Login| Sign Up| Help| Contact|

Patent Searching and Data


Title:
A DIRECTIONAL CONTROL VALVE GROUP INSTALLABLE ON A TRUCK FOR COMMANDING A DOUBLE-ACTING HYDRAULIC USER, AND A HYDRAULIC PLANT COMPRISING THE DIRECTIONAL CONTROL VALVE GROUP.
Document Type and Number:
WIPO Patent Application WO/2016/116840
Kind Code:
A1
Abstract:
The invention relates to a directional control valve group (27), installable on a truck for commanding a double-acting hydraulic user (25), comprising: a directional control valve group (34) that comprises a stem (35) that is mobile between three positions (I, II, III), and six internal conduits (41, 42, 43, 44, 45, 46); a maximum pressure valve (47); a flow regulating valve (50). A hydraulic plant for commanding a double-acting hydraulic user is also disclosed, for commanding a single-acting hydraulic user, which comprises: the directional control valve group (27); an oil discharge (T); a hydraulic pump (P); a second directional control valve group (56) for commanding a single- acting hydraulic user (20), comprising in turn a second directional control valve (57); wherein the second directional control valve (56) is arranged downstream of the hydraulic section (55) with respect to the oil supply direction.

Inventors:
PRAMPOLINI SILVANO (IT)
MUNERATI LUCA (IT)
LANDUZZI DANIELE (IT)
Application Number:
IB2016/050190
Publication Date:
July 28, 2016
Filing Date:
January 15, 2016
Export Citation:
Click for automatic bibliography generation   Help
Assignee:
INTERPUMP HYDRAULICS SPA (IT)
International Classes:
F15B13/02; F15B13/01; F15B13/04; F15B13/08
Foreign References:
US3937128A1976-02-10
DE2521048A11976-11-25
EP2107253A22009-10-07
Attorney, Agent or Firm:
DALL'OLIO, Giancarlo et al. (Via Delle Armi 1, Bologna, IT)
Download PDF:
Claims:
CLAIMS ).A directional control valve group (27) installable on a truck for commanding a double-acting hydraulic user (25), wherein: it comprises a directional control valve (34) which comprises: a stem (35) provided with recesses (36) which form a plurality of oil conveying channels; a hollow body (37) which internally forms a chamber (38) and which forms at least six internal conduits which originate from the chamber (38), i.e. a first internal conduit (41), a second internal conduit (42), a third internal conduit (43), a fourth internal conduit (44), a fifth internal conduit (45) and a sixth internal conduit (46); the stem (35) is mobile along the chamber (38) among at least three positions, i.e. a first position (I), a second position (II) and a third position (III); the stem (35) and the hollow body (37) are conformed with respect to one another so that: when the stem (35) is in the first position (I) the first internal conduit (41) is in fluid communication with fourth internal conduit (44), the third internal conduit (43) is in fluid communication with the sixth internal conduit (46); when the stem (35) is in the second position (II) the second internal conduit (42) is in fluid communication with the fifth internal conduit (45); when the stem (35) is in the third position (III) the first internal conduit (41) is in fluid communication with the sixth internal conduit (46) and the third internal conduit (43) is in fluid communication with the fourth internal conduit (44); the second internal conduit (42) is connectable to a pressurised oil supply; the third internal conduit (43) is connectable to an oil discharge (T); the fourth internal conduit (44) is connectable to a first hydraulic port (23) of a double-acting hydraulic user (25); the sixth internal conduit (46) is connectable to a second hydraulic port (24) of the double-acting hydraulic user (25); it comprises a maximum pressure valve (47) having a first inlet (48) and a first outlet (49) which is connectable to the oil discharge (T), designed in such a way that when the oil present at the first inlet (48) reaches a pressure that exceeds a predetermined pressure value, the first inlet (48) is set in fluid communication with the first outlet (49); it comprises a flow regulating valve (50) having a second inlet (51) and a second outlet (52) which is connectable to the oil discharge (T), designed such that when the oil present at the second inlet (51) reaches a flow rate that exceeds a predetermined flow rate, the quantity of oil in excess is switched onto the second outlet (52); characterised in that: the stem (35) and the hollow body (37) are reciprocally conformed so that: when the stem (35) assumes the first position (I) the second internal conduit (42) is in fluid communication with the first internal conduit (41) and with the fourth internal conduit (44); when the stem (35) assumes the third position (III) the second internal conduit (42) is in fluid communication with the first internal conduit (41) and with the sixth internal conduit (46); the first internal conduit (41) is connected to the first inlet (48) of the maximum pressure valve (47) and with the second inlet (51) of the flow regulating valve (50).

2) .The directional valve control group (27) of the preceding claim, wherein the hollow body (37): conforms a first housing (53) for receiving the maximum pressure valve (47); forms a second housing (54) for receiving the flow regulating valve (50); forms the connection of the first internal conduit (41) with the first inlet (48) of the maximum pressure valve (47) and with the second inlet (51) of the flow regulating valve (50).

3) .A hydraulic section (55) installable on a truck for commanding a double-acting hydraulic user (25), comprising: the directional control valve group (27) according to any one of the preceding claims; a first hydraulic line (61) which connects the first internal conduit (41) with the first inlet (48) of the maximum pressure valve (47) and with the second inlet (51 ) of the flow regulating valve (50); a second hydraulic line (62) which connects the second internal conduit (42) with the pressurised oil supply; a third hydraulic line (63) which connects the third internal conduit (43) with the oil discharge (T); a fourth hydraulic line (64) which connects the fourth internal conduit (44) with a first hydraulic port (23) of a double-acting hydraulic user (25); a fifth hydraulic line (65) which connects the sixth internal conduit (46) with a second hydraulic port (24) of the double-acting hydraulic user (25). ).A hydraulic plant installable on a truck for commanding at least a double-acting hydraulic user (25) and for commanding a single-acting hydraulic user (20), comprising: the hydraulic section (55) according to the preceding claim; the oil discharge (T); a hydraulic pump (P) which is connected to the second hydraulic line (62) for supplying pressurised oil; a second directional control valve group (56) for commanding a single-acting hydraulic user (20), comprising in turn a second directional control valve (57); a sixth hydraulic line (66) which connects the fifth internal conduit (45) with the second directional control valve (57); wherein the second directional control valve (56) is arranged downstream of the hydraulic section (55) with respect to the oil supply direction.

Description:
A DIRECTIONAL CONTROL VALVE GROUP INSTALLABLE ON A TRUCK FOR COMMANDING A DOUBLE-ACTING HYDRAULIC USER, AND A HYDRAULIC PLANT COMPRISING THE DIRECTIONAL CONTROL VALVE GROUP.

FIELD OF THE INVENTION

The present invention relates to the technical sector concerning a directional control valve group for commanding a double-acting hydraulic user. In particular, the invention relates to a direction control valve group which can be installed on a truck or, more specifically, on a road tractor.

DESCRIPTION OF THE PRIOR ART

Figure 1 illustrates the hydraulic circuit of a first hydraulic plant of a known type, which is installed on-board a road tractor (not illustrated) for commanding a single-acting cylinder (20). The first hydraulic plant comprises a directional control valve group that comprises a directional control valve (1) and a maximum pressure valve (2).

The directional control valve (1) in turn comprises: a stem (not illustrated) provided with recesses which form a plurality of oil conveying channels; a hollow body (not illustrated) which internally forms a chamber and which forms three internal conduits which originate from the chamber, i.e. a first internal conduit (3), a second internal conduit (4), and a third internal conduit (5). The stem is mobile along the chamber between three positions, i.e. a first position (I), a second position (II) and a third position (III); the stem and the hollow body are conformed with respect to one another so that: when the stem is in the first position (I) the first internal conduit (3) is in fluid communication with the third internal conduit (5); when the stem assumes the second position (II) the first internal conduit (3) is in fluid communication with the second internal conduit (4); when the stem is in the third position (III), the first internal conduit (3), the second internal conduit (4) and the third internal conduit (5) are in fluid communication with one another. The first hydraulic plant also comprises: a single-acting cylinder (20) which is connected to the third internal conduit (5) via a first hydraulic line; an oil tank (T) which is connected to the second internal conduit (4) via a second hydraulic line; a hydraulic pump (P) having pressurised oil outlet which is connected to the first internal conduit (3) via a third hydraulic line and an inlet which is connected to the oil tank (T) (via a fourth hydraulic line, not illustrated).

The maximum pressure valve (2) has an inlet connected to the third hydraulic line and an outlet connected to the oil tank (T).

When the stem assumes the first position (I), the oil in outlet from the hydraulic pump (P) is conveyed towards the single-acting cylinder (20) through the first hydraulic line; when the stem assumes the second position (II), the oil in outlet from the hydraulic pump (P) is conveyed into the oil tank (T) via the second hydraulic line; lastly, when the stem assumes the third position (III), the oil in outlet from the hydraulic pump (P) and the oil coming from the single-acting cylinder (20) are conveyed into the oil tank (T).

The maximum pressure valve (2) is calibrated to a predetermined value, and has the function of protecting the first hydraulic plant when the oil reaches pressure values exceeding the predetermined value; in other words, if the oil in inlet to the maximum pressure valve (2) exceeds the predetermined pressure value, the inlet to the maximum pressure valve (2) is set in fluid communication with the outlet of the maximum pressure valve (2).

The first hydraulic plant can be mounted on-board a road tractor (not illustrated) and can further comprise an oil filter (not illustrated), mounted at a first through-hole made in the oil tank (T), and an air filter (not illustrated), mounted at a second through-hole made in the oil tank (T). The road tractor; for example, bears a trailer provided with a tipper which is mobile in rotation to release gravel or other materials loaded on the tipper; in this case, the single- acting cylinder (20) activates the rotation of the tipper.

In a small percentage of cases (generally 10-20%), hydraulic plants mounted on-board road tractors also comprise an additional hydraulic section for commanding rotation of the sides of the trailer, so as to regulate outflow of the material contained in the tipper once the tipper has been rotated by a certain angle; in this case, the rotation of the trailer is commanded by a double-acting cylinder. Figure 2 illustrates the hydraulic circuit of a second hydraulic plant of known type, comprising a main hydraulic section (28), which commands the rotation of the tipper, and the additional hydraulic section (29), which is arranged downstream of the main hydraulic section (28) with respect to the supply direction of the oil. The main hydraulic section (28) comprises a first directional control valve group that comprises a directional control valve (6) and a maximum pressure valve (11).

The first directional control valve (6) in turn comprises: a stem (not illustrated) provided with recesses which form a plurality of oil conveying channels; a hollow body (not illustrated) which internally forms a chamber and which forms four internal conduits which originate from the chamber, i.e. a first internal conduit (7), a second internal conduit (8), and a fourth internal conduit (10). The stem is mobile along the chamber between three positions, i.e. a first position (I), a second position (II) and a third position (III); the stem and the hollow body are conformed with respect to one another so that: when the stem is in the first position (I) the first internal conduit (7) is in fluid communication with third internal conduit (9) and the second internal conduit (8) is in fluid communication with the fourth internal conduit (10); when the stem (35) is in the second position (II) the second internal conduit (7) is in fluid communication with the third internal conduit (9); when the stem (35) is in the third position (III) the first internal conduit (7) is in fluid communication with the fourth internal conduit (10).

The main hydraulic section (28) further comprises: a single-acting cylinder (20) which is connected to the fourth internal conduit (10) via a first hydraulic line and which commands, as specified, the rotation of the trailer tipper. The maximum pressure valve (11) is calibrated on a first maximum pressure value, has an inlet connected to the first hydraulic line and an outlet connected , to the oil tank (T).

The first internal conduit (7) is connected to the outlet of the hydraulic pump (P) via a second hydraulic line; the second internal conduit (8) is connected to the oil tank (T) via a third hydraulic line; the third internal conduit (9) is connected to a fourth hydraulic line.

The additional hydraulic section (29) comprises a second directional control valve group that comprises a second directional control valve (12), a second maximum pressure valve (13) and a flow regulating valve (26).

The second directional control valve (12) comprises: a stem (not illustrated) provided with recesses which form a plurality of oil conveying channels; a hollow body (not illustrated) which internally forms a chamber and which forms six internal conduits which originate from the chamber, i.e. a fifth internal conduit (14), a sixth internal conduit (15), a seventh internal conduit (16), an eighth internal conduit (17), a ninth internal conduit (18) and a tenth internal conduit (19). The stem is mobile along the chamber between three positions, i.e. a first position (I), a second position (II) and a third position (III); the stem and the hollow body are conformed with respect to one another so that: when the stem is in the first position (I) the fifth internal conduit (14) is in fluid communication with the eighth internal conduit (17) and the seventh internal conduit (16) is in fluid communication with the tenth internal conduit (19); when the stem is in the second position (II) the sixth internal conduit (15) is in fluid communication with the ninth internal conduit (18), while the eighth internal conduit (17), the tenth internal conduit (19) and the seventh internal conduit

(16) are in reciprocal fluid communication; when the stem is in the third position (III) the fifth internal conduit (14) is in fluid communication with the tenth internal conduit (19) and the seventh internal conduit (16) is in fluid communication with the eighth internal conduit (17).

The fourth hydraulic line connects the third internal conduit (9) of the first directional control valve (6) with the sixth internal conduit (15) of the second directional control valve (12).

The additional hydraulic section (29) further comprises a double-acting cylinder (25) which commands, as specified, the rotation of the sides of the trailer tipper; the double-acting cylinder (25) is provided with a first hydraulic port (23) and a second hydraulic port (24): to push the double-acting cylinder piston (25) in a first direction the oil enters the first hydraulic port (23) and exits from the second hydraulic port (24), while to push the piston in a second direction, opposite the first direction, the oil enters the second hydraulic port (24) and exits from the first hydraulic port (23). The first hydraulic port (23) is connected via a fifth hydraulic line to the eighth internal conduit (17), while the second hydraulic port (24) is connected via a sixth hydraulic line to the tenth internal conduit (19).

The second maximum pressure valve (13) is calibrated on a second maximum pressure value, has an inlet connected to the fourth hydraulic line and an outlet connected to the oil tank (T).

The flow regulating valve (26) has an inlet connected to the fourth hydraulic line and an outlet connected to the oil tank (T).

The fifth internal conduit (14) is connected to the fourth hydraulic line. The seventh internal conduit (16) is connected to the oil tank (T) via a seventh hydraulic line. The ninth internal conduit (18) is connected to the oil tank (T) via an eighth hydraulic line.

During the design stage of the second hydraulic plant, the hydraulic pump (P) is dimensioned in accordance with the characteristics of the single-acting cylinder (20) which commands the rotation of the tipper. It will have a rated flow rate which, for example, can be 90 litres per minute.

The double-acting cylinder (25) of the additional hydraulic section (29), on the other hand, requires a flow rate that is generally lower than the rated flow rate of the hydraulic pump (P): this value is for example 30 litres per minute for enabling a gradual rotation of the side up to the desired position, with the aim of discharging the material contained in the tipper. The flow regulating valve (26) therefore has the task of discharging 60 litres per minute towards the oil tank (T).

For this reason the additional hydraulic section (29) is generally positioned downstream of the main hydraulic section (28).

Also of importance is the fact that it can be necessary to protect the single- acting cylinder (20) and the double-acting cylinder (25) with maximum pressure valve calibrated at different values with respect to one another: for example, the first maximum pressure valve (11) can be calibrated at a maximum value of 140 Bar, while the second maximum pressure valve (13) can be calibrated at a maximum value of 180 Bar. With reference to the first hydraulic plant of figure 1 , the maximum pressure valve (2) has been branched from the third hydraulic line which connects the hydraulic pump (P) to the first internal conduit (7) of the directional control valve (1). In the case of the second hydraulic plant the first maximum pressure valve (11) cannot be branched off from the second hydraulic line which connects the hydraulic pump (P) to the first internal conduit (7) of the first directional control valve (6): if this should occur, in fact, when the stem of the first directional control valve (6) is in the second position (II), the first maximum pressure valve (11) would also limit the oil pressure conveyed towards the additional hydraulic section (29), making the use of the second maximum pressure valve (13) useless. It is for this reason that the first maximum flow valve (11) has been branched off from the first hydraulic line.

There are cases in which it is necessary to arranged the additional hydraulic section upstream of the main hydraulic section with respect to the supply direction of the oil supplied by the hydraulic pump. This can happen, for example, if the first directional control valve of the main hydraulic section is predisposed to be fixed directly to the oil tank and to couplingly receive, optionally (according to the user's needs), also the second directional control valve of the additional hydraulic section. Or it can also happen that the additional hydraulic section is inserted only following the realisation and mounting of the hydraulic plant on the road tractor, and space problems impose arranging the additional hydraulic section upstream of the main hydraulic section.

Figure 3 illustrates the hydraulic circuit of a third hydraulic plant of known type, comprising an additional hydraulic section (30), which is arranged upstream of the main hydraulic section (31).

The main hydraulic section (31) is identical to what is described in the foregoing with reference to the first hydraulic plant of figure 1.

The first directional control valve (22) of the additional hydraulic section (30) is identical to the second directional control valve (12) described with reference to the second hydraulic plant of figure 2. Instead, the arrangement of the maximum pressure valve (21) and the flow regulating valve (32) are different, as they are now arranged branching from each of the two hydraulic lines connecting the first directional control valve (22) of the additional hydraulic section (30) with the first hydraulic port (23) and the second hydraulic port (24) of the double-acting cylinder (25): the number of these valves therefore doubles (two maximum pressure valves and two flow regulating valves). This is owing to the fact that it is not possible to have a flow regulating valve (32) branching from the hydraulic line connecting the outlet of the hydraulic pump (P) with the first directional control valve (22) of the additional hydraulic section (30) (as in the second hydraulic plant of figure 2), as an unacceptable oil flow limitation would occur, also for the second directional control valve (33) of the main hydraulic section (31).

This increase in the number of valves has up to now discouraged the design of a hydraulic plant in which the additional hydraulic section is arranged upstream of the main hydraulic section: when possible it is preferable to arrange the additional hydraulic section downstream of the main hydraulic section, as in the hydraulic plant illustrated in figure 2. In fact, each maximum pressure valve or flow regulating valve must be connected by fittings, tubing and manifolds to the rest of the hydraulic plant; in particular, a tubing must be included which connects each oil tank valve, which tubing can have a length of various metres. Each valve and the necessary connections for the connecting the valve to the rest of the hydraulic plant must be fixed to the frame of the road tractor, which requires much time and is often difficult as the available spaces are of small entity.

SUMMARY OF THE INVENTION

The aim of the present invention consists in obviating the above-mentioned drawbacks.

The above-mentioned aim is attained with a directional control valve group installable on a truck for commanding a double-acting hydraulic user, according to claim 1.

When the stem occupies the first position or the third position a closed-looped hydraulic circuit is defined by the horizontal pump, the double-acting hydraulic user (which for example is a double-acting cylinder) and the oil discharge (T); the maximum pressure valve and the flow regulating valve are branched between the first hydraulic port and the second hydraulic port of the double- acting hydraulic user; in this hydraulic circuit, the oil pressure and the oil flow rate are therefore kept below respectively a predetermined pressure level and flow rate of oil.

The directional control valve group can be used in a hydraulic plant which also comprises a second directional control valve group for commanding a single- acting hydraulic user (for example the single-acting hydraulic user is a single- acting cylinder commanding the rotation of a tipper of a trailer drawn by the truck).

If the directional control valve group is arranged upstream with respect to the second directional control valve there is the advantage of obtaining the same functional levels as the prior-art hydraulic plant, described in the foregoing with reference to figure 3, but with a smaller number of valves (only one maximum pressure valve and one flow regulating valve are used, instead of the maximum pressure valve and two flow regulating valves) and, consequently, fittings, manifolds and tubings.

If the directional control valve group is arranged downstream with respect to the second directional control valve there is the advantage of obtaining the same functional levels as the prior-art hydraulic plant, described in the foregoing with reference to figure 2; in fact, in both cases a single maximum pressure valve and a single flow regulating valve are used. However, the advantage of the directional control valve group of the present invention consists in the fact that the position of the maximum pressure valve and the flow regulating valve do not influence the second directional control valve group: in the invention, therefore, the first maximum pressure valve, with reference to figure 2, is branched between the first hydraulic line and the oil tank instead of being branched between the second hydraulic line and the oil tank, as has been done in the hydraulic plant of figure 1.

The possibility of using the directional control valve group of the invention upstream or downstream of the second directional control valve group is advantageous, , as it makes the directional control valve group very versatile.

It is therefore not necessary to realise a directional control valve group ad hoc, according to the position (upstream or downstream with respect to the second directional control valve) in which the directional control valve group is located internally of the hydraulic plant; a single directional control valve group is sufficient for all uses, which makes it possible to produce a greater number of pieces in series at lower costs. Additionally, to minimise the number of hydraulic connections, the hollow body can form: a housing for receiving the maximum pressure valve; a second housing for receiving the flow regulating valve; the connection of the first internal conduit with the first inlet of the maximum pressure valve and with the second inlet of the flow regulating valve.

In accordance with claim 4, a hydraulic plant is further defined that is installable on a truck for commanding at least a double-acting hydraulic user and for commanding a single-acting hydraulic user. The hydraulic plant comprises: a hydraulic section that in turn comprises the directional control valve group defined in claim 1 ; and a second directional control valve group for commanding the single-acting hydraulic user, which second directional control valve is arranged downstream of the hydraulic section with respect to the oil supply direction.

The advantage, previously specified, is that with respect to the hydraulic plant of figure 3 a maximum pressure valve less and a flow rate valve less is used, with all the positive implications that brings.

BRIEF DESCRIPTION OF THE DRAWINGS

Specific embodiments of the invention will be described in the following with reference to the present description, according to what is set down in the claims and with the aid of the appended tables of drawings, in which:

- figure 1 illustrates the hydraulic circuit of a first hydraulic plant of a known type, which commands a single-acting cylinder;

- figure 2 illustrates the hydraulic circuit of a second hydraulic plant of a known type, which commands a single-acting hydraulic user and a double- acting hydraulic user;

- figure 3 illustrates the hydraulic circuit of a third hydraulic plant of a known type, which commands a single-acting hydraulic user and a double-acting hydraulic user;

- figure 4 illustrates a part of a hydraulic plant which comprises a directional control valve group according to the present invention;

- figures 5-7 illustrate section view of the directional control valve group of figure 4 when the directional control valve group is in a same number of operating configurations; - figure 8 illustrates a hydraulic circuit of a hydraulic plant that is also an object of the present invention, which hydraulic circuit comprises the part of hydraulic circuit of figure 4.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

With reference to figure 4-8, reference numeral (27) denotes a directional control valve group (27) installable on a truck for commanding a double-acting hydraulic user (25). The directional control valve group (27) comprises (figure 5-7) a directional control valve (34) which in turn comprises: a stem (35) provided with recesses (36) which form a plurality of oil conveying channels; a hollow body (37) which internally forms a chamber (38) and which forms at least six internal conduits which originate from the chamber (38), i.e. a first internal conduit (41), a second internal conduit (42), a third internal conduit

(43) , a fourth internal conduit (44), a fifth internal conduit (45) and a sixth internal conduit (46). The stem (35) is mobile along the chamber (38) among at least three positions, i.e. a first position (I), a second position (II) and a third position (III). The stem (35) and the hollow body (37) are conformed with respect to one another so that: when the stem (35) is in the first position (I) (the arrows in figure 5 denote the direction of the pressurised oil coming from the hydraulic pump), the first internal conduit (41) is in fluid communication with fourth internal conduit (44), the third internal conduit (43) is in fluid communication with the sixth internal conduit (46); when the stem (35) is in the second position (II) (the arrows in figure 6 denote the direction of the pressurised oil coming from the hydraulic pump), the second internal conduit (42) is in fluid communication with the fifth internal conduit (45); when the stem (35) is in the third position (III) (the arrows in figure 7 denote the direction of the pressurised oil coming from the hydraulic pump), the first internal conduit (41) is in fluid communication with the sixth internal conduit (46) and the third internal conduit (43) is in fluid communication with the fourth internal conduit

(44) . The second internal conduit (42) is connectable to a pressurised oil supply; the third internal conduit (43) is connectable to an oil discharge (T); the fourth internal conduit (44) is connectable to a first hydraulic port (23) of a double-acting hydraulic user (25); the sixth internal conduit (46) is connectable to a second hydraulic port (24) of the double-acting hydraulic user (25).

The directional control valve group (27) comprises a maximum pressure valve (47) having a first inlet (48) and a first outlet (49) which is connectable to the oil discharge (T), designed in such a way that when the oil present at the first inlet (48) reaches a pressure that exceeds a predetermined pressure value, the first inlet (48) is set in fluid communication with the first outlet (49); a flow regulating valve (50) having a second inlet (51) and a second outlet (52) which is connectable to the oil discharge (T), designed such that when the oil present at the second inlet (51) reaches a flow rate that exceeds a predetermined flow rate, the quantity of oil in excess is switched onto the second outlet (52).

The stem (35) and the hollow body (37) are reciprocally conformed so that: when the stem (35) assumes the first position (I) the second internal conduit (42) is in fluid communication with the first internal conduit (41) and with the fourth internal conduit (44); when the stem (35) assumes the third position (III) the second internal conduit (42) is in fluid communication with the first internal conduit (41) and with the sixth internal conduit (46).

The first internal conduit (41) is connected to the first inlet (48) of the maximum pressure valve (47) and with the second inlet (51) of the flow regulating valve (50).

The double-acting hydraulic user (25) is preferably a double-acting cylinder.

The truck can be a road tractor.

The hollow body (37) preferably: conforms a first housing (53) for receiving the maximum pressure valve (47); forms a second housing (54) for receiving the flow regulating valve (50); forms the connection of the first internal conduit (41) with the first inlet (48) of the maximum pressure valve (47) and with the second inlet (51) of the flow regulating valve (50). In addition, the hollow body (37) can also form the connection of the third internal conduit (43) with the first outlet (49) of the maximum pressure valve (47) and with the second outlet (52) of the flow regulating valve (50). See figures 5-7.

The directional control valve group (27) defined in the foregoing can be part of a hydraulic section (55) which is also the object of the present invention.

The hydraulic section (55) further comprises: a first hydraulic line (61) which connects the first internal conduit (41) with the first inlet (48) of the maximum pressure valve (47) and with the second inlet (51) of the flow regulating valve (50); a second hydraulic line (62) which connects the second internal conduit (42) with the pressurised oil supply; a third hydraulic line (63) which connects the third internal conduit (43) with the oil discharge (T); a fourth hydraulic line (64) which connects the fourth internal conduit (44) with a first hydraulic port (23) of a double-acting hydraulic user (25); a fifth hydraulic line (65) which connects the sixth internal conduit (46) with a second hydraulic port (24) of the double-acting hydraulic user (25).

A further object of the present invention relates to a hydraulic plant (figure 8) installable on a truck for commanding a double-acting hydraulic user (25) and for commanding a single-acting hydraulic user (20), comprising: the hydraulic section (55) defined in the foregoing; the oil discharge (T); a hydraulic pump (P) which is connected to the second hydraulic line (62) for supplying pressurised oil; a second directional control valve group (56) for commanding a single-acting hydraulic user (20), comprising in turn a second directional control valve (57); a sixth hydraulic line (66) which connects the fifth internal conduit (45) with the second directional control valve (57). The second directional control valve group (56) is arranged downstream of the hydraulic section (55) with respect to the oil supply direction.

The single-acting hydraulic user (20) is preferably a double-acting cylinder.

The second directional control valve group (56) can comprise a second directional control valve (58).

The second directional control valve group (56) can be identical to the one described with reference to figure 1 relating to the prior art. The oil discharge (T) can be an oil tank (T).