HYDRAULIC TRANSLATION UNIT FOR AN ACTUATOR DEVICE

Description

[0001] The present invention relates to a hydraulic transmission unit for an actuator device, which can be filled with a hydraulic fluid and has a first and a second chamber that are hydraulically connected to one another, one of which is designed as a drive chamber and the other as an output chamber. Furthermore, the invention relates to an actuator device with such a hydraulic transmission unit.

[0002] Piezohydraulic actuators are primarily known from the prior art. These typically comprise a piezo actuator and a hydraulic transmission unit, with the piezo actuator acting as the drive for the hydraulic transmission unit. A key feature of such combined actuator devices is that the presence of a hydraulic unit allows a significantly greater mechanical stroke to be achieved than with the piezo actuator alone. This can be achieved, for example, by a transmission ratio in the hydraulic unit and / or by a pumping effect in the hydraulic unit, which summates the effect of numerous small individual movements of the piezo actuator. This overcomes a major disadvantage of the piezo actuator and other known solid-state actuators, namely their short stroke. Such piezohydraulic actuators are known, for example, from the published patent applications DE 102016213654 A1 and DE 102013219759 A1.

[0003] The known hydraulic transmission units are typically implemented either as piston systems or as bellows systems. Regardless of the exact design, they always have a drive chamber and an output chamber which are hydraulically connected to one another. In a piston system, the drive chamber has a drive piston that can move within it, and the output chamber has a driven piston that can move within it. The two chambers are fluidically coupled, so that a movement of the drive piston can cause a movement of the output piston. A desired transmission ratio for the two movements can be achieved depending on the area ratio of the two pistons. In particular, a relatively small stroke of a piezo actuator can be increased to a value required for a specific application by the hydraulic transmission unit mechanically connected in series.

[0004] The problem with such a piston system is that sealing the working volume from the external environment in the area of ​​the movable piston is relatively difficult. For the piston to move within the relevant chamber, a certain gap must exist between the piston and the surrounding cylinder wall. Hydraulic fluid can leak through this gap. This can, on the one hand, lead to undesirable changes in the hydraulic parameters during extended operation of the transmission device. On the other hand, it can also lead to undesirable contamination of the environment with hydraulic fluid.

[0005] Alternatively, the hydraulic transmission unit can be implemented as a bellows system. Here, the two chambers are not delimited by movable pistons, but by bellows-like outer walls. For example, the side walls of the chambers can be formed by so-called bellows, resulting in a variable volume in each chamber. Due to the fluidic coupling of the two chambers, compression in one chamber causes expansion in the other chamber, and vice versa. Here, too, a desired path-transmission ratio can be set by selecting a specific ratio between the cross-sectional areas of the two bellows. One advantage of such a bellows system over the piston system described is that the bellows can be designed to be fluid-tight, thus preventing hydraulic fluid from escaping from the system.

[0006] However, such a bellows system also has several disadvantages: The area between the bellows corrugations often accounts for a comparatively high proportion of the chamber's fluid volume, which reduces the fluidic stiffness and thus the dynamics of the transmission unit. In addition, a wall designed as a bellows always has limited stiffness in the lateral direction (i.e., perpendicular to the main direction of movement during deformation of the bellows). This also leads to reduced dynamics of the transmission. A further disadvantage is that, given the possibility of high pressure peaks in the chamber in question, the bellows must be designed with a sufficiently thick wall and correspondingly high mechanical stiffness. This leads to comparatively high mechanical losses in the transmission unit.

[0007] Furthermore, FR 825 344 A discloses a device for transmitting remote orders. Furthermore, FR 1 370 931 A discloses a hydraulic control system. Furthermore, US 5 287 700 A discloses an actuator system.

[0008] The object of the invention is therefore to provide a hydraulic transmission unit that overcomes the aforementioned disadvantages. In particular, a transmission unit is to be provided that exhibits high impermeability to the hydraulic fluid during operation and, at the same time, offers particularly high dynamic response and low energy losses. A further object is to provide an actuator device with such a hydraulic transmission unit.

[0009] These objects are achieved by the hydraulic transmission unit described in claim 1 and the actuator device described in claim 13. The hydraulic transmission unit according to the invention is designed as a transmission unit for an actuator device. It can be filled with a hydraulic fluid and has a first and a second chamber, which are hydraulically connected to one another. Of the two chambers, one is designed as a drive chamber and the other as an output chamber. At least in the first chamber, a first

[0010] Pistons are arranged to be movable along a piston axis, so that this first piston divides the first chamber into a first working chamber of variable volume and a first rear chamber. The first rear chamber is at least partially delimited by a first bellows element of variable axial length.

[0011] The described first chamber with the additional properties mentioned can be either the drive chamber or the output chamber of the transmission unit. Both chambers are designed with the described features. The advantages described below, as well as the advantageous design variants described, apply accordingly to both chambers.

[0012] For each chamber, a local axial direction is defined by the direction of piston movement. In the following, the term "axial" always refers to the local direction of the piston axis in the respective chamber. The axial directions of the individual chambers can be either the same or different. In the following, the term "lateral" always refers to a direction perpendicular to the respective axial direction.

[0013] In the inventive design of the first chamber, this is divided by the piston into a working chamber and a rear chamber. The position and thus the ratio of the division can be varied by the movement of the piston. The side of the piston facing the working chamber is referred to below as the front of the piston. Accordingly, the rear chamber is located in the region of the rear of the piston. The working chamber of the first chamber is fluidically coupled in particular to a corresponding working chamber of the second chamber, so that volume changes in the two working chambers can compensate for each other through a corresponding flow of hydraulic fluid. In this way, a movement of a drive body arranged in the region of the drive chamber can be translated into a corresponding movement of a driven body arranged in the region of the output chamber.

[0014] The rear chamber is at least partially delimited by a bellows element: in other words, at least part of the wall of the rear chamber is formed as a bellows-like deformable wall. This bellows element should have a variable axial length: in other words, the bellows element should be designed so that the length of the rear chamber can be adjusted in the axial direction. This advantageously makes it possible to achieve length compensation, which can in particular compensate for a change in the axial length of the rear chamber caused by the movement of the piston. The change in length caused by the movement of the piston can thus be compensated either partially or even completely. This length compensation can in particular also bring about volume compensation for the volume of the rear chamber.

[0015] The described effect of the bellows element can be used to keep the volume of the rear chamber essentially constant during movement of the piston.

[0016] As explained in more detail below, the volume does not have to be completely constant. What is essential in the context of the present invention is only that the bellows element undergoes a change in length upon piston movement, and that this change in length is suitable for counteracting a change in volume of the rear chamber caused by the piston movement. The change in volume of the rear chamber caused by the piston movement can, in principle, be either partially or completely compensated, or even overcompensated.

[0017] A significant advantage of the transmission unit according to the invention compared to conventional pure piston systems is that the encapsulated design of the rear chamber in the area of ​​the rear of the piston results in essentially complete tightness for the hydraulic fluid. Even if a slight leak occurs between the working chamber and the rear chamber during piston movement, a loss of hydraulic fluid to the outside environment can still be avoided by encapsulating the rear chamber. Furthermore, such a leak between the chambers, which occurs in a given direction of movement, can be at least partially reversed by a subsequent backward movement. The disadvantages associated with the leakage susceptibility of conventional piston systems are thus avoided.

[0018] A significant advantage of the transmission unit according to the invention compared to conventional pure bellows systems is that a high level of rigidity and thus a high level of dynamics for the transmission of motion between the drive side and the output side can be achieved much more easily.

[0019] In this context, "high dynamics" of the transmission unit should be understood as a fast temporal response. In other words, "high dynamics" means that a short, fast movement on the input side is translated into a correspondingly short, fast movement on the output side with a small time offset and little temporal expansion.

[0020] An advantage in connection with the present invention is that the bellows element is only used in the area of ​​the rear chamber and thus the areas between the bellows waves do not contribute to the described working volume.

[0021] It is therefore practical to avoid any bellows elements as limiting elements in the area of ​​the actual working volume. This also achieves high rigidity for the transmission, because the bellows element, which is deformable (always also laterally), only leads to deformation of the rear chamber. Undesirable lateral deformation in the area of ​​the working volume is avoided.

[0022] Overall, the described transmission unit enables a transmission with high dynamics, high rigidity (and thus low energy losses) and, at the same time, high tightness against the hydraulic fluid.

[0023] The actuator device according to the invention comprises an actuator and a hydraulic transmission unit mechanically connected in series with the actuator. In particular, the actuator is mechanically connected to the transmission unit on the drive side. In this way, a movement of the actuator can be translated by means of the hydraulic transmission unit into a corresponding mechanical movement on the output side. The transmission ratio implemented in the transmission unit changes both the stroke of the movement and the transmitted force accordingly. The advantages of the actuator device according to the invention correspond to the advantages of the transmission unit according to the invention described above.

[0024] In the second chamber of the transmission unit, a second piston is movably arranged along a piston axis, so that this second piston separates the second chamber into a second working chamber of variable volume and a second rear chamber, wherein the second rear chamber is at least partially delimited by a second bellows element with a variable axial length. According to the invention, both the drive chamber and the output chamber are designed as described above. This allows the described advantages with regard to the liquid-tight encapsulation, the high rigidity, and the high dynamics for the entire transmission unit to be particularly effectively realized. In particular, with this "double-sided" embodiment, all other advantageous configurations can also be implemented accordingly on both sides of the transmission unit—i.e., on both the drive side and the output side.

[0025] The transmission unit additionally has a reservoir chamber for the hydraulic fluid, which is fluidically coupled and / or can be coupled to the at least one rear chamber. This can be particularly advantageous when a piston movement for the rear chamber is not completely volume-neutral. A small volume change in the rear chamber can thus be advantageously compensated for by a fluidic coupling to the reservoir chamber.

[0026] Such high dynamics can be easily achieved with the described transmission unit primarily by keeping the overall working volume low. The working volume corresponds to the total volume of hydraulic fluid available for transmitting movement via the transmission unit. This working volume is composed of the volumes of the two facing working chambers (on the drive and output sides) as well as the volume fractions of the connecting line(s) and the additional fluidically connected storage chamber. The lower this working volume can be kept, the stiffer and more dynamic the transmission unit behaves.

[0027] The respective rear chamber is delimited by a respective lateral boundary wall, which is divided into a respective straight cylinder wall and the respective bellows element.

[0028] Advantageous embodiments and further developments of the invention will become apparent from the claims dependent on claims 1 and 13, as well as from the following description. The described embodiments of the transmission unit and the actuator device can generally be advantageously combined with one another.

[0029] The storage chamber for the hydraulic fluid can be fluidically coupled to both rear chambers.

[0030] Thus, the first piston of the first chamber can have a piston body and a piston pin. Furthermore, the associated first rear chamber can have an end plate in its axial end region facing away from the piston body, through which the piston pin extends into the first rear chamber and to which the piston pin is firmly connected.

[0031] The term "firmly connected" is to be understood in particular as meaning that the piston pin and the end plate cannot move relative to each other in the axial direction. Alternatively, they can also be fixed relative to each other in other spatial directions. The actual separation of the first chamber into a working chamber and a rear chamber is thus achieved by the piston body. The piston pin, on the other hand, effects force transmission—either the transmission of a force from an external element to the transmission unit on the drive side or the transmission of a force from the transmission unit to an external element on the output side. The side of the first chamber on which the described end plate is located is also referred to as the end face. To enable force transmission between the piston and an external element in the area of ​​this end face, the piston pin protrudes through the end plate.Since the bellows element described above allows for length compensation of the rear chamber, the piston pin can still be firmly connected to the end plate. A key advantage of such a fixed connection is that it can be designed to be fluid-tight for the hydraulic fluid used. For example, the piston pin and end plate can be connected to each other with a force-locking and / or positive locking. In particular, they can be welded and / or glued together.

[0032] Generally advantageously, the first chamber can be designed such that when the first piston moves along the piston axis, the volume of the first rear chamber is compensated for by the first bellows element.

[0033] In particular, the first chamber can be designed such that a movement of the piston for the rear chamber can be essentially volume-neutral. "Essentially volume-neutral" should be understood here, for example, to mean that the volume of the rear chamber changes by no more than 10% during a piston movement within the specified working range. Such a volume change can particularly advantageously be limited to a maximum of 5%. To achieve this, the rear chamber as a whole can be designed such that the hydraulic area of ​​the movable piston effective in the rear chamber essentially corresponds to the effective hydraulic area of ​​the bellows element. A volume change in the rear chamber caused by the piston movement can then be essentially compensated for by a corresponding, opposing volume change in the bellows element.

[0034] Since in practice the piston movement can only be carried out approximately volume-neutrally and not exactly volume-neutrally, an additional volume compensation for the rear chamber can optionally be provided. For this purpose, for example, a line can be provided that fluidically connects the rear chamber of the first chamber with the corresponding rear chamber of the second chamber. Such mutual compensation between the drive side and the output side can be sufficient, in particular, if the hydraulic area ratio of the two bellows elements (on the drive and output sides) essentially corresponds to the hydraulic area ratio of the two piston elements (on the drive and output sides).

[0035] Generally advantageously, the first rear chamber can be encapsulated in a fluid-tight manner against the external environment. In particular, the rear chamber can be sealed with respect to the hydraulic fluid used. This advantageously prevents fluid exchange with the external environment, even in the event of a leak between the working chamber and the rear chamber.

[0036] The first bellows element can be configured, for example, as a convoluted bellows and / or as a diaphragm bellows. It can thus be designed, in particular, as an annular side wall with a fold-like profile. The fold-like profile can, in particular, have a regular sequence of a plurality of corrugations. Such an annular side wall can advantageously be formed by a correspondingly folded or corrugated, elastically deformable (but liquid-tight) membrane. In general, and regardless of the precise geometric configuration, the bellows element can advantageously be formed from a metallic material or at least comprise such a metallic material.

[0037] Since the described bellows element is only required for volume compensation of the rear chamber, it can advantageously be designed with a significantly thinner wall thickness and significantly lower rigidity than if the bellows itself were to form the lifting element of the working chamber. Compared to a pure bellows system according to the state of the art, a comparatively thinner wall thickness of the bellows element can be selected. This also advantageously reduces the mechanical losses incurred by the movement of the bellows element.

[0038] The first chamber is laterally delimited by a cylinder wall, wherein the associated first piston is arranged to be axially movable relative to the cylinder wall. The direction of movement of the piston corresponds to the cylinder axis. A gap with a gap width in the range below 10 µm and in particular between 0.5 µm and 10 µm can advantageously be formed between the cylinder wall and the first piston. When the piston moves, a small amount of hydraulic fluid can be moved between the working chamber and the rear chamber through the small lateral gap. A gap width in the described range is, on the one hand, sufficiently large to allow the piston to move in the axial direction with little friction. On the other hand, the gap width is sufficiently small to keep the volume of fluid flowing through it low. This is advantageous in order to avoid a pressure loss (or an undesirable

[0039] The aim is to keep the pressure drop (e.g., pressure increase) in the working chamber area as low as possible, which in turn minimizes overall mechanical losses and improves the rigidity and dynamics of motion transmission. In principle, however, there is no lower limit on the gap width, as transitional adjustments are also possible during honing. The shape of the cylinder wall can, in particular, be circular-cylindrical. However, this is not absolutely necessary, and straight cylinders with other cross-sectional geometries can also be used.

[0040] Generally advantageously, the described cylinder gap can be designed without a seal. In other words, the piston is then moved relative to the surrounding cylinder wall without an additional sealing element. In this embodiment, therefore, in addition to the actual material of the piston body, no additional sealing element made of a different material should be present between the piston body and the cylinder wall.

[0041] In general, the hydraulic transmission unit can be filled with a hydraulic fluid. In this embodiment, the hydraulic fluid is already part of the transmission unit. To implement the invention, however, it is generally sufficient if the transmission unit has a chamber system suitable for filling with the hydraulic fluid. A suitable hydraulic fluid is, for example, a silicone oil, a glycol, or even a liquid metal. When the transmission unit is filled with the hydraulic fluid, it is found in both the drive chamber and the output chamber (and, if necessary, in both the working chamber and the rear chamber) and in the storage chamber, as well as in one or more optionally provided connecting lines.

[0042] In general, the drive chamber and the output chamber can either be fluidically connected by a line or can merge directly into each other as sub-areas of the higher-level chamber volume.

[0043] The connection to the storage chamber is also useful for compensating for a change in the volume of hydraulic fluid caused by a change in temperature. In a particularly preferred variant of this embodiment, the storage chamber can be pressurized. Such a pressurization option can be implemented, for example, by an additional bellows element, a preloaded spring and / or a piston in the region of the storage chamber. This allows the storage chamber to be pressurized, which can initially be higher or lower, for example, than the pressure in the rear chamber fluidically coupled to the storage chamber. For example, by means of an actuating element located in the region of the storage chamber, the entire hydraulic system can be preloaded to a desired output pressure, whereby in particular a desired starting position of an output body located on the output side can be set.The initial position of the output body depends on the stiffness of the bellows elements used as well as the preload forces acting on the actuator body and the output body.

[0044] According to an advantageous embodiment, the transmission unit can be designed as a pumpable transmission unit, so that a cumulative movement in the region of the output chamber can be generated by several successive individual movements in the region of the drive chamber. Such a pumping effect is described, for example, in DE 102017214697 A1 and in the European patent application with the file number 17203689.9, which are therefore intended to be included in the disclosure content of the present application. In such an embodiment, not only a transmission takes place, but also a summation of the individual movements of a drive body to form a cumulative total movement of an output body. For this purpose, for example, one or more check valves can be provided in the hydraulic line between the drive-side working chamber and the output-side working chamber.Optionally, one or more pump reservoirs for the hydraulic fluid can be provided, which can be hydraulically coupled to the working volume.

[0045] According to an advantageous embodiment, the transmission unit can be designed to transmit a movement of a drive body arranged in the region of the drive chamber with a transmission ratio of less than 1 to an output body arranged in the region of the output chamber. With a transmission ratio below 1, the stroke on the output side is greater than the stroke on the drive side. The transmission ratio mentioned here should therefore generally be understood as the ratio of the stroke on the drive side to the stroke on the output side of the respective transmission device. As the stroke increases, this transmission ratio is correspondingly less than 1. In this way, a greater stroke can be achieved on the output side than the stroke that triggers the movement on the drive side.In this way, the disadvantage of the comparatively low primary stroke of the solid-state actuator can be compensated, particularly in an actuator device with a solid-state actuator. Particularly advantageously, the hydraulic transmission unit can generally have a transmission ratio of 1:2 or less. With a transmission ratio below 1:2, a more than doubled stroke increase is achieved. In other words, the stroke on the output side is then at least doubled in relation to the stroke on the drive side. Particularly advantageously, the transmission ratio can be in the range between 1:10 and 1:2.

[0046] According to an alternative advantageous embodiment, the transmission unit can also be designed to transmit a movement of a drive body arranged in the region of the drive chamber with a transmission ratio of more than 1 to an output body arranged in the region of the output chamber. In this way, a greater force can act on the output side than the force available on the drive side (with a reduction in the stroke). This embodiment is therefore generally advantageous for applications where high forces are required. Particularly advantageously, the transmission ratio of the hydraulic transmission unit can generally be greater than 2 and in particular lie in the range between 2 and 10.

[0047] In order to set a desired transmission ratio, the hydraulic surfaces of the pistons in the drive chamber and the output chamber are dimensioned in an appropriate ratio.

[0048] Generally advantageously, the total working volume of the hydraulic booster unit can be 1 ml or less. In particular, the working volume can be in the range below 0.5 ml or even below 0.1 ml, and in particular between 0.01 ml and 0.5 ml or between 0.01 ml and 0.1 ml. With such a low working volume, a booster unit with high rigidity and / or high dynamics can be realized particularly easily.

[0049] Advantageously, the total working volume can be lower than the total back volume. This back volume consists of the volumes of both existing back chambers and, if applicable, one or more fluidically coupled lines and storage chambers.

[0050] According to a preferred embodiment of the actuator device, the actuator connected in series with the hydraulic transmission unit is a solid-state actuator. With such a solid-state actuator, the described advantages of the transmission unit according to the invention are particularly effective, since the stroke of a solid-state actuator is particularly limited in practice and, depending on the actuator type, high rigidities are advantageous for power transmission. Thus, a solid-state actuator typically has a high natural frequency and thus advantageously high dynamics.

[0051] According to a particularly preferred variant, the solid-state actuator is a piezo actuator. Piezo actuators have proven to be particularly promising solid-state actuator designs in a hydraulic actuator device. They can achieve particularly precise movement. Their main disadvantage, namely their short mechanical stroke, can be compensated for by the downstream hydraulic unit, as described.

[0052] Particularly preferably, the piezo actuator of the actuator device is designed as a piezo stack actuator. A piezo stack actuator is a series circuit, generally known from the prior art, consisting of several individual piezo elements arranged as a layered stack. Such a stack actuator is particularly advantageous for achieving a higher motion amplitude with the piezo actuator than would be possible with a single piezo element.

[0053] However, the invention is not limited to a piezo actuator as a solid-state actuator. Many of the known advantages and disadvantages of piezo actuators also apply to other types of solid-state actuators. For these, too, a comparatively small output stroke can be increased by the downstream hydraulic transmission unit. According to a preferred embodiment, the solid-state actuator is, for example, a magnetostrictive actuator or an electrostrictive actuator. Alternatively, the solid-state actuator can also be a shape memory actuator. According to a further advantageous embodiment of the actuator device, it can have two or more subsystems, wherein each subsystem has an actuator and a hydraulic transmission unit mechanically connected in series with the actuator.Advantageously, the individual transmission units are coupled or can be coupled to a common higher-level output element in the area of ​​their respective output chambers, so that simultaneous (and acting in the same direction) control of the individual actuators leads to a common movement of the output element by means of the individual transmission units. Such doubling or multiplication of the actuators and hydraulic transmission units and their mechanical parallel connection can, in particular, ensure that a correspondingly higher amount of energy is available for the movement of the output body. A symmetrical, identical design of the individual subsystems is particularly advantageous, whereby a doubling or multiplication of the available energy can be achieved.Particularly with a mirror-symmetrical arrangement of two subsystems, an almost doubling of the energy can be advantageously achieved with a straight, fluid movement of the output body, since canting is advantageously avoided. The mechanical coupling to a common output body can be achieved either by direct connection or indirectly via an optional additional mechanical transmission unit. The coupling to the common output body can also be achieved indirectly via two or more individual mechanical transmission units connected in parallel, so that the individual parallel overall systems are only mechanically connected after this additional transmission stage. Particularly advantageous embodiments of such a system are described in more detail in the international application titled "Stroke transmitter for an actuator device" filed by Siemens AG on the same filing date.

[0054] The invention will now be described by way of some preferred embodiments with reference to the attached drawings, in which: Figure 1 shows a schematic representation of an actuator device not belonging to the invention with a piston system according to the prior art, Figure 2 shows a detailed view of a possible variant of a piston from the Figure 1 shows, Figure 3 shows a schematic representation of an actuator device not belonging to the invention with a bellows system according to the prior art, Figure 4 shows a schematic representation of an actuator device not belonging to the invention, Figure 5 shows a detailed view of the actuator device not belonging to the invention of the Figure 4shows, Figure 6 shows a schematic representation of an actuator device according to a first embodiment of the invention and Figure 7 shows a schematic representation of an actuator device according to a second embodiment of the invention.

[0055] In the figures, identical or functionally identical elements are provided with the same reference symbols.

[0056] In Figure 1an actuator device 1 according to the prior art is shown in schematic longitudinal section. The actuator device has an actuator 3 and a hydraulic transmission unit 5 mechanically connected in series with the actuator. Accordingly, side a of the transmission unit shown in the figure below can be referred to as its drive side and side b shown in the figure above can be referred to as its output side. On the drive side a, a mechanical stroke SA of a drive body 21a can be generated using the actuator 3. This stroke SA can be translated by the hydraulic transmission unit 5 on its output side b into a stroke SB of the output body 21b. The ratio between the stroke SB and the stroke SA corresponds to the transmission ratio of the hydraulic transmission unit 5. In principle, it can be greater than, equal to, or less than 1.

[0057] The translation unit 5 of the Figure 1has two chambers, a drive chamber 11a and an output chamber 11b. A first working chamber 15a is provided as part of the drive chamber 11a and a second working chamber 15b is provided as part of the output chamber 11b. These two working chambers are filled with a hydraulic fluid 7 and are hydraulically coupled to one another via a hydraulic line 16. This results in a total working volume for the hydraulic fluid, which is made up of the two working chambers and the hydraulic line. In order to pump hydraulic fluid back and forth between the two working chambers during operation of the transmission unit 5, two pistons are provided, namely a first piston 13a (as the drive piston) and a second piston 13b (as the output piston). The first piston 13a has a piston pin, which here forms the drive body 21a.The transmission ratio of the transmission unit 5 is determined by the ratio of the hydraulic areas of the two pistons 13a and 13b (more precisely, by the ratio of the corresponding piston bodies). The respective area is linearly included in the volume change which results from a corresponding axial movement of the respective piston. Since the total working volume is constant, an axial movement of the drive piston 13a leads to a correspondingly increased or decreased axial movement of the output piston 13b. In the example shown, the area of ​​the output piston 13b is comparatively smaller, so that a correspondingly increased stroke SB results on the output side b, as indicated here by the greater length of the arrow. The aforementioned axial direction of movement of the pistons is to be understood here as a movement along the local longitudinal axis A. In the example of the . Figure 1This axis for the two pistons coincides with a common longitudinal axis A (which, however, is not absolutely necessary in other embodiments). The mechanical mass is symbolically represented at various points on the actuator device and is designated 20 in each case.

[0058] As already described above, a significant disadvantage of such a piston system is that the sealing of the two working chambers 15a and 15b against the two movable pistons 13a and 13b is difficult. The difficulty of fluidic sealing is caused by Figure 2 illustrated in more detail. Figure 2 shows a detailed view of a possible variant of the drive piston 13a of the Figure 1 . Shown is approximately the Figure 1marked by a dashed oval. This is the area in which the drive piston 13a slides in the axial direction past a cylinder wall 23, which laterally delimits the drive chamber. During the axial movement, the hydraulic fluid 7 should remain as far as possible within the first working chamber 15a and not pass through the piston gap into the (often exposed) area of ​​the rear side of the piston. The gap width of the piston gap is in Figure 2 denoted by g. This gap width cannot be chosen arbitrarily small, so that the piston 13a can move easily in the axial direction within the cylinder wall 23. In the transmission unit of the Figure 2However, it is locally reduced by inserting two additional sealing elements 25 between the piston 13a and the cylinder wall. Such sealing elements can help reduce unwanted leakage of hydraulic fluid into the external environment. However, they often lead to a deterioration in the linearity and / or dynamics of the transmission unit, since during operation there is a constant alternation between static friction conditions and sliding friction conditions between the piston 13a and the cylinder wall 23. Therefore, it is advantageous to avoid such additional sealing elements 25 if possible. Figure 3shows a schematic representation of another actuator device 1 according to the prior art. Here, too, an actuator 3 is mechanically arranged in series with a hydraulic transmission unit 5. Here, too, the hydraulic transmission unit has a drive chamber 11a and an output chamber 11b, wherein the two working volumes of these chambers are coupled by a hydraulic line 16. In contrast to the previous variant, the two working chambers 15a and 15b are delimited by two associated bellows elements, namely a drive bellows 31a and an output bellows 31b. These two drive bellows replace the two pistons from the transmission unit of the Figure 1. Accordingly, on the drive side a, the actuator 3 is coupled to an end plate of the drive bellows 31a. A corresponding stroke SA leads to an extension or compression of the drive bellows, and thus to a change in the volume of the first working chamber 15a. Due to the fluidic coupling, this leads to a corresponding change in volume in the second working chamber 15b. This leads to a corresponding extension or compression of the output bellows 31b and thus to a stroke SB on the output side b, which can be transmitted to an output body 35.

[0059] With such a bellows system, the risk of hydraulic fluid leakage is significantly reduced. However, the disadvantages described above still arise, especially with regard to the reduced rigidity and dynamics of the system. Temperature compensation is also not possible. Therefore, when the temperature rises, the pressure in the entire system increases.

[0060] In Figure 4A schematic representation of an actuator device 1 not belonging to the invention is shown. This actuator device 1 also has an actuator 3 and a hydraulic transmission unit 5 arranged mechanically in series therewith. The basic operating principle of this transmission unit 5 is similar to the transmission unit of the Figure 1 Here, too, the stroke SA from the drive side a is translated into a stroke SB on the output side b by the hydraulically coupled interaction of two pistons 13a and 13b. Here, too, the transmission ratio is determined by the ratio of the hydraulic areas of the two piston bodies. Here, too, the first working chamber 15a forms a portion of the drive chamber 11a that can be varied by the piston movement, and the second working chamber 15b forms a portion of the output chamber 11b that can be varied by the piston movement there.

[0061] In contrast to the translation unit of the Figure 1However, here the rear volumes of the two chambers 11a and 11b are encapsulated. In other words, each of the two chambers 11a and 11b is separated by the piston into a working chamber 15a and 15b, respectively, and a rear chamber 17a and 17b, respectively. The two rear chambers are each fluidically encapsulated from the external environment. They are each at least partially delimited by a bellows element 19a and 19b, respectively, with a variable axial length. In the example shown, a part of the side wall of the respective rear chamber is formed by such a bellows. This bellows allows the rear chamber to be encapsulated and nevertheless allows volume compensation to take place during the movement of the respective piston. In the example of the Figure 4 Both the drive chamber 11a and the output chamber 11b are realized with such a flexibly encapsulated rear chamber.

[0062] Figure 5 shows a detailed view of the actuator device of the Figure 4in the area of ​​the drive chamber 11a, in order to better illustrate the design with the flexibly encapsulated rear chamber 17a. The first piston 13a is divided into a piston body 22 and a piston pin 21a. The piston pin 21a in turn forms the drive body of the transmission unit. The piston body 22 divides the drive chamber 11a into a working chamber 15a and a rear chamber 17a, so that the volume of the working chamber 15a changes when the piston moves. The volume of the rear chamber 17a would also change if the lateral boundary wall were designed rigidly. In this design, however, the lateral boundary wall is divided into a straight cylindrical wall 23 (in the area of ​​the piston body) and a laterally delimiting bellows element 19a (in the part of the rear chamber facing away from the piston body). This bellows element 19a is so flexible that its axial length is variable.If the axial length changes, the cross-sectional area of ​​the bellows element should change as little as possible. On the side facing away from the piston body 22, the bellows element 19a is connected to an end plate 33. This end plate 33 is in turn connected to the piston pin 21a, which extends through it. This connection 34 between the piston pin 21a and the end plate 33 is designed such that, on the one hand, it is fluid-tight and, on the other hand, the two elements cannot be moved against one another in the axial direction. This rigid connection ensures that the bellows element 19 is stretched when the piston moves downwards and compressed when the piston moves upwards. This axial length compensation leads to the described volume compensation of the rear chamber 17a when the piston moves.

[0063] If the hydraulic surface of the bellows element 19a is sufficiently adapted to the hydraulic surface of the cylinder wall 23 (whereby the surface of the bolt 21a is not hydraulically effective) and if, at the same time, the purely axial flexibility of the bellows element is sufficiently high, further measures for volume compensation of the rear chamber can be dispensed with. However, further measures for volume compensation can also be taken, as described in the Figure 6 for a first embodiment of the invention is shown: Figure 6 shows an actuator device 1, whose hydraulic transmission unit 5 is essentially similar to the example of Figure 4 The representation of the mechanical masses 20 has been partially omitted here for the sake of clarity. In contrast to the Figure 5However, here the two rear chambers 17a and 17b are fluidically coupled by an additional line 37 to a storage chamber 41, which is also filled with the hydraulic fluid 7. This storage chamber is also delimited on the outside by a bellows element 43, so that the volume of the storage chamber is variable. On the side of the bellows element 43 facing away from the line 37, a cover plate 45 is arranged, with the help of which a stroke SR can also be set on the storage chamber. This design ensures that the storage chamber can not only compensate for undesired volume changes in the rear chamber, but that it can also be used specifically to preload the system. The storage chamber 41 can thus be pressurized by setting a predetermined stroke position SR in the area of ​​the cover plate 45.If a corresponding counterforce is simultaneously applied to the output body 21b, this preset pressure can be used to preset the output body 21b to a specific, predetermined stroke position SA. A counterforce on the output body 21b can, in turn, be adjusted, for example, via an additional spring or via the stiffness of the bellows 19b.

[0064] The axially movable arrangement of the piston 13a within the cylinder wall 23 can be designed similarly to the detailed view of the Figure 2, but here without the additional sealing elements shown there. Thus, in particular, in the embodiment according to the invention, a piston gap with a uniform gap width g should be present. Hydraulic fluid can leak through the piston gap from the working chamber 15a into the encapsulated rear chamber 17a, but not into the external environment. The hydraulic transmission unit can therefore be designed to be fluid-tight overall. Figure 7 shows a schematic representation of an actuator device according to a second embodiment of the invention. The actuator device of the Figure 7 has two subsystems that are symmetrical to each other, each of which is similar to the example of the Figure 6can be configured. The actuator device 1 thus has two individual actuators 3, which act mechanically in parallel to one another. These two actuators 3 are each mechanically connected in series with an associated hydraulic transmission unit. In the example shown, the individual hydraulic transmission units are not fluidically coupled to one another. Alternatively, however, they could in principle also be fluidically coupled, for example via a coupling of the two storage chambers 41 or by a configuration with a common storage chamber. The two subsystems 71 and 72 of the actuator device are mechanically connected in parallel here. The two output bodies 21b are configured such that by simultaneous and rectified control of the two actuators, a rectified stroke SB is generated at the two output bodies 21b. In the example of the Figure 7The two output bodies 21b are jointly coupled to a higher-level output element 75. This ensures that approximately twice the mechanical energy available for the movement of the higher-level output element 75 is available compared to the movement of the individual output bodies 21b.

Claims

1. A hydraulic transmission unit (5) for an actuator device (1), which hydraulic transmission unit can be filled with hydraulic fluid (7) and comprises a first and a second chamber (11a, 11b), which are hydraulically connected to each other and of which one is formed as a drive chamber (11a) and the other is formed as an output chamber (11b), - wherein a first piston (13a) is arranged movably along a piston axis (A) in the first chamber (11a) such that this piston (13a) separates the first chamber (11a) into a variable-volume first working chamber (15a) and a first rear-side chamber (17a), wherein the first rear-side chamber (17a) is at least partially delimited by a first bellows element (19a) with variable axial length, - wherein a second piston (13b) is arranged movably along a piston axis (A) in the second chamber (11b) such that this second piston (13b) separates the second chamber (11b) into a variable-volume second working chamber (15b) and a second rear-side chamber (17b), wherein the second rear chamber (17b) ist at least partially delimited by a second bellows element (19b) with variable axial length, - and wherein the transmission unit (5) additionally has a reservoir chamber (41) for the hydraulic fluid (7), which is and / or can be fluidically coupled to the at least one rear-side chamber (17a); characterized in that the respective rear-side chamber (17a, 17b) is delimited by a respective lateral boundary wall which is subdivided into a respective straight cylindrical wall (23) and into the respective bellows element (19a, 19b).

2. The hydraulic transmission unit (5) according to claim 1, in which the reservoir chamber (41) for the hydraulic fluid (7) is fluidically coupled to both rear chambers (17a, 17b).

3. The hydraulic transmission unit (5) according to claim 1, - in which the piston (13a) comprises a piston body (22) and a piston pin (21a), - and in which the associated first rear-side chamber (17a) comprises an end plate (33) in its axial end region facing away from the piston body (22), through which the piston pin (21a) protrudes into the first rear-side chamber (17a) and to which the piston pin (21a) is fixedly connected.

4. The hydraulic transmission unit (5) according to any one of claims 1 or 2, in which the first chamber (11a) is configured such that upon a movement of the first piston (11 a) along the piston axis (A), a volume compensation is effected by the first bellows element (19a) for the volume of the first rear-side chamber (17a).

5. The hydraulic transmission unit (5) according to any one of the preceding claims, in which the first rear-side chamber (17a) is fluid-tightly encapsulated against the outer environment.

6. The hydraulic transmission unit (5) according to any one of the preceding claims, in which the first bellows element (19a) is formed as a corrugated bellows and / or as a diaphragm bellows.

7. The hydraulic transmission unit (5) according to any one of the preceding claims, in which - wherein the associated first piston (13a) is arranged axially movably in relation to the cylinder wall (23), - wherein a gap with a gap width (g) below 10 µm is formed between the cylinder wall (23) and the piston (13).

8. The hydraulic transmission unit (5) according to any one of the preceding claims, which is filled with a hydraulic fluid (7).

9. The hydraulic transmission unit (5) according to any one of the preceding claims, in which the reservoir chamber (41) can be applied with pressure.

10. The hydraulic transmission unit (5) according to any one of the preceding claims, which is formed as a pumpable transmission unit, such that a summed movement can be generated in the region of the output chamber (11b) by multiple consecutive single movements in the region of the drive chamber (11a).

11. The hydraulic transmission unit (5) according to any one of the preceding claims, which is formed to transfer a movement of a drive body (21 a) arranged in the region of the drive chamber (11 a) to an output body (21 b) arranged in the region of the output chamber (11 b) with a transmission ratio of 1:2 or less.

12. The hydraulic transmission unit (5) according to any of claims 1 to 10, which is formed to transfer a movement of a drive body (21a) arranged in the region of the drive chamber (11a) to an output body (21b) arranged in the region of the output chamber (11 b) with a transmission ratio of at least 2.

13. An actuator device (1) with an actuator (3) and a hydraulic transmission unit (5) according to any one of the preceding claims, mechanically connected in series with the actuator (3).

14. The actuator device (1) according to claim 13, which comprises two partial systems (71, 72), wherein each partial system (71, 72) comprises an actuator (3) and a hydraulic transmission unit (5) mechanically connected in series with the actuator (3), wherein the two transmission units (5) can be mechanically coupled to a common superordinated output element (75) in the region of their respective output chambers (11 b), such that a simultaneous control of the two actuators (3) results in a common movement of the superordinated output element (75) by means of the two hydraulic transmission units (5).