Technical Field

The present invention relates to a load- sensing control device for priority valves.

Background Art

In a hydraulic circuit in which several user points with different priorities have to be supplied, the use is known of valves, commonly known as "priority valves", which receive oil from a piston pump and which are adapted to supply the various user points according to the relative priorities.

These valves provide a load-sensing line, through which a pressure signal is sent corresponding to the operating pressure of the priority user point. When the circuit is supplied by a pump, the load-sensing signal is also sent to the control device of the pump so as to vary the pressure and flow rate according to requirements.

The priority valves of known type generally have a body inside which is formed a seat communicating with a supply line of a working fluid, which is in turn also connectable to a piston pump, a priority output line, connected to a priority user point, and a further output line connectable to further user points. Inside the seat a spool is accommodated in a sliding manner on which operates, on the one hand, a first chamber communicating with the load- sensing line and inside which elastic means are housed and, on the opposite side, a second chamber communicating with the priority output line.

The elastic means are adapted to push the spool towards the priority position, corresponding to the position in which the priority output line is placed in communication with the supply line and the further output line is closed. When the pressure level in the priority output line allows reaching the force applied by the elastic means, the spool shifts in contrast to the latter and opens the connection with the further output line, so that the pressure along the priority output line remains more or less constant and that the exceeding flow rate is diverted towards the further output line.

In the case of the priority user point requiring additional working fluid, the control device of the priority user point itself sends to the priority valve a corresponding pressure signal by means of the load- sensing line; this signal then goes to operate on the spool adding itself to the action of the elastic means, thus causing a shift thereof towards the priority position.

These valves of known type do have some drawbacks.

In fact, both the shift of the spool and of the control device of the pumping means requires the use of a volume of the working fluid which must then be drained off when the request of the priority user point is no longer there to avoid the pumping means remaining under pressure. This volume of the working fluid increases with the increase in diameter of the valve spool and its management can result in a delay in the operation of the same.

Another drawback of the priority valves of known type consists in the fact that the volume of the working fluid which is drained off when there is no longer any request from the priority user point may result in a signal for the control of the pumping means, due to the considerable difference in volume between the spool of the priority valve and the spool which controls the pumping means themselves.

Due to the large volume of the working fluid moved, the circuits involving the use of the priority valves of known type are unstable due to the presence of pressure peaks.

Description of the Invention

The main aim of the present invention is to provide a load- sensing control device for priority valves which allows reducing, compared to the known control devices, the volume of the working fluid required for the shift of the relative spool.

Within this aim, one object of the present invention is therefore to reduce, with respect to the devices known today, the delay in the actuation.

Another object of the present invention is to avoid that the drain off of the volume of the working fluid required for the shift of the spool involves the undesired drive of the pumping means.

Not the last object of the present invention is to reduce, compared to the devices of known type, the instability and noise of the related hydraulic circuit.

Another object of the present invention is to provide a load-sensing control device for priority valves which allows overcoming the mentioned drawbacks of the prior art within the ambit of a simple, rational, easy, effective to use as well as affordable solution.

The above mentioned objects are achieved by the present load-sensing control device for priority valves according to claim 1.

Brief Description of the Drawings

Other characteristics and advantages of the present invention will become better evident from the description of a preferred, but not exclusive, embodiment of a load-sensing control device for priority valves, illustrated by way of an indicative, but non-limiting, example in the accompanying drawings, in which: Figure 1 is a schematic view of a first type of a control device according to the invention in a first embodiment;

Figure 2 is a schematic view of a first type of a control device according to the invention in a second embodiment;

Figure 3 is a schematic view of a first type of a control device according to the invention in a third embodiment;

Figure 4 is a schematic view of a second type of a control device according to the invention in a first embodiment;

Figure 5 is a schematic view of a second type of a control device according to the invention in a second embodiment;

Figure 6 is a schematic view of a second type of a control device according to the invention in a third embodiment;

Figure 7 is a schematic view of a third type of a control device according to the invention.

Embodiments of the Invention

With particular reference to such figures, reference number 1 globally indicates a load- sensing control device for priority valves.

The device 1 comprises a valve body 2 inside which is formed at least a first seat 3 communicating, by means of relevant lights, with at least a supply line 4 of a working fluid, with at least an output line 5, 6 of the working fluid, and with at least a load-sensing line 7 adapted to send a pressure signal corresponding to the working pressure of at least a priority user point. More in detail, the first seat 3 has at least a supply gap 4a, connectable to the supply line 4, at least an output gap 5a, 6a, connectable to at least an user point, and at least a load-sensing gap 7a, connectable to the load-sensing line 7.

The supply line 4 is connectable to pumping means for pumping the working fluid such as, e.g., a piston pump.

The device 1 then comprises at least a spool 8 accommodated in a sliding manner inside the first seat 3 to control the flow rate of the working fluid towards the output line 5, 6.

On the spool 8 operate at least a first chamber 9 communicating with the load- sensing line 7 and at least a second chamber 10 communicating with the priority user point, where the first chamber 9 operates on a first extremity 8a of the spool 8 and the second chamber 10 operates in contrast with the first chamber 9. Inside the first chamber 9 are accommodated elastic means 11 adapted to push the spool 8 in contrast with the action applied by the second chamber 10.

According to the invention, inside the first seat 3 is also defined a third chamber 14 communicating with the first chamber 9 and operating on a portion of the second extremity 8b of the spool 8 opposite the first extremity 8a and the second chamber 10 operates on the remaining portion of the second extremity 8b.

By the term "extremity" are meant the axial surfaces of the spool turned outwards. The first and the third chamber 9 and 14 are put in connection with each other by means of a channel 15.

Conveniently, the load- sensing gap 7 a can be defined at the first chamber 9 and/or at the third chamber 14.

It follows therefore that the useful surfaces operating on the spool 8 on mutually opposite sides correspond to the surface of the remaining portion on which operates the pressure present in the second chamber 10.

Advantageously, the second chamber 10 operates on a control element 12 accommodated in a sliding manner inside a second seat 13 obtained in one of the body 2 and the spool 8 and adapted to rest against the second extremity 8b of the spool itself opposite the first extremity 8a and against the bottom wall 3a of the first seat 3, respectively. The useful surfaces of the spool 8, i.e. the surfaces that determine the movement of the spool itself, on which operate the pressures present in the first and in the second chamber 9 and 10 correspond to the useful surface of the control element, i.e. to its surface on which operates the pressure present in the second chamber 10.

In a first type of embodiment, shown in the Figures 1 to 3, the control element 12 is accommodated sliding inside a second seat 13 obtained inside the spool 8 and has an extremity arranged facing the second chamber 10 and the opposite extremity which protrudes from the second extremity 8b of the spool 8 and which rests against the bottom wall 3a of the first seat 3. The pressure present in the second chamber 10 which operates on the control element 12 therefore releases against the bottom wall 3a of the first seat 3, while the pressure present in the third chamber 14 and which operates on the surface of the second extremity 8b of the spool 8 arranged around the control element 12 is balanced by the pressure present in the first chamber 9 and which operates on the equivalent surface of the first extremity 8a of the spool itself. It follows, therefore, that the useful surfaces, i.e. as has already been said, those that determine the shift of the spool 8 if they are not balanced the one with the other, are the surface of the first extremity 8a facing the first chamber 9 and the surface facing the second chamber 10 and opposite the control element 12. The spool 8 therefore moves by effect of the different pressure operating on such surfaces.

In a second type of embodiment, shown in the Figures 4 to 6, the control element 12 is accommodated sliding inside a second seat 13 formed in the body 2 and has an extremity facing the second chamber 10 and the opposite extremity which is adapted to rest against the second extremity 8b of the spool 8 by crossing the third chamber 14. The pressure present in the second chamber 10 which operates on the control element 12 therefore releases on the second extremity 8b of the spool 8, while the pressure present in the third chamber 14 and which operates on the surface of the second extremity 8b arranged around the control element 12 is balanced by the pressure present in the first chamber 9 and which operates on the equivalent surface of the first extremity 8a of the spool itself. It follows, therefore, that the useful surfaces, i.e., as has already been said, those that determine the shift of the spool 8 are the surface of the first extremity 8a and the surface of the second extremity 8b corresponding to that of the control element 12. The spool 8 therefore moves by effect of the different pressure operating on such surfaces, that is of the pressure present in the first chamber 9 and operating on the surface of the first extremity 8a corresponding to the area of the control element 12 and to the pressure present in the second chamber 10 operating on the control element itself.

In the preferred embodiments shown in the figures, the control element 12 is the type of a small cylinder having a diameter less than that of the spool 8 and the useful surface of the spool itself on which operate the pressures present in the first and in the second chamber 9 and 10 corresponds to the area of the circumference of such small cylinder.

In the preferred embodiments shown in the Figures 1 and 4, the first seat 3 comprises both a priority output gap 5a, communicating with a priority output line 5 in turn connectable to the priority user point, and an output gap of the exceeding flow rate 6a communicating with an output line of the exceeding flow rate 6 in turn connectable to a secondary user point. In these embodiments, the spool 8 is movable between at least a priority position, in which it closes the output gap of the exceeding flow rate 6a to convey the whole amount of the working fluid coming from the supply line 4 towards the priority output line 5, and at least an unloading position, in which it places the supply gap 4a in communication with the priority output gap 5a and with the output gap of the exceeding flow rate 6a so as to deflect a part of the working fluid towards the secondary user point.

More in detail, the elastic means 11 push the spool 8 towards the priority position, so that the working fluid entering the first seat 3 through the supply line 4 flows within the priority output line 5. When the level of pressure present along the priority output line 5, and therefore also within the second chamber 10 reaches the force applied by the elastic means 11, the spool 8 starts moving towards the unloading position, in contrast to the elastic means themselves. In the embodiment of Figure 1 the pressure present in the second chamber 10 operates directly on the spool 8 since the control element 12 releases its force on the bottom wall 3a, while in the embodiment of Figure 4, the pressure present in the second chamber 10 actuates the control element 12, which in turn pushes the spool 8 towards the unloading position.

In the event of the priority user point requiring a greater fluid flow rate, the load-sensing line 7 therefore conveys the working fluid under pressure (corresponding to the work pressure of the priority user point) inside the first and the third chambers 9 and 14. Such pressure therefore operates on the useful surface of the first chamber 9 in contrast to the force applied by the pressure present in the second chamber 10 on the relevant useful surface. The force applied by the pressure present in the load-sensing line 7 on the useful surface of the first chamber 9 is thus added to the action of the elastic means 11. When the sum of such forces exceeds that applied by the pressure present inside the second chamber 10, the spool 8 shifts again towards the priority position so as to close the connection with the output line of the exceeding flow rate 6 and to convey the working fluid entirely towards the priority output line 5.

The second and third embodiment, represented in the diagrams of Figures 2, 5 and 3, 6 respectively, identify two devices according to the invention, one of which having only the priority output gap 5a and the other only the output gap of the exceeding flow rate 6a, intended to operate in parallel with each other. In the device 1 of Figures 2 and 5, the second chamber 10 is placed in communication with the priority output line 5 and the spool 8 is adapted to progressively close the priority output gap 5a as the pressure increases along the priority output line itself.

In the device 1 made according to the diagrams of Figures 3 and 6 the second chamber 10 is placed in communication with the priority user point by means of the supply line 4 and the spool 8, depending on the pressure present along the load-sensing line 7, i.e. on the pressure required by the priority user point, chokes or closes the flow of the working fluid through the output gap of the exceeding flow rate 6a.

In a third type of embodiment according to the invention, represented in Figure 7, the spool 8 is made in a single body piece and its second extremity 8b has a portion which faces the third chamber 14, and therefore communicating with the first chamber 9, and the remaining portion which faces the second chamber 10. In this embodiment, devoid of the control element 12, the portion on which operates the pressure present in the third chamber 14 is isolated hydraulically with respect to the remaining portion on which operates the pressure present in the second chamber 10.

Preferably, the shifting speed of the spool 8 is controlled by means of one or more orifices 16, arranged along at least one of the load-sensing line 7, the channel 15 and the channel 17 which connects the priority output line 5 to the second chamber 10.

Advantageously, in a further embodiment not shown in the figures, the device 1 comprises a connecting channel between the second chamber 10 and the chambers 9, 14, so as to obtain a so-called "dynamic load sensing"; in other words this connecting channel, along which an orifice is preferably arranged, has the purpose of supplying the load-sensing line 7 with a flow of the working fluid coming from the priority output, where this flow allows making the system more reactive and maintain the temperature of the priority supplied device.

It has in practice been ascertained that the described invention achieves the intended objects and in particular it is underlined that the fact of balancing the forces operating on opposite sides of the spool except for the area of the control element allows significantly reducing, compared to the valves of known type, the surface of the spool sensitive to the pressure difference present between the first and the second chamber and, consequently, the volume of the working fluid required to move the spool itself.

This volume corresponds in fact to the area of the control element on which operates the pressure present in the second chamber multiplied by the travel completed by the spool, because the volume corresponding to the remaining portions of the spool is self-compensated, i.e., passes from the first to the third chamber during the shift of the spool itself.