Pressure-compensating directional control valve

A pressure-compensating directional control valve, for actuating hydraulic actuators, comprising at least one modular valve body, with one through receptacle for a slidable shuttle, a driving fluid delivery port connected to a pump, a discharge fluid port, a first output opening and a second output opening, connected to the first and second chamber, of a hydraulic actuator, at least one bridge for selective communication, by way of the shuttle, of the delivery port with the first or second chambers of the actuator, for actuation thereof, a unidirectional hydrostat connected to the bridge to draw selectively a pressure signal of the load of the actuator, the signal for adjusting selectively the delivery pressure of the pump so as to keep substantially constant the pressure drop between the delivery port and the actuator in any load condition.

BACKGROUND OF THE INVENTION

The field of hydraulic systems, particularly with reference to circuits for controlling a plurality of actuators suitable to drive machines of various kinds, generally uses switching valves of the shuttle type provided with a compensating element arranged downstream. This technical solution is disclosed for example in U.S. Pat. No. 5,579,642. This compensating element is designed to keep as constant as possible the pressure drop across the control valve of the hydraulic actuator: this allows to operate the actuator with the chosen behavior. In such a case, the flow-rate delivered to the chambers of the actuator in fact depends exclusively on the passage section, which can be changed by the operator by way of the traditional means.

These switching valves are first of all typically associated with circuits for transmitting the load signal to the compensating elements; such circuits are designed to draw, by means of adapted selection valves, the highest load signal that is present in the various uses. This of course entails a certain constructive complication, which is often too expensive.

As an alternative to this, check valves are used which are directly integrated in the shuttle of the compensating element (as disclosed for example in U.S. Pat. No. 5,305,789), which in any case require the fitting of a so-called compensated “bleed-off” (which in the particular field is also known as “bleed”), which comprises a flow regulator.

A further alternative is constituted by the use of check valves fitted in parallel with respect to the compensating element, which is associated with a bleed-off.

Even these solutions, which in various situations have been optimized, are all characterized by high constructive complexity, which recommends against their use both as regards production costs and as regards installation and subsequent maintenance.

Secondly, moreover, in traditional applications the load signal is typically connected to the discharge by means of a so-called compensated bleed-off, which therefore entails installing additional hydraulic components, which considerably increase the complexity of the system.

Thirdly and finally, the load signal is usually drawn from the so-called bridge of the switching valve, and this fact entails a distinctly bulky design in the upper part of the component: in some applications, this is particularly disadvantageous.

EP-A-0 368 636 and DE 39 12 390 disclose hydraulic control systems with directional control valves having a combination of elements as set forth in the pre-characterizing portion of the appended claim1.

SUMMARY OF THE INVENTION

The aim of the present invention is to obviate the above mentioned drawbacks, by providing a pressure-compensating directional control valve that allows to provide the effective actuation of hydraulic actuators with the desired behavior, i.e., with a preset speed, avoiding all the constructive complications and the high production costs that characterize the technical solutions that have been provided traditionally.

Within this aim, an object of the present invention is to provide a valve that is simple, relatively easy to provide in practice, safe in use, effective in operation, and has a relatively low cost.

This aim and these and other objects, which will become better apparent hereinafter, are achieved by the present pressure-compensating directional control valve, particularly for actuating hydraulic actuators, of the type that comprises at least one modular valve body, which is affected by at least one through receptacle for at least one shuttle which can slide bidirectionally, by at least one driving fluid delivery port connected to a pump, by at least one discharge port for said fluid, by at least one first output opening and by a second output opening, which are connected respectively to the first chamber and to the second chamber of a hydraulic actuator, said shuttle being controlled by remote operation means and being adapted to selectively connect said delivery port to said first output opening and said discharge port to said second output opening and vice versa, in said valve body there being further at least one bridge for the selective communication, by way of said shuttle, of said delivery port with said first chamber or with said second chamber of said actuator, so as to actuate the actuator in one direction or the other, characterized in that it comprises at least one unidirectional hydrostat, which is connected to said bridge by means of a supply duct and is adapted to draw selectively a pressure signal of the load of said actuator, said signal being designed to adjust selectively the delivery pressure of the pump so as to keep substantially constant the pressure drop between said delivery port and said actuator in any load condition.

Advantageously, said modular valve body is associated with at least one actuation head, which comprises at least one main hydrostat adapted to connect selectively, under the action of at least one contrast spring and of said load pressure signal, the delivery duct of said pump to said discharge, so as to adjust said delivery pressure to an appropriate value, which is preset according to the load.

In accordance with the invention, there is provided a pressure-compensating directional control valve, particularly for actuating hydraulic actuators, as defined in the appended claims.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the exemplary embodiment that follows, individual characteristics may actually be interchanged with other different characteristics that exist in other exemplary embodiments.

Moreover, it is noted that anything found to be already known during the patenting process is understood not to be claimed and to be the subject of a disclaimer.

With reference toFIG. 1, the reference numeral1generally designates a pressure-compensating directional control valve according to the invention.

The valve is preferably but not exclusively adapted to provide integrated control and management, via remote operation on the part of the operators, of the fluid-operated actuators installed in machines (for example earth-moving machines and the like), typically a series of hydraulic actuators, which are subjected to often high loads. In greater detail, the valve is designed to ensure that all the actuators of the machine can operate with a load and a speed suitable for the specific applications and in any operating condition in relation to the commands imparted by operators.

As shown inFIG. 1and in greater detail inFIG. 2, the pressure-compensating directional control valve comprises at least one modular valve body, generally designated by the reference numeral2, which is affected by at least one through receptacle3, which is substantially cylindrical and has suitable cross-sections (as clarified hereinafter), and in which at least one shuttle4is fitted so that it can slide bidirectionally. The shuttle4has a first end5, which protrudes from the modular valve body2and is adapted to be associated with remote operation means, which are controlled by the operator and are not shown in the figure (for example a lever, an electric valve, and others), which provide the translational motion of the shuttle4along its own axis in the two directions; the shuttle4further has a second end6, which protrudes from the modular valve body2and is affected by a threaded end hole7, in which a screw8for fixing a cup9and a complementary cup10, provided with respective rims9a,10a, is engaged. The rim9aof the cup9abuts directly against the outer surface of the valve body2, while the rim10aof the complementary cup10actuates a contrast spring11, which is interposed between the cup9and the complementary cup10, keeps the shuttle4in a preset position and contrasts its translational motion to the right with reference toFIGS. 1 and 2. The second end6of the shuttle4is covered by a protective cap12, which is fixed to the valve body2by means of screws13.

The modular valve body2is further affected by at least one delivery port14for actuation fluid (typically oil), which is connected to a hydraulic pump, which is not shown in the figures but is of a substantially traditional type, and by at least one discharge port15for said fluid, which is connected to the oil tank, not shown in the figures; the valve body2is also affected by at least one first output opening16and by at least one second output opening17, which are connected respectively to the first chamber and to the second chamber of a hydraulic actuator of the double-acting type, also not shown in the figures but of a traditional type. The first output opening16and the second output opening17are associated with respective safety valves18,19, of a substantially traditional type, which connects the openings16,17to the oil discharge if intolerable pressure peaks occur.

The shuttle4, which as mentioned is controlled by remote operation means operated by the operator, is adapted to connect selectively, by means of its bidirectional translational motion, by way of an impulse transmitted by the operator, the delivery port14to the first output opening16and the discharge port15to the second output opening17and vice versa: this is achieved, in a substantially traditional manner, by virtue of suitable passages obtained by virtue of expansions20,20a,20b,20c,20d,20eof the diameter of the receptacle3in preset positions and by virtue of corresponding grooves21,21a,21b,21c,21dprovided along the outer surface of the shuttle4. Along the shuttle4, and in portions having a larger diameter, there are also central flow-rate control recesses21eand lateral flow-rate control recesses21f.

The modular valve body is also affected, in a substantially traditional manner, by at least one bridge22for selective communication, provided by the appropriate translational motion of the shuttle4, alternately of the delivery port14with the first output opening16or with the second output opening17, i.e., with one or the other of the chambers of the actuator according to the specific operating situation.

According to the invention, the valve body2comprises advantageously at least one unidirectional hydrostat, generally designated by the reference numeral23, which is connected to the bridge22by virtue of a suitable supply duct24, which is adapted to selectively draw a load pressure signal (so-called “load sensing”) LS, to which the hydraulic actuator is subjected: said load pressure signal LS is conveniently intended to adjust selectively the delivery pressure of the pump, so as to keep substantially constant pressure drop between the delivery port14and the hydraulic actuator in any load condition. This allows to provide a flow-rate delivery that no longer depends on the pressure drop between upstream and downstream of the valve and on the passage section but depends exclusively on the latter: this, as it is known, allows to ensure the optimum operation of each actuator even in critical situations, such as for example situations with very high loads applied to the actuator itself, which require a high delivery pressure.

The unidirectional hydrostat23is engaged in a respective cylindrical seat25, which is provided in the modular valve body2and is substantially parallel to the receptacle3of the shuttle4. The unidirectional hydrostat23comprises a cylindrical slider26, which is associated with a respective contrast spring27, which is adapted to connect selectively the delivery port14to the bridge22across a secondary branch28connected to the expansion20cof the receptacle3; the contrast spring27of the cylindrical slider26is accommodated in a plug29, which is screwed in a respective recess30provided in the modular valve body2.

The unidirectional hydrostat23further comprises a spherical flow control element31, which is engaged in the opening of a bush32, which is threaded externally and is screwed into a recess32aformed in the cylindrical slider26; a contrast spring33of the spherical flow control element31is accommodated within the bush32. A channel34is formed in the cylindrical slider26and connects the outer surface of the slider26to the flow control element31and consequently connects the supply duct of the bridge24to an outlet hole35of said valve body by means of an expansion36of the diameter of the cylindrical seat25: the outlet hole35therefore allows to transfer the load pressures signal LS externally.

As mentioned earlier, practical applications generally use a plurality of modular valve bodies2fitted side by side and adapted to control the motion of respective hydraulic actuators, fitted for example on the same machine: this situation is shown inFIG. 3, with the corresponding circuit diagrams provided with the traditional symbols adopted universally in hydraulics.

As shown byFIGS. 2 and 3, the modular valve body is, according to the invention, conveniently associated with at least one actuation head, generally designated by the reference numeral37, which comprises at least one main hydrostat, designated by the reference numeral38, which is adapted to connect selectively, under the action of at least one respective contrast spring39and of the load pressure signal LS, the delivery duct P of the pump to the discharge S, so as to adjust said delivery pressure to a suitable value which is preset in relation to the load.

The actuation head37comprises advantageously at least one slide valve40, which is adapted to selectively connect the load pressure signal LS to the discharge S. Advantageously, the opening of the slide valve40is controlled by means of a line, designated by the reference numeral41inFIG. 3, which passes through each modular valve body2and is connected to the discharge S, so as to provide a controlled decompression of said load pressure signal: this allows to give optimum stability to the operation of the system in any load condition of all the actuators.

As can be seen inFIG. 1a, in greater detail each modular valve body2is affected by a pair of holes41a,41b(also shown inFIG. 1in broken lines), which allow to connect, by virtue of respecting expansions41c,41dof the diameter of the receptacle3and a groove41eof the shuttle4, the discharge S to the slide valve40of the actuation head37, so as to drive the decompression of the signal LS.

The actuation head37comprises a substantially parallelepipedal body affected by a delivery orifice42, which is connected to the delivery duct P, and a withdrawal orifice43, which is connected by means of a withdrawal duct44to each hole35of each modular valve body2, so as to transmit the signal LS of all the actuators to the actuation head37.

The actuation head37forms a first cylindrical chamber45, which accommodates the main hydrostat38; the first cylindrical chamber45is connected to the withdrawal orifice43by means of a first branch46. A closure plug47is fitted in the first cylindrical chamber45and has an abutment surface48for the helical contrast spring39of the main hydrostat38.

The actuation head37further forms a second cylindrical chamber49, which accommodates the slide valve40. The second cylindrical chamber49is connected to the withdrawal orifice43by means of a second branch50; it is further connected to the delivery orifice42by means of a third branch50a, in which a check valve with a choke51is inserted.

The second cylindrical chamber49is further connected to an opening52for the discharge of the signal LS by means of a fourth branch53and to a driving opening54by means of a fifth branch55; the driving opening54is connected to the line41, as also shown inFIG. 3.

The slide valve40is associated with a respective contrast spring56, which abuts against a hermetic closure element57, and is affected by a through channel58, which is connected to the discharge opening52.

Finally, the actuation head57comprises at least one maximum pressure valve58, which allows to connect the pump to the discharge in functional situations in which the pressure is too high.

The operation of the valve according to the invention is summarized hereinafter.

The pump delivers pressurized oil through the delivery duct P, and said oil must flow into one chamber or the other of each actuator depending on the commands imparted by the operator, which are transmitted by means of the translational motions of the shuttles4. The shuttle4, during its full stroke, provides a series of connections, which allow the oil, which at present is at low pressure in the secondary branch28, to flow at a pressure defined by the load in the output openings16,17. In the first step of the stroke of the shuttle4, the groove41ecloses the discharge circuit of the slide valve40; a further movement of the shuttle4allows the load signal LS, drawn through the bridge22and sent to the main hydrostat38across the spherical flow control element31of the unidirectional hydrostat23, to activate the system at the pressure of the load. At this point, with a further movement of the shuttle4, the pressurized oil contained at the delivery port14flows, through the central flow-rate control recesses21e, into the secondary branch28, thus opening, when the load pressure is reached, the unidirectional hydrostat23and from there, across the bridge22, to the output openings16,17, through the lateral flow-rate control recesses21fthat have opened last in the sequence of functions.

Advantageously, the load signal LS is selectively connected to the discharge by the slide valve40, so as to ensure operating stability of the set of actuators provided in the machine.

The valve according to the invention is particularly advantageous in particular situations in which one of the actuators of the machine is subjected to a very high load: the compensation of each of the modular valve bodies in fact ensures that all the actuators of the machine are actuated independently of each other at the chosen speed.

As described, an important and considerable advantage achieved by the present invention is the presence of the slide valve40for managing the load signal LS, generated by the movement of the shuttle4across the line41.

Further, the withdrawal of said load signal LS, and particularly the highest one among all the actuators that are present, occurs by opening the flow control element31provided in the unidirectional hydrostat23and not, as in traditional systems, by moving all the selection valves of all the sections: this last method in fact entails an inevitable delay in the transmission of the load signal LS, and consequently entails excessive slowness in starting the actuators and therefore in performing the corresponding mechanical functions.

All the details may further be replaced with other technically equivalent ones.

In practice, the materials used, as well as the shapes and the dimensions, may be any according to requirements without thereby abandoning the scope of the protection of the appended claims.

The disclosures in European Patent Application No. 06425362.8 from which this application claims priority are incorporated herein by reference.