A hydraulic device for controlling a piloting pressure

Abstract: The hydraulic device for controlling a piloting pressure (18) comprises a two-way valve (2) located on a hydraulic piloting conduit (17) which provides a piloting pressure to a controlling overcentre valve (16). The piloting pressure is taken from a delivery branch (15) of a hydraulic actuator (9) during a load lowering phase (12). The two-way valve (2) is normally open and is closed by effect of a predetermined pressure on the delivery branch (15). An adjustable choke (19) is arranged in parallel to the two-way valve (2) on an auxiliary by-pass conduit (20). The device enables a rapid and progressive activation of the hydraulic actuator (9) during the load lowering phase.

Description: Specifically, though not exclusively, the invention is usefully applied in an actuator hydraulic transmission circuit, for controlling the piloting pressure of an overcentre valve in turn predisposed for controlling a flow rate in a backline of the circuit during a discharge phase. The prior art includes a hydraulic circuit activator in a hydraulic actuator, for example a winch arm cylinder, in which a first circuit branch connects the hydraulic distributor with the actuator chamber associated to load lifting and a second branch connects the distributor with the lowering chamber. The circuit has an overcentre valve predisposed for controlling the flow rate in the first branch during the load descent phase; a pilot line takes a piloting pressure from the second branch which is used to open the overcentre valve during the load descent phase. This type of circuit is prone to instability and oscillation in the overcentre valve on activation of the cylinder or on reversing its direction. In particular, when the load is lowered, there can be a frequent succession of stops and starts in the actuator before it finally stabilises, causing the load to oscillate dangerously. To solve the problem an adjustable choke on the pilot conduit has been used, which determines a loss of localised load by effect of which the pilot pressure P PIL which opens the overcentre valve becomes gradual and controlled with respect to the increase in pressure P B in the second branch (i.e. the branch which during the load lowering phase is the delivery branch). In the diagram of figure 1 the curve S represents the progress of piloting pressure P PIL in relation to the pressure P B in the second branch. A drawback in the above-described prior art solution is the delay in cylinder activation after the operator has selected it. This is especially evident when the liquid operating in the hydraulic circuit is very viscous (for example when cold). This delay is due to the fact that the piloting pressure Ppil reaches value Pv, the value at which the overcentre valve opens (which value is predetermined by the valve spring calibration) when cylinder delivery pressure P B has already reached a relatively high P S value (see figure 1). This means that the cylinder actuation during the lowering phase starts when the pressure P B reaches value P S . The time necessary for pressure P B to reach value P S (to which value Pv of the piloting pressure Ppil corresponds) can be relatively high, resulting in the above-mentioned delay. A hydraulic device according to preamble of claim 1 is known from EP-A-499 694. The main aim of the present invention is to provide a device for controlling a hydraulic piloting pressure which can overcome the above-described drawback in the prior art, i.e. reduce the delay in response to the hydraulically-piloted organ. An advantage of the invention is that it provides a device for controlling piloting of a hydraulically piloted organ, affording immediate and progressive activation of the organ itself. The activation is immediate inasmuch as the activation of the hydraulically-piloted organ follows the operator's command with a very rapid response time, reducing the delay to a minimum, and is also progressive inasmuch as it proceeds gradually and controlledly subsequent to activation. A further advantage of the present invention is to make available a control device which is particularly useful in a hydraulic activation circuit of a hydraulic actuator for piloting an overcentre valve, being able considerably to reduce the delay in overcentre valve opening and thus prevent occurrence of instability and oscillation phenomena in the valve itself. These aims and advantages and more besides are all attained by the present invention according to the appended claims. Further characteristics and advantages of the present invention will better emerge from the detailed description that follows of some preferred but non-exclusive embodiments of the invention, illustrated purely by way of a nonlimiting example in the accompanying figures of the drawings, in which: figure 1 is a pilot Ppil pressure diagram following pressure P B in the delivery conduit during the load lowering phase, respectively for a known valve (S curve) and for a valve made according to the invention (T curve); figure 2 shows a section of a first embodiment of a device made according to the invention; figure 3 is a symbolic representation of the device of figure 2; figure 4 is a diagram of a control system of a hydraulic actuator, comprising the device of figures 2 and 3; figure 5 is a diagram of a control system of a hydraulic actuator, comprising a second embodiment of the device of the invention; figure 6 is the device of the invention applied on a liquid-delivery hydraulic control organ. With reference to figures 2 and 3, 1 denotes in its entirety a hydraulic device for controlling a piloting pressure. The device 1 comprises a two-way valve 2 destined to operate on a hydraulic pilot conduit operating on at least one hydraulically piloted organ. The two-way valve 2 has a first line 3 connected to a piloting pressure and a second line 4 connected to the organ which is to be hydraulically piloted. The piloting pressure, supplied by the first line 3 of the two-way valve 2, is supplied to the organ to be piloted through the second line 4. The two-way valve 2 can assume an open position in which it enables communication between the first line 3 and the second line 4, and a closed position in which it prevents passage of the operating liquid in the pilot conduit from the first line 3 to the second line 4. The valve 2 is normally open and is predisposed to close by effect of a predetermined pressure on the first line 3. The two-way valve 2 is provided with an obturator, which is a body of revolution, in the illustrated embodiment a sphere, axially mobile inside an internal conduit of the two-way valve 2; the conduit is passed through by the operative liquid of the hydraulic pilot conduit. A first elastic element 6, which is adjustable, can open the obturator 5 by means of an interpositioning of a piston arm 7. The obturator 5 is located between a first end of the piston arm 7 and a second elastic element 8 i.e. a helix spring, opposing the first elastic element 6 but having a considerably lower load than the first elastic element 6. A second end of the piston arm 7, opposite to the first end, is in communication with the outside environment, normally at a pressure (for example atmospheric pressure) which is lower than the pressure internally of the valve 2. The obturator 5 closes automatically when the directional thrust of the piston arm 7 due to the internal pressure of the valve 2 overcomes the thrust due to the load of first elastic element 6 acting in the opposite direction. Between the obturator 5 and the walls of the conduit housing the obturator there is a relatively narrow annular passage (in the shape of a circular crown). The obturator 5 is drawn by the liquid towards the closed position by effect of the thrust following the fall in pressure the liquid passing through the annular passage undergoes. Consequently, the closure of the obturator 5 is abrupt in a case where there is a relatively high liquid flow rate flowing to the first line. Figure 4 shows a control system for a hydraulic actuator 9 which applies the device 1 of figures 2 and 3. The hydraulic actuator 9 has a first chamber 10 and a second chamber 11 associated respectively to the lifting and lowering of a load. The control system comprises: a hydraulic distributor 13; a hydraulic circuit having a first branch 14 which connects the distributor 13 with the first chamber 10 and a second branch 15 which connects the distributor 13 with the second chamber 11; an overcentre valve 16 for controlling the flow rate into the first branch 14 during the load 12 lowering phase; a piloting conduit 17 which takes from the second branch 15 a piloting pressure which opens the flow-rate control, or overcentre valve 16. The flow-rate control valve is an overcentre valve 16 of known type, having a first connection which is connected to the first chamber 10 and a second connection which is connected to the distributor 13. The overcentre valve has an axially-mobile first obturator which operates between the first and the second connection, which is closed by a spring and opened by a piloting pressure provided through a piloting connection. The overcentre valve comprises a single-acting valve predisposed in parallel with the first obturator to allow flow from the second to the first connection. The first obturator is destined to open by effect of the pressure at the piloting connection. The hydraulic control device 1 of figures 2 and 3 is predisposed on the piloting conduit 17; the first line 3 is connected to the second branch 15, i.e. the delivery branch during the discharge phase, and the second line 4 is connected to the overcentre valve 16 for controlling the flow rate. During operation, on initiating the load lowering phase, that is, when the distributor begins sending the pressurised liquid to the second chamber 11 of the actuator through the second branch 15, the pressure P B in the second branch 15 increases, and so does the pressure in the piloting conduit 17. Since the two-way valve 2 is open, the piloting pressure P PIL acting to open the overcentre valve 16 is the same as pressure P B in the second branch 15. The piloting pressure P PIL at the pilot connection of the overcentre valve 16 reaches the predetermined value at which the overcentre valve 16 opens in a relatively short time. This piloting pressure P PIL is limited by the two-way valve 2 which closes the piloting conduit 17 when the pressure P B in the first line 3 exceeds the calibration value of the first elastic element 6 or spring. Figure 5 illustrates a control system for a hydraulic actuator which comprises all of the elements of the system shown in figure 4 (the same elements have the same numbers). In this embodiment, however, the control device 18 comprises, apart from the two-way valve 2, also a choke 19 (or any other device which causes a considerable loss of localised load in the circuit), which is located in parallel with the two-way valve 2 on an auxiliary by-pass conduit 20. The choke 19 can be fixed or adjustable. The first elastic element 6 of the two-way valve 2 is calibrated so that the two-way valve 2 closes when the pressure in the first line 3 has a value Px which is slightly lower than that of value Pv of the piloting pressure determining the start of the opening of the overcentre valve 16 for controlling the flow rate (see figure 1). During operation, on starting the load lowering phase the two-way valve 2 is open and the overcentre valve 16 closed. The pilot connection of the overcentre valve 16 is directly connected, through the piloting conduit 17, to the second branch 15 of the circuit. The operator working the control system commands an increase in pressure of delivery P B to the second chamber 11. In figure 1 the curve T indicates the piloting pressure provided to the overcentre valve 16 according to the pressure P B in the second branch 15. When the pressure P B reaches a certain predetermined value Px the two-way valve 2 automatically closes. In this situation the piloting connection of the overcentre valve 16 (still closed at this point) communicates with the second branch 15 through the by-pass conduit 20. On increasing the pressure P B the piloting pressure P PIL also continues to increase, but at a lower gradient than when the two-way valve 2 was open (see curve T of figure 1). This gradient depends on the fall in pressure caused by the stabilising choke 19 located in the by-pass conduit 20. The piloting pressure reaches a predetermined value Pv at which the overcentre valve 16 opens when the pressure P B is at a predetermined value P T . By observing the curve S of figure 1, which indicates the progress of the piloting pressure for a control device of known type, constituted by a choke to stabilise the actuator discharge phase, it can be seen that the piloting pressure reaches value Pv, at which the overcentre valve 16 begins to open when the pressure P B in the delivery branch has reached value P S during the discharge phase. By comparing the two curves, T and S, Pr emerges as considerably lower than P S , so that thanks to the device of the invention the overcentre valve 16 controlling the flow rate opens well before the prior art valves. Thus, thanks to the device of the invention, the start-up of the actuator during the load lowering phase follows the operator's input command very quickly. In other words, the actuator response to the initialising of the descent phase of the load follows the operator's command very promptly. It has been seen that the choke 19, which has the task of stabilising the actuator 9 operation during the load lowering phase, carries out this task effectively even if the passage section of the choke itself is relatively large. In particular, the choke 19 of the device of the invention can be decidedly more "open" with respect to a stabilising choke of known type. This is evidenced in figure 1, from the fact that the gradient of curve S, relative to a choke of known type, is less than the gradient of the second tract (in which P PIL is greater than Px) of the curve T, relative to the choke used in the device of the invention. It has been seen that this confers on the operator a more direct and immediate degree of control of the actuator. The actuator response is even more immediate to any and every variation in position of the command distributor 13, with a consequent enormous facilitation in the guiding of the actuator 9. The control device 18 operatively associated with the system illustrated in figure 5 enables the overcentre valve 16 to be automatically closed when the pressure P B in the second branch 15 falls. The control devices 1 and 18 of the systems illustrated in figures 4 and 5 can be separate from the overcentre valve 16 and arranged on the piloting conduit 17, or can also be incorporated in a single body with the overcentre valve 16. Figure 6 shows a hydraulic distributor 21 with a double pilot, in which each pilot is controlled by a control device 18 as in figure 5. Two piloting conduits 22 and 23 are connected to the distributor 21 and each is also connected to a supply of a piloting pressure. A two-way valve operates on each piloting conduit; the two-way valves are normally open and are closed by effect of the piloting pressure coming from the above-mentioned supply. When a two-way valve 2 is closed, the distributor 21 is connected to the corresponding supply through the choke 19 on the by-pass conduit 20. The control device can be used for piloting any hydraulically piloted organ, with the aim of obtaining a very rapid activation of the piloted organ in response to an external command supplied through the supply of piloting pressure. The device prevents delays in the activation of the hydraulically-piloted organ and at the same time prevents instability phenomena in the operation of the piloted organ after activation.

Claims: A hydraulic device for controlling a piloting pressure (1, 18) comprising: a pilot pressure delivery; a two-way valve (2), operating in a hydraulic piloting conduit (17, 22, 23) connected to at least one valve (16, 21) to be hydraulically piloted, which two-way valve (2) is provided with at least a first line (3) which receives the piloting pressure (1, 18) from said pilot pressure delivery and a second line (4) through which the piloting pressure is supplied to the at least one valve (16, 21); the two-way valve (2) being able to assume an open position in which it enables a communication between the first line (3) and the second line (4), and a closed position, in which it prevents flow in the hydraulic piloting conduit (17, 22, 23) from the first line (3) to the second line (4); a choke (19) arranged in parallel with the two-way valve (2) on an auxiliary by-pass conduit (20); characterised in that the two-way valve (2) is normally open at the pilot delivery pressure and is predisposed to stay open until the pressure in the first line (3) exceeds a calibration value of the first elastic element (6) or spring, said pressure exceeding the calibration value of the first elastic element (6) or spring being slightly lower than the value of the piloting pressure which determines the start of the opening of said at least one valve (16, 21), so that the two-way valve (2) remains open along a major portion of the curve (Fig.1) representing pilot pressure increase vs. delivery pressure increase, and closes only at a piloting pressure slightly lower than the opening pressure of said at least one valve (16, 21). The device of claim 1 , characterised in that the choke (19) can be calibrated. The device of any one of the preceding claims, characterised in that the two-way valve (2) comprises at least one obturator (5) thrust into an open position by at least one elastic element (6) through an interpositioning of a piston arm (7), through which piston arm (7) a difference in pressure between an inside of the two-way valve (2) and an external environment acts antagonistically against the elastic element (6). The device of any one of the preceding claims, characterised in that the two-way valve (2) is provided with at least one obturator (5) having a shape of a body of revolution, which at least one obturator (5) is axially mobile inside a conduit crossed by a liquid of the hydraulic piloting conduit (17, 22, 23), the at least one obturator (5) being drawn by the liquid towards the closed position by effect of a thrust due to a fall in pressure in the liquid crossing an annular passage afforded between the obturator (5) and a wall of the hydraulic piloting conduit (17, 22, 23). A control system of a hydraulic actuator (9), in which: the hydraulic actuator (9) has a first chamber (10) and a second chamber (11) respectively associated to a lifting and a lowering of a load (12); the control system comprises at least one distributor (13), at least one hydraulic circuit having a first branch (14) which connects the distributor (13) with the first chamber (10) and a second branch (15) which connects the distributor (13) with the second chamber (11); at least one valve (16) for controlling a flow rate in the first branch (14) during a load lowering phase; at least one hydraulic piloting conduit (17) which takes from the second branch (15) a piloting pressure which is used to open the valve (16) controlling the flow rate; characterised in that it further comprises a hydraulic device (1, 18), predisposed on the hydraulic piloting conduit (17) for controlling the piloting pressure, made according to any one of the preceding claims.

Inventors: STORCI ANDREA, STORCI, ANDREA
Applicants: OIL CONTROL SPA, OIL CONTROL S.P.A.
Application year: 2000
Main classification: F15B11
IPC codes: F15B11, F15B21