Electric linear actuator and construction machine with such a

Abstract

The invention relates to an electric linear actuator, particularly for a mobile crane, comprising a housing and a movable part which is linearly movable relative to the housing by means of an electric motor. According to the invention, the electric motor is housed within the movable part and connected to a gear unit that moves with the movable part and translates the rotary motion of the electric motor into a linear motion of the movable part. The invention further relates to a construction machine, particularly a mobile crane, equipped with such an electric linear actuator.

Description

[0001] The present invention relates to an electric linear actuator according to the preamble of claim 1.

[0002] Construction machinery often has an internal combustion engine as the traction motor and one or more hydraulic drives to operate one or more work functions. Mobile cranes, for example, are well known for their self-contained drive system. A diesel-powered internal combustion engine, in addition to the traction drive function, typically provides the primary energy required to drive the crane components. Such crane components include the hoist, slewing gear, luffing cylinder, and telescopic cylinder.

[0003] The slewing gear and hoist are usually driven by hydraulic motors. A pump distribution gearbox is provided to supply power to the hydraulic motors, which is driven by the combustion engine via a mechanical shaft. Several hydraulic pumps are mounted on the pump distribution gearbox, which supply hydraulic oil to the respective crane actuators or motors for the various crane components. The power supply to the various crane actuators, primarily hydraulically driven motors or hydraulic motors, as well as hydraulically driven linear drives or hydraulic cylinders, has so far been predominantly hydraulic.

[0004] In recent years, there has been an increasing trend towards the electrification of construction machinery in order to reduce CO2 emissions and increase energy security. As part of this electrification, electric drives were used in certain crane functions such as the slewing gear or the hoist. These drives are often used in locations where sufficient electrical energy can be provided locally, for example ports, ships and other transshipment points. However, those crane components that particularly required a powerful linear drive continued to be driven hydraulically. As part of the electrification process, the combustion engines used to provide primary energy were sometimes replaced by electric drives (e.g. in electric cranes) or at least supplemented (e.g. in hybrid cranes).However, even with these solutions, the output shaft of the electric motor is connected to a pump distribution gearbox, which takes over the hydraulic supply of the still hydraulically operated drives, especially the powerful linear drives.

[0005] Due to the high power requirements and high load requirements of linear drives in such construction machinery (examples include luffing cylinders, telescopic cylinders, and outrigger cylinders of mobile cranes), complete electrification of all drives has so far been hampered. However, for various reasons, it would be desirable to replace such linear actuators with electric linear drives.

[0006] For example, hydraulic linear actuators for the aforementioned applications require a considerable amount of transported oil, which is primarily generated by the differential oil (volume piston side - volume ring side) of the large hydraulic cylinders. The oil tank itself required for this, as well as the residual oil volume, which serves a significant part to stabilize the oil (so that, for example, air bubbles can escape from the oil), increase costs and weight.

[0007] Furthermore, the comparatively poor efficiency of hydraulic drives compared to electric drives results in corresponding heat generation. To avoid damaging the hydraulic system and any diesel engine, this heat must be dissipated using oil coolers or a combination cooler, which also increases costs and weight. To somewhat improve hydraulic efficiency, hydraulic components such as pipes, hoses, and blocks are increasingly being made larger in existing cranes. However, this also results in higher costs and greater weight.

[0008] In LS cranes (LS = load-sensing), despite complex hydraulic main control blocks, the power consumption of different components cannot be separated, which can slow down parallel movements. Furthermore, hydraulic cylinders have the disadvantage that the cylinder coating deteriorates at different rates depending on the environment. Furthermore, electric drives offer the advantage over hydraulic actuators that energy recovery or recuperation is easily possible across multiple components.

[0009] Until now, the electrification of large and highly loaded hydraulic cylinders such as luffing cylinders or telescoping cylinders has been a particular challenge. These cylinders not only represent drive elements when luffing and telescoping the boom, generating the necessary adjustment forces, but are also essential elements in the static analysis of the permissible lifting loads of the crane. The luffing cylinder in particular is subject to buckling stress when the lift load is supported on the luffing cylinder and must be designed and dimensioned accordingly. Due to these special requirements, until now only relatively "small" hydraulic cylinders could be replaced with electric linear drives. In relation to cranes, this would include cabin adjustment cylinders and needle adjustment cylinders, for example.

[0010] The present invention is therefore based on the object of providing an electric linear drive that is suitable for use under high loads and capable of exerting high forces. In particular, the electric linear drive should be suitable for use as a luffing cylinder, telescoping cylinder, or outrigger cylinder in mobile cranes.

[0011] According to the invention, this object is achieved by an actuator having the features of claim 1. Advantageous embodiments of the invention emerge from the subclaims and the following description.

[0012] Accordingly, an electric linear actuator is proposed, which is particularly designed for use on a mobile crane, for example, as a luffing cylinder, telescopic cylinder, or support cylinder. The linear actuator comprises a housing and a movable part, which can be moved linearly relative to the housing by means of an electric motor. The linear movement of the movable part relative to the housing allows the electric linear actuator to be retracted and extended. When used instead of a hydraulic cylinder, the movable part replaces the previous piston rod.

[0013] According to the invention, the electric motor is not mounted on or in the housing, but rather is housed in the moving part and thus moves with it. Furthermore, the electric motor is connected to a gear unit that moves with the moving part and translates the rotary motion of the electric motor into a linear motion of the moving part. The linear actuator is thus extended and retracted by actuating the electric motor.

[0014] By locating the electric motor in the moving part, no additional installation space is required for the electric drive of the linear actuator. The saved installation space can be used to increase the strength of the linear actuator or to reduce material and weight. Furthermore, the components of the electric drive and the electric motor are protected from damage.

[0015] Especially when the linear actuator is designed to be large, for example when used as a tilting cylinder, telescopic cylinder or support cylinder, which requires a correspondingly large diameter of the moving part, there is sufficient space within the moving part to accommodate the electric motor.

[0016] Because such an electric linear actuator (e.g., in the form of an electric cylinder) can now be used instead of a hydraulic cylinder, there is no longer any need for a correspondingly large annular surface on the piston to apply the required force. This allows the moving part to be larger or with a larger diameter while maintaining essentially the same housing dimensions, counteracting the limiting buckling. When used as a tilting cylinder or telescopic cylinder, this can lead to an increase in the maximum load capacity.

[0017] The outer diameter of the moving part can therefore be essentially the same as the inner diameter of an inner wall of the housing or slightly smaller. This allows more space within the moving part to accommodate the electric drive or electric motor.

[0018] The provision of an electric linear actuator that meets the corresponding requirements regarding load, buckling, and generated force enables, in particular, the full electrification of construction machinery, in which both the travel drive and all working functions are electrically powered. By eliminating the space-consuming and weight-consuming components of previous hydraulic systems (especially the oil tank), the freed-up installation space and weight can be used, for example, to reinforce the construction machinery, e.g., by adding more steel, thus increasing the load capacity. Alternatively, weight and space can be saved.

[0019] The term "gear unit" should be interpreted broadly and does not necessarily imply a torque or speed transmission. Rather, a gear unit should be understood as any device that converts a rotational movement of the electric motor (or an output shaft driven by it) into a linear movement of the moving part. This does not preclude the moving part from performing other movements in addition to the linear movement (e.g., a rotational movement around its longitudinal axis).

[0020] The electric motor may comprise a single or multiple electric motors.

[0021] The electric motor's power can be varied along its length because there is sufficient space in the long, moving part.

[0022] In principle, the movable part can have any cross-sectional shape, in particular a rectangular or round cross-sectional shape.

[0023] In one possible embodiment, the gear unit comprises a gear head rotatably mounted in the housing, which is mechanically coupled to the electric motor. The gear head has an external thread on an outer side, in particular on a radially outer peripheral side, which meshes or engages with an internal thread formed on an inner wall of the housing. The thread thus formed enables a linear movement of the movable part relative to the housing through rotation of the threaded head, driven by the electric motor. The thread can be designed, for example, as a trapezoidal thread or comprise a ball screw.

[0024] Depending on the coupling between the moving part and the gear head, the moving part can rotate around its longitudinal axis during the linear movement or perform a rotationally rigid linear movement. The latter option is preferred, as a connecting element arranged at a free end of the moving part for connecting the linear actuator to a component to be driven or moved (e.g., a cantilever) then does not rotate.

[0025] In another possible embodiment, the housing has a cylindrical inner wall, and the internal thread meshing with the external thread of the gear head extends along the inner wall. The internal thread on the inner wall extends in the longitudinal direction of the housing over more than 50%, preferably over more than 75%, of the length of the housing. This allows for a greater extension length of the movable part from the housing.

[0026] In another possible embodiment, the movable part is designed as a rod with a round cross-section, thus assuming the function of the piston rod in traditional hydraulic cylinders. The electric motor is housed in a hollow space formed in the rod, with the rod preferably being designed as a hollow tube, at least in sections. The electric motor is at least partially, but preferably completely, housed in the hollow space of the rod, providing optimal protection against damage and saving space. The wall thickness of the rod in the hollow tube section is appropriately thickened depending on the intended application.

[0027] The housing is preferably also cylindrical. At the very least, however, the housing has a cylindrical inner wall to accommodate the movable rod with a round cross-section. However, the outer contour of the housing can also differ from that of the inner wall.

[0028] The electric linear actuator can have an external shape similar to a corresponding hydraulic cylinder, with a rod mounted for linear movement within a cylinder housing. In this case, the electric linear actuator can also be referred to as an electric cylinder. This makes it particularly easy to replace conventional hydraulic cylinders, as the components to be driven or moved and their connecting elements do not need to be adapted.

[0029] In another possible embodiment, the transmission unit comprises a gear unit with a speed ratio. This allows the insertion and extension speed to be adapted to the respective application. The transmission can be a planetary gear unit or comprise a planetary gear unit.

[0030] In a further possible embodiment, a sleeve is provided which is rotationally rigidly connected to the movable part and arranged within the housing. The sleeve is connected to the electric motor and has a passage through which an output shaft of the electric motor is guided to the gear unit. The sleeve is thus moved linearly with the movable part. The sleeve preferably encloses the gear unit, in particular a gear of the gear unit, at least partially. This allows moments and forces to be absorbed and transmitted more effectively. The sleeve can have an opening on a side facing away from the movable part, i.e. can be open towards one end.

[0031] The sleeve may have a radially outer projection forming a mechanical stop that prevents the movable part from being completely pulled out of the housing. The radially outer projection, in particular, forms a section of the sleeve with the greatest radial extension and may be located at an end of the sleeve facing away from the electric motor.

[0032] In another possible embodiment, the gear unit comprises a gear arranged at least partially within the sleeve, which connects the output shaft of the electric motor to the gear head. The gear head preferably comprises a threaded portion located outside the sleeve and axially spaced from the sleeve, which carries the aforementioned external thread. The threaded portion can simultaneously support or guide the movable part in the housing, as is the case with the piston in conventional hydraulic cylinders.

[0033] The gear head preferably further comprises a connecting section located within the sleeve and connected to the gear. The gear head is connected to the gear via the connecting section, and via the gear, in turn, to an output shaft that is rotationally driven by the electric motor. When the electric motor is actuated, the gear head rotates at a specific speed relative to the speed of the electric motor (this ratio can be equal to 1, less than 1, or greater than 1, depending on the design of the gear). This, in turn, results in a linear movement of the movable part.

[0034] The gear head can be constructed in multiple parts. For example, the gear section and the connecting section can be screwed together.

[0035] In a further possible embodiment, a bearing is arranged between the sleeve and the gear head, via which bearing the sleeve is supported on the gear head when the moving part is loaded or extends. The bearing is in particular an axial bearing. Said bearing reduces the friction between the gear head and the sleeve and thus decouples in particular the rotational movement of the gear head from the moving part, which does not rotate about its own axis during a linear movement (rotationally rigid linear movement). The bearing is located on the gear head side, preferably in the region of an end-face annular surface of the gear head formed on the threaded section. Preferably, the bearing is located on the sleeve side in the region of an end face of the sleeve forming an annular surface. The bearing can be designed, for example, as a plain bearing or as a rolling bearing.

[0036] The bearing can, for example, be designed as a double-row axial cylindrical roller bearing if sliding friction is to be avoided. In the case of a plain bearing, one of the end faces of the sleeve or gear head may not be annular, but rather have special bearing sections projecting in the axial direction, which slide along an annular sliding surface (formed on the other component).

[0037] In a further possible embodiment, at least one bearing is arranged between the sleeve and the connecting section in order to reduce the friction between the rotationally rigid sleeve and the rotating connecting section. Preferably, at least one radial bearing is provided between the sleeve and the connecting section. This can be designed as a plain bearing or roller bearing. Alternatively or additionally, at least one axial bearing can be provided between the sleeve and the connecting section, which can be designed, for example, as a plain bearing or roller bearing. An embodiment with at least one radial bearing and at least one axial bearing is preferred. The said axial bearing can be arranged between a shoulder or a step of the connecting section forming an annular circumferential end face and a radially inner projection of the sleeve.Alternatively, a tapered roller bearing can be arranged between the sleeve and the connecting section, which transmits both axial and radial forces.

[0038] In a further possible embodiment, it is provided that a power supply and / or a coolant supply for the electric motor and / or a coolant supply for the transmission is provided from an end of the movable part located outside the housing. Said end of the movable part is in particular the end via which the movable part is connected to a component to be moved (e.g. a boom). The electric motor and / or the transmission can, but does not have to, be cooled. If a cooling device is provided, which is also arranged within the movable part, the coolant must be guided to the cooling device or to the electric motor and / or to the transmission via corresponding supply lines or coolant lines.

[0039] The supply lines (i.e., the power lines and / or coolant lines) run, at least in sections, within the movable part. This results in a compact design, with the supply lines being protected from contamination and damage. In the case of coolant lines, these can be designed, at least in sections, as corresponding bores. Preferably, at an end section of the movable part located outside the housing, connections for connection to an external power supply (e.g., an external mains connection or a battery, e.g., a battery of a construction machine) and / or an external coolant supply (e.g., a coolant circuit of a construction machine) are arranged.

[0040] In a further possible embodiment, the electric linear actuator comprises a position sensor, by means of which a position of the movable part relative to the housing can be detected. This makes it possible to detect the end positions (maximum retracted position / maximum extended position) and / or any defined or definable intermediate positions of the movable part, and preferably to control the electric motor accordingly depending on the detected position (e.g., it can be provided that the electric motor is stopped when the reaching of a defined position of the movable part is detected). For this purpose, a control unit can be provided that is electrically connected to both the electric motor and the position sensor.The control unit can be integrated into the housing or the moving part or can be located outside the linear actuator and connected to the position sensor and electric motor via appropriate control cables.

[0041] The position sensor (multiple position sensors can also be provided) eliminates the need for a mechanical stop for the moving part. Accordingly, it is preferred that the electric linear actuator not include a mechanical stop to define the end position of the moving part relative to the housing. By eliminating mechanical stops, some components can be made lighter, thus saving weight.

[0042] In another possible embodiment, the position sensor is designed as a rotary encoder, which is preferably located in the electric motor or in the gear unit. This results in a space-saving design. The rotary encoder can be located in a gear head or in a gear unit connecting the gear head to the electric motor. The phrase "in the electric motor" or "in the gear unit" is also intended to encompass an arrangement on the electric motor or on the gear unit.

[0043] In a further possible embodiment, a connecting element for connecting to another component (in particular one of two components that can be moved relative to one another by means of the electric linear actuator) is formed on an end section of the movable part that lies outside the housing and / or on an end section of the housing that is opposite or facing away from the movable part, wherein the connecting element preferably comprises a bolt eye. The linear actuator preferably has a bolt eye on its two outer end sections (one end section at the free end of the movable part and one end section at the end of the housing opposite the movable part), as is the case with conventional hydraulic cylinders at the free end of the piston rod and at the opposite end of the cylinder housing. As a result, the linear actuator according to the invention can be used on existing orThey can be installed in conventional connection positions (e.g., between the superstructure and boom or in a telescopic boom). Due to this design, the ends can also be used for moment transfer, although other types of moment transfer are also conceivable, for example, via moment supports.

[0044] The present invention further relates to a construction machine, in particular a mobile crane, comprising at least one electric linear actuator according to the invention. This obviously results in the same advantages and properties as described for the linear actuator according to the invention, so a repetitive description is omitted here. Preferably, the construction machine has an electric drive. This allows the construction machine to be, in particular, a fully electrically operated construction machine, e.g., an electric crane, whose working functions are also fully electrically operated.

[0045] In one possible embodiment, the construction machine is designed as a mobile crane comprising a mobile undercarriage (in particular with a crawler or wheeled chassis), a superstructure rotatably mounted on the undercarriage, and a telescopic boom connected to the superstructure so as to pivot about a horizontal axis. The telescopic boom can be luffed up and down by means of a luffing cylinder, with the electric linear actuator according to the invention forming the luffing cylinder. Alternatively or additionally, the telescopic boom can comprise a telescoping cylinder for retracting and extending one or more telescopic sections, with the electric linear actuator according to the invention forming the telescoping cylinder.

[0046] It is also conceivable that further linear actuators of the mobile crane, for example one or more support cylinders but also smaller actuators such as a cabin adjustment cylinder and / or a needle adjustment cylinder, are designed as an electric linear actuator according to the invention.

[0047] In principle, the linear actuator according to the invention can be designed not only to replace large hydraulic cylinders, but also for use as a smaller linear actuator.

[0048] Further features, details, and advantages of the invention will become apparent from the following exemplary embodiments explained with reference to the figures. They show: Fig. 1: a side view of the mobile crane according to the invention according to an embodiment; Fig. 2: a longitudinal section through an embodiment of the linear actuator according to the invention in a retracted position; Fig. 3: the linear actuator according to Fig. 2 in an extended position; and Fig. 4: an enlarged view of the sleeve and gear head according to another embodiment of the linear actuator according to the invention.

[0049] In the Fig. Figure 1 shows a side view of an embodiment of the mobile crane 1 according to the invention. The mobile crane 1 has an undercarriage 2 with a wheeled chassis and an uppercarriage 3 mounted on the undercarriage 2 via a slewing gear about a vertical axis of rotation. The uppercarriage 3 comprises a telescopic boom 4 mounted so as to be luffable about a horizontal axis, a counterweight device 9 arranged at the rear of the uppercarriage, and an uppercarriage cabin 8. The telescopic boom 4 can be luffed up and down about the horizontal axis by means of a luffing cylinder 5. The telescopic boom 4 comprises an articulated section articulated to the uppercarriage 3, in which several telescopic sections are displaceably mounted. The telescopic sections can be telescoped in and out using one or more telescoping cylinders 6. Furthermore, the mobile crane 1 shown here comprises a support device with several support cylinders 7, which lift the undercarriage 2 from the ground by extending vertically.

[0050] In the Fig. 2 and Fig. 3 shows an embodiment of the electric linear actuator 10 according to the invention (hereinafter also referred to as “linear actuator”) in a lateral sectional view along the longitudinal axis of the linear actuator 10, wherein the Fig. 2 the linear actuator 10 in the retracted position and the Fig. 3 shows the linear actuator 10 in the extended position. In the following, the axial direction refers to the direction parallel to the aforementioned longitudinal axis.

[0051] The linear actuator 10 comprises a housing 12 with a chamber 11 formed within the housing 12. Within the chamber 11, a movable part 14 is mounted such that it can be linearly displaced relative to the housing 12 along the longitudinal axis of the linear actuator 10. In the exemplary embodiment shown here, the movable part 14 is designed as a rod with a round cross-section, with the inner wall of the chamber 11 also being cylindrical. The housing 12 can have a cylindrical shape overall (although other shapes are also conceivable, e.g., a cuboid outer contour).

[0052] The rod 14 has a free end projecting from the housing 12 with an end section 16, which comprises a connecting element 17 in the form of a bolt eye in order to connect the rod 14 with one of two components to be moved against each other (e.g. the linkage of the telescopic boom 4 of the mobile crane 1 according to Fig. 1) to be able to connect or bolt them. At its end opposite the free end of the rod 14, the housing 12 also has an end section 18 with a connecting element in the form of a bolt eye 19, in order to connect the housing 12 to the other of the two components to be moved relative to each other (e.g., the upper carriage 3). Of course, other types of connecting elements are also conceivable (e.g., hooks, screws, etc.).

[0053] The linear movement of the rod 14 relative to the housing 12 is driven by an electric motor 20, which is arranged within a cavity 15 formed in the rod 14. The rod 14 can preferably be designed as a hollow profile, with the electric motor 20 located within the interior of the rod 14 defined by the hollow profile. The required installation space is available because the rod 14 can be designed with a correspondingly large diameter. This is possible because, in contrast to a comparable hydraulic cylinder, no defined annular space needs to be formed to generate the required force. Instead, the outer diameter of the rod 14 in the linear actuator according to the invention can be only slightly smaller than the inner diameter of the inner wall of the housing 12.

[0054] The linear actuator 10 comprises a gear unit 30, which translates the rotary movement of the electric motor 20 into a linear movement of the rod 14. In the embodiment shown here, the gear unit 30 comprises a mechanical gear 34 with a speed ratio, wherein the gear 34 can in particular be a planetary gear.

[0055] The rod 14 is connected at its end opposite the free end or end section 16 (which is always located within the chamber 11 of the housing 12) to a sleeve 40, to which the electric motor 20 is fastened. The sleeve 40 is open on its end face facing away from the rod 14 and has a round cross-sectional shape, in particular at each of its axial positions. In the embodiment shown here, the gear 34 is located within the sleeve 40. The latter is connected at the gear input to an output (not shown) (in particular an output shaft) of the electric motor 20 and at the gear output or

[0056] The transmission output is connected to a transmission head 32 of the transmission unit 30. Rotation of the output shaft of the electric motor 20 thus results in rotation of the transmission head 32 at a specific speed relative to the speed of the electric motor 20. Alternatively, a transmission 34 could be dispensed with and the transmission head 32 could be connected, for example, directly to the output of the electric motor 20. The sleeve 40 preferably has a corresponding passage 42 on its end face facing the electric motor 20 (cf. Fig. 2), through which the output or output shaft of the electric motor 20 is guided to the gearbox 34.

[0057] The gear head 32 has a connecting portion 37, which is connected to the gear 34 within the sleeve 40 and, in particular, is arranged radially between the gear 34 and the sleeve 40. The gear head 32 further comprises a threaded portion 36, which is axially spaced from the sleeve 40, i.e., located outside the sleeve 40, and on the outer circumferential surface of which an external thread 33 is formed (see Fig. 3). This meshes with an internal thread 13 formed on the inner wall of the housing 12 or the chamber 11. Similar to the piston in conventional hydraulic cylinders, the threaded section 36 guides the rod 14 in the housing 12 and forms a bearing point for the rod 14.

[0058] The internal thread 13 can extend substantially along the entire axial extent of the cylindrical inner wall so that the rod 14 can be extended to its maximum extent.

[0059] By rotating the gear head 32, which is effected by the electric motor 20, the gear head 32 screws up and down in the axial direction relative to the housing 12, whereby the rod 14 is extended out of the housing 12 or retracted into it. Preferably, the gear 34 is designed such (e.g., as a planetary gear) that the rod 14 does not rotate during the linear movement, i.e., a rotationally rigid linear movement occurs, as would be the case with a comparable hydraulic cylinder.

[0060] The threaded portion 36 of the gear head 32 has, in particular, a larger diameter and the connecting portion 37 of the gear head 32 has, in particular, a smaller diameter than the sleeve 40.

[0061] As in the embodiment shown, the sleeve 40 may have an annular, circumferential web 44 at its end region opposite the rod 14, which forms a radially outer projection. This radially outer projection 44 forms a mechanical stop that prevents the rod 14 from being fully extended and, in the fully extended position, abuts against a corresponding counter-stop of the housing 12.

[0062] Due to its rotation, the gear head 32 causes the linear retraction or extension movement of the rod 14. During this rotation, the gear head 32 must be supported on the flanks of the internal thread 13 and on the sleeve 40 in order to drive the two connecting elements 17 and 19 apart. To reduce the friction due to the relative rotational movement between the gear head 32 and the sleeve 40, a bearing 50 is preferably provided between the sleeve 40 and the gear head 32, which in the embodiment shown forms an axial bearing. This can be, for example, a plain or rolling bearing. If sliding friction is to be avoided, the bearing 50 can be designed, for example, as a double-row axial cylindrical roller bearing.

[0063] As in the Fig. 2 and Fig. 3, the bearing 50 in the embodiment shown here is arranged between the annular end face formed on the radially outer projection 44 and a likewise annular end face of the gear head 32 facing the sleeve 40, which end face results from the step or sudden diameter reduction between the threaded section 36 and the connecting section 37.

[0064] In the embodiment shown here, the sleeve 40 is extremely long and surrounds the entire connecting section 37. This length serves to improve the transmission of the force pairs occurring during operation. The force transmission through the piston, previously known from hydraulic cylinders, occurs in the linear actuator 10 according to the invention, particularly via the threaded section 36. Additional forces are transmitted in the end section of the rod 14. All these forces (forces and force pairs resulting from moments) flow via the connection between the sleeve 40 and the connecting section 37. The great length of the sleeve 40 limits the magnitudes of the transmitted force pairs.

[0065] A further embodiment of the linear actuator 10 according to the invention is shown in Fig. 4 - also as a longitudinal section through the linear actuator 10 along its longitudinal axis. Here, only an enlarged section of the sleeve 40 and the gear head 32 with the connecting section 37 and the threaded section 36 is shown. The linear actuator 10 is in the retracted position. The features and properties discussed in relation to the previous figures also apply in particular to the embodiment according to Fig. 4.

[0066] As in the Fig. 4, a radial bearing 54, for example in the form of a plain bearing, can be located between the sleeve 40 and the connecting section 37. In addition, an axial bearing 52 can be provided between the sleeve 40 and the connecting section 37, which can also be designed as a plain bearing. The axial bearing 52 can be arranged between a radially inner projection 46 of the sleeve 40 and a step or shoulder formed in the connecting section 37. The radially inner projection 46 can merge radially into the radially outer projection 44 (ie be at the same axial "height" as the latter). The latter can, as already explained and contrary to the illustration in the Fig. 4, project radially beyond the rod 14 and form a mechanical end stop which prevents the rod 14 from being completely pulled out of the housing 12.

[0067] The connecting section 37 and the gear section 36 can be screwed together, as shown in the Fig. 4 is shown.

[0068] A key advantage of the linear actuator 10 according to the invention is that the electric motor 20 is housed in the rod 14. This eliminates the need for additional space, and the drive components 20 are protected from damage. Depending on the application, the diameter of the rod 14 should be selected to be sufficiently large (with a correspondingly thick wall) so that the required buckling stiffness is achieved (e.g., when used as a rocker cylinder 5). This large diameter also provides sufficient space to accommodate the electric motor 20. With a large rod diameter, the wall thickness of the rod 14 can be made thinner, since the diameter still provides sufficient section modulus for the static tasks of the linear actuator 10.

[0069] The bolt eyes 17, 19 present in the embodiments shown, which connect the linear actuator 10 with the components to be moved against each other, each allow only one degree of freedom of movement (pivoting movement around the center of the respective bolt eye 17, 19) and are designed strong enough to safely absorb the forces and loads that occur depending on the application.

[0070] In a preferred embodiment, the linear actuator 10 comprises at least one position sensor in the form of a rotary encoder 22. This indirectly detects an axial position of the rod 14 relative to the housing 12 by measuring the angular position of a rotating component of the electric motor 20, the output, a rotating component of the gear 34 or the gear head 32. The rotary encoder 22 can thus be arranged in the electric motor 20, in the gear 34 or in the gear head 32 (in the Fig. 2, the rotary encoder 22 is indicated by way of example in the area of ​​the electric motor 20. This allows, among other things, the end positions of the rod 14 (fully extended / fully retracted) to be detected without a mechanical stop. By eliminating the mechanical stop, some components can be made lighter and weight can be saved. The rotary encoder 22 can be connected to a control unit arranged in the linear actuator 10, which in turn controls the electric motor 20 depending on the detected rod position. Alternatively, the control unit can be provided outside the linear actuator 10 and connected to the rotary encoder 22 and electric motor 20 via control lines. These can run from the end section 16 inside the rod 14.

[0071] The power supply of the electric motor 20 can preferably be effected from the free end or the end section 16 of the rod 14, as shown in the Fig. 2 and Fig. 3. For this purpose, the rod 14 can have corresponding power connections 63 in the area of ​​the end section 16 for connection to an external energy source (e.g. a battery of the mobile crane 1). The power lines 61, which are located in the Fig. 2 and Fig. 3 are indicated as dashed lines, preferably run within the rod 14 to the electric motor 20.

[0072] Optionally, a cooling device for cooling the electric motor 20 and / or the gear 34 can be provided within the rod 14 (not shown). In this case, corresponding connections 64 for connection to an external coolant system can also be provided in the area of ​​the end section 16, wherein the coolant lines 62 (cf. dashed lines in the Fig. 2 and Fig. 3) can also run within the rod 14.

[0073] With reference to the Fig.In the mobile crane 1 shown in Figure 1, the luffing cylinder 5 and / or the telescoping cylinder(s) 6 and / or the support cylinders 7 could be designed as an electric linear actuator 10 according to the invention. The rod 14 and the housing 12 are then to be designed according to the respective requirements and loads.

[0074] Supplying the electric motor 20 from the rod end 16 results in a particularly advantageous and technically simple design, since the relative movements between the linear cylinder 10 and the component to be moved (in a luffing cylinder 5, this would be the telescopic boom 4) are comparatively small and limited to a single degree of freedom. When used as a telescoping cylinder 6, this is even ideal, since in this case the rod 14 is generally connected to the linkage of the telescopic boom 4, and thus there is no relative movement at all between the rod 14 and the boom 4 (neither during boom luffing nor during telescoping). Even when used as a support cylinder, no relative movement occurs.

[0075] The forces generated and the speeds of movement of the linear actuator 10, as well as the power of the electric motor 20, must be selected to suit the application. Ideally, the crane operator should experience a similar working sensation to that with a conventional hydraulic cylinder. The distance traveled by the rod 14 to luff the boom 4 is known, as is the time required for this. The pitch of the thread 13, 33 determines the required speed. This also means that the torque to be generated by the electric motor 20 is known. The technical property of peak power is very advantageous for an electric motor 20. This is frequently used (e.g., boost in an electric car) and is available for a sufficiently long time for the task to be performed until the rated power comes into effect.

[0076] With the linear actuator 10 according to the invention and its preferred use in a mobile crane 1, the finite capacity of the batteries present on the mobile crane 1 can be optimally utilized to optimize crane operation. With a fully electric mobile crane 1, there is no need to carry an oil tank or other hydraulic components; the resulting freed-up space and weight can be used to reinforce the steel structure of the mobile crane 1, resulting in an increased load capacity.

[0077] When the linear actuator 10 according to the invention is used as a telescopic cylinder 6, the problem existing with hydraulic cylinders regarding the amount of oil to be displaced when the cylinder is retracted (here the power limitation is often activated; empty or unloaded cylinder when retracting) is no longer relevant.

[0078] However, the linear actuator 10 according to the invention can also be used as a smaller actuator on the mobile crane 1, for example in a hoist, slewing gear or the like. List of reference symbols: 1 construction machine (mobile crane) 2 undercarriages 3 superstructures 4 telescopic booms 5 rocker cylinders 6 telescopic cylinders 7 support cylinders 8 Superstructure cab 9 Counterweight device 10 Electric linear actuator 11 Chamber 12 housings 13 internal threads 14 Moving part 15 cavity 16 End section of the movable part 17 Connecting element 18 End section of the housing 19 Connecting element 20 electric motor 22 Position sensor 30 Gear unit 32 Gear head 33 external threads 34 gearboxes 36 threaded section 37 connecting section 40 sleeve 42 Implementation 44 Radial outer projection 46 Radial inner projection 50 warehouses 52 thrust bearings 54 radial bearings 61 Supply line (power line) 62 Supply line (coolant line) 63 Connection (power supply) 64 Connection (coolant supply)

Claims

[1] Electric linear actuator (10), in particular for a mobile crane (1), with a housing (12) and a movable part (14) which is linearly movable relative to the housing (12) by means of an electric motor (20), characterized by that the electric motor (20) is accommodated in the movable part (14) and is connected to a gear unit (30) which moves with the movable part (14) and which translates the rotary movement of the electric motor (20) into a linear movement of the movable part (14). [2] Electric linear actuator (10) according to claim 1, wherein the gear unit (30) comprises a gear head (32) which is rotatably mounted in the housing (12) and mechanically coupled to the electric motor (20), which has an external thread (33) which meshes with an internal thread (13) formed on an inner wall of the housing (12), wherein the thread (13, 33) is preferably designed as a trapezoidal thread or comprises a ball screw. [3] Electric linear actuator (10) according to claim 2, wherein the housing (12) has a cylindrical inner wall and the internal thread (13) on the inner wall extends in the longitudinal direction of the housing (12) over more than 50%, preferably over more than 75% of the length of the housing (12). [4] Electric linear actuator (10) according to one of the preceding claims, wherein the movable part (14) is designed as a rod with a round cross-section, wherein the electric motor (20) is received in a cavity (15) formed in the rod (14), wherein the rod (14) is preferably designed at least in sections as a hollow tube. [5] Electric linear actuator (10) according to one of the preceding claims, wherein the gear unit (30) has a gear (34) with speed transmission, which preferably comprises a planetary gear. [6] Electric linear actuator (10) according to one of the preceding claims, further comprising a sleeve (40) which is rotationally rigidly connected to the movable part (14) and arranged within the housing (12), which is connected to the electric motor (20) and has a passage (42) through which an output shaft of the electric motor (20) is guided to the gear unit (30), wherein the sleeve (40) preferably at least partially encloses the gear unit (30). [7] Electric linear actuator (10) according to claims 2 and 6, wherein the gear unit (30) comprises a gear (34) arranged at least partially within the sleeve (40), which connects the output shaft of the electric motor (20) to the gear head (32), wherein the gear head (32) preferably comprises a threaded portion (36) lying outside the sleeve (40) and axially spaced from the sleeve (40), which comprises the external thread (33), and a connecting portion (37) lying inside the sleeve (40) and connected to the gear (34). [8] Electric linear actuator (10) according to the preceding claim, wherein a bearing (50) is arranged between the sleeve (40), preferably an end face of the sleeve (40) forming an annular surface, and the gear head (32), preferably an end face annular surface of the gear head (32) formed on the threaded portion (36), via which bearing the sleeve (40) is supported on the gear head (32) in the event of a load or extension movement of the movable part (14). [9] Electric linear actuator (10) according to claim 7 or 8, wherein at least one bearing, preferably at least one axial bearing (52) and / or at least one radial bearing (54), is arranged between the sleeve (40) and the connecting portion (37). [10] Electric linear actuator (10) according to one of the preceding claims, wherein a power supply and / or a coolant supply of the electric motor (20) takes place from an end of the movable part (14) lying outside the housing (12) and the supply lines (61, 62) run at least partially within the movable part (14), wherein connections (63, 64) for connection to an external power supply and / or an external coolant supply are preferably arranged on an end section (16) of the movable part (14) lying outside the housing (12). [11] Electric linear actuator (10) according to one of the preceding claims, further comprising a position sensor (22) by means of which a position of the movable part (14) relative to the housing (12) can be detected, wherein the electric linear actuator (10) preferably does not comprise a mechanical stop for defining an end position of the movable part (14) relative to the housing (12). [12] Electric linear actuator (10) according to the preceding claim, wherein the position sensor (22) is designed as a rotary encoder, which is preferably arranged in the electric motor (20) or in the gear unit (30), in particular in a gear head (32) or a gear (34) of the gear unit (30) connecting the gear head (32) to the electric motor (20). [13] Electric linear actuator (10) according to one of the preceding claims, wherein a connecting element (17, 19) for connection to another component is formed on an end section (16) of the movable part (14) located outside the housing (12) and / or on an end section (18) of the housing (12) opposite the movable part (14), wherein the connecting element (17, 19) preferably comprises a bolt eye. [14] Construction machine (1), in particular a mobile crane, comprising at least one electric linear actuator (10) according to one of the preceding claims, wherein the construction machine (1) preferably has an electric travel drive. [15] Construction machine (1) according to the preceding claim, which is designed as a mobile crane and comprises a mobile undercarriage (2), a superstructure (3) rotatably mounted on the undercarriage (2) and a telescopic boom (4) connected to the superstructure (3) so as to be pivotable about a horizontal axis, wherein the telescopic boom (4) can be tilted up and down by means of a luffing cylinder (5) designed as an electric linear actuator (10) according to one of claims 1-13 and / or can be telescoped in and out by means of a telescopic cylinder (6) designed as an electric linear actuator (10) according to one of claims 1-13.

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