EP2786959A1

EP2786959A1 - Anti cavitation device for a hydraulic cylinder

Info

Publication number: EP2786959A1
Application number: EP13425049.7A
Authority: EP
Inventors: Andrea Storci
Original assignee: Bosch Rexroth Oil Control SpA
Current assignee: Bosch Rexroth Oil Control SpA
Priority date: 2013-04-05
Filing date: 2013-04-05
Publication date: 2014-10-08
Anticipated expiration: 2033-04-05
Also published as: EP2786959B1

Abstract

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; 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.

Description

The present invention relates to an anti-cavitation device for a hydraulic cylinder.
The invention refers in particular to the field of operating vehicles predisposed for the lifting and lowering of a load.
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.
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.
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.
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.
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.
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.
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.
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.
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.

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).
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.
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).
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).
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.
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).
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.
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.
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.
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).
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.
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).
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.
The operation of the anti-cavitation device according to the present invention takes place as follows.
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).
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.
The anti-cavitation device according to the present invention provides important advantages.
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.

Claims

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.
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).
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).
Anti-cavitation device according to claim 1, wherein the shut-off valve (6) is an electromechanical control valve.