[0001] The present invention relates to an anti-cavitation device for a hydraulic cylinder.
[0002] The invention refers in particular to the field of operating vehicles predisposed
for the lifting and lowering of a load.
[0003] Operating vehicles of this type normally have a jib that can be lifted or lowered
by a hydraulic cylinder. The cylinder can be supplied with pressurised working fluid,
typically oil, from the bottom side or the rod side, respectively, to cause the lifting
or lowering of the load.
[0004] On the conduit that supplies oil to the bottom side of the cylinder there is a control
valve. Such control valve has the function of allowing the free supply of oil to the
bottom side of the cylinder, and controlling or stopping the unloading of the oil
from the bottom side of the cylinder. In particular, the control valve is a pilot
valve that is normally closed. In the absence of a pilot pressure, the valve remains
closed and prevents the drainage of the oil, so as to guarantee the support of the
load and prevent the uncontrolled descent of the load itself. In the presence of a
pilot pressure, the valve opens in a controlled manner allowing the drainage of the
working fluid and the consequent controlled descent of the load. The pilot pressure
is normally taken from the conduit that supplies the oil to the rod side of the cylinder.
[0005] The supply of the oil to the bottom side or the rod side of the cylinder is normally
established by means of a distributor that has a central position, wherein it closes
both supply conduits to the cylinder, a first position, wherein the oil is supplied
to the bottom side of the cylinder, while the rod side is connected to a drain, and
a second position, wherein the oil is supplied to the rod side of the cylinder, while
the bottom side is connected to the drain through the control valve.
[0006] In many cases, to save energy, the load is lowered by exploiting gravity, i.e. by
generating a motive thrust limited to the rod side of the cylinder. In these cases,
it is, however, necessary that a sufficient flow rate of oil be supplied to the rod
side of the cylinder to keep the annular chamber full, so as to prevent any cavitation
phenomena arising.
[0007] In many cases, current operating vehicles comprise command distributors activated
by hydraulic or electro-hydraulic manipulators and, in order to open and keep the
valve controlling the descent open, the same pressure that the manipulator sends to
the distributor control rod can be used. It may happen that the opening of the descent
control valve allows the flow of a higher flow rate of oil with respect to the flow
rate that can be provided by the activation circuit of the distributor and the descent
control valve. The annular chamber may therefore stay partially empty. This condition
can have negative effects on the movement of the load. For example, in the event that
the load, after being rested on the ground, must also be pressed downwards, the partially
empty annular chamber causes a delay in the response to the command given by the operator.
Furthermore, if the annular chamber remains partially empty, after the stopping the
load does not remain stopped and held by the cylinder and could therefore be subject
to jolts or undesired movements. Such disadvantages are particularly significant in
the event of self-propelled operating vehicles equipped with a liftable jib to which
a tool such as a shovel, an excavator or the like is articulated.
[0008] The object of the present invention is to offer an anti-cavitation device for a hydraulic
cylinder that allows the disadvantages currently encountered in the field to be overcome.
[0009] An advantage of the device according to the present invention is that it allows the
annular chamber to be supplied with the necessary flow rate of oil during the descent
of the load, in a continuous way and without significant pressure peaks.
[0010] Another advantage of the device according to the present invention is that it does
not require the use of the pilot circuit to supply the annular chamber, allowing the
energy consumed during the descent of the load to be reduced.
[0011] Further characteristics and advantages of the present invention will become clear
from the following detailed description of an embodiment of the invention in question,
illustrated by way of non-limiting example in the attached figures wherein:
- Figure 1 shows a first embodiment of the anti-cavitation device;
- Figure 2 shows a second embodiment of the anti-cavitation device;
- Figure 3 shows a third embodiment of the anti-cavitation device.
[0012] The anti-cavitation device according to the present invention is preferably used
in a supply circuit for a hydraulic cylinder intended to cause the lifting and lowering
of a load (LOAD).
[0013] The lifting and lowering of the load (LOAD) are performed through a cylinder (C)
illustrated schematically in the figures. The cylinder (C) normally has two chambers
(C1, C2) separated by a piston to which the rod is associated which, in various ways,
is connected to the load to be lifted. A first chamber (C1), typically the chamber
that is located on the bottom side of the cylinder, is intended to receive pressurised
oil to cause the lifting of the load. A second chamber (C2), arranged on the rod side
of the cylinder (C) and, therefore, of an annular shape, is predisposed to receive
pressurised oil and cause the lowering of the load.
[0014] A distributor (D), usually with four ways and three positions, is predisposed to
cause the supply of pressurised oil to the first chamber (C1) or the second chamber
(C2) and, simultaneously, to put the chamber that is not supplied by the pressurised
oil in communication with a drain. In the embodiment schematically illustrated, the
distributor (D) is equipped with a drawer that can assume a first position, wherein
the first chamber (C1) is placed in communication with a source of pressurised fluid
and the second chamber (C2) is placed in communication with a drain. Such first position
is illustrated on the left side of the distributor (D). The drawer can also assume
a second position, illustrated on the right side of the distributor (D); wherein opposite
connections to those in the first position are performed. The drawer may also assume
a central position wherein the first and the second chamber (C1, C2) are not in communication
with the fluid source (P).
[0015] The anti-cavitation device according to the present invention comprises a first conduit
(2), predisposed to connect the first chamber (C1) of the cylinder (C) with a distributor
(D). A second conduit (3) is predisposed to connect the second chamber (C2) of the
cylinder (C) with the distributor (D).
[0016] A control valve (4), arranged along the first conduit (2), is predisposed to allow
the free flow of fluid from the distributor (D) towards the first chamber (C1) and
to allow the free flow of fluid from the first chamber (C1) towards the distributor
(D) only if it is supplied with a pilot pressure over a minimum value. The control
valve (4), known to a person skilled in the field, substantially has the function
of preventing the drainage of the working fluid from the first chamber (C1), unless
a precise command is given by an operator. This is necessary to prevent uncontrolled
descents of the load, also in the event of failures or fluid leaks. The control valve
(4) essentially comprises a shutter that is pushed towards a closed position, wherein
it prevents the drainage of the fluid from the first chamber (C1), by means of a spring.
The shutter can be moved from the closed position towards an open position exerting
an opposite and greater thrust on the shutter itself than the thrust exerted by the
spring. This opening thrust is exerted by means of the working fluid which, following
a command, can be supplied to the shutter with a sufficient pressure to overcome the
thrust exerted by the spring.
[0017] The anti-cavitation device according to the present invention further comprises a
third conduit (5), which connects the second conduit (3) with a first tract (21) of
the first conduit (2) arranged between the control valve (4) and the distributor (D).
A shut-off valve (6) is arranged along the third conduit (5). Such shut-off valve
(6) is mobile, following a command, between an open configuration, wherein it allows
the flow along the third conduit (5), and a closed configuration, wherein it prevents
the flow along the third conduit (5).
[0018] The activation valve (6) comprises a shutter that is mobile between a closed position,
wherein it totally obstructs the third conduit (5), and an open position, wherein
it frees the third conduit (5) to the flow of oil. The shutter is pushed towards the
closed position by means of a spring, so that, in the absence of a command, the shut-off
valve (6) remains in the closed configuration.
[0019] To move the shutter from the closed position towards the open position it is necessary
to exert on the shutter itself a greater and opposing force to the force exerted by
the spring. This opening force may be exerted, for example, through a pilot pressure
or through an electromechanical actuator.
[0020] In any case, the activation valve (6) is configured to receive an opening command
whenever a load descent command is sent, and only in the presence of a descent command.
In other words, the activation valve (6) is configured to receive an opening command
only if the control valve (4) is supplied with the pilot pressure to allow the descent
of the load.
[0021] In a first embodiment the shut-off valve (6) is a hydraulic pilot valve. As shown
in Figures 1 and 2, the command of the shut-off valve (6) takes place by means of
a pilot pressure that can be sent to the shut-off valve (6) itself through a pilot
conduit (P1). Such pilot conduit (P1) is predisposed to be connected to a pilot circuit
(P) in turn connected to the control valve (4).
[0022] In particular, the supply of oil for opening the shutter of the control valve (4)
takes place by means of a pilot circuit (P) which, in turn, is only supplied in the
presence of a load descent command. By way of example, Figure 1 shows a pilot circuit
(P) with a hydraulic manipulator (M) predisposed to command the distributor (D) and
the control valve (4). The pilot conduit (P1) of the shut-off valve (6) is connected
to the branch of the pilot circuit (P) that supplies the oil to the control valve
(4) and to the descent side (L) of the distributor (D). In this way, whenever the
operator, by acting on a command, decides to lower the load, the pilot pressure is
supplied simultaneously to the distributor (D), to bring it into the descent position,
to the control valve (4), to bring it into the open position, and to the shut-off
valve (6), which puts the first conduit (2) in communication with the second conduit
(3). In Figure 2, the pilot circuit (P) for the distributor (D) differs from the example
of Figure 1 in that the command is electromechanical and comprises two solenoid valves
(E1, E2) respectively predisposed to cause the sending of the pilot pressure to the
ascent side (H) or the descent side (L) of the distributor. Also in this case the
pilot conduit (P1) of the shut-off valve (6) is connected to the branch of the pilot
circuit (P) which supplies the oil to the control valve (4) and to the descent side
(L) of the distributor (D), hence the activation of the shut-off valve (6) in the
open configuration takes place simultaneously to the load descent command.
[0023] In both solutions of Figures 1 and 2, a one-way valve (7) can be arranged along the
third conduit (5). Such one-way valve (7) is predisposed to allow only the direct
flow from the first conduit (2) towards the second conduit (3). The function of the
one-way valve (7) is to ensure a seal with no blow-by from the second conduit (3)
towards the first conduit (2).
[0024] In a second embodiment the shut-off valve (6) is an electromechanical control valve.
In that case, it is not necessary for the shut-off valve (6) to be connected to a
pilot circuit. The shut-off valve (6) is connected to a control panel, not illustrated,
which provides to bring it into the open configuration in presence of a load descent
command.
[0025] The operation of the anti-cavitation device according to the present invention takes
place as follows.
[0026] In the presence of a load ascent command, with the distributor shifted into its ascent
position (H), the pressurised oil is sent to the first chamber (C1) of the cylinder
(C). The control valve (4) allows the flow from the distributor (D) to the first chamber
(C1) and the shut-off valve (6) is in the closed configuration, so that all the flow
rate of oil flows into the first chamber (C1).
[0027] In the presence of a descent command, in the solutions of Figures 1 and 2, the pilot
pressure is supplied simultaneously to the distributor (D), to take it into the descent
position, to the control valve (4), to take it into the open position, and to the
shut-off valve (6), which puts the first conduit (2) in communication with the second
conduit (3). The oil can therefore flow from the first chamber (C1) through the control
valve (4) towards a drain. A part of the flow rate of oil that flows from the first
chamber (C1) is supplied to the second chamber (C2) through the third conduit (5)
and the shut-off valve (6) which, as already mentioned, is in the open configuration.
The flow rate of oil which, through the third conduit (5) is conveyed to the second
chamber (C2) depends substantially on the increase in volume of the second chamber
(C2) in the unit of time during the descent of the load. The second chamber (C2) may
not be totally filled by the oil coming from the distributor, since the intention
is to exploit gravity. In fact, the missing oil from the complete filling is sucked
into the second chamber (C2) through the third conduit (5) due to the effect of the
sliding of the piston towards the bottom of the cylinder which causes the increase
in volume of the second chamber (C2). The operation is substantially the same also
in the solution illustrated in Figure 3, except for the fact that the opening command
to the shut-off valve (6) is electromechanical and not directly connected with the
opening command of the control valve (4) through the pilot circuit (P), but, in any
case, it takes place at the same time as the latter.
[0028] The anti-cavitation device according to the present invention provides important
advantages.
[0029] Above all, it allows the annular chamber to be supplied with the necessary flow rate
of oil during the descent of the load, continuously and without significant pressure
peaks. In fact, as already mentioned previously, the necessary flow rate of oil is
conveyed into the second chamber (C2) of the actual cylinder at low pressure, i.e.
at the slight pressurisation present in the drainage conduit (21). Another advantage
of the device according to the present invention is that it does not require the use
of the pilot circuit to guarantee a correct and complete supply of the annular chamber,
allowing the energy consumed during the descent of the load to be reduced.
1. Anti-cavitation device for a hydraulic cylinder, comprising: a first conduit (2),
predisposed to connect a first chamber (C1) of a cylinder (C) with a distributor (D);
a second conduit (3), predisposed to connect a second chamber (C2) of the cylinder
(C) with the distributor (D); a control valve (4), arranged along the first conduit
(2), which is predisposed to allow the flow of fluid from the distributor (D) towards
the first chamber (C1) and to allow the flow of fluid from the first chamber (C1)
towards the distributor (D) only if it is supplied with a pilot pressure over a minimum
value; characterised in that it comprises: a third conduit (5), which connects the second conduit (3) with a tract
of the first conduit (2) between the control valve (4) and the distributor (D); a
shut-off valve (6), arranged along the third conduit (5), which is mobile, following
a command, between an open configuration, wherein it allows the flow along the third
conduit (5), and a closed configuration, wherein it prevents the flow along the third
conduit (5); the activation valve (6) is configured to receive an opening command
only if the control valve (4) is supplied with the pilot pressure.
2. Anti-cavitation device according to claim 1, wherein the command of the shut-off valve
(6) takes place by means of a pilot pressure that can be sent to the shut-off valve
(6) through a pilot conduit (P1) predisposed to be connected to a pilot circuit (P)
in turn connected to the control valve (4).
3. Anti-cavitation device according to claim 2, comprising a one-way valve (7) arranged
along the third conduit (5) and predisposed to allow only the direct flow from the
first conduit (2) towards the second conduit (3).
4. Anti-cavitation device according to claim 1, wherein the shut-off valve (6) is an
electromechanical control valve.