GB2134187A

GB2134187A - Hydraulic circuit for adjusting on operating cylinder of excavating equipment

Info

Publication number: GB2134187A
Application number: GB08332249A
Authority: GB
Inventors: Udo Reinecke; Jurgen Gerber; Udo Leskien; Wolfgang Finken
Original assignee: O&K Orenstein and Koppel GmbH
Current assignee: CNH Industrial Baumaschinen GmbH
Priority date: 1982-12-03
Filing date: 1983-12-02
Publication date: 1984-08-08
Also published as: JPS59109627A; BE898332A; FR2537184A1; DE3245288A1; GB8332249D0

Abstract

A hydraulic circuit for adjusting an operating cylinder 1 of excavating equipment, in which, to save energy, the working fluid which is discharged under pressure from the cylinder space (2) on one side of the piston when a component of the equipment is lowered under gravity is conveyed to the cylinder space (3) on the other side of the piston. <IMAGE>

Description

SPECIFICATION Hydraulic circuit for adjusting an operating cylinder of excavating equipment The invention relates to a hydraulic circuit for adjusting an operating cylinder of excavating equip ment, for examplethe boom cylinderorthearm cylinder of an hydraulic excavator.

Hitherto, the lowering ofthe boom and the arm of an excavator has been carried out by conveying fluid under pressure into the operating spaces of the appropriate cylinders. This method does not take into accountthe potential energy, both in the boom and in the arm, that could be used at least to assist this operation.

An object ofthe invention is to enable external forces acting on the boom and the arm of excavating equipmentto be exploited during lowering of the boom and/or arm fortransporting theworking fluid into the appropriate operating cylinders.

The present invention provides a hydraulic circuit for adjusting an operating cylinder of excavating equipment, the circuit including a pump unit and a reservoir connectible to the cylinderto adjustthe latter, and valve means operable to interconnect the cylinder spaces on each side ofthe piston when a component of the equipment is lowered under gravity, whereby fluid discharged from one cylinder space is conveyed to the other cylinder space.

The invention further provides a hydraulic circuit for adjusting an operating cylinder of excavating equip ment,whose cylinder spaces on each side ofthe piston can be connected via control valve means to a pump unit and a reservoirto adjust the cylinder, the valve means also having a switching position in which a componentofthe equipment can be lowered under gravity, in which position the valve means blocks the supply linefrom the pump unitand provides an operational connection between one ofthe cylinder spaces and a line extending between the other cylinderspaceandthe reservoir, such thatfluid discharged from one cylinder space is conveyed to the other cylinder space.

In yet anotherform, the invention provides a hydrauliccircuitfor adjusting an operating cylinder of excavating equipment, whose cylinder spaces on each side ofthe piston can be connected via control valve means to a pump unit and a reservoirto adjust the cylinder, the valve means having three switching positions which represent respectively the following line associations:: 1. a) a passage from the pump unitto one cylinder space and b) a return from the other cylinder space to the reservoir, 2. a) passage from the pump unit blocked, and b) return to the reservoir blocked, 3. a) a passage from the pump unit to the said other cylinder space, and b) a return from the said one cylinder space to the reservoir, the circuit also including a lowering valve connected between the cylinderspaces and operable, when a component of the equipment is being lowered under gravity, to provide an operational connection between the said one cylinder space and a line extending between the other cylinder space and the reservoir, such that fluid discharged from the said one cylinder space is conveyed to the other cylinder space, and in which a biased valve is connected in the said line between the operational connection and the reservoir.

Byway of example, embodiments of the invention will now be described with reference to the accompanying drawings, in which: Figures 1 to 3 show different designs of a first form of hydraulic circuit and Figures 4 and 5 show different designs of a second form of hydraulic circuit.

In the individual Figures ofthe drawings, corresponding parts have the same reference numerals.

Figure lisa basic circuitforthe operating cylinder 1 of a component of the excavating equipment of an hydraulic excavator. The cylinder space 2 on the piston side and the cylinder space 3 on the rod side of the cylinder 1 can be connected via operating lines and a control valve 4to a pump unit 5 and a reservoir 6. The illustrated control valve 4 can assume any one of three switching positions, two of which represent the following line associations: 1. a) asupplylinefromthe pumpunit5tothe cylinder space 2 on the piston side, b) a return from the cylinder space 3 on the rod side to the reservoir 6, 2. a) supply line from pump unitS blocked, b) return to reservoir 6 blocked.

The above-mentioned line associations can, however, be supplemented by others corresponding to the third switching position of the control valve 4, when the supply line from the pump unit 5 is blocked and a line 7 between the cylinder space 3 and the reservoir 6 is operational. In this case, there is provided a further operational connection 8 from the cylinder space 2 to the line 7.

In thefirst (left-hand) position of the control valve 4, the cylinder 1 can be extended underthe action ofthe working fluid from the pump unit 5 on the piston surface in cylinder space 2whilefluid displaced from cylinderspace 3 passes unhindered to the reservoir 6.

In the third (right-hand) position ofthe control valve 4 the cylinder can be retracted undertheweight ofthe excavating equipment acting on the piston rod to displace fluid from the cylinder space 2 into the cylinder space 3 and to the reservoir 6. Since experience has shown that a relatively high line resistance isto be expected in the connection to the cylinder space 3, a biased valve 11 is provided in the connection to the reservoir 6 to ensure that connection to the cylinder space 3 has priority.

The hydraulic circuit shown in Figure 1 cannot be used when there are no external forces acting on the piston rod to retract the cylinder, that is, when the dead centre position has been exceeded.

Figure 2 shows a hydraulic circuit which has automaticchange-overto normal operation (ie. retraction of cylinder 1 underthe action ofthe working fluid from the pump unit 5) when the dead centre position has been reached. The circuit is similar to that shown in Fig. 1 with the addition of an external change-over valve 12 and a non-return valve 13 inserted, in the valve 4, between the junction 9 ofthe line 7 and operational connection 8 and the supply 14 ofworking fluid the cylinder space 3. The non-return valve 13 has a blocking action with respect to fluid flow from the supply 14to the junction 9.

Parallel to the control valve 4, that is to say by-passing the control valve, is a by-pass line 15 by which the pump unit 5 is connected to a change-over valve 12. The change-over valve 12 has a control input 16 which can be connected to the cylinder space 2 either directly via a control line 22 when the valve 4 is in the position shown or, when the valve 4 is in the right-hand position, indirectly through the connection ofthe control line 22 to the line interconnecting the cylinder spaces 2 and 3. In this way, the cylinder pressure is used as a switching signal forthe valve 12.

When the dead centre position is reached during retraction ofthe cylinder 1, that is to say when there are no external forces, for example gravity, acting on the piston rod, the cylinder pressure moves towards zero and allows the change-over valve 12 to move, underthe action of the biasing spring, into the position illustrated. The change-over valve 12 must be able to render possible at Ieastthefollowing two lines associations.

1. Passage open from pump unit 5to the cylinder space 3 (as illustrated).

2. Passage blocked.

Figure 3 shows an alternative arrangementfor control ofthe change-overvalve 12. In this case, the control input 16 of the valve is connected via a control line 17to an operating connection 18 of a solenoid valve 19. The other operating connections 20a and 20b ofthe solenoid valve 19 are provided with respective lines 21a and 2lbwhich lead to the pump unit 5 and the reservoir6whereby, in one position ofthe solenoid valve 1 9,the control input 16 of the changeovervalve 12 is connected to the pump 5 and, in the other position, is connected to the reservoir 6.

Operation ofthe cylinder 1, using the hydraulic circuits shown in Figures 2 and 3, is as follows: In orderto extend the cylinder, the control valve 4 is brought into a switching position having the following line associations.

a) Connection of the pump unit 5 to the cylinder space 2 and b) connection ofthecylinderspace3tothe reservoir 6.

The working fluid, conveyed by the pump unit 5, then acts on the piston surface in the cylinder space 2 and the volume of fluid displaced from the cylinder space 3 passes unhindered into the reservoir 6.

Inorderto retractthe cylinder,the control valve 4 is changed overt the right-hand switching position shown in the Figures. As a result of the external forces acting onthe piston rod,a reaction pressure isformed in the cylinder space 2 and, in the Fig. 2 circuit, acts via the control line 22 on the change-overvalve 12 so that the external connection 1 5 from the pump unit Sto the cylinder space 2 is blocked.In the Fig. 3 arrangement, the same result is achievedthrough the action ofthe solenoid valve 19. Atthe same time, the connection from the pump unit5to the cylinder space 2 via the control valve 4 is interrupted and the cylinder space 2 is connected instead to the connection 8 leading, within the control valve, to the biased valve 11 and non-return valve 13. Only some ofthevolume of fluid displaced from the cylinder space 2 passes via the biased valve 11 to the reservoir 6 since the pressure at the biased valve 11 is adjusted to be higherthanthe line resistance via the non-return valve to the cylinder space 3 so that the latter is given priority.

When the dead centre of the movement ofthe excavator equipment is reached there is no longer an external force on the piston rod and, consequently, also no reaction pressure from the cylinder space 2. In the Fig. 2 arrangement, this results in the change-over valve 12 being switched into the position illustrated in whichthe passage 15fromthe pump unit5 is connected to the cylinder space 3 that the pump unit causes the retraction ofthe cylinderto continue.

The connection from cylinder space 3to the reservoir 6 is blocked by the non-return valve 13 butthe working fluid displaced from the cylinder space 2 passes to the reservoir6viathebiasedvalve 11.

In the Fig. 3 arrangement, an electrical command pulse is used for actuating the change-overvalve 12 via the solenoid valve 1 9to continue the retraction of the cylinder 1.

Also shown in Figure 3 is a top-up line 23 which can feed intothecylinderspace2 viatop-up line nonreturn valve 24. The top-up supply is used during operation of the excavator equipment in a so-called "floating position" as will be described below.

Finally, Figure 3 shows a pilot-operated pressure relief valve 25, which is conventionally provided for safety reasons in the cylinders of excavator equip ment,togetherwith an upper pilot valve 26, a lower pilot valve 27 and a further solenoid valve 28 the function of which will also be described below. The terms "upper" and "lower" with respectto the pilot valves referto the pressure values or pressure ranges in which they control the pressure relief valve 25.

Preferably the upper pilot valve 26 is set at a pressure approximately 1 Otimes greaterthan the lower pilot valve 27. Operation of excavator equipment in the "floating position" is important in practice to the users of excavators and, accordingly, a desired feature of excavator equipment. It implies the possibility ofthe position of the excavator equipment being changed, either upwards or downwards, by external forces acting on it. In particular, it is required that, underthe force of gravity, the equipment (especiallythe bucket fastened to the arm) should be able to approach the ground or rest on it but that the bucket should also be lifted againsttheforce ofgravitywhen acted upon by external forces resulting from the uneveness of the ground.

With the hydraulic circuit shown in Figure 3, the above-mentioned floating position can be produced as follows. Firstly, forthe cylinderto be capable of being retracted in the "floating position" for example as a resultofthe action of gravity,theconnectionfrom the pump unit 5 to the cylinder space 3 is blocked externally and internally. This is achieved when the controlvalve4has been broughtintothe right-hand switching position and the change-over valve 12 is in the position shown. An external load which pushes in the direction of retraction ofthe cylinderthen causes working fluid to be fed from the cylinder space 2 via the non-return valve 13 into the cylinder space 3.

Some ofthe volume of fluid from the cylinder space 2 is removed via the biased valve 11 to the reservoir, this being necessary because the total volume of the cylinder space 2 is greater than that of the cylinder space 3.

The second possibility, that is, where an external force acts against the direction of gravity, (for example, as a result ofthe unevenness ofthe ground) can also be accommodated as follows. The command signal that brings the control valve 4 into the position already described is accompanied by a command signal forthe solenoid valve 28. The result is that the pilot-operated pressure relief valve 25 is adjusted to a low pressure range viathe lower pilot valve 27 and working fluid can then escape from the cylinder space 3 via the adjusted pressure relief valve 25 to the reservoir 6. A corresponding volume of working fluid for the cylinder space 2 flows in via the top-up line 23 and the top-up line non-return valve 24. Because the working fluid is able to flowfreely between the cylinder spaces, the position ofthe equipment is not locked but freely movable.

Finally, with regard to the hydraulic circuit shown in Figure 3,the retraction ofthecylinderundertheaction ofthe pump unit 5will also be explained for completeness since it involves the upperpilotvalve 26. The control valve 4 is again in the right-hand switching position already described. In addition, there is emitted by an external command source, to the solenoid valve 19, a special signal which is at the same time an erasing signal forthe other solenoid valve 28.The pressure reliefvalve 25 is thereby adjusted to the high pressure range viathe upper pilot valve 26 and, as a result of the switching of the solenoid valve 19 and thereforethe change-overvalve 12, the pump unit 5 feeds working fluid via the by-pass line 15 and the change-over valve 12 into the cylinder space 3. The working fluid from the cylinder space 2 on the piston side passes via the biased valve 11 to the reservoir 6.

Figure 4 shows anotherform of hydraulic circuit in accordance with the invention. As in the previouslydescribed circuits, a cylinder 1 on a hydraulic excavator has cylinder spaces 2,3 on the piston side and rod side, which can be connected via working fluid lines and a control valve 4to a pump unit 5 and a reservoir6.

In this circuit the three switching positions of the control valve 4 represent the following line associations.

1. a) passage from the pump unit 5 via a line 29a to the cylinder space 2 on the piston side, b) return from the cylinder space 3 on the rod side viaa line 29bto the reservoir 6, 2. a) passage from the pump unit 5 blocked, b) return to reservoir 6 blocked, 3. a) passage from the pump unit 5 viathe line 29b to the cylinder space 3 on the rod side, b) returnftornthe cylinder space 2 on the piston side vithe line 29ato the reservoir 6.

Between the lines29a, 29bfrom the cylinder spaces 2, 3to the control valve 4, a lowering valve 31 is arranged in a line 30. Parallel to the downstream section ofthe line 30 there is provided, via a biased valve 32, a diverting line 33 to the reservoir6whilethe downstream section ofthe line 30 itself includes a non-return valve 34which allows passage in the direction ofthe line 29b.

In an alternative arrangement, shown in Figure 5, the lowering valve 31 of Figure 4 is replaced by a modified lowering valve 38 in which the parallel connection shown in Figure4downstream of the valve is already effected by the valve 38 itself so that it is then no longer necessaryto provide the non-return valve 34.

In both Figures 4 and 5, the control valve 4 is shown with control connections 35a and 35b and the lowering valve 31 has a control input 36. The latter and the control connection 35bare actuated bythe operating outputs of a change-over slide valve 37.

Finally, Figure 5 shows an additional top-up line 39 and non-return valve 40 connected to the cylinder space 2.

The mode of operation of the hydraulic circuits according to Figures 4 and 5 is as follows: The extension of the cylinder 1 requires a line association through the control valve 4 such that the pump unit 5 is connected to the cylinder space 2, and the cylinderspace 3 is connected to the reservoir 6.

Thiscorrespondstothe left-hand switching position ofthe control valve 4, as shown immediately next to the control connection 35a.

When the cylinder is retracted under the action of an external force, forexample the load of the excavator equipment,the change-overslide valve 37 is in the position shown in the drawings and a control signal passes to the lowering valve control input 36 which brings the lowering valve into the opposite position to that shown. Flow is then possible from the cylinder space 2 viathe lowering valve 31 (and, in Figure 4, the non-return valve 34) to the line 29b and thence to the cylinder space 3. At the same time, some of the working fluid flows from the cylinder space 2 via the biased valve 32 and the diverting line 33 to the reservoir 6.

If the excavator equipment comes to rest as a result of coming into contact with the ground, the cylinder 1 remains in the retracted position it has reached.

Further retraction ofthe cylinder, now under the action of the pump unit 5, requires the emission of a switching pulse to the input of the change-over slide valve 37 so that this valve moves into the other switching position. The active signal forthe lowering valve control input 36 is, therefore, interrupted and a signal is passed to the control connection 35bof the control valve 4 so that it assumesthe right-hand switching position shown immediately nextto the control connection 35b. The pump unit 5 is then connected via the control valve 4 and the line 29b to the cylinder space 3 and, at the same time, the working fluid escapes from the cylinder space 2 via the control valve 4 into the reservoir 6.

An especially simple means of achieving operation of the excavator equipment in the floating position is permitted bythe modified hydraulic circuit according to Figure 5.

The extension and retraction of the cylinder are, as already indicated, carried out by the switching operations just explained.

In orderfortheexcavatorequipmentto reach a floating position, the change-over slide valve 37 must be in the position shown and a command signal is passed to the lowering valve control input so that the lowering valve 38 moves into the right-hand switching position. As already described, the lowering valve 38 then connects the cylinder space 2 to the cylinder space 3 via the line 29b and the cylinder 1 is retracted until the equipment contacts the ground and then remains in this position. As a result of other external forces, resulting, for example, from the contact with the ground and acting in the opposite direction, an extension of the cylindertakes place since, duetothe connection described above, a free flow of the working fluid between the cylinder spaces is possible.A differential quantity of the working fluid which may possibly be required is supplied viathe top-up line 39.

This floating position is cancelled and the cylinder 1 is locked by removing the command signal previously-applied atthe lowering valve control input 36. A new signal is emitted to the input ofthe change-over slide valve 37 which switches into the opposite position to that shown and passes a signal to the control connection 35b ofthe working fluid control member 4. The previously-described switching position ofthe control valve 4 is thus again produced, in which the pump unit 5 feeds via the line 29b into the cylinder space 3 and the cylinder 1 is retracted.

It is readily possible to replace the hydraulic signal supply to the control connections 35a and 35b and to the control input 36 by mechanical, pneumatic or electrical signal lines.

The cylinder may be the boom cylinder of an excavator or it may bethe arm cylinder of the excavator. Moreover, the cylinder 1 need not be a single cylinder but could be formed bythe parallel connection of a plurality of cylinders.

Claims

1. Ahydrauliccircuitforadjusting an operating cylinder of excavating equipment, the circuit including a pump unit and a reservoirconnectibletothecylinder to adjust the latter, and valve means operable to interconnectthe cylinder spaces on each side of the piston when a component of the equipment is lowered under gravity, whereby fluid discharged from one cylinder space is conveyed to the other cylinder space.

2. A hydraulic circuit according to claim 1, including means operable, when the pressure ofthe fluid discharged from the cylinder space falls to a predeter mined value,to connect the cylinderto the pump unit to be adjusted thereby.

3. A hydraulic circuit according to claim 2, in which the predetermined value is approximately equal to zero.

4. A hydraulic circuit according to any one of claims 1 to 3, in which the valve means is operable to interconnectthe cylinder spaces by providing an operational connection between one of the cylinder spaces and a line extending between the other cylinder space and the reservoir.

5. A hydrauliccircuitfor adjusting an operating cylinder of excavating equipment, whose cylinder spaces on each side of the piston can be connected via control valve meansto a pump unit and a reservoirto adjust the cylinder, the valve means also having a switching position in which a componentofthe equipment can be lowered under gravity, in which position the valve means blocks the supply line from the pump unit and provides an operational connection between one ofthe cylinder spaces and a line extending between the other cylinder space and the reservoir, such that fluid discharged from one cylinder space is conveyed to the other cylinder space.

6. A hydraulic circuit according to claim 5, including a biased valve connected in the said line between the operational connection and the reservoir.

7. A hydraulic circuit according to claim 6, including a non-return valve connected in thesaid line between the cylinder space and the operational connection to blockfluidflowtowardsthe operational connection.

8. A hydraulic circuit according to any one of claims 5 to 7, including a by-pass line connected parallel to the valve means and including a changeover valve operable to connectthe pump unittothe said other cylinder space via the by-pass line.

9. A hydraulic circuit according to claim 8, in which the change-overvalve has a control input connected to the said one cylinder space.

10. A hydraulic circuit according to claim 8, in which the change-overvalve has a control input connected to an operating connection of a solenoid valve.

11. A hydraulic circuit according to claim 10, in which the solenoid valve has other operating connections connected, respectively, to the pump unit and to the reservoir.

12. A hydraulic circuit according to claim 10 or claim 11, in which a pressure reliefvalve is connected to the said other cylinder space.

13. A hydraulic circuit according to claim 12, in which the pressure relief valve has an operating characteristic which can be adjusted to lie within one or other of two predetermined pressure ranges.

14. A hydraulic circuit according to claim 13, in which the pressure ranges differ by a factor of approximately 10.

15. A hydraulic circuit according to any one of claims 10 to 14, in which a top-up line is connected, via a non-return valve, to the said one cylinder space.

16. A hydraulic circuit for adjusting an operating cylinder of excavating equipmentwhose cylinder spaces on each side ofthe piston can be connected via control valve means to a pump unit and a reservoirto adjust the cylinder,the valve means having three switching positions which represent respectively the following line associations::

1. a) a passage from the pump unit to one cylinder space and b) a return fromthe other cylinderspaceto the reservoir,

2. a) passage from the pump unit blocked, and return to the reservoir blocked,

3. a) a passage from the pump unitto thesaid other cylinder space, and b) a returnfromthesaid onecylinderspacetothe reservoir, the circuit also including a lowering valve connected between the cylinder spaces and operable, when a component of the equipment is being lowered under g ravity, to provide an operational con nection between the said one cylinder space and a line extending between the other cylinder space and the reservoir, such thatfluid discharged from the said one cylinder space is conveyed to the othercylinder space, and in which a biased valve is connected in the said line between the operational connection and the reservoir.

17. A hydraulic circuit according to claim 16, including a non-return valve connected in the said line between the said other cylinder space and the operational connection to block fluid flowtowards the operational connection.

18. A hydraulic circuit according to claim 15or claim 16, in which the control valve means and the lowering valve have control connections connected to the outputs of a change-overvalve.

19. A hydraulic circuit according to any one of the preceding claims in which the cylinder is formed by the parallel connection of several individual cylinders.

20. A hydraulic circuit according to any one of the preceding claims, in which the cylinder is a boom cylinder of an hydraulic excavator.

21. A hydraulic circuit according to any one of claims 1 to 19, in which the cylinder is an arm cylinder of an hydraulic excavator.

22. A hydraulic circuit for adjusting an operating cylinder of excavating equipment, substantially as described herein with reference to and as illustrated by Fig. 1 or Fig. 2 or Fig. 3 or Fig. 4 or Fig. 5 ofthe accompanying drawings.