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FIELD OF THE INVENTION

The present invention concerns a hydraulic circuit able to command in a coordinated manner two pairs of actuators of a pumping unit used in an apparatus to distribute concrete. To be more exact, a first pair of actuators is able to alternately pump a determinate quantity of concrete, while a second pair of actuators is able to alternately position, and in a manner coordinated with the pumping, the terminal part of a pipe for delivering the concrete in correspondence with one or the other of the actuators of the fist pair, which is pumping the concrete.

BACKGROUND OF THE INVENTION Hydraulic circuits associated with units for pumping concrete are known, used to pump concrete and installed on heavy work vehicles employed in the building sector, both to command two pairs of actuators able to pump the concrete alternately, and also to move a delivery pipe in a coordinated manner.

Said heavy work vehicles normally comprise a lorry or truck, on which one or more building devices are installed, such as for example pumpmixers, concrete pumps or others.

Generally, known circuits comprise a hydraulic pump that, by means of a pipe, feeds oil to the actuators, a plurality of electro valves, and other electric and electronic components which divert the flow of oil, so as to drive in coordination the actuators for pumping, and alternately move the delivery pipe in correspondence with the actuator that is actually pumping the concrete.

To be more exact, two types of hydraulic circuits of this type are known: a so-called "open" type and a so-called "closed" type.

The known open hydraulic circuit is normally provided with a hydraulic pump which takes in the oil from a tank, sends it to the actuators which effect the pumping and movement, and finally send the oil back to the tank again., In order to guarantee coordination between the actuators for pumping the concrete and those for moving the pipe, this first type of circuit provides various electric end- of-travel consent devices, or electro valves, located in proximity with the actuators themselves. Moreover, these electro-hydraulic devices can be necessary to pass from the concrete-pumping function to the function recall to the hopper .

On the contrary, two main types of closed circuit are known: a. provided with a hydraulic pump with a single or double action that causes the continuous circulation of the oil in the actuators. To guarantee coordination between the alternation of pumping and moving the delivery pipe, both in the pumping step and in the suction step, electro valves and or electrical end-of-travel devices are provided, which divert the circulation of the oil in synchronized manner in the various actuators; b. provided with two pumps, a first hydraulic pump that commands the actuator cylinders which thrust the concrete, and a second hydraulic pump that commands, in a separate hydraulic circuit, the actuators that alternately move the pipe that distributes the concrete.

In order to synchronize the alternate flow of oil between the two hydraulic pumps, electric end-of-travel, electro-hydraulic and electronic devices are installed.

Considering that the material to be pumped is concrete, the pumping actuators and the other components of the

pumping unit are frequently subjected to washing, so as to prevent incrustations .

The need for these frequent washings, the vibrations generated and the significant working temperatures of the oil, however, do not make the electric plant reliable, consisting as it does of the various end-of-travel devices that coordinate the various components. Moreover, if malfunctions or breakages of the electric plant occur, it is difficult, or substantially impossible, to coordinate the functioning of the pumping unit manually, since the synchrony of movement of the various actuators is prejudiced.

One purpose of the present invention is to achieve a simple and functional hydraulic circuit which allows to coordinate the movement of the pumping actuators and the delivery pipe without providing electric or electronic components .

The Applicant has devised, tested and embodied the present invention to overcome the shortcomings of the state of the art and to obtain these and other purposes and advantages .

SUMMARY OF THE INVENTION

The present invention is set forth and characterized in the main claim, while the dependent claims describe other characteristics of the invention or variants to the main inventive idea.

In accordance with the above purpose, a hydraulic circuit for a pumping unit for concrete according to the present invention is able to command in coordinated manner a plurality of actuators of the pumping unit.

To give an example, the actuators can be divided into two pairs, wherein a first pair is able to alternately pump the concrete towards a delivery pipe, while the second pair is

able to displace the delivery pipe in correspondence with the actuator of the first pair that effects the pumping, so as to have a substantially continuous flow of concrete inside the delivery pipe. According to the present invention, the hydraulic circuit comprises pumping means of the oil-dynamic type connected to the actuators, distribution means able to alternately drive the actuators, and command means able to command the distribution means, so as to coordinate the alternate actuation of the actuators.

According to a characteristic of the present invention, the command means are of the oil-dynamic type and use the same fluid circulating in the pumping means both for the pumping functions and also for the suction functions. In this way, since the hydraulic circuit according to the invention is able to coordinate autonomously the alternate actuation of the actuators, and since it uses totally hydraulic components fed in common by the pumping means, it is therefore not necessary to have auxiliary electronic elements, such as end-of-travel elements or suchlike, in order to coordinate the alternate movement of the actuators .

With the present invention, therefore, the shortcomings of the state of the art are obviated, and it is thus possible to subject the various components to washing, even frequently, without causing malfunctions or breakages that compromise the reliability and synchronism of movement of the actuators .

Moreover, since the circuit is commanded oil-dynamically, the coordination of drive of the actuators can also be done manually, for example using a pump with a variable flow rate, selectively invertible by means of a manual command lever.

According to a preferential form of embodiment of the present invention, it is provided that the distribution means comprises a first distributor member that alternately drives a first and a second of the actuators, and a second distributor member that alternately drives a third and a fourth of the actuators.

In this case, the command means comprises at least a command pipe that connects the first actuator and the second actuator to the second distributor member, and the third and fourth actuator to the first distributor member.

In this way, the alternate movement of the first and second actuator determines the coordinated command of the fourth actuator and the third actuator, so as to keep the four actuators always in the correct alternation of movement.

To be more exact, the command means also comprises, connected to the command circuit, two command valves, also of the oil-dynamic type, associated respectively with the front part and rear part of the first actuator. In this way, the command to the second distributor member to move the third and fourth actuator only takes place when inside the front or rear zone of the first cylinder a determinate pressure of the circulating fluid is reached.

In any case, the hydraulic circuit according to the present invention, while being precise and reliable, consists of a limited number of components, and thus has reduced production and maintenance costs compared with solutions known in the state of the art.

BRIEF DESCRIPTION OF THE DRAWINGS These and other characteristics of the present invention will become apparent from the following description of a preferential form of embodiment, given as a non-restrictive example with reference to the attached drawings wherein:

- fig. 1 is a lateral view of a heavy work vehicle on which the hydraulic circuit according to the present invention is installed;

- fig. 2 is a functioning diagram of the hydraulic circuit according to the present invention in a first operating step;

- fig. 3 is a functioning diagram of the hydraulic circuit in fig. 2 in a second operating step;

- fig. 4 is a functioning diagram of the hydraulic circuit in fig. 2 in a third operating step;

- fig. 5 is a functioning diagram of the hydraulic circuit in fig. 2 in a fourth operating step. DETAILED DESCRIPTION OF A PREFERENTIAL FORM OF EMBODIMENT

The attached drawings show a hydraulic circuit 10 according to the present invention, able to command a pumping unit 11 installed in a heavy work vehicle 12, in this case provided with a distribution arm, otherwise known as placing boom, 17 associated with a delivery pipe 19, for casting concrete during the construction of buildings. The heavy vehicle 11 also comprises a truck 13 mobile on wheels 14 and provided with a cabin 15, a supporting frame 16 on which the pumping unit 11 is mounted.

To be more exact, the pumping unit 11 comprises a tank 18 to collect the concrete, a first actuator 20 and a second actuator 21 which alternately pump the concrete present in the tank inside the delivery pipe 19, and a third actuator

22 and a fourth actuator 23, which put a terminal part 19a of the delivery pipe 19 in cooperation, alternately, with the first actuator 20 or the second actuator 21, so that inside the delivery pipe 19 the concrete is pumped substantially continuously.

As shown in fig. 2, the first actuator 20 and the second actuator 21 are of the linear type, and the respective

pistons 20a and 21a are antagonist: that is, when one is in thrust or pumping mode, the other is in suction mode. This antagonist condition is maintained by means of a hydraulic connection 24 which connects the two actuators 20 and 21 at the rear. The respective pistons 22a and 23a, of the third actuator 22 and the fourth actuator 23, are antagonist with respect to each other, but in this case this condition is maintained by the respective rods 22b and 23b, attached on opposite sides of the terminal part 19a of the delivery pipe 19.

The hydraulic circuit 10 according to the invention comprises, connected to the pumping unit 11, an oil-dynamic pump 25, two hydraulic distributors 26 and respectively 27, and two logic valves 29 and respectively 30, also of an oil-dynamic type.

The hydraulic circuit 10 also comprises a drive pipe 33, a command pipe 35, two power factor correction valves 31 and respectively 32, and two non-return valves 36 and respectively 37. To be more exact, the drive pipe 33 consists of two segments 33a and 33b, in each which the oil can flow in both directions, according to the direction of delivery of the oil-dynamic pump 25. The segments 33a and 33b are connected to the four actuators 20, 21, 22 and 23, and to the two hydraulic distributors 26 and 27, while the command pipe 35 consists of a first hydraulic pilot circuit 35a which connects the logic valves 29 and 30 to respective command valves 45, 46 of the hydraulic distributor 27, and a second hydraulic pilot circuit 35b, independent of the hydraulic pilot circuit 35a, which connects the third actuator 22 and the fourth actuator 23 to respective command valves 42, 43 of the hydraulic distributor 26.

The connections between the drive pipe 33 and the relative components of the circuit 10, and between the command pipe 35 and the relative components of the circuit 10, are such as to allow the oil pumped by the oil-dynamic pump 25 to flow both in the drive pipe 33 and also in the command pipe 35.

The oil-dynamic pump 25 is of the type with a closed circuit with variable flow rate, is commanded by a relative service pump 39 and is regulated at a pressure of about 20 bar. Two respective maximum pressure valves 40 and respectively 41 are also associated with the oil-dynamic pump 25, which allow to regulate the maximum pressure of the oil circulating in the drive pipe 33.

Each of the two hydraulic distributors 26 and 27 is connected, as we said, to the drive pipe 33 and is hydraulically commanded by the command pipe 35. Moreover, each hydraulic distributor 26, 27 can selectively assume two distinct connection positions, that is, a first position in which it keeps the segment 33a separate from the segment 33b, imposing a determinate direction of drive on the actuators 20, 21, 22 and 23, and a second position in which it allows the oil to pass from the segment 33a to the segment 33b, in order to invert the direction of drive of the actuators 20, 21, 22 and 23. To be more exact, the hydraulic distributor 26 commands the first actuator 20 and the second actuator 21, while the hydraulic distributor 27 commands the third actuator 22 and the fourth actuator 23.

The logic valve 29 is connected, on one side, to the front part of the first actuator 20 and, on the other side to the command valve 45 of the hydraulic distributor 27, so that, when the first actuator 20 is in the thrust step, and the pressure of the oil in its front part reaches a determinate value, that is, when it is substantially at the

end of its travel, the logic valve 29 opens, determining the passage of the distributor 27 from its first position to its second position.

The logic valve 30 is connected, on one side, to the rear part of the first actuator 20 and on the other side to the command valve 46 of the hydraulic distributor 27 so that, when the first actuator 20 is in the suction phase, and the pressure of the oil in the rear part reaches a determinate value, that is, when it is substantially at the end of its travel, the logic valve 30 opens, determining the passage of the distributor 27 from its second position to its first position.

The two power factor correction valves 31 and 32 are connected to the front part and respectively to the rear part of the second actuator 21, and automatically maintain the correct quantity of oil in the first actuator 20 and the second actuator 21.

The non-return valve 36 is connected to the oil-dynamic outlet of the third actuator 22 and commands the piloting of the oil to the command valve 42 of the hydraulic distributor 26, so that when the third actuator 22 is in the thrust step, we have the passage of the distributor 26 from its second position to its first position.

The non-return valve 37 is connected to the oil-dynamic outlet of the fourth actuator 23 and commands the piloting of the oil to the command valve 43 of the hydraulic distributor 26, so that when the fourth actuator 23 is in the thrust step, we have the passage of the distributor 26 from its first position to its second position. The hydraulic circuit 10 also comprises other hydraulic components, such as for example filters for the oil, manometers, suction pipes, tanks to contain oil and others,

of a substantially known type and not described in detail here.

The hydraulic circuit 10 as described heretofore functions as follows . For a better understanding, in figs. 2 to 5, the pipes of the hydraulic circuit 10 in which the oil is under pressure have been drawn with a thicker line compared with the pipes where the oil is in the phase of returning towards the oil- dynamic pump 25. In an initial condition, shown schematically in fig. 2, the hydraulic distributor 26 is in the first position, while the hydraulic distributor 27 is in the second position.

The oil is pumped by the oil-dynamic pump 25 into the segment 33a and, due to the effect of the positioning of the two hydraulic distributors 26 and 27, the first actuator 20 and the fourth actuator 23 are simultaneously fed. This feed entails a suction step by the first actuator 20, with a consequent thrust step by the second actuator 21, and a thrust step by the fourth actuator 23, with a consequent return of the third actuator 22.

These operating conditions thus entail the pumping of the concrete by the second actuator 21 and the displacement towards the right, that is, towards the second actuator 21, of the terminal part 19a of the delivery pipe 19.

In this first operating condition, the oil exiting from the fourth actuator 23, by means of the command valve 43, keeps the hydraulic distributor 26 in its first position. When the oil pumped inside the first cylinder 20 reaches a determinate pressure, the logic valve 30 opens (fig. 3), so as to command, by means of the command valve 46, the displacement of the hydraulic distributor 26 from its second position to its first position.

As a result of this displacement, the oil is fed to the third actuator 22 instead of the fourth actuator 23, with a consequent passage of the third actuator 22 from the return step to the thrust step. In the operating condition shown in fig. 4, the oil exiting from the third actuator 22, by means of the command valve 42, commands the hydraulic distributor 26 to pass from its second position to its first position, thus entailing the feed of the second actuator 21. In this operating condition, the terminal part 19a of the delivery pipe 19 is taken by the third actuator 22 towards the left, that is, to the side of the first actuator 20.

At the same time, the first actuator 20 passes from the suction step to the thrust or pumping step and, vice versa, the second actuator 21 passes from the thrust or pumping step to the suction step.

Therefore, we have the first actuator 20 which pumps the concrete into the delivery pipe 19, while the second actuator 21 takes, from the tank 18, the concrete to be pumped in a subsequent step.

As shown in fig. 5, when the oil in the first actuator 20 has reached, in the front part, a determinate pressure, the logic valve 29 opens so as to command, by means of the command valve 45, the displacement of the hydraulic distributor 27 from its first position to its second position, entailing the feed of the fourth actuator 23 instead of the third actuator 22.

The oil exiting from the fourth actuator 23, by means of the command valve 43, commands the displacement of the hydraulic distributor 26 from its second position to its first position, thus also inverting the oil-dynamic feed of the first actuator 20 and the second actuator 21.

In this way, the operating conditions shown in fig. 2 are re-established, thus starting a new cycle of concrete pumping.

It is clear that modifications and/or additions of parts may be made to the hydraulic circuit 10 as described heretofore, without departing from the field and scope of the present invention.

For example, it comes within the field of the present invention to provide that the third actuator 22, or the fourth actuator 23, can be absent, providing a single actuator which moves the terminal part 19a of the delivery pipe 19.

It also comes within the field of the present invention to provide that the logic valve 30 can be connected to the front part of the second actuator 21 instead of to the rear part of the first actuator 20.

It is also clear that, although the present invention has been described with reference to specific examples, a person of skill in the art shall certainly be able to achieve many other equivalent forms of hydraulic circuit for pumping concrete, having the characteristics as set forth in the claims and hence all coming within the field of protection defined thereby.