EP2325499A1

EP2325499A1 - A pressure balancing valve for two cylinders operated in parallel

Info

Publication number: EP2325499A1
Application number: EP09425475A
Authority: EP
Inventors: Andrea Storci
Original assignee: Bosch Rexroth Oil Control SpA
Current assignee: Bosch Rexroth Oil Control SpA
Priority date: 2009-11-19
Filing date: 2009-11-19
Publication date: 2011-05-25

Abstract

A pressure balancing valve for two cylinders operated in parallel, comprising: a main conduit (21, 22) predisposed to be connected to a first cylinder (31) and to connect to a balancing conduit (40) connected to a second cylinder (32); an obturator (3), interposed between a first tract (21) and a second tract (22) of the main conduit (21, 22), which is mobile between a closed position, in which the first tract and the second tract of the main conduit (21,22) are not in mutual communication and the main conduit (21, 22) is interrupted, and an open position, in which the first tract and the second tract of the main conduit (21, 22) are in mutual communication; thrust means (4), predisposed to push the obturator (3) towards the closed position; piloting means (5, 6), predisposed to push the obturator (3) towards the open position, which comprise a first piloting conduit (5) that places the second tract (22) of the main conduit (21, 22) in communication with a thrust surface of the obturator (3), such that the pressure internally of the tract of the second tract (22) of the main conduit (21, 22) exerts a force which acts on the thrust surface of the obturator (3) in order to push the obturator (3) towards the open position.

Description

There exist various types of work machines and industrial plants which are activated by hydraulic apparatus in which one of the mobile organs (e.g. the arm of an excavator, the lift arm of a crane or a lift truck, etc.) is moved via two hydraulic cylinders which work contemporaneously in parallel, either because the thrust required would actually necessitate a cylinder of excessive proportions, or in order to share the stress forces in two different points, with a consequent advantage in terms of size and construction.
In many cases, security standards require that each of these cylinders be equipped with a device of its own, typically a block and control valve of the load descent, in order to avoid uncontrolled falls in a case of breakage of the oil pipes. It follows that in order to activate the descending or lowering movement of the load, the command system of the machine has to send a signal, for example a piloting pressure, which contemporaneously opens the two block and control devices of the descent in each of the two cylinders.
It often occurs, even when the two cylinders are connected in parallel to one another and are connected to the same structure, that the hydraulic pressure induced in the cylinders is not identical, for example due to asymmetry in the lifted weight, or due to elasticity of the structure, or because the two cylinders are positioned distant from one another, or because the machine is inclined with respect to the horizontal, or for other reasons.
If the pressures in the cylinders are considerably different from each other, the opening of the two block and control devices of the oil flow cannot be perfectly synchronised, which is a generally necessary condition in order to for the operator to have fine and sensitive control of the movement.
To obviate this drawback, generally there is a connecting tube between the two cylinders, which functions as a balancing tube, such that the two pressures are balanced with one another. On the other hand this connecting tube represents, in turn, a source of danger. If there is a breakage, there could be an uncontrolled loss of oil. In order to avoid this problem, each cylinder affords small-diameter choke orifices, in general comprised between 0.8 and 1.0 mm, such as very much to limit any oil leakage in a case of pipe breakage. These chokes, however, enable only static pressure balance, as the limited oil flow which they allow through is not sufficient to guarantee balance under dynamic conditions too.
The aim of the present invention is to provide a device which enables the drawbacks in the balancing circuits of known type to be obviated.
The set aim is attained by a pressure balancing valve for two cylinders activated in parallel according to the present invention.
An advantage of the valve is that is provides excellent response characteristics in both static conditions and dynamic load conditions.
A further advantage of the valve is that in case of a breakage of the connecting conduit between the two cylinders, the loss of oil is limited to very small amounts.
Further characteristics and advantages of the present invention will better emerge from the following description, provided by way of non-limiting example in a preferred but not exclusive embodiment of the pressure balancing valve, made with reference to the accompanying figures of the drawings, in which:

figure 1 is a first version of the valve of the present invention;
figure 2 is a second version of the valve of the present invention;
figure 3 is a third version of the valve of the present invention.

The valve of the present invention is particularly useful internally of a hydraulic control circuit for two cylinders 31, 32 activated in parallel. This circuit comprises a first supply conduit circuit V2-C2 predisposed for supplying an operating fluid to supply port C2 of the base of the two cylinders 31, 32, with the aim of causing extension of the stem of the two cylinders and, consequently, raising of a load. A second conduit circuit V1, C1 is predisposed to supply the operating fluid to the supply port C1 of the annular chamber (the chamber in which the stem is arranged) of the two cylinders, with the aim of determining return of the stems and consequently the descent of the load. Two valves 33, 34 for control of the descent are interposed between the supply port C2 of the base of the two cylinders and the pressurised fluid source, indicated by V2 in the figures. The valves 33, 34, widely available on the market, have the function of preventing the discharge of the operating fluid from the bottom of the respective cylinder in the absence of a load descent command, such as to guarantee that the load stays in a stationary position. In the presence of a load descent command, the valves 33, 34 for load descent control enable a controlled discharge of the fluid from the bases of the two cylinders, such that the descent of the load is initially done at a contained speed. To this end, the load decent control valves 33, 34 are provided with shaped obturators which can take on a closed position, in which they do not enable discharge of the operating fluid from the base of the cylinders, and an open position, in which they enable discharge of the fluid from the bases of the cylinders 31, 32. Elastic means push the two obturators towards the closed position, while the displacement towards the open position is normally determined by means of a piloting pressure exerted by a piloting fluid supplied via a conduit Pil. Alternatively the piloting fluid could be directly sourced from the conduit V1-C1. The description that follows, and the accompanying figures of the drawings, for the sake of simplicity refer to a case in which the two cylinders 31, 32 support a load or, in any case, generate a thrust by sending a pressurised fluid into the bases of the two cylinders. The balancing valve of the present invention could also be used in a case in which the support of the load or the force transmitted are generated through the sending of pressurised fluid into the annular chambers of the two cylinders, i.e. when the two cylinders work in traction rather than in thrust. The balancing valve 1 of the present invention comprises a main conduit 21, 22 predisposed to be connected to a first cylinder and to be connected to a balancing conduit 40 which, in turn, is predisposed to connect to a second cylinder 32. The balancing tube 40 can comprise a flexible tract, or can be entirely flexible.
An obturator 3, preferably of a two-way two-positioned type, is interposed between a first tract 21 and a second tract 22 of the main conduit 21, 22. The obturator 3 is mobile between a closed position, in which the first and the second tract of main conduit 21, 22 are not in mutual communication and the main conduit 21, 22 is closed to fluid passage, and an open position, in which the first and the second tract of the main conduit 21, 22 are in mutual communication. In the open position of the obturator 3, the main conduit 21, 22 is open to fluid passage such that the base of the first cylinder 31 and the balancing conduit are in mutual communication. Thrust means 4, preferably of an elastic type, are predisposed to push the obturator 3 towards the closed position. In a preferred embodiment, the thrust means 4 are constituted by an spring having an adjustable or fixed calibration, located in a low-pressure environment by means of an opening to air or a connection to the operating fluid tank, as illustrated in the figures. Piloting means 5, 6 are predisposed to push the obturator 3 towards the open position, exerting an antagonistic action to that of the thrust means 4 by means of a piloting pressure. In the absence of a piloting pressure, the piloting means 5, 6 exert no thrust, so that the obturator 3 is brought into a closed position by effect of the thrust exerted by the thrust means 4.
The piloting means comprise a first piloting conduit 5 which places the second tract 22 of the main conduit 21, 22 in communication with a thrust surface of the obturator 3, such that the pressure internally of the second tract 22 of the main conduit 21, 22 exerts a force which acts on the thrust surface of the obturator in order to push the obturator 3 towards the open position. In this way, the presence of pressurised fluid internally of the balancing conduit 40, which is in communication with the second tract 22 of the main conduit 21, 22 of the valve, maintains the obturator 3 in an open position. In these conditions the base of the first cylinder 31 is in communication with the balancing conduit 40 and, consequently, it is in communication with the base of the second cylinder 32.
The presence of pressurised fluid internally of the balancing conduit 40 is typical of a condition in which there is a load present which is acting on the two cylinders 31, 32 and creating pressure internally of the bases of the two cylinders .This pressure is transmitted to the obturator 3 which stays in the open position such that the bases of the two cylinders 31, 32 are in communication with one another and the pressures present internally thereof equal out perfectly. The perfect equalling-out between the pressures present internally of the two bases enables a perfectly similar response to be given to the two cylinders 31, 32 to a command to descend.
In a case in which fluid leaks from the balancing conduit 40, for example during a breakage of the conduit 40 itself, the pressure in the balancing conduit 40 drops and with it also the piloting pressure which, via the first piloting conduit 5, acts on the obturator 3. The drop in piloting pressure which acts on the obturator 3 leads to the obturator 3 itself moving into the closed position by effect of the thrust exerted by the thrust means 4. In this way, the fluid in the base of the first cylinder 31 cannot discharge through the balancing conduit 40. In order to prevent the operating fluid from unloading from the base of the second cylinder 32 in these conditions, a second balancing valve 1a is interposed between the second cylinder 32 and the balancing chamber 40 in a same way as for the first balancing valve 1. In a case of operating fluid leakage from the balancing conduit 40, the obturator 3 of the second balancing valve 1a too, entirely similarly to the first balancing valve1, is brought into the closed position by effect of the thrust exerted by the thrust means 4. If, on the contrary, there are no leakages from the balancing conduit and internally thereof there is pressurised fluid, both the obturators 3 are kept in the open position and perfect fluid communication is maintained between the bases of the two cylinders 31, 32.
The piloting means 5, 6 preferably comprise a second piloting conduit 6 which places the first tract 21 of the main conduit in communication with the first piloting conduit 5. The second piloting conduit 6 might be afforded through the valve body, but alternatively might be afforded through the obturator body 3, or it could be constituted by a small passage of fluid between the obturator 3 and the sliding seat of the obturator 3. The presence of the second piloting conduit 6 enables a very rapid opening of the obturator 3 to be obtained, as soon as the operating fluid is supplied to the bases of the two cylinders 31, 32, even in a case in which the pressure internally of the bases and the balancing conduit 40 is initially nil, as happens for example when the load is rested on the ground.
The second piloting conduit 6 is provided with a fixed choke 7 (figures 1 and 2) or a flow rate regulator 7a (figure 3) predisposed to limit the flow of fluid which can transit through the second piloting conduit 6. These two devices enable the oil flow which can discharge through the second piloting conduit 6 in a case of leakage from the balancing conduit 40 to be limited to a very small amount. In particular, the flow rate regulator 7a can be compensated, i.e. able to limit the maximum flow rate of fluid that can discharge from the second piloting conduit 6 independently of the fluid pressure in the base of the cylinder 31, 32.
The first tract 21 of the main conduit 21, 22 can also be provided with a fixed choke 8 (figure 1) or a flow rate regulator 8a (figures 2 and 3), possibly of the compensated type, predisposed to limit the fluid flow rate which can transit through the first tract 21 of the main conduit 21, 22. The choke 8 or flow rate regulator 8a enable excessive movement of oil between the two cylinders to be limited. The choke 8 or the flow regulator 8a of the first tract 21 of the main conduit 21, 22 can be combined equally with the choke 7 or the flow regulator 7a of the second piloting conduit 6. In order to guarantee a quick communication of fluid between the first cylinder 31 and the second cylinder 32, including during a malfunctioning or at sudden pressure peaks, the valve of the present invention can be provided with a by-pass conduit 9 provided with a check valve 10. In the case of the valve applied to the first cylinder 31, the check valve allows the operating fluid to flow only from the second cylinder 32 towards the first cylinder 31. Vice versa, in the case of the valve applied to the second cylinder 32, the check valve 10 allows fluid to flow only from the first cylinder 31 towards the second cylinder 32. In both cases the by-pass conduit is arranged in parallel with the main conduit 21, 22 of the valve. The valve of the present invention provides important advantages. Firstly, it enables a very rapid and precise balancing of the pressure in the bases of the two cylinders. The presence of a balancing conduit which is substantially lacking in chokes enables rapid transmission of fluid between the two cylinders. On the other hand, while offering the possibility of connecting the two cylinders substantially without interposing chokes, the valve can greatly limit any fluid leakage due to a breakage of the balancing conduit. This is due to the presence of the obturator 3, piloted to open by the pressure internally of the balancing conduit which, should there be a drop in pressure due to breakage of the balancing conduit, is rapidly brought into the closed position, blocking the transmission of the fluid towards the balancing conduit. The very small leakage of residual oil is discharged via the first piloting conduit 5 of the obturator, which fluid leakage can be further reduced with the use of the fixed choke 7 or the compensated flow regulator 7a.
The valve is further simple to use and install, as it can be applied directly to the bases of the two cylinders.

Claims

A pressure balancing valve for two cylinders operated in parallel, characterised in that it comprises: a main conduit (21, 22) predisposed to be connected to a first cylinder (31) and to connect to a balancing conduit (40) connected to a second cylinder (32); an obturator (3), interposed between a first tract (21) and a second tract (22) of the main conduit (21, 22), which is mobile between a closed position, in which the first tract and the second tract of the main conduit (21, 22) are not in mutual communication and the main conduit (21, 22) is interrupted, and an open position, in which the first tract and the second tract of the main conduit (21, 22) are in mutual communication; thrust means (4), predisposed to push the obturator (3) towards the closed position; piloting means (5, 6), predisposed to push the obturator (3) towards the open position, which comprise a first piloting conduit (5) that places the second tract (22) of the main conduit (21, 22) in communication with a thrust surface of the obturator (3), such that the pressure internally of the tract of the second tract (22) of the main conduit (21, 22) exerts a force which acts on the thrust surface of the obturator (3) in order to push the obturator (3) towards the open position.
The valve of claim 1, wherein the piloting means (5, 6) comprise a second piloting conduit (6) which places the first tract (21) of the main conduit in communication with the first piloting conduit (5).
The valve of claim 2, wherein the second piloting conduit (6) is afforded in the body of the pressure balancing valve (1).
The valve of claim 2, wherein the second piloting conduit (6) is afforded through the obturator body (3).
The valve of claim 2, wherein the second piloting conduit (6) is constituted by a space arranged between the obturator (3) and a sliding seating of the obturator (3).
The valve of one of claims from 1 to 4, wherein the second piloting conduit (6) is provided with a fixed choke (7).
The valve of one of claims from 1 to 4, wherein the second piloting conduit (6) is provided with a flow regulator (7a) predisposed to limit a fluid flow which can transit through the second piloting conduit (6).
The valve of one of the preceding claims, wherein the first tract (21) of the main conduit (21, 22) is provided with a fixed choke (8).
The valve of one of claims from 1 to 7, wherein the first tract (21) of the main conduit (21, 22) is provided with a flow regulator (8a) predisposed to limit a fluid flow which can transit through the first tract (21) of the main conduit (21, 22).
The valve of one of the preceding claims, comprising a by-pass conduit (9), arranged in parallel to the main conduit (21, 22) provided with a check valve (10).
A balancing device for balancing pressure of two cylinders activated in parallel, characterised in that it comprises: a balancing conduit (40); a first valve (1) and a second valve (1a) according to one of the preceding claims, connected to ends of the balancing conduit (40) by means of the second tract (22) of the main conduit (21, 22).