in the lower end of each leg,
or numerically, for example by measuring the pressures of actuator
lines with pressure sensors. When the force directed to the leg is
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known, it is also possible to recognize the step contact to the ground
and thus to select the pressurized medium supply to the leg from the
pump circuit of the supporting stage. The transfer to the transfer stage
can normally be deduced from the position data alone, but the force
data gives further (possibly necessary) confirmation that the leg is off
from the ground. By means of the automatic control system, it is also
possible to carry out a suitable timing, for example so that the valve
shifts to the additional pump B first after the leg has moved a certain
small distance after it has lost its contact with the ground.
When pressurized medium is directed to different actuators or groups
of actuators, intented to transfer the implements and manipulating
devices and to receive the load caused by them, the same automation
principle can be applied, whereby the valves are connected to the
automatic control system of the work stages of implements and manipu-
lating devices.
Fig. 4 illustrates pressurized medium supply to one leg along the line
from the block L. The line branches into actuators required by the three
joints of the leg, that is to the hydraulic cylinder 9 of the extensor joint,
to the torsion motor 10 of the hip joint (normally a pair of two hydraulic
cylinders) and to the torsion motor 11 of the knee joint (normally a pair
of two hydraulic cylinders). Consequently, a pressure level determined
by the pump A or B is achieved for all actuators. The movements of the
joints are normally controlled by direction control valves 12. Further-
more, Fig. 3 illustrates the transmission of pressure data from the line
pair between the direction control valve 12 and the actuator electrically
along lines 13 to a control unit 14.
In connection with implements and manipulating devices it is possible
to apply the connection principle illustrated in Fig. 4 for example in
swinging booms of a working machine where several actuators are
required for performing different movements.
Pressurized medium supply either from the pump A or from the pump B
to each leg can be selected freely according to the need by means of
the system according to the invention: either based on the step
sequence and contact to the ground, or in some special cases for
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example in a fixed manner so that the middlemost legs in the longitudi-
nal direction of the machine receive their pressurized medium from the
pump B, and the other legs from the pump A. Further, in the coupling
logic based on the step sequence, the moment of switching between
pumps A and B can be shifted with respect to the step sequence so
that both pumps function as well as possible in their operating range, in
other words the aim is not to exceed the output of either of the pumps.
As for the pumps A and B themselves, they are variable-displacement
pumps, in which it is possible to set the supply pressures mutually dif-
ferent either with a constant pressure regulator, or they are set at dif-
ferent levels by means of a load-sensing system. In pumps equipped
with a constant pressure regulator, the pressure level of the additional
pump B is set at a lower level than that of the pump A of the supporting
stage. Furthermore, it is easy to calculate the load at the transfer stage
and the consequently required pressure in advance, and thus it is pos-
sible to preset the pressure level of the additional pump B fairly accu-
rately.
Even though the invention has been described above on one hand with
reference to the walking technique and on the other hand with respect
to moving different implements and manipulating devices, it is possible
that the invention is used to supply both the actuators for the legs that
bring about the advancing movement and the actuators for implements
and manipulating devices. In that case, in the coupling illustrated in Fig.
2 some of the connectors can lead to the legs and some to the
actuators that move the implements and manipulating devices.
Even though the invention, relating to mobile hydraulics, is especially
suitable for different types of mobile machines, it is also applicable in
stationary machines and equipment, depending on the nature of the
stages of operation they perform.
