EP1254319B1 - Device for saving energy in working appliances that can be actuated hydraulically - Google Patents

Abstract

The invention relates to a device for saving energy in working appliances (10) that can be actuated hydraulically and have a piston-type accumulator (12). The aim of the invention is to improve the known device in such a way that said device is only used when actuation of the working appliances in the normal operational mode makes this seem appropriate and that special working procedures carried out by the machine are not impeded, whereby the working appliances are fully discharged or are used intensively during said procedures. A fluid control device (30) is provided with a control device (36) by means of which the piston-type accumulator (12) can be connected to or disconnected from a fluid circle (34) of the working appliance (10). The control device (36) is provided with a monitoring device for the connecting/disconnecting procedures. Said monitoring device detects at least system states of the working appliance (10) and/or the piston-type accumulator (12).

Description

The invention relates to a device for saving energy in hydraulically actuated work equipment with the features of the preamble of claim 1.

A generic energy saving and recovery device is known from EP-A-0 897 480 and DE-A-196 17 950. The pistons of the piston accumulator, which are positively coupled to one another via the coupling part, result in a decreasing preload space within the piston accumulator in one direction of travel with a simultaneous increase in the internal gas pressure, which decreases in the sense of relaxation as soon as the pistons relax. move in the other direction of travel with an increase in the volume of the prestressing space. The amount of gas enclosed in the prestressing space forms a kind of energy store comparable to a mechanical spring, and the kinetic energy of the working equipment introduced into the store by the movement can be called up again.

The use of the known double piston accumulator described above for the energy saving device has shown that it In terms of energy savings, it is particularly favorable to assign a medium piston or boom position of the hydraulically actuated work equipment to a high internal gas pressure in the pretensioning space, which relaxes from this central position while releasing energy, provided that the boom may need to be lifted under load. The energy-saving device mentioned need not be limited to working machines, such as excavators or the like, but may also be used in hydraulic brake systems, in elevators and in hydraulic motors or the like. Find use. In these cases, it is advantageous to provide a large volume for the preload space in order to achieve a low spring constant. To achieve this, it has already been proposed in the known solution to connect the prestressing space to a further gas supply device, in particular in the form of a nitrogen store, as a buffer.

In any case, in the solutions described above, the piston accumulator is permanently connected to the work equipment as a central part of the energy saving and recovery device, so that energy is continuously stored in the piston accumulator and retrieved from there, depending on the work movement of the work implement. Particularly in the case of work machines, such as excavators or the like, the pertinent permanently connected energy saving and recovery device has proven to be disadvantageous in certain work situations, although otherwise the efficiency of the energy recovery can be rated as very good. So it has been shown in the known device that in special positions of the ejector, for example in the fully raised area and thus with full activation of the working equipment, the permanently connected piston accumulator contributes little to efficiency, which also applies to the case, if at Work operations a high pressure on the piston side of the implement is to be exerted, for example when the boom of the implement in the form of an excavator shovel or the like. Shaking operations are carried out or, if the machine has got stuck, it is lifted out of this stuck position via the boom. In such cases, the piston accumulator for energy recovery takes away part of the working energy, which is then no longer available to the machine for these processes.

From US-A-4 541 241 it is known to design a hydraulic accumulator to be connectable and disconnectable by means of a control device with respect to a fluid circuit of an implement, and to detect the system states of the implement and / or the piston accumulator by means of a monitoring device assigned to the control device. The known solution relates to a hydraulic control arrangement for reciprocable, i.e. masses to be accelerated and decelerated cyclically (work tools), which are coupled to a hydraulic rotary piston motor via a rack and pinion drive.

To save energy during the operation of the hydraulic control arrangement, it has hydraulic accumulators as energy storage elements, which can be activated and deactivated again by means of the control device in the fluid circuit of the implement. The acceleration behavior of the rotary piston engine and the fluid pressure conditions in its working chambers are recorded by means of the monitoring device. As with the solution mentioned at the outset, only continuous or permanent operation is essentially possible with the risk of damage to the known arrangement if work-related increased pressure loads occur in the system. In such cases of overuse there is basically only the possibility of switching off the system in the known solution.

Based on this prior art, the invention is therefore based on the object to further improve the known device in such a way that it is in use when an operation of the working equipment in normal working conditions makes this appear necessary and that special work processes with the work machine which the work equipment is completely relieved or very heavily loaded, is not hindered by the energy saving device. A corresponding object is achieved by a device having the features of claim 1.

Characterized in that according to the characterizing part of claim 1, the control device for the relevant switching operations has a monitoring device which detects at least system states of the working equipment and the piston accumulator and that the monitoring device monitors the end position of the pistons of the piston accumulator for this purpose and the working position of the working equipment, it is possible, depending on the working position of the boom and therefore the work equipment and with regard to special applications, such as shaking or lifting with the boom, to decouple the then unnecessary and possibly even disruptive energy saving and recovery device from the fluid circuit with the work equipment and without this the special one. To carry out work. The relevant connection and disconnection processes for the energy saving and recovery device can be carried out manually by an operator of the working machine, but this is preferably done automatically by the monitoring device detecting the system state of the working equipment and the piston accumulator and correspondingly via the fluid control with the control device Controlled piston accumulator as an energy saving and recovery device.

With the fluid control and the control device as well as the monitoring device, the design for the energy saving and the energy recovery can be designed for a predeterminable partial working area of the working machine, which, for example, requires the highest pressure for a working process for the working equipment. Another advantage is that the device according to the invention can be designed very small in size and that existing machines can be retrofitted with the energy saving and recovery device in question. The retrofitting can be done regardless of the cylinder size of the working cylinder of the implement. This means that series retrofitting of machines of different sizes is easily possible.

In a preferred embodiment of the device according to the invention, the control device has a controllable switching valve which is arranged in the fluid circuit between the piston accumulator and a machine control part as part of the fluid control. Using the machine control part in question, manual switching on and off of the double piston accumulator is possible in particular if it interferes with special work tasks; For example, for operations that require high pressure on the piston side of the implement. The latter is the case if, as already mentioned, the working machine has to be used to jog the boom or a lifting process for the entire working machine if it has got stuck in the ground, for example.

If the machine control part is connected downstream of the motor-pump unit, which supplies the fluid circuit from the tank with hydraulic fluid, different control concepts are possible due to the control devices when using control pumps as hydraulic pumps. In this way, an increase in speed can be achieved at the same engine speed, the hydraulic pump not having to regulate the volume flow. In addition, machine noise can be achieved with a low engine speed as the drive for the hydraulic pump and the same working speed, which plays an increasingly important role in the constantly increasing noise protection requirements.

Serve to monitor the working position of the work equipment either a position measuring system and / or an angle encoder and / or a pressure detection device in the fluid circuit. The monitoring device in question is inexpensive to implement and reliable in operation.

In a further preferred embodiment of the device according to the invention, the partition of the piston accumulator separates a fluid space from a gas space, a piston in the fluid space dividing the latter into two fluid subspaces and in the gas space the other piston in turn separating them into two gas subspaces. In particular in connection with the control device, a compact design can then be achieved for the piston accumulator, because only a small amount of fluid has to be taken up to control the working equipment and because the main supply is via the fluid circuit with the machine control part via the drivable hydraulic pump. Accordingly, the gas space mentioned can also be designed smaller because of the smaller pressure work area, which in turn benefits the compact design mentioned. Furthermore, with regard to the described configuration, a better efficiency can be achieved, since the prestressing pressure in the gas space can be selected higher and the pressure-volume characteristic curve of the accumulator is therefore more favorable in the area of the high pressures in the cylinder floor space, because it lies in the flat area of the characteristic curve in question ,

In a further preferred embodiment of the device according to the invention, the one gas subspace can be connected to a gas supply device, the other gas subspace being vacuumed or having ambient air. Due to the connectable gas supply facility it is possible to enlarge the preload space in the manner of a buffer, provided that a lower spring constant should prove to be favorable. If the gas sub-area is preferably provided with the ambient air and connected to the tank of the working machine, a tank pressure that may be present in the tank can be introduced into the piston accumulator via the stored ambient air and thus further increase the preload pressure, which in turn benefits the efficiency in energy storage.

Further advantageous embodiments of the device according to the invention are the subject of the further subclaims.

In the following, an embodiment of the device for energy saving and energy recovery according to the invention is explained in more detail with reference to the drawing.

In principle and not to scale, the only figure shows a circuit diagram of the claimed device.

The device shown in the figure as a circuit diagram is used for energy saving and energy recovery in hydraulically actuated tools, which are designated as a whole by 10. The device also has a piston accumulator 12 which is designed in the manner of a double piston accumulator and has a housing 14. At least two longitudinally movable pistons 16, 18 are arranged in the housing 14. These are with the piston 18, which is located opposite each other or 16 firmly connected to one another via a rod-like coupling part 20. The coupling part 20 itself is guided longitudinally approximately in the middle in a partition 22 of the housing 14. The dividing wall 22 delimits a fluid space 24 and a gas space 26 with essentially the same volumes with the two pistons 16, 18 located opposite one another. The piston 18 on the left as viewed in the direction of the figure, in turn, delimits with the other housing 14 a partial gas chamber 28 which serves as a preload chamber and which is provided with a predeterminable internal gas pressure which corresponds to the preload pressure.

The detailed structure of a piston accumulator of this kind is described in the basic structure in EP 0 897 480, so that no further details will be given here.

The device furthermore has a fluid control, designated as a whole by 30, which is connected to a fluid supply of the work machine, designated as a whole by 32. With the aforementioned fluid control 30 and the fluid supply 32, the implement 10 can be controlled via a closed fluid circuit 34 for the respective work process. For this purpose, the fluid control 30 also has a control device 36, by means of which the piston accumulator 12 can be switched on or off in the fluid circuit 34 of the working device 10. The control device 36 has a monitoring device designated 38 as a whole for the switching operations in question, which detects at least the system states of the implement 10 and the piston accumulator 12.

The control device 36 has a controllable switching valve 40, in particular in the form of an electrically actuable 2/2-way switching valve, the spring-loaded returns to its starting position shown in the circuit diagram by itself. The mentioned switching valve 40 is arranged in the fluid circuit 34 between the piston accumulator 12 and a machine control part 42 as part of the fluid control 30. The machine control part 42 in turn has inputs for two pressure switches 44, each of which, for example, operated by hand using so-called joysticks (mechanical-hydraulic connection) enable the boom (not shown) of the implement 10 to be raised and lowered manually. Furthermore, the machine control part 42 is connected on the input side to the fluid supply, which in particular has a tank 46 and a motor-hydraulic pump unit 48. The hydraulic pump can be designed as a control pump. The inlet and outlet lines between tank 46 and machine control part 42 are part of the fluid circuit 34.

The above-mentioned monitoring device 38 monitors, among other things, the end position of the pistons 16, 18 of the piston accumulator 12 and the respective working position of the implement 10. For monitoring the end position of the pistons 16, 18 of the piston accumulator 12, the latter is provided with limit switches 50 on the end of the housing which provide an electrical switch Issue a signal as soon as the pistons 16 or 18 have reached their respective possible final travel positions. The electrical signal transmission is shown in the basic illustration according to the figure via the electrical lines shown in part. A position measuring system 52 and an angle sensor 54 and a pressure detection device 56, which has a pressure switch which is arranged in the fluid circuit 34 between the outlet side of the switching valve 40 and the inlet side of the implement 10, are used in a secondary branch to monitor the working position of the implement 10. The pressure switches show the direction of movement (up / down) of the memory. The measuring system 52, the angle encoder 54 and the pressure detection device 56 can be used in combination, as shown in the circuit diagram, or can only be used individually, depending on the requirements for the control and its convenience. Ultimately, however, they all give a statement about the state of movement and work for the work tool 10.

The fluid space 24 is divided by the piston 16 into two fluid subspaces 24a, b; this also applies to the gas space 26, which is divided into two gas subspaces 26a, b by the other piston 28. The one gas subspace 26a is equal to the prestressing space 28 with a predetermined internal gas pressure. A gas supply device 60, in particular filled with nitrogen, can be connected to the gas subspace 26a or the prestressing space 28 via a valve device 58. The other gas subspace 26b is either vacuum-sealed or, as shown, can be connected via a connection device 62 and thus has ambient air. In an embodiment not shown in detail, it is also possible to connect the gas subspace 26b to the tank 46. If the tank 46 then has an increased working pressure, the relevant preload pressure can be passed on to the gas subspace 26b. Regarding the circuit according to the figure, it must also be said that the working equipment 10 has two hydraulic working cylinders 64, which are customary for such working machines. The two working cylinders 64 are connected to one another in a fluid-carrying manner on the rod side 66 as well as on the piston side 68 via corresponding fluid lines.

The rod side 66 is in turn connected to the machine control part 42 in a fluid-carrying manner and the piston side 68 is fluid-carrying in connection with the control device 36 with a switching valve 40. Furthermore, the control device 36 is connected in a fluid-carrying manner to the piston accumulator 12 and to the machine control part 42, in particular via the switching valve 40 the two fluid subspaces 24a, 24b. According to the switching diagram, the switching valve 40 is shown in the unactuated state, the fluid flow from the machine control part 42 to the piston accumulator 12 being blocked, but being made to the piston side 68 of the implement 10. In the actuated switching position, there is then a fluid flow from the machine control part 42 to the piston accumulator 12, in particular to the fluid subspace 24a, and furthermore the piston side 68 of the implement 10 is in fluid communication with the fluid subspace 24b of the piston accumulator. However, nothing changes in the fluid-carrying connection between the machine control part 42 and the rod side 66 of the two working cylinders 64.

For better understanding, the device according to the invention will now be explained in more detail based on its function.
If the switching valve 40 is not actuated in its initial state in accordance with the switching diagram shown, the machine control part 42 supplies the piston side 68 of the two working cylinders 64 via the fluid supply 32 and the working device 10 with its boom extends, that is to say it is moved upward as seen in the switching diagram. The displaced fluid from the rod-side fluid spaces of the two working cylinders 64 is then returned, bypassing the switching valve 40, directly to the machine control part 42 and from there into the tank 46 38 detected with their individual sensors and the piston accumulator 12 connected as an energy saving and recovery device in the fluid circuit 34. During the downward movement in this way, the switching valve 40 is switched on via the control device 36 in the energetically sensible area and, when viewed in the direction of the switching diagram, assumes its right switching position with crossed fluid paths. The piston pushed out Fluid from the working cylinders 64 is then forwarded via the cross-fluid guide of the switching valve 40 into the fluid subspace 24b and, under the action of the fluid pressure, the piston arrangement 16, 18 moves to the left in the direction of view of the figure and increases the biasing pressure in the biasing space 28 or in the gas subspace 26a with simultaneous increase in volume of the gas subspace 26b.

The amount of fluid displaced in the fluid subspace 24a during the movement of the piston 16 from right to left is displaced in the direction of the machine control part 42 and towards the tank 46 via the associated fluid line and the switching valve 40. When the piston 18 reaches its limit switch 50 assigned to it, the work involved in taking up the piston accumulator 12 can also be switched off. If the boom 10 is now to be raised again for a work process, the fluid quantity of the fluid supply 32 can be brought into the subspace 24a with the switching valve 40 actuated via the machine control part 42 and the prestressed gas volume in the prestressing space 28 or gas subspace 26a relaxes with the result that the energy previously introduced in this way is now called up during the return movement of the piston 16 from left to right and the amount of fluid ejected from the fluid subspace 24b in turn reaches the piston chamber of the delivery cylinder 64 via the switching valve 40 in a crossed switching position and thus supports the lifting process of the implement 10. This Fluid pushed out on the rod side 66 in turn reaches the tank 46 via the assigned fluid line and the machine control part 42. The pushing-out movement movement of the piston arrangement 16, 18 can be carried out, for example, via the assigned limit switch 50 to the piston 16 and then switch off while switching on the control device 36.

The embodiment described above can also be modified in such a way that instead of two working cylinders 64, only one working cylinder is used or, if appropriate, more than two. The device described above has also proven to be energetically advantageous if the boom is in a static position or is operated in the end-of-travel range.

Claims (9)

1. An energy saving device for hydraulically operated implements (10) with a piston accumulator (12) with a housing (14) in which at least two longitudinally movable pistons (16, 18) are arranged, each of them being connected together to an adjacent opposite piston (18, 16) via a coupling part (20) which is longitudinally movable in a partitioning wall (22) of the housing (14) which, together with the two adjacent opposite pistons (16, 18), delimits the chambers (24, 26), whereby at least one of the pistons (18) delimits a preloading chamber (28) at a specified inside gas pressure at least partly, and with a hydraulic control unit (30) which is connected to a hydraulic supply unit (32) and can be controlled by means of the implement (10) via a hydraulic circuit (34) to perform an operation, whereby the hydraulic control unit (30) has a control device (36) by means of which the piston accumulator (12) can be connected to or cut off from the hydraulic circuit (34) of the implement (10), characterised in that the control device (36) has a monitoring device (38) for the respective switching operations, which covers at least the system states of the implement (10) and of the piston accumulator (12), and that the monitoring device (38) monitors for this purpose the limit position of the pistons (16, 18) of the piston accumulator (12) and the operating position of the implement (10).
2. A device according to Claim 1, characterised in that the control device (36) has a biasable control valve (40) which is arranged in the hydraulic circuit (34) between the piston accumulator (12) and a machine control part (42) as part of the hydraulic control unit (30).
3. A device according to Claim 1 or 2, characterised in that to monitor the limit position of the pistons (16, 18) of the piston accumulator (12), the latter has limit switches (50) and that a displacement measurement system (52) and/or an angle measuring pick-up (54) and/or a pressure detecting device (56) within the hydraulic circuit (34) serves the purpose of monitoring the operating position of the implement (10).
4. A device according to one of the Claims 1 to 3, characterised in that the partitioning wall (22) of the piston accumulator (12) separates a hydraulic chamber (24) from a gas chamber (26), that a piston (16) in the hydraulic chamber (24) divides it into two hydraulic part chambers (24a, b) and that the other piston (28) in the gas chamber (26) divides it into two gas part chambers (26a, b).
5. A device according to Claim 4, characterised in that one gas part chamber (26a) can be connected to a gas supply device (60) and that the other gas part chamber (26b) is vacuated or contains ambient air.
6. A device according to Claim 5, characterised in that the gas part chamber (26b) is connectable to ambient air via a connecting device (62) or is connected to the tank (46) of the hydraulic supply unit (32).
7. A device according to Claim 5, characterised in that the implement (10) has two operating cylinders (64) which are connected together hydraulically at the piston end as well as the piston rod end and that the piston rod end (66) is hydraulically, connected to the machine control part (42) and the piston end (68) is hydraulically connected to the control device (36).
8. A device according to Claim 7, characterised in that the control device (36) is further connected hydraulically to the piston accumulator (12) and to the machine control part (42), especially to the two hydraulic part chambers (24a, 24b).
9. A device according to Claims 2 and 8, characterised in that the control valve (40) in its unoperated state blocks the hydraulic flow from the machine control part (42) to the piston accumulator (12) and restores it to the piston end (68) of the implement (10) and in its operated state restores the hydraulic flow from the machine control part (42) to the piston accumulator (12) and from it to the piston end (68) of the implement (10).