EP3705733A1 - Linear drive with closed hydraulic circuit - Google Patents

Abstract

A linear drive is specified, with a hydraulic pump (10), the delivery volume of which can be changed, and with a hydraulic linear device (13), with a cylinder (14) and a piston (15) that can be moved linearly back and forth in the cylinder (14) ), wherein in the direction of movement of the piston (15) a first cylinder chamber (16) is formed in front of the piston and a second cylinder chamber (17) is formed behind the piston, a first hydraulic line (11) being provided which connects the first cylinder chamber (16) an output of the pump (10), and wherein a second hydraulic line (12) is provided which connects the second cylinder chamber (17) directly to an input of the pump (10). In addition to the cylinder (14), an additional hydraulic cylinder (19) can be provided in which an additional piston (20) can be moved linearly back and forth, the piston (15) mechanically with the additional piston (20) or the additional cylinder (19) can be coupled, and wherein a cylinder chamber of the cylinder (14) can be hydraulically coupled to a cylinder chamber of the additional cylinder (19).

Description

The invention relates to a linear drive, in particular for a hydraulically actuated linear movement, for example as a cylinder drive on a hydraulically operated construction machine.

Mobile work machines such as construction machines (excavators, loaders, etc.) are often operated hydraulically. For example, rotary drives (hydraulic motors) or single or double-acting linear drives (hydraulic cylinders), which can be fed by a common hydraulic circuit or separate hydraulic circuits, are used as consumers.

Fig. 1 shows a schematic illustration of a typical example of such a structure.

At least one motor 1 drives at least one pump 2 to rotate, which sucks in hydraulic fluid (hydraulic oil) as a pressure medium from a reservoir 3 and conveys it to a plurality of control valves 5 via a hydraulic line 4. The control valves 5 are switched as required in order to guide the pressurized hydraulic fluid to individual consumers (actuators), namely cylinder drives 6 or hydraulic motors 7. After the energy has been released, the now essentially pressureless hydraulic fluid is fed back into the storage container 3 via a hydraulic line 8.

The pump 2 can be used as a constant pump or - as in Fig. 1 shown - be designed as a variable displacement pump. The control valves 5 are part of a throttle control in which the common volume flow is distributed to the actuators 6, 7 by means of the control valves 5, so that the individual actuation of the individual actuators 6, 7 is guaranteed.

Due to the principle, however, flow losses occur at each control valve, which reduce the energy efficiency. Valves in particular have very high system-related losses. To increase efficiency, however, these losses should be minimized as far as possible.

The invention is therefore based on the object of specifying a linear drive in which the energy efficiency can be increased compared with the prior art.

The object is achieved by a linear drive with the features of claim 1. An alternative embodiment is specified in the independent claim. Advantageous embodiments are defined in the dependent claims.

A linear drive is specified, with at least one hydraulic pump, the delivery volume of which is variable, and with at least one hydraulic linear device, with at least one cylinder and at least one piston that can be moved linearly back and forth in the cylinder, with one piston in front of the piston in the direction of movement of the piston first cylinder chamber and behind the piston a second cylinder chamber is formed, wherein at least one first hydraulic line is provided which connects the first cylinder chamber to an output of the pump, and wherein at least one second hydraulic line is provided which connects the second cylinder chamber to an input of the pump .

The terms input and output of the pump are to be understood depending on the type of pump and its operating situation. The principle is that the pump delivers from one connection and sucks in via a second connection. When using a variable displacement pump, delivery in two directions may be possible, depending on the type of pump and the current position of the adjustment mechanism. Accordingly, the hydraulic fluid can flow both in and out of both connections of the pump, so that each pump connection can be both the inlet and the outlet, depending on the operating situation.

The port in which the hydraulic fluid leaves the pump is referred to as the outlet, whereas the port in which the hydraulic fluid flows into the pump is referred to as the input. If, therefore, one speaks of an inlet and outlet of the pump, this is only done in order to distinguish the two connections of the pump and does not necessarily serve to define a necessary flow direction of hydraulic fluid in the hydraulic structure.

The pump can be designed as a fixed displacement pump.

The pump can in particular be a variable displacement pump in order to implement the displacement control aimed at here.

The piston can be designed as a single-acting or double-acting piston and in particular have a piston rod. A double acting piston can be designed as a differential or synchronous piston (alternatively also called differential or synchronous cylinder). Accordingly, the piston surfaces or active surfaces can be of different sizes on both sides, since they are reduced on one side by the piston rod attached there.

The linear device can be a typical piston-cylinder unit or a hydraulic drive that can be used, for example, to move an excavator arm, a shovel or a spoon.

The above statement that “a first cylinder chamber is formed in front of the piston and a second cylinder chamber is formed behind the piston” is to be understood in general terms. This is initially only intended to express that there are cylinder chambers in front of and behind the piston in the direction of movement. The choice of names "first" and "second" is arbitrary and only serves to differentiate. The assignment of the cylinder chambers only becomes relevant at a later point in time, as will be explained later.

The hydraulic lines between the pump and the cylinder chambers are closed so that a direct, pressure-tight connection between the pump and the cylinder chamber is made possible. The hydraulic lines can consist of pipe elements, hose sections, etc. in a suitable manner. In this way, a closed hydraulic circuit is formed, in contrast to the open circuit according to the prior art, in which the hydraulic fluid is first returned to the tank and only then returned to the pump. The hydraulic fluid that goes directly from the cylinder back to the pump is not returned to a storage container or tank and only then pumped again, but is fed directly from the consumer to the pump via the second hydraulic line, where energy is added or removed . In particular, with the selected construction, hydraulic fluid under pressure can be fed to the pump in the return.

Another advantage of the selected design is that no control elements are provided in the hydraulic lines that conduct pressurized hydraulic fluid between the at least one pump and the at least one hydraulic linear device that influence the flow of the hydraulic fluid in regular operation. There are therefore no switching elements or throttles for regulating the quantity. The line between the pump and the hydraulic linear device is circuit-free. Elements that are only used in an emergency (ie not in regular operation) are not considered circuit elements. This are, for example, pipe burst protection devices or load holding valves which are arranged in hydraulic lines and on hydraulic linear devices and prevent the loss of hydraulic fluid and uncontrolled movements of the machine in the event of a leak in a hydraulic line.

The invention thus relates to a linear drive with a closed hydraulic circuit, which is controlled with the aid of a displacement control.

In a variant, the piston can be a double-acting piston, on one side of which a piston rod is provided, wherein the piston rod can be guided out of the cylinder. In particular, the object to be driven by the linear drive, for example an excavator arm, can be attached to the piston rod in order to achieve the desired force effect.

The first cylinder chamber can be arranged with respect to the piston opposite that side on which the piston rod is provided, wherein the second cylinder chamber can be arranged on the side of the piston rod. With this information, the cylinder chambers and their position in relation to the piston are now more precisely specified.

The piston can accordingly have two opposite piston surfaces on the front side, each of which adjoins the first or the second cylinder chamber, wherein the piston surface facing the first cylinder chamber can be larger than the piston surface facing the second cylinder chamber. The decisive factor here is the effective piston area, which converts the hydraulic pressure acting on it into a force for moving the piston. As already explained above, the piston surface to which the piston rod is attached is in principle smaller than the opposite piston surface.

In principle, the linear drive can be operated in a closed circuit in this way, at least within certain limits. However, it should be noted that the volume displacement on both sides of the piston is also different due to the different piston areas. This means that the volume flow in the area of the first cylinder chamber is greater than in the area of the second cylinder chamber, which - due to the closed hydraulic circuit - must be compensated for by the mostly low compressibility of the hydraulic fluid.

To solve this problem, it is possible that, in addition to the cylinder, a hydraulic auxiliary cylinder can be provided in which an auxiliary piston is linearly movable back and forth, the piston being mechanically coupled to the auxiliary piston or the auxiliary cylinder, and a cylinder chamber of the cylinder is hydraulically coupled to a cylinder chamber of the additional cylinder.

Mechanically coupled in this case means that the piston should be rigidly connected to the additional piston or the additional cylinder, so that the force acting on the piston is also transmitted to the additional piston or the additional cylinder. The mechanical coupling can expediently be implemented by coupling the piston rods connected to the two pistons to one another. This forces the piston and additional piston to move together.

The hydraulic coupling between the cylinder chamber of the cylinder and the cylinder chamber of the additional cylinder can be brought about by a hydraulic connection between the two chambers, for example by a hydraulic line.

The term "addition" is not intended to mean that this is a fundamentally different structure. Rather, this addition is only used for clearer naming and differentiation between the various cylinders and pistons. Accordingly, the cylinders and pistons are also sometimes referred to below with the additions "additional" or "main".

The mechanical coupling of the piston to the additional piston represents a first variant of this embodiment, while the mechanical coupling of the piston to the additional cylinder represents a second variant.

In both variants it is possible that the additional piston is a double-acting piston, on one side of which a piston rod is provided which is led out of the additional cylinder, the additional cylinder having a first cylinder chamber which is arranged opposite the side with respect to the additional piston is on which the piston rod is provided, and wherein the auxiliary cylinder has a second cylinder chamber which can be arranged on the side of the piston rod.

According to the first variant, the piston can be mechanically (rigidly) coupled to the additional piston, the second cylinder chamber of the cylinder and the second cylinder chamber of the additional cylinder can be hydraulically coupled to one another.

The first cylinder chamber of the additional cylinder can be configured in such a way that it cannot be acted upon by hydraulic pressure. For example, the first cylinder chamber can be open to the environment or connected to the tank and thus have no function.

With this variant, an area compensation is realized which enables compensation for the differently sized effective piston areas on the (main) piston. By connecting the additional cylinder in the form of the mechanical and hydraulic coupling, volume flows can be generated or increased on the side with the smaller piston area - with the appropriate dimensions - so that the volume flows on both sides of the (main) piston when this piston moves are identical. This means that the closed hydraulic circuit can also be operated over a larger linear movement path of the (main) piston. The fluid balance on both sides of the pump (inlet and outlet) is always balanced.

In a further embodiment, a pressure accumulator device can be provided, wherein the first cylinder chamber of the additional cylinder can be coupled fluidically, in particular hydraulically or pneumatically, in a communicating manner with the pressure accumulator device. Load compensation can be achieved as a result, as described below.

While it was explained above that the first cylinder chamber of the additional cylinder should not be able to be acted upon by hydraulic pressure, i.e. could for example be open to the environment in order to accomplish the area compensation, the pressure storage device now to be connected there can enable a load compensation. In particular, the additional cylinder or the additional piston can thus be preloaded so that a force can also be produced when the pump is in the rest position. This makes it possible, for example, to keep the dead weight of an excavator arm permanently with the help of the pressure accumulator. When the excavator arm moves, the pump then no longer has to provide the entire power to compensate for the weight of the excavator arm, but only the power that is still required for the actual movement. The excavator arm is supported against the pressure accumulator.

In the second variant, the piston can be mechanically coupled to the additional cylinder (instead of the mechanical coupling to the additional piston), in which case the second cylinder chamber of the cylinder and the first cylinder chamber of the additional cylinder can be hydraulically coupled to one another.

In this second variant, the two cylinders are twisted against each other, so to speak, and act in opposite directions. The connections (mechanical, hydraulic) are cross-connected. In this case, too, the desired area compensation is possible through the appropriate arrangement.

In this variant, the second cylinder chamber of the additional cylinder should not be able to be acted upon by hydraulic pressure and should, for example, be open to the environment.

In the second variant, too, a pressure accumulator device can be provided for load compensation, in which case the second cylinder chamber of the additional cylinder can then be hydraulically coupled to the pressure accumulator device. With this arrangement, the use of a single-acting hydraulic cylinder (plunger cylinder) is possible as an additional cylinder.

The variants and features of the invention explained so far relate essentially to a piston that is designed as a single-acting or double-acting piston. Alternatively, however, a multi-surface cylinder can also be provided. Multi-surface cylinders are known and consist of several pistons and cylinders which are coaxially assigned to one another and integrated with one another. A general example of such a multi-surface cylinder shows DE 20 2013 002 497 U1 .

According to the independent claim, a linear drive is specified with a hydraulic pump, the delivery volume of which can be changed, and with a hydraulic linear device with a multi-surface cylinder, the multi-surface cylinder having at least two pistons which are arranged on a common central axis and displaceable relative to one another, of which a first piston is in a cylinder is movable and a second piston is integrally connected to this cylinder, the two pistons and the cylinder being movably arranged in an outer cylinder, a first cylinder chamber being formed between the first piston and the cylinder and between the second piston and the outer cylinder a second cylinder chamber is formed, wherein a first hydraulic line is provided, which the first cylinder chamber or the second cylinder chamber connects to an output of the pump, and wherein a second hydraulic line is provided which connects the remaining cylinder chamber with an input of the pump or wherein a first hydraulic line is provided which connects the third cylinder chamber or the second cylinder chamber to an output of the pump and wherein a second hydraulic line is provided which connects the remaining cylinder chamber with an input of the pump.

Thus, instead of the combination of cylinder and piston given above, the multi-surface cylinder is used in this example and is connected to the pump in a suitable manner.

The cylinder can in particular be an inner cylinder, wherein the first piston can be an inner piston that can be moved linearly to and fro in the inner cylinder, the first cylinder chamber being formed between an end face of the inner piston and the inner cylinder. The outer cylinder can at least partially surround the inner cylinder in a ring shape, the second piston being an outer piston that surrounds the inner cylinder in a ring shape and is connected in one piece to the inner cylinder, the outer cylinder ring-like enclosing the outer piston, and between an end face of the outer piston and the Outer cylinder, the second cylinder chamber and between an opposite end face of the outer piston and the outer cylinder, a third cylinder chamber can be formed.

The third cylinder chamber can thus be present between the outer cylinder and the second piston (outer piston). It can either be open to the environment or connected to the tank, i.e. it can be depressurized, whereby an area compensation can be achieved as described above. The third cylinder chamber can also be coupled to a pressure accumulator for load compensation.

Fig. 1

einen offenen Hydraulikkreislauf mit einer bekannten Drosselsteuerung gemäß dem Stand der Technik;

Fig. 2

eine Kombination aus der bekannten Drosselsteuerung und einer erfindungsgemäßen Verdrängersteuerung mit geschlossenem Hydraulikkreis ;

Fig. 3

eine Detailansicht zur Verdrängersteuerung;

Fig. 4

eine Variante mit Flächenkompensation;

Fig. 5

eine Variante mit Lastkompensation;

Fig. 6

einen Ausschnitt zu der Variante von Fig. 4 mit Flächenkompensation;

Fig. 7

eine Variante zu der Ausführungsform von Fig. 6;

Fig. 8

eine Detailansicht der Variante von Fig. 5 mit Lastkompensation;

Fig. 9

eine Variante zu der Ausführungsform von Fig. 8;

Fig. 10

eine Variante mit Mehrflächenzylinder mit Flächenkompensation; und

Fig. 11

die Variante von Fig. 10 mit Lastkompensation.

These and further features and advantages of the invention are explained in more detail below on the basis of examples with the aid of the accompanying figures. Show it:

Fig. 1

an open hydraulic circuit with a known prior art throttle control;

Fig. 2

a combination of the known throttle control and a displacement control according to the invention with a closed hydraulic circuit;

Fig. 3

a detailed view of the displacement control;

Fig. 4

a variant with area compensation;

Fig. 5

a variant with load compensation;

Fig. 6

an excerpt from the variant of Fig. 4 with area compensation;

Fig. 7

a variant of the embodiment of Fig. 6 ;

Fig. 8

a detailed view of the variant of Fig. 5 with load compensation;

Fig. 9

a variant of the embodiment of Fig. 8 ;

Fig. 10

a variant with a multi-surface cylinder with surface compensation; and

Fig. 11

the variant of Fig. 10 with load compensation.

Fig. 2 shows in an analogous representation to Fig. 1 in the right part of the picture a throttle control according to the Fig. 1 with an open hydraulic circuit and in the left part of the picture a displacement control with a closed circuit.

Accordingly - is analogous to Fig. 1 - At least one motor 1 is provided, which drives at least one pump 2, which in turn delivers hydraulic fluid from a reservoir 3 via a hydraulic line 4 and control valves 5 to various consumers or actuators (cylinder drives 6, hydraulic motors 7). The control valves 5, which form the core of the throttle control, are subject to high losses for the volume flows. In one variant, several motors 1 or several pumps 2 can easily be provided for operating the hydraulic circuit.

The components form an open circuit, since the hydraulic fluid flowing back essentially without pressure from the consumers via the hydraulic line 8 is first fed into the open storage container 3 before it can be sucked in again by the pump 2 and conveyed.

In the left part of the image Fig. 2 In contrast, a hydraulic circuit which is closed according to the invention is shown. A pump 10, which is driven by the engine 1, is also provided there. For the closed circuit it is not necessary that the in Fig. 2 The open circle shown is present. Rather, the closed circuit can also be operated separately, so that the motor 1 can also operate the pump 10 exclusively.

The pump 10 can in particular be designed as a constant or variable displacement pump in order to achieve the desired volume flow. The pump 10 is connected via hydraulic lines 11 and 12 to a piston-cylinder unit 13 serving as a linear device, for example, which in turn has a cylinder 14 and a piston 15 designed as a differential piston.

A first cylinder chamber 16 is formed in front of the piston 15 in the direction of movement and a second cylinder chamber 17 is formed opposite it.

The first cylinder chamber 16 is connected to the output of the pump 10 via the hydraulic line 11, while the second cylinder chamber 17 is connected to the input of the pump 10 via the hydraulic line 12.

When the engine is operating, the pump 10 delivers the pressure medium (hydraulic fluid or hydraulic oil) located in the hydraulic lines 11, 12 into the first cylinder chamber 16, as a result of which the piston 15 moves linearly. Accordingly, hydraulic fluid is pressed out of the second cylinder chamber 17 and returned directly to the pump 10 via the hydraulic line 12. There is no intermediate buffering with the aid of a storage container (cf. storage container 3) or tanks, as this is a closed hydraulic circuit. In addition, no switching elements are provided in the hydraulic lines 11, 12 which are used in trouble-free operation. Such switching elements are not necessary in a closed hydraulic circuit, since the volume flow can be controlled with the direction of rotation and / or speed and / or setting of the pump.

Fig. 3 shows in greater detail the structure of a variable displacement pump designed as a variable displacement pump 10, in which case a hydraulic motor 7 is connected as a consumer instead of a linear device.

Fig. 4 is based on the variant of Fig. 2 . In addition, a so-called area compensation is implemented. Fig. 6 shows an enlarged section Fig. 4 .

How to compare to Fig. 2 shows, in addition to the piston-cylinder unit 13 and the cylinder 14 (master cylinder) and the piston 15 (master piston), an additional piston-cylinder unit 18 is provided, with an additional cylinder 19 and an additional piston 20.

The two pistons, namely the piston 15 and the additional piston 20, are rigidly connected to one another via a mechanical coupling 21. The mechanical coupling 21 can be, for example, a rod screw connection or other structural connection. In particular, for the mechanical coupling of the two pistons 15, 20, the two piston rods present in each case can be rigidly connected to one another.

In addition, a first cylinder chamber 22 is provided in front of the additional piston 20 and a second cylinder chamber 23 is provided in the additional cylinder 19 behind the additional piston 20.

The second cylinder chamber 23 is hydraulically connected to the second cylinder chamber 17 of the cylinder 14 via a hydraulic connection 24. A hydraulic fluid or pressure equalization between the two second cylinder chambers 23, 17 can thus take place.

To distinguish between the additional cylinder 19 and the additional piston 20, the cylinder 14 can also be referred to as the master cylinder and the piston 15 as the master piston.

The first cylinder chamber 22 of the additional cylinder 19 is open to the environment, as shown by an outlet 25.

By providing the additional piston-cylinder unit 18, it is possible to transfer the movement of the piston 15 to the additional piston 20, so that a common movement of the two pistons 15, 20 also leads to an increased volume flow in the two second cylinder chambers 17, 23 leads. With appropriate dimensioning, it can be ensured that the volume flow between the pump 10 and the first cylinder chamber 16 is in equilibrium with the total volume flow from the second cylinder chambers 17, 23 combined with one another is, so the volume flow balance is balanced. In this case, the two pistons 15, 20 can also be moved over longer distances, because the same amount of hydraulic fluid is always refilled into the first cylinder chamber 16 as it escapes from the second cylinder chambers 17, 23 via the hydraulic line 12.

Fig. 5 shows another variant with a load compensation. Fig. 8 shows an enlarged detail Fig. 5 .

The structure essentially corresponds to the structure of Fig. 4 . Here, too, it is not necessary to keep the structure with throttle control shown in the right half of the figure. Rather, it is all about the left part of the picture with the closed cycle.

While the variant of Fig. 4 the first cylinder chamber 22 in the additional cylinder 19 was open to the environment (outlet 25), a pressure accumulator 26 is now hydraulically coupled to the first cylinder chamber 22. This has the effect that - depending on the joint movement of the pistons 15, 20 - the pressure medium in the pressure accumulator 26 is compressed or relaxed. In this way, a load permanently acting on the (main) piston 15 can be compensated for, in particular via the additional piston 20. For example, the weight of an excavator arm can be compensated for with the aid of the pressure accumulator 26, so that the pump 10 and the closed circuit only need to effect a movement of the arm without, however, bearing the full weight of the excavator arm.

Fig. 7 shows a variant of the embodiment of FIG Fig. 4 and 6th .

The piston-cylinder unit 13 and the additional piston-cylinder unit 18 are operatively rotated by 180 ° with respect to one another and coupled with one another crosswise. In this case, the mechanical coupling 21 couples the piston 15 or its piston rod to the additional cylinder 19. The hydraulic connection 24 connects the second cylinder chamber 17 to the first cylinder chamber 22 of the additional cylinder 19. The second cylinder chamber 23 of the additional cylinder 19 is via the outlet 25 open to the environment. The second cylinder chamber 23 can also be omitted when using a single-acting plunger cylinder.

A similar variation arises with regard to the Figures 8 and 9 .

Figures 8 and 9 show arrangements in which the piston-cylinder unit 13 and the additional piston-cylinder unit 18 are rotated by 180 °, as above with reference to FIG Fig. 7 already explained.

The pressure accumulator 26 is provided at the outlet 25 in order to cope with the desired load compensation. The pressure accumulator 26 is thus connected to the cylinder chamber 22 in Figure 8 or the cylinder chamber 23 in Figure 9 of the additional cylinder 19 hydraulically connected.

Fig. 10 shows a variant in which the piston-cylinder unit 13 and the additional piston-cylinder unit 18 are replaced by a multi-surface cylinder 30. The multi-surface cylinder 30 has an inner cylinder 31, in the interior of which an inner piston 32 can be moved linearly to and fro.

The inner cylinder 31 is ring-shaped by an outer piston 33 and rigidly mechanically connected to it. The outer piston 33 is in turn guided to be linearly movable back and forth in an outer cylinder 34.

A first cylinder chamber 35 (“A”) is formed between the inner cylinder 31 and the inner piston 32 and is connected to the pump 10 (not shown) via the hydraulic line 11 (partially shown in phantom).

A second cylinder chamber 36 (“B”) is formed between the outer piston 33 and the outer cylinder 34 and is connected to the pump 10 via the hydraulic line 12.

Finally, opposite the second cylinder chamber 36, a third cylinder chamber 37 (“C”) is formed between the outer piston 33 and the outer cylinder 34. The third cylinder chamber 37 is open to the environment via the outlet 25.

Alternatively, the third cylinder chamber 37 (C) and the second cylinder chamber 36 (B) can each be connected to the pump. In this variant, the first cylinder chamber 35 (A) is open to the environment via an outlet.

With the multi-surface cylinder from Fig. 10 the desired area compensation can thus also be achieved.

Fig. 11 again shows a variant in which the pressure accumulator 26 is connected to the outlet 25 in order to achieve load compensation.

In the examples shown, only one variable displacement pump (pump 10) is shown for the closed circuit. However, several pumps (variable or fixed displacement pumps) can easily be used to achieve the desired performance.

The displacement control described is particularly suitable for cylinder drives that can be used in working machines, in particular for the construction industry, such as earth-moving machines such as excavators, wheel loaders, telehandlers, etc.

The at least one pump can be driven in different ways. A variant for driving the pump is the drive by means of an internal combustion engine. Alternatively, the drive can take place by means of at least one electric motor. The drive can be set up to drive the at least one pump in two directions of rotation, provided that the at least one pump is designed as a fixed displacement pump. If the at least one pump is designed as a variable displacement pump whose range of adjustment enables delivery in two directions, the drive can be designed to drive the pump in only one direction of rotation.

In a variant, the electric motor can also be set up to act on the speed of the pump with a defined braking torque.

The electric motor can draw its drive energy from a rechargeable electrical energy storage device that is carried on the work vehicle. In this way, the work vehicle is independent of the supply of external energy for at least a certain period of time and can maximize its operating time due to the efficient hydraulic linear drive according to the invention. Alternatively, the electrical energy for operating the work machine can be provided at least temporarily in combination from the electrical energy store and an external energy supply, such as for example by means of a power cable.

The linear drive described can also be combined with at least one further pump which works in an open circuit or which has switching elements or throttles for volume regulation in the associated line system are. In particular, a hydraulic motor can be provided in the associated line system in order, for example, to actuate the swivel mechanism of an excavator with which an upper carriage can be pivoted on an undercarriage.

A linear drive of the type described can therefore be provided in a first hydraulic circuit with a first pump with a hydraulic motor for driving a swivel mechanism in a second line system with an associated second pump. The first and the second pump can in particular be operated by different drives, so that they can be driven and controlled independently of one another.

The linear drive can be used in mobile work machines with a work device, wherein at least one function of the work device, such as lifting / lowering, retraction / extension, can be hydraulically driven. The working device can be a lifting arm, as is known, for example, from wheel loaders, telescopic loaders or excavators. Such work machines and their work devices are usually used to move or transport material such as bulk material (sand, earth).

Claims (14)

Linear drive, with - At least one hydraulic pump (10), the delivery volume of which can be changed; and with - At least one hydraulic linear device (13), with at least one cylinder (14) and at least one piston (15) movable linearly to and fro in the cylinder (14);
in which - In the direction of movement of the piston (15) a first cylinder chamber (16) is formed in front of the piston and a second cylinder chamber (17) is formed behind the piston; - At least one first hydraulic line (11) is provided which connects the first cylinder chamber (16) to an outlet of the pump (10); and where - At least one second hydraulic line (12) is provided which connects the second cylinder chamber (17) to an inlet of the pump (10). Linear drive according to claim 1, wherein - The piston (15) is a double-acting piston, on one side of which a piston rod is provided; and where - the piston rod is led out of the cylinder (14). Linear drive according to one of the preceding claims, wherein - The first cylinder chamber (16) is arranged with respect to the piston (15) opposite from the side on which the piston rod is provided; and where - The second cylinder chamber (17) is arranged on the side of the piston rod. Linear drive according to one of the preceding claims, wherein - The piston (15) has two opposite piston surfaces on the front side, each of which adjoins the first (16) or the second cylinder chamber (17); and where - The piston surface facing the first cylinder chamber (16) is larger than the piston surface facing the second cylinder chamber (17). Linear drive according to one of the preceding claims, wherein - In addition to the cylinder (14), a hydraulic auxiliary cylinder (19) is provided, in which an auxiliary piston (20) can be moved linearly to and fro; - The piston (15) is mechanically coupled to the additional piston (20) or the additional cylinder (19); and where - A cylinder chamber of the cylinder (14) is hydraulically coupled to a cylinder chamber of the additional cylinder (19). Linear drive according to claim 5, wherein - The additional piston (20) is a double-acting piston, on one side of which a piston rod is provided which is led out of the additional cylinder (19); - The additional cylinder (19) has a first cylinder chamber (22) which, with respect to the additional piston (20), is arranged opposite the side on which the piston rod is provided; and where - The additional cylinder (19) has a second cylinder chamber (23) which is arranged on the side of the piston rod. Linear drive according to claim 6, wherein - The piston (15) is mechanically coupled to the additional piston (20); and where - The second cylinder chamber (17) of the cylinder (14) and the second cylinder chamber (23) of the additional cylinder (19) are hydraulically coupled to one another. Linear drive according to claim 7, wherein the first cylinder chamber (22) of the additional cylinder (19) cannot be acted upon by hydraulic pressure. Linear drive according to one of claims 6 to 8, wherein - A pressure storage device (26) is provided; and where - The first cylinder chamber (22) of the additional cylinder (19) is fluidically coupled to the pressure storage device (26). Linear drive according to claim 6, wherein - The piston (15) is mechanically coupled to the additional cylinder (19); and where - The second cylinder chamber (17) of the cylinder (14) and the first cylinder chamber (22) of the additional cylinder (19) are hydraulically coupled to one another. Linear drive according to claim 10, wherein the second cylinder chamber (23) of the additional cylinder cannot be acted upon by hydraulic pressure. Linear drive according to claim 10 or 11, wherein - A pressure storage device (26) is provided; and where - The second cylinder chamber (23) of the additional cylinder (19) is hydraulically coupled to the pressure storage device (26). Linear drive, with - At least one hydraulic pump (10), the delivery volume of which can be changed; and with - At least one hydraulic linear device with a multi-surface cylinder (30);
in which - The multi-surface cylinder (30) has at least two pistons (32, 33) arranged on a common central axis and displaceable relative to one another, of which a first piston (32) can be moved in a cylinder (31) and a second piston (33) with this Cylinder (31) is integrally connected; - The two pistons (32, 33) and the cylinder (31) are movably arranged in an outer cylinder (34); and where - A first cylinder chamber (35) is formed between the first piston (32) and the cylinder (31) and a second cylinder chamber (36) is formed between the second piston (33) and the outer cylinder (34);
in which - A first hydraulic line (11) is provided which connects the first cylinder chamber (35) or the second cylinder chamber (36) to an outlet of the pump (10); and where - A second hydraulic line (12) is provided which connects the remaining cylinder chamber (35, 36) to an inlet of the pump (10); or where - A first hydraulic line (11) is provided which connects the third cylinder chamber (37) or the second cylinder chamber (36) to an outlet of the pump (10); and where - A second hydraulic line (12) is provided which connects the remaining cylinder chamber (37, 36) to an inlet of the pump (10). Linear drive according to claim 13; in which - The cylinder is an inner cylinder (31) and the first piston is an inner piston (32) that can be moved linearly back and forth in the inner cylinder, the first cylinder chamber (35) being formed between an end face of the inner piston (32) and the inner cylinder (31) ; - The outer cylinder (34) at least partially surrounds the inner cylinder (31) in an annular manner; - The second piston is an outer piston (33) which surrounds the inner cylinder (31) in a ring shape and is integrally connected to the inner cylinder (31); - The outer cylinder (34) surrounds the outer piston (33) in a ring shape; and where - The second cylinder chamber (36) is formed between one end of the outer piston (33) and the outer cylinder (34) and a third cylinder chamber (37) is formed between an opposite end of the outer piston (33) and the outer cylinder (34).

Images