Linear actuator and method for operating such a linear actuator

The linear actuator comprises a double-chamber solenoid pump comprising at least one pump coil, a multi-way valve and at least one pump armature that can be moved by energizing the at least one pump coil and is provided with a switching armature by means of which the multi-way valve can be switched and which can be moved by energizing the at least one pump coil. In the method, both the switching armature and the pump armature are moved by energizing the pump coil.

This application is the National Stage of International Application No. PCT/EP2015/066534, filed Jul. 20, 2015, which claims the benefit of German Patent Application No. 10 2014 215 110.4, filed Jul. 31, 2014. The entire contents of these documents are hereby incorporated herein by reference.

BACKGROUND

The present embodiments relate to a linear actuator and a method for operating such a linear actuator.

Linear actuators are previously disclosed in numerous designs. Stepping motors are disclosed, for example; however, in many cases, these are accurate only to a limited degree. Also previously disclosed are pneumatic and hydraulic linear drives that are connected via a two-way valve to a compressed air reservoir or via a hydraulic pump. Precise regulation is also difficult in the case of these embodiments. Electrodynamic linear motors that are configured as electrical driving machines are also previously disclosed. The electrodynamic linear motors are of fast and accurate construction; however, the electrodynamic linear motors are complicated and are incapable of sufficiently space-saving design. Linear actuators based on piezo crystals or magnetostrictive materials find an application in specific areas; however, the linear actuators based on piezo crystals or magnetostrictive materials are designed only for very small movement paths. Although piezo motors based on frictional contacts have the ability to execute larger strokes, the piezo motors are frequently restricted in terms of service life and are susceptible to environmental influences. Artificial muscles based on electrostatic action mechanisms are also previously disclosed, although the artificial muscles are limited with respect to maximum power and service life.

SUMMARY AND DESCRIPTION

Linear actuators may be constructed with the smallest possible dimensions and, wherever possible, may be operable electrically and for long periods in the absence of wear. Linear actuators may be as robust as possible in the face of adverse environmental conditions (e.g., contamination). Such linear actuators may be readily interconnectable. A number of linear actuators are to be positioned in the case of complicated actuator configurations. Such a linear actuator may exhibit the smallest possible number of electrical conductors or conductor terminations for electrical connection, therefore, in order to minimize the overall number of required lines.

The present embodiments may obviate one or more of the drawbacks or limitations in the related art. For example, a linear actuator that is space-saving and/or capable of the simplest possible electrical connection is provided. As another example, a method for operating such a linear actuator is provided.

The linear actuator includes a solenoid pump (e.g., a dual-chamber solenoid pump). The linear actuator may include a hydraulic cylinder that is hydraulically connected to the solenoid pump. The hydraulic cylinder exhibits a hydraulic piston. The hydraulic piston is capable of being driven into and out of the hydraulic cylinder by the solenoid pump. The linear actuator may include a reservoir connected to the solenoid pump for the supply or removal of hydraulic oil.

According to one or more of the present embodiments, the solenoid pump in the linear actuator exhibits at least one pump coil, one multi-way valve, and at least one pump armature that may be moved by energizing the at least one pump coil. In the linear actuator, the solenoid pump includes a switching armature, by which the multi-way valve may be switched. According to one or more of the present embodiments, the switching armature in the solenoid pump of the linear actuator may be moved by energizing the at least one pump coil.

In the linear actuator, a bidirectional pump flow may be brought about by the multi-way valve. For this purpose, the multi-way valve may be fluidly connected to the inlet and the outlet of the solenoid pump. The linear actuator may include a suchlike multi-way valve for this purpose, which allows a bidirectional pump flow in the connection to the inlet and outlet of the solenoid pump. The hydraulic piston guided in the hydraulic cylinder may be guided bidirectionally by the bidirectional pump flow. The multi-way valve may be switched in order to change the direction of the pump flow. According to one or more of the present embodiments, the switching of the multi-way valve may be effected by energizing the at least one pump coil, which is to be energized in order to move the at least one pump armature. Previously disclosed linear actuators may include a pump and a multi-way valve separately. A dedicated drive is provided in each case for a pump and a multi-way valve. Consequently, an electrical control in each case and thus at least one pair of conductors are provided. One or more of the present embodiments integrate a solenoid pump and a multi-way valve advantageously in a single device. For example, a magnetic flow utilized according to one or more of the present embodiments is used both for operating the pump and, at the same time, for switching the multi-way valve. Consequently, this results in a particularly low electrical interconnection cost for the linear actuator. At the same time, a highly accurate adjustment path may be set with a linear actuator having a solenoid pump. The adjustment path is basically not restricted. Solenoid pumps also do not require a large installation space and are capable of being operated for long periods without wear and, for example, robustly in the face of adverse environmental conditions, such as contamination. Because of the extremely low interconnection cost, only a few electrical lines or conductors or conductor terminations are provided (e.g., in configurations having a multiplicity of linear actuators).

For example, only a single pair of electrical conductors or a single pair of conductor terminations is provided for the linear actuator of one or more of the present embodiments. As a result, the wiring cost is low and the reliability is high in the linear actuator.

In addition, the linear actuator of one or more of the present embodiments may use a dual solenoid pump in place of a simple solenoid pump. In the dual solenoid pump, the volumetric flow does not drop to zero for a prolonged period. Accordingly, pulsations in the volumetric flow and the pressure and associated disadvantages such as noise generation or increased wear as a result of induced vibrations may be avoided.

The solenoid pump (e.g., the dual solenoid pump) includes pot magnets. The pot magnets possess the advantage, when compared with otherwise frequently present yoke disks, that the fluid damping of yoke disks typically increases disproportionately shortly before impacting the yoke. Typical solenoid pumps use additional damping devices or incur special costs for the reduction of noise and vibration (see, for example, EP 1985857). A suchlike functional mechanism is already integrated advantageously in this further development, in which the solenoid pump or the dual solenoid pump includes pot magnets.

In the linear actuator of one or more of the present embodiments, the multi-way valve is a 4/2-way valve, or the multi-way valve exhibits a 4/2-way valve. In this way, the pump flow from the solenoid pump may be reversed particularly easily, in that the inlet and the outlet of the solenoid pump are connected to the switchable inlets and outlets of the 4/2-way valve.

Appropriately, in the solenoid pump of the linear actuator of one or more of the present embodiments, the multi-way valve may be switched by movement of the switching armature. The multi-way valve may be connected with movement to the switching armature for this purpose, so that a movement of the switching armature leads to a spatial displacement of the inlets and the outlets of the multi-way valve relative to the inlet and the outlet of the solenoid pump of the linear actuator. The multi-way valve may be switched particularly easily in this way.

In one embodiment, in the solenoid pump of the linear actuator, the pump armature is connected or is capable of being connected with a magnetic flow to a pump coil yoke. The switching armature is connected or is capable of being connected with a magnetic flow to the pump coil yoke. The connectability or the connection of the pump coil yoke with a magnetic flow to the pump armature and to the switching armature permits a movement of the switching armature to be achieved particularly easily by energizing the at least one pump coil.

In the solenoid pump of the linear actuator, at least two pump coils, each with a pump coil yoke, are present. The pump coil armature is capable of movement between the pump coil yokes or between at least two pump coil yokes. In one embodiment, in this case, a respective pump coil with a respective pump coil yoke belongs to a respective chamber of a solenoid pump that is configured as a dual-chamber solenoid pump.

In a further development of the linear actuator, there is present in the solenoid pump at least one flow-conducting device, by which the pump coil yokes are connected to one another in a flow-conducting manner. In another advantageous further development of the linear actuator, flow-conducting devices are embodied in one piece with the pump coil yokes in the solenoid pump, as previously described. This further development results from a particularly simple construction. In a further development of the linear actuator, the flow-conveying device or at least one of the pump coil yokes in the solenoid pump includes a permanent magnet, or a permanent magnet is arranged on the flow-conducting device or on at least one of the pump coil yokes. In this further development of the method, the permanent magnet may be used as a flow-generating element that attenuates or intensifies a magnetic flow that is generated with the at least one pump coil. In this way, in the linear actuator, a magnetic degree of freedom may be offered for the purpose of switching by the switching armature.

In a further development of the linear actuator, in the solenoid pump, the switching armature is capable of being defined by a magnetic flow that is generated by the permanent magnet, and, for example, is also conducted through the flow-conducting device. A further degree of freedom is accordingly also offered for the movement of the switching armature.

In the dual-chamber solenoid pump of the linear actuator, the at least one pump coil is electrically switched, and/or the at least one pump coil is arranged such that the magnetic flow generated thereby counteracts the magnetic flow that has been generated by the at least one permanent magnet, at least in a region of the flow-conducting means and/or at least one pump coil yoke. For example, the magnetic flow, which has been generated by the at least one permanent magnet, may be overcome. Accordingly, switching may be provided by the at least one pump coil.

The solenoid pump of the linear actuator may exhibit only a single pair of conductors or pair of conductor terminations, by which the solenoid pump is connected electrically. In this way, the electrical interconnection cost and/or the cost of activating the solenoid pump of the linear actuator, and thus the wiring cost of the linear actuator, is reduced significantly.

In this case, for example, the single pair of conductors or pair of conductor terminations is in electrical contact with the at least one or more pump coils.

In a further development, at least two pump coils that are configured in the form of pot magnets are present in the solenoid pump of the linear actuator. The pump armature and/or the switching armature may be movably guided transversely in relation to the pot bases of the pot magnet form. A simple and compact spatial construction may thus be achieved.

Diodes are present in the solenoid pump of the linear actuator. Positive signal portions of a signal that is present on the pair of conductors or the pair of conductor terminations may be transmitted to a first pump coil, and negative signal portions may be transmitted to a second pump coil by the diodes.

In the method for operating a linear actuator according to one or more of the present embodiments, the switching armature is set in a predetermined position in relation to the position of the multi-way valve by the energization of the at least one pump coil of the solenoid pump, and is moved, while maintaining the predetermined opposition, by energizing the at least one pump coil of the pump armature. In this way, the switching armature may be set, so that the multi-way valve is set appropriately for the operation of the pump. In this position, the pump armature is movable and the solenoid pump pumps in the intended unidirectional operation. In a further development of the method, the at least one pump coil is energized to a lesser degree for the movement of the pump armature than for the movement of the switching armature. The amplitude of the activation of the at least one pump coil may consequently be set depending on whether only the pump armature or also the switching armature is intended to be moved.

DETAILED DESCRIPTION

The linear actuator represented inFIG. 1includes a dual-chamber solenoid pump10having a two-way valve20, by which hydraulic fluid is pumped from a reservoir30into a working area of a hydraulic cylinder40. A hydraulic piston50is movably guided in a linear fashion in the hydraulic cylinder40. By setting the two-way valve20to the respective other switching position, the pump direction of the dual-chamber solenoid pump10may be reversed, so that hydraulic fluid is pumped back into the reservoir30from the working area of the hydraulic cylinder40. The hydraulic piston50is moved forwards or backwards accordingly.

The construction of the dual-chamber solenoid pump10is depicted in more detail inFIGS. 2A and 2B. The dual-chamber solenoid pump10includes two pump coils60and70. The two pump coils60and70are each configured in the form of a pot magnet. Present between the pump coils60and70is a magnetic pump armature80. The magnetic pump armature80is guided in a direction90perpendicular to pot base planes of the two pump coils60,70. The pump armature80includes two soft-magnetic perforated disks100,110that are connected to each other by a non-magnetic connecting pipe120. The non-magnetic connecting pipe120, with a longitudinal extent in the direction90, extends perpendicularly to the pot base planes of the two pump coils60,70. The perforated disks100,110are each suspended in a freely oscillating manner on diaphragms130, which in each case delimits and seals hydraulic chambers140,150.

The hydraulic chambers140and150exhibit feed lines160,170that discharge respectively into the hydraulic chambers140,150to either side of the pump armature80via non-return valves180,190. In addition, the hydraulic chambers140,150exhibit outlet pipes200,210that lead away from the hydraulic chambers140,150via non-return valves220,230. The supply pipes160,170and the outlet pipes200,210are brought together respectively on the input side and on the output side to form a common inlet240and a common outlet250.

On the internal radius of the soft-magnetic perforated disks100,110the hydraulic chambers140,150are sealed by a non-magnetic pipe260, on which the pump armature80slides back and forth.

The pump effect is achieved by the activation of the pump coil60,70represented inFIG. 3(e.g., the current strength I of the energization of the left-hand pump coil60(curve EK) or the right-hand pump coil70(curve ZK) is shown in each case as a function of the time t). Either the left-hand pump coil60or the right-hand pump coil70is energized alternately. The pump armature80is drawn alternately to the left or to the right as a consequence of the magnetic reluctance principle (e.g., the desire to close the magnetic flow circuit appropriately). The arrows270,280illustrate the underlying magnetic flow through the pump coil yoke290,300in each case enclosing a pump coil60,70partially around a corresponding circumference. The pump coil yoke290,300in each case respectively encloses the pump coils60,70on respective sides facing away from the other pump coil70,60, in each case partially around the corresponding circumference. The hydraulic volume that is present between the pump coil60,70and the pump armature80is reduced and increased alternately by the movement of the pump armature80to the left or to the right. This hydraulic volume is filled with hydraulic fluid (e.g., silicon oil or glycerin in the represented illustrative embodiment). The pulsating changes in pressure consequently result in a unidirectional flow of the hydraulic oil from the inlet240to the outlet250.

In order to change the direction of the unidirectional flow, a two-way valve20in the form of a 4/2-way valve is provided, as illustrated inFIG. 1. The two-way valve20is moved by a switching armature310and is therefore switched. The switching armature310is integrated into the dual-chamber solenoid pump10, as illustrated inFIG. 4.

A non-magnetic guide rod320is passed through the non-magnetic tube260at the center in the direction90perpendicularly to the pot base planes. This non-magnetic guide rod320is able to slide in the direction90perpendicularly to the pot base planes (e.g., horizontally in the representation according toFIG. 4). A switching armature310made of a soft-magnetic material is attached to the non-magnetic guide rod320. In order to move the switching armature310in the horizontal direction (e.g., in the direction90), the pump coil yoke290and the pump coil yoke300are connected via a flow-conducting device330radially remotely from the non-magnetic connecting pipe120in the horizontal direction90. In the radial direction, the flow-conducting device330exhibits protrusions340that extend radially in the direction of the non-magnetic connecting pipe120.

At an internally situated radial end, a radially extending bar magnet350is attached in each case to the protrusion340. The switching armature310also exhibits corresponding protrusions360that extend along the switching armature310in the horizontal direction to such an extent that the protrusions360constantly overlap in the horizontal direction with the radially inward-facing protrusions340of the flow-conducting device330, when the switching armature310makes contact with the left-hand pump coil yoke290or the right-hand pump coil yoke300(FIGS. 4A and 4B). If the switching armature310is present in the left-hand position, as depicted inFIG. 4A, the magnetic flow of the bar magnet350is conducted mainly over the air gap (e.g., minimal air gap) and through the left-hand pump coil yoke290, because of the lower magnetic reluctance on this side. A holding force, which holds the switching armature310in this position, is produced there as a result. Analogously, according toFIG. 4B, the switching armature is held in the right-hand position (e.g., the switching armature310is held in a position in each case both in the left-hand position of the switching armature310and in the right-hand position of the switching armature310).

In order to move the switching armature310from one position to the next position, a high current signal HSS is used for a short time, as depicted inFIG. 6. By way of example, the switching armature310is moved to the right by this short-time high current signal HSS. The right-hand pump coil70is subjected to a high current signal HSS for a short time. As a result of this current signal HSS, the temperature of the right-hand pump coil70increases for a short time (e.g., the pump coils60,70in each case are not actually designed for currents at a high level such as that reached in the case of the current signal HSS). Alternatively, the pump coils60,70may be configured for such high currents in further, not especially represented illustrative embodiments.

Before the normal pump sequence (see alsoFIG. 4) is resumed, the right-hand pump coil70is thus able to cool down during a short waiting period.

The magnetic behavior during the switching operation is depicted inFIG. 5. The presence of the high current actually causes the pump armature80to be drawn onto the side of the right-hand energized pump coil70, as is also the case in the pump sequence. The energization of the pump coil70is nevertheless so high that the magnetic circuit through the right-hand pump coil yoke300and the pump armature80(e.g., thin arrows400enclosing the right-hand pump coil70around the circumference of the righthand pump coil70) rapidly becomes supersaturated. The magnetic flow will thus also flow via the flow-conducting device330of the bistable actuator. The magnetic flow F′ depicted with broken lines flows in the opposite direction to the flow of the bar magnet350on the holding side of the switching armature310. By the appropriate choice of the current amplitude in conjunction with the energization of the pump coil70, it is possible to provide that the flow of the pump coil70in the opposite direction is equally as high as the magnetic flow F of the bar magnet350. As a result, the holding force of the switching armature310is effectively increased. A magnetic flow410(e.g., thick, drawn through), however, flows via the large air gap to the right of the switching armature310. This flow produces an attracting force, which finally draws the switching armature310to the right. The current may then be switched off, and the switching armature310remains stable at that point as a result of the flow path depicted inFIG. 4B.

A switching operation is thus initiated by a briefly excessive energization (e.g., by a short-time current signal HSS having an excessive amplitude). The actuator as a whole is finally interconnected according to the principle drawing inFIG. 1. Together with the envisaged two-way valve20, this is represented schematically inFIG. 7, which corresponds toFIG. 1. The circuit depicted inFIG. 8is used to transmit the current signals, which act upon two pump coils (e.g., pump coil60and pump coil70), as depicted inFIG. 3andFIG. 6, via a single pair of conductors. A signal source SQ supplies a single input signal ES with positive and negative signal components. The linear actuator includes two diodes D1, D2, by which the positive signal component EK is switched onto the pump coil60, and the negative signal component ZK is switched onto the pump coil70. This is depicted inFIG. 9by way of example.

The two-part pump actuator80, as represented inFIG. 2, includes two magnetic perforated disks100,110and a non-magnetic connecting pipe120. For reasons of stability, the connection of the two perforated disks100,110may also be effected with further, stabilizing connecting parts500that are arranged additionally to the non-magnetic connecting pipe120as supporting cylindrical elements between the perforated disks100,110.

The protrusions340of the flow-conducting device330represented inFIG. 4lie between the perforated disks100,110and may not be of a rotationally symmetrical embodiment, as represented inFIG. 10(B), but may protrude radially onto the non-magnetic connecting pipe120from four directions offset from one another at a right angle.

As represented inFIG. 11, a two-part armature may be entirely avoided. For example, the pump armature80′ may be realized as a single perforated disk100′. In this case, however, the pump armature80′ is to be guided on the internal radius (e.g., by a further bellows). Magnetic flow is generated by a permanent magnet PM. In this case, the magnetic flow may only be led out “to the rear” from the pump coils60′,70′ in the direction of the bistable switching armature310′. A magnetic constriction ENG is thus incorporated here.

The linear actuator of one or more of the present embodiments is of thin and elongated configuration in a further embodiment (e.g., “pencil-like”). Longitudinal bellows LB are used in place of diaphragm bellows, as depicted inFIG. 12, and the two-part pump armature80″ is provided with longitudinal bellows LB both on the internal radius and on the external radius. The guiding is realized by a number of non-magnetic guide rods FS. In other respects, the design (e.g., the magnetic design) is completely identical withFIG. 4.