Hydraulic system with automatic boom extension locking

Abstract

 A hydraulic system comprises:
- a first fluid distribution line (A) and a second fluid distribution line (B) communicating with a stem chamber (11) of a double-acting cylinder (10) destined to move two reciprocally mobile parts;
- a third fluid distribution line (O) communicating with a single-acting cylinder (20) for blocking the mobile parts;
- a solenoid distributor (2) which intercepts the third line (O) and switches the third line (O) between a first position in which it pressurises the single-acting cylinder (20) and a second position in which it discharges the single-acting cylinder (20);
- a first bistable selector valve (7) sending in outlet a pressure signal when a pressure difference between the first line (A) and the second line (B) exceeds a certain value;
- a pressure sensor (8) communicating with the first selector valve (7) and associated to the solenoid distributor (2) such as to switch the solenoid distributor (2) into the second position when the fluid pressure coming from the outlet of the first selector valve (7) exceeds a predetermined value.

Description

[0001] The invention relates to a hydraulic system with an automatic block for telescopic booms.

[0002] The prior art contains tracked vehicles having a hydraulic variable width by means of special telescopic booms which enable the two lateral tracks to be distanced and neared with respect to the vehicle frame, in order to adapt the track-base to the necessities of good vehicle positioning.

[0003] The booms are constituted by a fixed beam and a mobile beam telescopically introduced in the fixed beam, and are activated by a double-acting cylinder which positions the booms and therefore the tracks, in the case of a tracked vehicle, at a desired distance. Once the desired position has been reached, the booms are blocked in position by plunger pistons, at least one for each boom.

[0004] Operatively, each time the position of the tracks is to be changed, it is first necessary to unblock the booms, by unloading the blocker plunger pistons and activating the double-acting cylinder. Once the displacement operation is completed, the block must be re-applied, by pressurising the blocker cylinders.

[0005] One of the drawbacks encountered in the prior art is that the double-acting cylinder may be activated either deliberately or by accident without the necessary first discharge of the blocker cylinder.

[0006] This can lead to damage both to the plunger cylinders and to the double-acting cylinder, which encounters excessive resistance due to the completed braking action of the plunger cylinders, as well as to the booms, which can seize with inevitable consequent breakage.

[0007] For these reasons, the boom-displacing operation must be done at all times with great care and by trained personnel, whose ability is relied upon to perform the necessary boom-displacing operations correctly.

[0008] There is therefore a strongly-felt need to have available a hydraulic system which with a single operation enables activation of the double-acting cylinder in order to move the booms and automatically discharge the blocking cylinders, as well as to automatically reset the pressure in the blocking cylinders at the end of the boom-displacement operation, thus obviating the need to perform various operations separately and in a predetermined order, with a consequent simplification as well as the certainty that the operator doing the task will not make errors; and all in the ambit of a simple and rational constructional solution. The aim of the present invention is to provide a hydraulic system having an automatic block of the booms, which has structural and functional characteristics that satisfy the above-cited requirements and which at the same time obviates the drawbacks mentioned with respect to the prior art.

[0009] The aim is attained by a hydraulic system with automatic blocking for booms, in agreement with appended claim 1.

[0010] The dependent claims delineate preferred and particularly advantageous embodiments of the hydraulic system with automatic boom block according to the present invention.

[0011] Further characteristics and advantages of the invention will emerge from a reading of the following description, provided by way of non-limiting example with the aid of the figures illustrated in the appended drawings, in which:

• Figures 1-3 show a schematic view of a hydraulic control circuit of a single boom, according to the present invention, in three different operative conditions. With reference to the figures of the drawings, 1 denotes in its entirety a hydraulic circuit of a hydraulic system having an automatic boom block, in agreement with the present invention.

[0012] The hydraulic system comprises, in summary:

• a first fluid distribution line, denoted by A, communicating with the stem chamber 11 of a double-acting cylinder 10 which moves two reciprocally-mobile parts connected to respective booms (not illustrated);
• a second fluid distribution line, denoted by B, communicating with the piston chamber 12 of the double-acting piston 10;
• a third fluid distribution line, denoted by O, communicating with single-acting pistons 20, in the embodiment two plunger cylinders arranged in parallel and blocking the mobile parts of the boom when they are charged with pressurised fluid which passes along the third line O.

[0013] In the present invention, the third line O is intercepted by a two-position switch distributor 2, which in the illustrated embodiment is a three-way solenoid valve.

[0014] A first position (figure 1) is one in which the third line O is placed in communication with a pump which aspirates the fluid, for example oil, from a reservoir 4 and a second position (figures 2, 3) is one in which it places the third line O in communication with the discharge, which in the illustrated embodiment is represented by the reservoir 4 itself.

[0015] Thus, in the first position, the two plunger cylinders 20 are pressurised and block the boom, while in the second position they are uncharged and unblock the boom, which can be freely moved by the double-acting cylinder 10.

[0016] In particular, in the second position the solenoid 2, on one side, obstructs the delivery conduit of the pump 3, forcing the delivery oil to cross a pressure relief valve 6 which opens once a certain pressure value has been reached and sends the oil through a discharge conduit 5 to the reservoir 4, and on the other side places the remaining third line O, in which is between the plunger cylinders 20 and the solenoid 2, in communication with the discharge conduit 5 in order to unload the cylinders 20.

[0017] The first and second line A and B communicate with a bistable selector valve 7 of the OR type, located between the first line A and the second line B, and allows only the oil presenting the greater pressure in one of the two lines to pass, i.e. alternatively coming from A or B. The oil in outlet from the selector valve 7 communicates with a pressure gauge 8 which acts on a switch connected to a current generator 14.

[0018] The pressure gauge 8 is calibrated such that when the pressure of the oil in outlet from the selector valve 7 exceeds a certain value, it activates the switch 9 which closes the electrical circuit with the generator 14, which generator 14 sends an electrical signal to the solenoid 2, switching it to the second position in which it unblocks the boom (figures 2, 3).

[0019] When the oil pressure drops below the calibrated value, i.e. when both line A and line B are discharged, the pressure gauge 8 returns into the initial position and reopens the electrical circuit, with a consequent return of the solenoid valve 2 into the first position, in which it blocks the boom (figure 1).

[0020] In substance, when the line A or the line B are pressurised because the cylinder 10 moving the boom is to be activated, the line O is automatically discharged directly by the delivery pressure along line A or B, without any need for a separate operation to be carried out.

[0021] In the present invention, the pressurising and discharging of the lines A and B is done by means of a control distributor 16 having three different positions: a first position in which it places line A under pressure, connecting it to a pump 15, in the preferred embodiment a pump 15 activated by the shaft activating the pump 3 of line O, and discharges line B (figure 2); a second position in which it pressurises line B, connecting it to the pump 15 once more and discharging line A (figure 3); and a third position in which it discharges both the lines A and B (figure 1).

[0022] In particular, the control distributor 16 automatically returns into the third position at the end of the activation of the double-acting cylinder 10. Further, in the third position the pump 15, which is always functioning, is connected, again via the control distributor 16, to a line 40 directed to the discharge reservoir 4.

[0023] With the aim of further improving the safety of the whole system, two two-way distributors 17, 18, in the embodiment two four-way valves, are used, which singly intercept line A and line B and can assume a first position in which they place line A and line B in communication respectively with the stem chamber 11 and the piston chamber 12 of the cylinder 10, and a second in which they interrupt the connection with the respective chambers.

[0024] In particular, the two distributors 17, 18 are servopiloted by the pressure of the fluid in the third line O to which they are hydraulically connected in parallel with each other and with the plunger cylinders 20 via a line 41 intercepted by a selector valve 37.

[0025] The distributors 17, 18 are both pushed into the second position when the third line O is pressurised, i.e. when the cylinders 20 block the boom.

[0026] Thus, should the solenoid 2 not switch the line O to discharge, for example due to problems with the generator 14, in the presence of oil under pressure in one of the two lines A or B, the pressurised oil in the line A or B will not in any case be able to reach the double-acting cylinder 10, since as long as the plunger cylinders 20 are pressurised, so too will be the line 41 piloting the two distributors 17, 18, which will therefore stay in the position in which communication with the chambers 11, 12 of the cylinders is interrupted.

[0027] Differently, when line O is discharged, thanks to the correct activation of the solenoid 2, the two distributors 17, 18 are brought into the position (figures 2, 3) which allows the pressurised oil in the line A or B to reach the chambers 11, 12 of the cylinder 10.

[0028] Any losses of oil in the two distributors 17, 18 are conveyed to the reservoir 4 through a discharge line 19.

[0029] As is well known in the sector, the oil pressure in the plunger cylinders 20 is kept substantially constant by a storage system, denoted by 30 in the figures, comprising a reserve tank 31 communicating with the third line O through a conduit 32 intercepted by a single-acting flow regulator valve 33 and a cock 34 which is always open and closed only for any eventual controls and/or maintenance of the system itself.

[0030] The reserve tank 31 is further connected to the reservoir 35 via a conduit which is intercepted by a pressure relief valve 36 which opens when a certain pressure is exceeded.

[0031] In the illustrated embodiment, the third line O is intercepted by a piloted check valve 38, located, with respect to the allowed flow direction, downstream of the solenoid 2 and upstream of the storage system 30, the plunger pistons 20 and the distributors 17, 18.

[0032] The check valve 38 is in effect a further obstacle to accidental discharge of the devices downstream thereof.

[0033] The check valve 38 is structured such as to be unblocked, in order to enable passage of the oil in line O in an opposite direction, towards the discharge, by the pressure exerted against the valve 38 by the pressurised oil coming from line A or B.

[0034] In particular, lines A and B communicate with a further bistable selector valve 39 located between lines A and B and sending in outlet only oil at a higher pressure. The outlet of the selector valve 39 is connected with the check valve 38, which is unblocked when reached by pressurised oil coming from the selector valve 39.

[0035] Operatively, and with reference to the diagram of figures 1-3, the system 1 is completely managed by the three-way control distributor 16. Normally it is placed in the third position with the lines A and B which discharge to the reservoir (figure 1).

[0036] In the absence of pressure in lines A and B, the solenoid 2 connects line O to the pump 3 which pressurises the plunger cylinders 20, bringing them into the blocked position.

[0037] The pressurised oil in line O also reaches the two distributors 17, 18 which are pushed into the position in which they prevent the oil present in lines A and B from reaching the double-acting cylinder 10, further increasing the safety.

[0038] When the double-acting cylinder 10 is to be activated, the control distributor 16 is brought into the first or second position, according to the direction the boom is to be moved in.

[0039] In order to activate the piston of the double-acting cylinder 10 towards the right in the figures, the control distributor 16 is moved into the first position in order to connect the line A to the pump 15 (figure 2).

[0040] The pressurised oil in line A first reaches the selector valve 7 through which it activates the switch 9 which commutes the solenoid 2 into the discharge position of line O. The oil proceeds along line A and reaches the second selector valve 39, through which it unblocks the check valve 38 in order to enable free discharge of the plunger pistons 20 and the line 41 leading to the distributors 17, 18, which, in the absence of a thrust from the pressurised oil, move into the open position, connecting the lines A and B to the respective chambers 11, 12 of the double-acting cylinder 10. The oil proceeds along line A until it reaches the distributor 17, the higher in the figures, which distributor 17 allows the pressurised oil to reach the stem chamber 11, pushing the piston towards the right. The oil present in the piston chamber 12 is discharged along line B, which is connected to the reservoir 4, passing through the distributor 18, the lower in the figures.

[0041] When the desired displacement has been made, the control distributor 16 is brought back into the third position, discharging line A. The absence of pressure along line A and therefore against the valve 7 returns the switch 9 into the position in which it re-opens the electrical circuit, consequently returning the solenoid valve 2 into the position in which it places the line O under pressure, resetting the boom block.

[0042] To activate the piston of the double-acting cylinder 10 towards the left in the figures, the control distributor 16 is brought into the second position in order to connect line B to the pump 15 (figure 3).

[0043] The pressurised oil in line B follows a course which is equivalent to the oil in line A and is therefore not described herein.

[0044] In the example, explicit reference has been made to a system 1 with two plunger cylinders and one only double-acting cylinder. However, any other configuration can be used according to need. For example, the number of double-acting cylinders can be two, with a single control or with independent controls. In the latter case, of independent controls, with respect to the system described herein, simple adjustments will be necessary, all well-known to experts in the sector.

[0045] As can be appreciated from the above description, the hydraulic system with automatic block for booms according to the present invention enables the needs outlined in the introductory part of the present description to be met and the drawbacks to be obviated, with reference to the prior art.

[0046] The system affords greater safety with respect to known systems, as every time the double-acting cylinder is activated to displace the booms, the blocking cylinders are first automatically discharged and at the end of the displacement, the system returns the cylinders to block the booms. If this does not occur, the supply of pressurised oil to the double-acting piston is stopped.

[0047] Obviously an expert in the sector, with the aim of satisfying contingent and specific requirements, might make numerous modifications and variations to the above-described hydraulic system with automatic boom-blocking, all entering within the ambit of protection of the invention as defined in the following claims.

Claims

1. A hydraulic system, comprising:

- a first fluid distribution line (A) communicating with a stem chamber (11) of a double-acting cylinder (10),

- a second fluid distribution line (B) communicating with a piston chamber (12) of the double-acting cylinder (10), which double-acting chamber (10) is destined to move two mobile parts connected to booms in a same direction;

- a third fluid distribution line (O) communicating with a single-acting cylinder (20) for blocking the mobile parts when the third line (O) is charged with pressurised fluid,

characterised in that it further comprises:

- a solenoid distributor (2) which intercepts the third line (O) and switches the third line (O) between a first position in which through a first pump (3) it pressurises the single-acting cylinder (20) and a second position in which it discharges the single-acting cylinder (20),

- a first bistable selector valve (7) communicating with both the first and second lines (A, B), the first selector valve (7) maintaining the first and second lines (A, B) hydraulically separate and sending in outlet a pressure signal when a pressure difference between the first line (A) and the second line (B) exceeds a certain value,

- a hydraulic pressure sensor (8) communicating with an outlet of the first selector valve (7) and associated to the solenoid distributor (2) such as to switch the solenoid distributor (2) into the second position thereof when the fluid pressure coming from the outlet of the first selector valve (7) exceeds a predetermined value, sufficient to activate the double-acting cylinder (10).

2. The hydraulic system (1) of claim 1, comprising means for switching (16) the system into three different configurations, a first configuration in which it pressurises the fluid in the first line and discharges the second line (B), a second configuration in which is pressurises the second line (B) and discharges the first line (A), a third configuration in which it discharges both the first line (A) and the second line (B), the hydraulic pressure sensor (8) being sensitive to the pressure of the means for switching (16) only when the system (1) is in the first configuration or the second configuration.

3. The hydraulic system (1) of claim 2, comprising a second pump (15) for alternatively pressurising the first line (A) or the second line (B) via the means for switching (16) the system (1).

4. The hydraulic system (1) of claims 2 and 3, the means for switching (16) the system (1) comprising a control distributor (16) having three different positions corresponding to the three configurations, the control distributor (16) always returning the system (1) into the third configuration at an end of the activation of the double-acting cylinder (10).

5. The hydraulic system (1) of claim 1, wherein the hydraulic pressure sensor (8) acts on a switch (9) connected to a current generator (14).

6. The hydraulic system (1) of claim 1, wherein the first line (A) and the second line (B) are intercepted between the first selector valve (7) and the double-acting cylinder (10) respectively by a first two-way distributor (17) and a second two-way distributor (18); in the open positions of both the first line (A) and the second line (B) are placed in communication respectively with the stem chamber (11) and with the piston chamber (12), and in the closed positions thereof communication with the stem chamber (11) and the piston chamber (12) are interrupted, the first distributor (17) and the second distributor (18) being hydraulically connected to the third line (O), in parallel with the single-acting cylinder (20), the first distributor (17) and the second distributor (18) remaining in the closed positions thereof when the third line (O) is pressurised and returning to the open positions thereof when the third line (O) is discharged.

7. The hydraulic system (1) of claim 6, wherein the first distributor (17) and the second distributor (18) communicate with the discharge via a discharge line (19).

8. The hydraulic system (1) of claim 6, wherein the third line (O) is in communication with a storage system (30) located in parallel with the single-acting cylinder (20) and comprising a tank (31) for storing pressurised fluid.

9. The hydraulic system (1) of claim 8, wherein the storage system (30) communicates with a line (35), intercepted by a pressure relief valve (36), which line (35) is directed to the discharge (4).

10. The hydraulic system of claim 8, wherein the first line (A) and the second line (B) communicate with a second bistable selector valve (39), located between the first selector valve (7) and the first and second distributors (17, 18), which second bistable selector valve (39) keeps the first line (A) and the second line (B) hydraulically separate and sends in outlet a pressure signal, coming alternatively from one of the first and second lines (A, B), to a piloted check valve (38) which intercepts the third line (O), the check valve (38) being located between the solenoid distributor (2) and the single-acting cylinder (20), the first and second distributors (17, 18) and the storage system (30); the check valve (38) being unblockable by the pressure signal in outlet from the second selector valve (39), in order to enable discharge of the single-acting cylinder (20), the first and second distributors (17, 18) and the storage system (30), the discharge of the storage system (30) being slowed by a single-acting flow regulator valve (33).

Drawing